Field of the invention

The invention relates to a method of conditioning air using a heat and mass exchange module comprising a plurality of air channels for air flow and a plurality of liquid channels, wherein a liquid channel is embodied as a layer of wicking material on a plate and is arranged adjacent to an air channel with a mutual exchange surface, which method comprises the steps of:

Providing flow of a liquid into the liquid channels, and

Providing air flow into the air channels.

The invention further relates to a heat and mass exchange module comprising a plurality of air channels for air flow and a plurality of liquid channels for flow of a liquid, wherein a liquid channel is embodied as a layer of wicking material on a plate and is arranged adjacent to an air channel with a mutual exchange surface, which liquid channel is provided with an entry and an exit and which air channel is provided with an inlet and an outlet.

Background of the invention

A heat and mass exchange module of the above mentioned type - hereinafter also HMX module - comprises a plurality of parallel plates which are typically provided with at least one layer of wicking material. In operation, a liquid is applied onto the surface of the plates. In the context of air conditioning, the liquid may be a liquid desiccant or alternatively an evaporative liquid. Liquid desiccants are used for dehumidification, and are suitably aqueous salt solutions, typically hygroscopic and preferably concentrated. The liquid desiccants need to be regenerated after use. The HMX module can be used as a dehumidifier module and as a regenerator module. Evaporative liquid are used in evaporative coolers. These liquids may not be toxic, aggressive, corrosive and the liquid's heat of evaporation is suitably big so as to result in significant cooling of the air. The evaporative liquid is more particularly water, such as demineralised water or tap water, which further may include an additive. The HMX module may be used as a evaporative cooler.

If the HMX module is a dehumidifier module, the water concentration in the liquid desiccant is typically reduced before entry, so that the liquid desiccant can take up humidity from the air.

Suitably, the liquid desiccant is also cooled. If the air-conditioner module is a regenerator or conditioner module, the liquid desiccant is suitably heated prior to entry, so as to facilitate evaporation of water from the liquid desiccant to the air. The HMX module may be further used as part of an air cooling (and/or heating) system. The term ΉΜΧ-module' is used within the context of the present invention to refer to any module for use in a conditioning system for air and/or another gas. Where reference is made to an air-conditioner module, this is to be understood as synonym. The conditioning system may be arranged to condition humidity and/or temperature of the air. The conditioning system is typically used for air, such as available in offices, stables, houses, theatres, museums, sport halls, swimming pools and other buildings. The conditioning system may alternatively be used for conditioning an industrial gas flow.

A major problem for all these modules is carry-over. This is the undesired transfer of certain components present in the liquid into the air. Carry-over is undesired when using liquid desiccants, since the salts applied as liquid desiccant are typically corrosive. It is furthermore undesired that conditioned air would contain any droplets of salt. Carry-over is further undesired in evaporative coolers. At the temperatures at which evaporative coolers are applied, there is a risk that the water contains any micro-organisms such as bacteria. Carry-over of such bacteria into the air is undesired from the perspective of hygiene and safety.

One such liquid desiccant type air conditioner (also referred to as LDAC, or LDVPAC = liquid desiccant vapour compression air conditioning) module is known from WO2013/094206 (Sharp). This module uses plates comprising internal channels for refrigerant, so as to cool the plates. The use of such cooled plates provided with layers of wicking material (at the surface), such as a flocked surface of 0.5 mm Nylon fibers, allows operation with low desiccant flow rates of 0.5-1.0 l/m2/hour. As stated in [0023], such a flow rate is desired for wetting the defined region with such flocked surface. As mentioned in [0027], the smooth profile of the used roll-bond plate minimizes air stream turbulence, thus minimizing both the potential for desiccant carryover and the fan power demand, but in [0052] it is argued that there are various applications wherein carryover would not be critical.

WO2013/94206 thereafter mentions in [0061] that its module may be operated economically, notwithstanding to the thicker plates, according to various aspects of the invention, i.e. to use counterflow rather than crossflow, both for mass exchange and heat exchange; to increase turbulence (i.e. higher localized velocities), and to enable higher flow bulk air velocities without risking droplet carryover. For instance, the turbulence is increased by means of gaps and sharp edges thereto as shown in Fig 5a. The higher flow bulk air velocities are achieved by using a roll- bond plate, with relatively smooth outer surfaces. Hence, it is understood that the said patent application foresees counterflow use and higher localized velocities with concomitant turbulence. However, the inventors of the present invention believe that turbulence likely results in carryover, which is to be avoided. Still it is desired to obtain a module that may be operated economically.

Another desiccant type air conditioner is known from US2012/0132513A1. The known apparatus may be operated in counter-flow or in cross-flow. It is based on hollow wavy plates that are constructed and assembled in such a way that the plates can thermally conduct heat. More particularly, the hollow plates are configured for flow of a refrigerant fluid inside them. The outside surfaces may be provided with a layer of a hydrophilic material, acting as a drain channel for liquid desiccant. Suitably a membrane is present on top of the drain channel. In use, there will thus be a predefined temperature difference between the thermally conductive plate and the air. Furthermore, humidity is driven from the air into the liquid, or out of the liquid into the air, resulting in liberating of condensation heat or withdrawal of evaporation heat.

In terms of flow dynamics, the situation of gas flow along a solid surface typically gives rise to a quasi viscous fluid layer at the interface with laminar flow, a buffer zone and a turbulent core of air. The behaviour in the buffer zone will be a mixture of turbulent and laminar flow; see f.i. R.B. Bird, W.E. Stewart & E.N. Lightfoot, Transport Phenomena (Wiley, page 375, fig 12-1.1, 18-5-1). In a situation of both mass transfer and heat transfer the temperature and velocity profile change in a non-linear manner, thus faster close to the interface with the liquid flow (Fig. 21.5-1).

In other words, the turbulence in the buffer zone may extend towards the interface with the liquid flow. The corrugation in the layer of wicking material further reduces the threshold for generation of droplets from the liquid flow. US2012/0132513 does not address this risk of carry over altogether, except in the provision of a membrane on top of the hydrophilic layer of wicking material. This is furthermore confirmed in paragraph [0133], first sentence, which specifies the exchange between air and liquid desiccant through a membrane, as well as the heat transfer to a refrigerant as essential to the invention. However, such an air conditioner is complex in a double sense: not only does it require a lot of different components, which typically increases manufacturing cost and reduces lifetime;

furthermore, many parameters in the system needs to be controlled to arrive at a suitable operation. It is observed that US2012/0132513 does not contain any experimental data, so that the operation and particularly the air-conditioning behaviour remains rather speculative . Summary of the invention

It is therefore an object of the invention to provide an improved method and an improved HMX module, which can be operated in an economically viable manner and does not have the risk of carryover of liquid desiccant into the air flow. According to a first aspect, the invention provides an heat and mass exchange module comprising a plurality of air channels for air flow and a plurality of liquid channels for flow of a liquid, , and wherein a liquid channel is arranged adjacent to an air channel with a mutual exchange surface, which liquid channel is provided with an entry and an exit and which air channel is provided with an inlet and an outlet, wherein

- the heat and mass exchange module is a cross-flow module in that the plurality of air

channel extend in a first flow direction from inlet to outlet and the plurality of liquid channels extend in a second flow direction from entry to exit, which second flow direction is different from the first flow direction,

the exchange surface is substantially planar when seen along the first flow direction, but is non-planar when seen along the second flow direction

the module comprises a plurality of corrugated sheets in a spaced-apart arrangement, wherein a first and a second air channel are mutually separated by means of a sheet and wherein a liquid channel is embodied as a layer of wicking material on a sheet and has a width defined by its entry, and wherein the mutual exchange surface is defined by the interface of the liquid channel and the air channel, and wherein the sheet comprises a pattern of ridges and valleys, when seen along the second flow direction.

According to a second aspect, the invention provides a method of conditioning air using a heat and mass exchange module of the invention and controlling the air flow in a laminar flow regime.

It is the insight of the invention, that appropriate operation without carry-over is achieved by means of a design that is made for laminar air flow. Such a design is based on cross-flow of the liquid desiccant and the air. The cross-flow design is suitably implemented with a plurality of sheets, rather being based on plates, each of which comprises several sheets. In this manner, the density of air channels may be increased, and therewith the total exchange surface within a module of a given size. The sheets are stiffened by means of corrugations for obtaining sufficient stability. However, such corrugations are configured and arranged such that the air flow is not hindered so as to create local turbulence. Particularly, the corrugations are designed such that the mutual exchange surface between an air channel and a liquid channel is substantially planar when following the first flow direction, and is non planar when following in the second flow direction. Thus, a first volume of a liquid flowing in the second flow direction will experience flow over a non-planar surface. However, a first volume of air flowing in the first flow direction will experience flow through a substantially straight channel. The terms 'substantially planar' and 'substantially straight' are used in the context of the present application in that the surface and the channel does not contain any interruptions or angles (for instance of 150 degrees or smaller, with fully straight defined as 180 degrees). It is not excluded that the substantially planar surface or substantially straight channel contains any slight curving, for instance leading to a deviation of less than 15 degrees, more preferably less than 10 or less than 5 degrees over the exchange surface. However, this is not preferred; a planar exchange surface when seen along the first flow direction, for instance allows that the edges of the sheet can be planar. This is deemed beneficial for the assembly of sheets and manifold and/or distance holders.

As the entire sheet is corrugated, a valley on one side corresponds to a ridge on an opposed side of the sheet. In one preferred embodiment, the sheet has a uniform thickness. This minimizes the volume within the module used by the sheets. However, this uniform thickness is not deemed necessary, and may be dependent on the manufacturing technique of the sheets. A sheet processed by thermoforming would typically have a substantially uniform thickness when the thermoforming starts from a planar sheet. A sheet processed by a moulding technique may easily have a varying width.

In a preferred embodiment, the corrugation has an amplitude that is at least 50% of the spacing between the sheets., and suitably at least 200%. More preferably, the amplitude is at least 80% of said spacing or even be in the range of 90-120%. Since the sheets are suitable identical in shape, such amplitude does not lead that the sheets would touch each other. For sake of clarity, it is observed that the spacing between the sheets is herein defined in the same direction as the amplitude of the sheet. Thus, suitably, a tip of a ridge of a first sheet extends substantially to or into a valley of an adjacent second sheet. In other words, the amplitude of the corrugation may be of substantially the same dimension as the spacing between the sheets.

Particularly preferred is an implementation wherein the corrugation is periodical, with a plurality of corrugations in the propagation direction of the liquid, for instance at least 6 periods per meter, or preferably at least 8 periods per meter or even at least 10 or 12 periods per meter. The periodic distance is for instance in the range of 1.0 to 15.0 cm, most preferably 1.0 to 5.0 cm. It has been found in experiments with sheets in the module of the invention, that good results were obtained with a pattern, wherein the ridges had a height which was smaller than the distance between neighbouring ribbons (as measured from heart-to heart, i.e. periodic distance). More preferably the height was at most half of the periodic distance, and more preferably at most one third. The distance between the plates is preferably at most 1.0 cm.

Such a corrugation has the advantage of providing an increase resistance against vibrations.

Furthermore, the exchange surface area is increased significantly. Moreover, a single volume of air propagating in the air channel is side -wise substantially surrounded by liquid channel. Without corrugation or with limited corrugation, the liquid channel would be present merely sidewise, but not above or below this volume. Therewith, the distance to the sheet is reduced, which is beneficial to obtain sufficient heat and mass exchange in a laminar flow regime.

Suitably, the air flow is controlled in an air flow rate and the liquid flow is controlled in a liquid flow rate, and a mass flow ratio of the liquid flow rate over the air flow rate is at most 3.0, more preferably at most 2.5 or even at most 2.0. It has been found that such a mass flow ratio can be achieved with the module of the invention, and that is furthermore provided a very high drying efficiency of over 60% up to even over 90%, when the said mass flow ratio increases towards 2.0. However, good results have also been achieved with mass flow ratios in the range of 0.5 to 1.5. In a preferred embodiment, the exchange surface between an air channel and a liquid channel is defined by a width of the liquid channel, rather than dimensions of the sheet. This width is understood to extend in the first flow direction and to be smaller than a distance between the inlet and the outlet of the air channel in the first flow direction. It is deemed preferable to define the exchange surface by means of the liquid channel, and thus particularly the arrangement of the entry, i.e. the entry points, of the liquid channel. This can be achieved in a rather precise manner.

Moreover, by limiting the width of the liquid channel, space is created outside the exchange surface for elements that may further stabilize the module, without having an impact on the flow and more particularly without creating a risk for carry over. More particularly, the air inlet and the air outlet may be configured to have a substantially rectangular cross-section. In fact, the non- planarity of the exchange surface when seen along the first flow direction corresponds to non- planarities along the width of the air channel.

In one suitable embodiment, an accommodation area is present between the inlet of the air channel and the exchange surface, when seen along the first flow direction. Such accommodation area is deemed beneficial to smoothen the air flow, and to provide a transition between a flow in a major pipe to flow through a plurality of air channels with limited height.

Preferably, the non-planarity of the exchange surface comprises a series of ridges and valleys. These ridges and valleys are suitably provided regularly. More particularly, the pattern of ridges and valleys along said direction suitably constitutes a wave shape, more particularly a sine wave shape.

In a preferred embodiment, the sheet further comprises at least one strengthening protrusion that is defined within an area extending substantially parallel to the liquid channel. Such strengthening protrusion is for instance arranged in the accommodation area and/or in an outlet area present between the exchange surface and the outlet of the air channel. Herewith stiffness of the sheet is further increased, therewith reducing the risk of carry over further. Such stiffness is for instance desired so as to prevent and/or suppress any vibrations that could otherwise influence the flow pattern in the air channel, and create larger carry-over from the liquid channel. The stiffness is further desired to counteract deformation of the sheets, which for instance may be due to expansion and/or contraction due to temperature differences, and more particularly differential thermal expansion between materials that are attached or bonded to each other. As a consequence of such deformation, the mutual distance between the sheets could decrease, so that droplets could bridge a first and a second liquid channel (actually separated by an air channel). Moreover, module manufacture is simplified by means of sheets of sufficient thickness. More preferably, the sheet comprises at least one strengthening portion in the accommodation area and at least one strengthening protrusion in the outlet area. In a further embodiment, the width of the liquid channel is smaller than a length of the liquid channel. For instance, the width of the liquid channel is at most 85%, preferably at most 70%, or even at most 60% of the length of the liquid channel. The set up of this further embodiment increases the maximum exchange surface. It is based on tests demonstrating that the humidity in an air channel is already taken out of the air channel in its first portion, notwithstanding the fact that the laminar flow is less effective with respect to mass transfer than a turbulent flow. Preferably, in this respect, the width of the liquid channel is at least 10%, more preferably at least 20% of the length of the liquid channel.

In another embodiment, the HMX module further comprises a distance holder between a first and a second sheet. Preferably, the distance holder is arranged at the entry of the liquid channel, so that the exchange surface between air and liquid desiccant is uninterrupted. Additional distance holders - for sake of clarity hereinafter referred to as spacers - may be present at the exit of the liquid channel, at the inlet and/or at the outlet of the air channel. The use of a distance holder has the advantage that the distance between the sheets is fixed. This contributes to a defined cross-section of the air channel. Such a well-defined cross-section at least largely prevents variations in the height of the air channel, which otherwise could have an impact on the flow, i.e. a local narrowing typically enhances the flow rate, with a higher risk of turbulence and thus carry-over. The distance holders, arranged between adjacent sheets of the module, suitably have a strip-like extension. They are arranged between two adjacent sheets, but they face merely a portion of the sheets. In fact, where the distance holders are located, there is no mutual exchange surface between an air channel and a liquid channel. It is an arrangement of the distance holders at the top of the module, between the container and the liquid channels, is deemed beneficial.

More preferably, a plurality of air channels has substantially the same height. Therewith, it is achieved a single flow generating means, such as a pump and/or a fan, may be used for said plurality of air channels without creating differences in air flow, and hence unexpected patterns etc. It is of course feasible that air channels have a different height. The provision of a module with a first set of air channels with a first height and a second set of air channels with a second height different to the first height may be used to tune the amount of humidity that is transferred from the air channel to the liquid or vice versa.

In a preferred implementation, the distance holder at the entry of the liquid channel extending along the first flow direction between said first and second sheet is configured for defining entry regions and closed regions, which entry regions define entry point for the liquid desiccant into and onto the layer of wicking material, in which closed regions the distance holder extends from the first sheet to the second sheet. The use of such a distance holder has proven to enable an adequate transmission of liquid desiccant from a container thereof into the wicking material and a surface thereof, substantially without droplet formation or carry-over. In a further implementation, this distance holder is provided, when in use, with an interface with the layer of wicking material on the sheet. The distance holder is configured and arranged such that the layer of wicking material is compressed locally, therewith forming a closed region.

In a more particular implementation of the distance holder, it is provided with a surface of hydrophobic material. It suitably has a bottom surface that is exposed to at least one air channel, which bottom surface has a concave shape between lower edges adjacent to the first and the second sheet and an upper region between said edges. Both these implementation measures contribute to reducing the risk of carryover. In fact, with this choice of material and this shape of the bottom surface of the distance holder, a barrier is provided against flow of liquid desiccant along the surface and against the formation of droplets anywhere at the bottom surface that would otherwise drop down into the underlying air channel. Preferably, the HMX module is designed, such that an air channel is present between a first and a second liquid channel of liquid desiccant, which liquid channels are defined by means of layers of wicking material on adjacent sheets. The number of sheets is suitably at least 10 preferably at least 30, more preferably at least 50, so as to arrive at a suitable surface area for exchange between the air channels and the liquid channels. However, this number may be changed, in dependence of climate, air volume to be conditioned, operation time, surface area of a single sheet, and other factors, such as available space. The individual sheets are preferably of uniform thickness.

Suitably, the sheets are laminates of a carrier and one, preferably two layers of wicking material, more particularly a textile material. Hence, they do not contain any channels for refrigerant.

In again a further embodiment, the surface area of the exchange surface per unit volume

('exchange surface area') is at least 300 m ² /m ³ . This high density of exchange surface area is achieved in the invention on the basis of the well defined sheets, allowing that the height of the air channel is relatively small, for instance lower than 0.6 cm or even 0.4cm or lower. Furthermore, due to the use of corrugated sheets without internal cooling, the thickness of an individual sheet is limited. Typically, in modules based on plates with internal cooling, the exchange surface area is in the order of 100 m ² /m ³ . This is far below the exchange surface area in the invention of at least

300m ² /m ³ , preferably even at least 400 m ² /m ³ . In preliminary designs, an exchange surface area of close to 450 m ² /m ³ was obtained. Improvements in the design to values above 500 m ² /m ³ are deemed realistic. The high density of exchange surface area not merely is an attractive alternative to a module based on cooled plates, but also provides an excellent distribution of heat. On the basis thereof, and by variation of the input temperature of the liquid desiccant, particularly LiCl, it is feasible to operate the module under conditions wherein the air will not heat up during the dehumidification step. By using a liquid desiccant at low temperature, for instance below 20°C, or even in the range of 10-15°C, or more generally of at least 8 degrees, preferably at least 10 degrees below room temperature, the air may even be cooled due to the convection.

Brief introduction to the figures

These and other aspects of the air-conditioner module and the method of air conditioning are further elucidated with reference to following figures, which are not drawn to scale and are merely diagrammatical in nature. Equal reference numerals in different figures refer to identical or corresponding elements. Herein: Fig. 1 shows a diagrammatical view of a first embodiment of the heat and mass exchange (HMX) module;

Fig. 2 shows a schematical view of a sheet used in the HMX module;

Fig. 3a, 3b and 4 show diagrammatical views of implementations of such a sheet;

Fig. 5a-c indicate the non-planarity of the sheets in the HMX module;

Fig. 6-9 show schematical side views of manifolds distributing the liquid desiccant over the sheets according to various implementations;

Fig 10a shows a schematical top view of a manifold in one preferred implementation;

Fig. 10b shows a detail of Fig. 10a;

Fig. 1 la-c shows side views of a sheet and manifold according to another implementation;

Fig. 12 shows a schematical side view of a module including a reservoir of liquid desiccant;

Fig. 13-15 show graphs with measurement results obtained with the HMX module,

Fig. 16-17 show in diagrammatical, cross-sectional views HMX modules according to further embodiments, and

Fig. 18a-d shows in diagrammatical view again a further embodiment of the module. Detailed description of illustrated embodiments

Fig. 1 shows in a diagrammatical view an HMX module 100 according to a first embodiment of the invention. The HMX module 100 comprises a plurality of sheets 10. The sheets are corrugated, as will be discussed with reference to following figures. Preferably, all have substantially the same design, as will be explained hereinafter with reference to the figures. Due to the corrugation and its orientation, the sheets, which are inherently flexible, are sufficiently stiffened so that they can be arranged at a relative short and uniform distance of each other without touching each other. If the sheets touched each at a contact point, liquid would get collected at the contact point. Preferably, each of the sheets has a thickness of at most 1.0 mm, more preferably at most 0.8 mm, or evenat most 0.6 mm. With air flowing along the contact point, there would be a high risk of carry-over. Each of the sheets 10 is in the preferred implementation provided with layers of wicking material 11 of both the front and the rear side of the sheet. As shown in this Figure 1 , the layer of wicking material 11 may be subdivided into two lateral portions. However, this is not deemed particularly beneficial or preferred. The HMX module 100 is designed as a cross-flow module, such that the air and the liquid run in mutually perpendicular directions through the HMX module 100. It will be clear that an entirely perpendicular design is deemed advantageous and most straightforward for manufacturing, since the sheets can be of rectangular shape. However, this is not deemed necessary. Alternative shapes, such as that of a parallelogram, are not excluded. Preferably, the module is configured such that the air channel extends laterally and that the liquid channel of the liquid desiccant extends vertically. For sake of clarity, it is observed that the exchange surface, which is defined at the edge of the layer of wicking material (constituting a liquid channel) and the adjacent volume of air (constituting an air channel), is free of any membrane or other intermediate layer, that limits exchange to some areas between the liquid channel and the adjacent air channel. Thus, it could be stated that the exchange surface covers at least 67% of an interface between the air channel and the liquid channel, preferably at least 80%, more preferably at least 90% and typically 100% or close to 100%, for instance 95-100%.

In this manner, the liquid desiccant will flow within the HMX module 100 under the impact of gravity. The module as shown in Fig. 1 comprises tube connections 18, 19 for the provision and removal of liquid desiccant. Their location is not deemed critical. Though not shown explicitly, it is furthermore deemed beneficial that a reservoir of liquid desiccant is present so as to overlie the sheets 10 of the HMX module. The advantage thereof is that the liquid may be distributed into and onto the layers 11 of wicking material through apertures in a bottom of such reservoir, and typically spread over the entire surface thereof. Therewith, it is prevented that an initial flow of the liquid in a lateral direction needs to be converted into flow in a vertical direction. The liquid in the module is preferably a liquid desiccant, though it alternatively may be an evaporative liquid such as water. While it is well-known that alcohols (particularly the lower alcohols such as methanol, ethanol, propanol etc.) are volatile liquids that are miscible with water, such alcohols are not preferred and even considered unsuitable for use as evaporative liquids in air conditioning. In fact, alcohol is not an ordinary component of air and its addition to room atmosphere is generally undesired.

The HMX module as shown in Fig. 1 may be used both as a dehumidifier and as a regenerator module, but also as any other module for use in an air-conditioning system, such as a cooling module. In a dehumidifier module - also referred to as a drier module - a stream of air is dried, and the liquid desiccant takes up humidity. In a regenerator module, a flow of liquid desiccant is dried and the air in the adjacent air channel is humidified. There is no need that exactly the same design of a module is used for the dehumidifier as for the regenerator module. The dehumidifier module may further be arranged to operate as a cooler by means of temperature control. The shown module as shown in Fig. 1 comprises a plurality of sheets. The number of sheets can be chosen as desired in dependence of climate, air volume to be conditioned and space. As apparent from Fig. 1 the liquid channel is suitably longer than the air channel, particularly in a drier module. With a well regenerated liquid desiccant, for instance an aqueous LiCl solution of sufficient concentration (i.e. typically close to the maximum loading concentration), drying turns out more effective in the first portion of the air channel. However, the liquid desiccant material does not need to be an aqueous LiCl solution, but could alternatively be a salt solution comprising various soluble salts. In a further implementation, an air conditioning system may contain an evaporative cooler module and a dehumidifier module. These modules are preferably arranged such the evaporative cooler module is located upstream to the dehumidifier module, with respect to the air flow. This is deemed a most effective combination, since the evaporation may result in cooler, more humid air. Subsequent drying of this air is more efficient than drying of warmer, less humid air. Thereto, it is deemed beneficial that a first air flow is transported from the evaporative cooler module to the dehumidifier module without intermediate mixing with any conditioned air. However, it is not excluded that any mixing of the first air flow with a second air flow occurs before the

dehumidification. This may for instance beneficial if the capacity of the dehumidifier module is larger than that of the evaporative cooler module, and/or if a bypass around the evaporative cooler module is available for reasons of tuning. Rather than a direct evaporative cooler, the dehumidifier module of the invention may be combined with an indirect evaporative cooler and/or any other heat exchanger. In an indirect evaporative cooler, cooled fluid from the evaporative cooler is transported into a heat exchanger with the air flow. It will be understood that such air conditioning system with an evaporative cooler module in series with a dehumidifier module will further comprise a regenerator module for regeneration of liquid desiccant after exchange with the air - both being integrated into a circuit with any further heat exchanger as known per se to the skilled person. It will further be understood that the air conditioning system suitably comprises a controller for controlling the operation of the modules and for conditioning of the air in accordance with a predefined programme and/or user-specified settings.

Fig. 2a shows in a schematical view a sheet 10 for use in the module of the invention. An air channel 20 is defined between two sheets 10 and is indicated for sake of reference. It is configured in a lateral direction. The air channel 20 is provided with an inlet 21 and an outlet 22. Air in the air channel 20 will first pass an accommodation area 23, then an active area 25 and finally an outlet area 24. The active area 25 is configured to enable exchange with the liquid channel 30 that is defined at the surface of the layer of wicking material (on the sheet 10). It is observed for clarity that the layer of wicking material may extend beyond the active area 25. However, the active area 25 is further defined by means of the entry regions of the liquid desiccant, which are defined at the inlet 31 of the liquid channel 30. These entry regions are typically defined by means of a manifold (shown in Fig. 7-12). The liquid channel 30 is ended at the outlet 32. This outlet 32 is suitably embodied as a container for the liquid of several parallel liquid channels 30. It can be seen that the liquid channel 30 thus has a width (i.e. substantially as defined by the active area 25), which is smaller than the length of the air channel 20 (i.e. the distance between the inlet 21 and the outlet 22 thereof). For sake of clarity, it is observed that the term 'air channel' refers in the context of the present application to a volume with a length and a width and a height, with dimensions that are typically for sheets of material. More specifically, the length and the width are much larger than the height of the air channel. In one embodiment, the length and width of the air channel are substantially identical to a width and length of a sheet. Similarly, the term 'liquid channel' particularly refers to a liquid layer at the surface of the wicking material. The dimensions are at most equal to the dimensions of the wicking material, but may be smaller, particularly as a result of the arrangement of the entry into the liquid channel.

Fig. 2b shows schematically the generation of a module from a plurality of sheets 10 and the air channels 20 in between of the sheets 10. Fig. 2c shows a representative corrugation when seen from the entry of the air channel 20. The arrow indicates the direction of the liquid. The view of Fig. 2c is in fact a cross-sectional view of the air channel. Fig. 2d shows a detail from Fig. 2c. It is apparent from this Figure 2c that in order to prevent carry-over, the liquid desiccant needs to have sufficient adhesion to the underlying surface. It preferably flows in a steady state. Most suitably, the film onto the surface of the layer 11 of wicking material (not shown in this Figure 2c) is sufficiently thin. The film thickness is thinned, in one preferred embodiment in accordance with the invention, by using a specific manifold, wherein the liquid desiccant first flows through a series of slots and is thereafter laterally distributed to cover the area of the liquid channel between the slots.

As shown in Fig. 2d, the distance between the sheets 10 varies somewhat due to the wave-shaped pattern of the sheets 10. In fact, the distance a is larger than distance b. This variation in the distance is an important reason for arranging the wave along the length of the liquid channel rather than along the length of the air channel. If arranged along the length of the air channel, the variation in distance would result in a temporary narrowing of the air channel, resulting in an increase in flow rate (followed by a reduction in flow rate). Such variations in air flow rate would increase the risk of carry-over. By arranging the waves along the length of the liquid channel, the air flows substantially parallel to the waves. This turns out to be beneficial. In fact, one may consider an air channel to be divided in a large number of parallel portions, extending laterally and each having a same length. The lateral portions will have slightly varying height (i.e. distance between the sheets). However, the height of a single lateral portion is substantially constant along its length, at least within the active area, where exchange with the liquid channel occurs. As a result, a single air drop travelling in a single lateral portion will not experience any changes in height within the active area. This therefore reduces a chance that the air drop starts to move in a turbulent manner, and therewith may interfere with the liquid channel to result in droplet formation of liquid desiccant, i.e. carry over. Additionally, it was found that this configuration has a lower pressure drop, as compared to an alternative configuration. In one implementation according to the invention - not shown - the height of a ridge and a valley is higher in the middle part of the air channel than close to the outlet area 24. Herewith, it may be prevented that carry-over occurs at the end of the air channel due to a sudden change in direction of the air channel. In one further or additional implementation according to the invention, the ridges and valleys extend from the active area 25 into the outlet area 24. Therewith, it is achieved that the end of said ridges and valleys, corresponding to a change in orientation of the air channel is at least substantially outside the exchange surface between air and liquid desiccant material.

In again one further implementation, the height of ridges and valleys may be lower in a bottom part of the air channel than in a top part. The liquid desiccant may gain velocity in the course of flowing downwards. In a dehumidifier module, it additionally may warm up. Therefore, the lower part is more sensitive to carry over. This may be compensated by less steep ridges and valleys, to prevent any ejection of single droplets of liquid desiccant.

Fig. 3a shows in a diagrammatical view the sheet 10 more specifically. Herein, it is indicated that the sheet 10 is provided with ridges 12 and valleys 13, in alternating arrangement. The sheet 10 suitably has a shape of a wave, wherein the ridges 12 extend into a first direction and the valleys 13 extend into the opposite direction. With these ridges 12 and valleys 13 a corrugated surface is created that is deemed positive for the necessary strength of the sheet 10, without increasing risk for carry-over. More particularly, the wave may be a sine wave. Its amplitude relative to the length of a period may be optimized, so as to prevent significant acceleration of droplets with the liquid desiccant that could spring away from the surface into the air. Moreover, the edges of the sheet 10 are at least substantially planar. This facilitates assembly of the sheet 10 into the module, particularly by means of a distance holder as will be explained with reference to further figures.

In the shown embodiment, the ridges 12 and valleys 13 extend parallel to the width of the liquid channel 30, such that the liquid channel 30 in fact includes a curved trajectory. However, the air channel 20 is substantially planar over the width of the liquid channel, i.e. in the area where the liquid channel and the air channel have an interface. This has the advantage of minimum disturbance of air flow. As a consequence, carry over can be prevented, at least substantially, while the sheets are very thin. In this manner, a large packing density of sheets per unit volume is achieved, resulting in a large exchange area between the air channels and the liquid channels. In tests with a preliminary version of the heat and mass exchange module according to the invention, wherein the air flow was laminar and a liquid channel wave-shaped, no carry-over was found to occur. The sheet 10 is suitably created in a multistep process. In a first process, layers of wicking material are added to a carrier. The carrier is suitably an engineering plastic, such as PET, polycarbonate, high-density polyethylene and polypropylene. Good results have been achieved with materials have high temperature resistance, such as polypropylene or high-density polyethylene, with polypropylene being particularly preferred. For dehumidifier modules that are not subjected to operation at high temperature for a long duration, other carrier materials are very suitable as well. The wicking material typically comprises a fibrous material, such as a textile material, for instance cotton, linen, rayon or nylon fibres. Alternative hydrophilic, fibrous materials, such as starch and particularly treated starches, are not excluded. Natural rather than synthetic fibres are deemed preferred as a basis for the wicking material, since they are chemically inert and stable to LiCl and other saline desiccants. Rayon, and particularly viscose, is deemed a particularly preferred choice. Rather than a single material, a blend of materials may be applied, for instance a blend of a viscose with a carrier material, for instance an engineering plastic, such as polyethylene terephthalate, polyethylene, polypropylene, polyvinylchloride, polyester. A blend with up to 50wt carrier material, for instance 25-40wt carrier material is deemed very suitable. Preferably, use is made of a non-woven material that appears to be beneficial for the further step of the process. Most preferably, the non-woven material is a spunlaced material. The addition process may be achieved either by dipping (passing of a bath), coating, or laminating. The laminating process is preferred. The carrier may have been pre-treated to improve adhesion, for instance by means of a surface treatment (such as a plasma treatment), or in the provision of an adhesion promoter or even a glue layer. In one advantageous embodiment, use is made of lamination under pressure, wherein an interlayer is formed between the carrier and the layer of wicking material. Good results have been obtained therewith. An advantage of this joining technique is that there is no glue needed, which could be sensitive to dissolution under the impact of the liquid desiccant that is typically very salty and corrosive. The glue may further have an impact on the porosity of the wicking material, and therewith on its wicking properties. In a further process step, the combined material is then thermoformed so as to create the corrugation of the surface, more particularly the ridges, valleys and any protrusions. Herein, the use of non-woven material is deemed beneficial, as it provides less resistance against the concomitant extension than any woven material. The thermoforming step was carried out in a manner so as to obtain an increase in surface area ('stretch') of 10-25%. It was found that this stretch could be made without any delamination occurring between the carrier and the layer of wicking material. The thermoformed sheet moreover turned out stable up to at least 100°C, or even up to 120°C. The thermoforming step may alternatively be carried out simultaneously with the laminating step.

Fig. 3a furthermore shows the presence of spacers 26, which preferably have a stripwise extension and are assembled to a plurality of sheets 10. The spacers 26 are arranged within the

accommodation area 23 and the outlet area 24, which are most preferably substantially or completely planar. Whereas Figure 3a shows 5 spacers 26 in said areas 23, 24, the actual number may vary. In the present configuration, a larger number of distance holders 26, for instance 12-25 per meter per area 23, 24, seems useful, so as to act as a stiffener. The spacers 26 in the accommodation area 23 are oriented downwards in the configuration shown in Fig. 3a. The spacers 26 in the outlet area 24 are oriented upwards in the configuration shown in Fig. 3a. In a rare occasion that any desiccant material may get in contact with a spacer 26 arranged outside the liquid channel, an oblique orientation is deemed beneficial to prevent any accumulation of liquid desiccant material. The oblique orientation makes that the liquid desiccant will flow downwards back onto one of the sheets 10. In order to prevent droplet formation, the spacer preferably is provided with a concave shape in the area between adjacent sheets, such as an inversed V-shape. Additionally, Fig. 3a shows spacers 35 at the bottom side, again for ensuring that the sheets are held at a uniform distance.

One further advantage of the design shown in Fig. 3a - as opposed to a design wherein the ridges 23 and valleys 13 are oriented along the width of the air channel 20, is that the bottom side of the sheet does not need to be fixed within a rigid holder, so as to provide sufficient stiffness. The absence of such a rigid holder allows the sheets to hang down, for instance in a bath of liquid desiccant, or in a sponge. The sheet may then expand and contract freely during temperature variations, i.e. between use and non-use, or between operating at different temperatures. As is well known, polymers have a large coefficient of thermal expansion (CTE). The expansion and contraction upon temperature variations may lead to warpage and other artefacts, particularly if a sheet with a large CTE is fixed to a sheet or component with a smaller CTE. Due to the free edge, the expansion, particularly in the vertical direction, will not cause problems. It is observed for clarity, that a free edge is not the only solution to the problem of differential thermal expansion. However, not all of these known solutions, such as the use of an elastomer interlayer with a very large CTE, is feasible in the context of air-conditioner modules with liquid desiccant. The liquid desiccant is known to be corrosive, but the lifetime of the air-conditioner module is still required to be high.

The configuration of Fig. 3b differs from that in Fig. 3a in the shape of the spacer 26. Herein, the distance holders are arranged in extending parts 27, which extend outside the sheet 10. The advantage hereof is that such an arrangement further reduces the risk that a spacer 26 will be covered with liquid desiccant. It is understood that the liquid desiccant, when it would flow outside the intended area of the liquid channel 30, would follow the edge of the sheet 10. Because the spacer 26 is present in extending part 27, it will remain dry. It is observed for clarity that extending parts 27 could be applied only in limited regions, wherein liquid flow can be expected. Fig. 4 shows a further configuration of the sheet 10 comprising a pattern of ridges 12 and valleys 13 as well as stiffening protrusions 15. In this preferred configuration, the pattern of ridges 12 and valleys 13 is repetitive, and is arranged so that the trajectory of the air in the air channel is straight, while the liquid channel is curved along its length. In addition, the sheet 10 comprises stiffening protrusions. These are arranged outside the active area 25, in which the pattern of ridges 12 and valleys 13 is arranged, and effectively within the accommodation area 23 and the outlet area 24. In the present configuration, a first and a second stiffening protrusion 15 are defined, both extending in this configuration along the width of the air channel (i.e. along the width of the active area 25 as shown in Fig. 2). While a longer stiffening protrusion is deemed beneficial, it is not excluded that this long protrusion is subdivided into two or more shorter protrusions. Moreover, more protrusions could be present, particularly in the accommodation area and in the outlet area. This is however neither deemed necessary nor deemed advantageous. Both protrusions 15 have the same dimensions in this configuration. Again, this may be useful, so as to obtain a design that is most symmetrical, but it does not appear necessary. The Figures 5 to 9 diagrammatically show various distribution units for use in accordance with the invention. A distribution unit for liquid desiccant is also known as a manifold. It is conventionally present on top of the plates. According to embodiments of the invention, the distribution unit is suitably at least partially present between the sheets 10 used in the invention. More particularly, the distribution unit extends to a planar part of the sheet with corrugations. Preferably, the distribution unit is also a distance holder between adjacent sheets 10.

Fig. 5 shows in a diagrammatical, cross-sectional view a first embodiment of the manifold 40, which is provided with grooves 43. The sheets 10 are inserted into said grooves 43. The manifold is further provided with apertures 44 extending from the top side 41 of the manifold up to the grooves 43. On top of the manifold, a reservoir of liquid desiccant may be arranged. Clearly, rather than fully on top of the manifold, such a reservoir could also be integrated into the manifold itself. The manifold 40 is herein suitably rigid. The grooves 43 are preferably designed such that upon absorption of liquid desiccant in the layer of wicking material, the groove 43 is substantially filled with the layer of wicking material. Therewith, it is prevented that a stream of liquid desiccant will run over the layer of wicking material and fall down into the space within the groove. The inner surface of the grooves 43 is more preferably hydrophobic, so as to prevent that liquid desiccant would accumulate thereon and form droplets that can fall into the air channel.

Fig. 6 shows a second embodiment of the manifold 40. The manifold 40 of this embodiment is based on a body 52 of porous material through which the liquid desiccant may flow downwards. The porous material is for instance a sponge material as known per se. The porous material is suitably sufficiently rigid so as to maintain fixed distances between the sheets 10 even when filled with liquid desiccant. The sheets are again inserted into grooves 43. At a bottom side 42, the sponge material is suitably closed off with a sealing layer 46. Herewith, it is avoided that droplets of liquid desiccant will drop off directly into the underlying air channel. Fig. 7a and 7b show a third embodiment of a manifold 40, as all the Figures 5-9 in diagrammatical, cross-sectional views. Fig. 7a shows the manifold 40 before assembly of the sheets 10. Fig. 7b shows the same manifold 40 after assembly of the sheets 10. The manifold of this embodiment comprises a rigid top layer 51 , provided with apertures 44, and a body 52 of porous material. The body 52 is provided with grooves 43. Upon insertion of the sheets 10 into the grooves 43, and adequate wetting, the porous body 52 will get attached to the surface of the sheets 10, thus effectively to the layer 11 of wicking material (not shown). As a result, liquid desiccant material flowing through the porous material of the body 52 can easily flow into and onto the layer of wicking material. The body 52 is further designed with supplementary grooves 53, which are envisaged for prevention of droplet formation in the area between the sheets 10. Rather than as a sponge material, the body 52 may be embodied with another material and optionally without top layer 51. It is then suitable as a distance holder to a side edge of the sheets 10.

Fig. 8 shows a fourth embodiment of a manifold 40, wherein sheets 10 are clamped between plastic strips 45 with grooves 43. The advantage hereof is that this one -part manifold 40 may be manufactured by injection moulding, and is thus easily manufacturable at low cost. Furthermore, the assembly of sheets 10 into the grooves 43 is good. The manifold is further provided with apertures 44 running through the strips 45, which are configured for transport of the liquid desiccant to the bottom side 42, where the liquid desiccant will be transferred into and onto the one or more layers of wicking material on the sheet 10.

Fig. 9 shows a fifth embodiment of the manifold 40. Herein, the manifold 40 is embodied as a plurality of strips 45 that are provided with a plurality of clamps 47. These clamps 47 are present at side faces of the sheets 10. Side walls 51 are present at the outside, so that the assembly of sheets and strips may be fixed and contained, particularly by means of a pressing operation. O-rings 52 may be present to avoid leakage of liquid desiccant along the walls 51. A reservoir 50 is present directly on top of the strips 45, and is defined by the same side walls 51. Although not shown, it would be perfectly possible to insert a bottom of the reservoir in the form of a sheet with apertures.

Fig. 10a and Fig. 10b show a top view of the manifold 40 as shown in Fig. 9. A similar design could also be made for a manifold as shown in Fig. 7, though it appears that it is most suitable for the manifold of Fig. 9. Herein the strip 45 is provided with a plurality of contact surfaces 47 that are in contact with the sheet 10, and particularly the layer 11 of wicking material present thereon. The contact surfaces 47 are mutually separated by means of cavities 48. It will be apparent that the number of contact surfaces 47 may be varied, as well as the aspect ratio of the cavities. The aspect ratio of the cavities is typically defined to accommodate swelling of the wicking material. A higher aspect ratio thus allows more swelling. The operation of this strip for the distribution of liquid desiccant is more specifically and still schematically shown in Fig. 10b. In fact, due to the pressing action onto the assembly of strips 45 and sheets 10 as shown in Fig. 9, the layer 11 of wicking material will be compressed opposite the contact surfaces 47. However, the layer 11 will not be compressed at the location of a cavity 48. This compression can be arranged that the layer of wicking material is effectively closed opposite a contact surface 47, thus forming a closed region 39. At the location of a cavity 48, the layer 11 of wicking material is not closed. This region thus constitutes an entry region 38, where liquid desiccant can enter from the reservoir 50 (as shown in Fig. 9) into the layer 11 of wicking material.

In the Figures 10(a) and 10(b), the distribution of the entry regions 38 is uniform over the length of the sheets 10. It is preferable that no entry regions 38 are present in an area not overlying the liquid channel 30, more particularly neither the portion overlying the accommodation area 23, nor the portion overlying the outlet area 24.

Fig. l la-c discloses again an alternative implementation of the distribution system in accordance with the invention. Herein the sheets 10 comprise slits 16. Figure 11a shows a schematical side view of a sheet 10. Fig. l ib shows a schematical front view of the sheet 10. Fig. 11c shows an assembly of a plurality of sheets 10 with strips 45. In accordance with the present implementation, the strips 45 extend along the sheets 10 and suitably have a uniform width. The sheets 10 are provided with slits 16. The slits 16 in this figure are closed. That seems beneficial for the stability of the sheet, but is not strictly necessary. Extensions 14 are present between the slits 16.

As shown in Fig. 11(b), and corresponding to the situation shown in Fig. 10(b), where the strip 45 is in contact with the sheet, i.e. at an extension 14, a contact surface is present. This results in closing off the layer 11 of wicking material, and a closed region 39. At the location of a slit 16, no contact is present, resulting in an entry region 38.

Fig. 12 is similar to the view of Fig. 1 lc. The figure additionally shows the presence of a reservoir 50 of liquid desiccant, present between the walls 51 that also press the strips 45 and the sheets 10 together. Although not shown, it will be apparent to the skilled person that further tools and means may be present to maintain this assembly together.

Fig. 13-16 show test results obtained with the invention. Tests were carried out with a research version of the air-conditioner module in accordance with the invention, in accordance with Fig. 1 and with the sheet as shown in Fig. 5 and the distance holder of Fig. 9. The test version of the module included 120 sheets, each having two layers of wicking material, so as to arrive at 240 exchange surfaces. A comparison is made between a module made with Celdek™ material with 5 mm thickness, such as known in the prior art, and that of the invention. The prior art module has a same size of that of the invention. In all experiments, unless otherwise stated, the liquid desiccant was a solution of LiCl, typically with 40wt . The temperature of the liquid desiccant upon entry of the module was 15 °C. The temperature of the ingoing air was 30 °C, with a relative humidity of 75%.

Fig. 13 shows the relationship between the pressure drop and the air flow rate through the module. The pressure drop is the pressure drop over the module. The results of the prior art are shown as a line with bullets. The results of the invention are shown as a straight line. The pressure drop was generated by means of a pump defining flow of the liquid desiccant. This figure shows that according to the prior art, the pressure drop strongly increases when the air flow rate is increased. The function is quadratic or exponential. A higher flow rate than 2500 m ³ /hr could not be achieved. This behaviour clearly shows the effect of turbulence. A higher pressure drop will furthermore strongly increase the risk of carryover and reduce the lifetime of the module. When setting the air flow rate in the low range, up to 1000 m ³ /hr, the pressure drop is very low. However, such a low air flow rate implies that the air-conditioner module needs to have a very large size to work for a specific air volume. Moreover, the prior art material is defined for operation under some turbulence, such that the drying efficiency with the low flow rate is low.

In contrast to the prior art, the dependence between the pressure drop and the air flow rate in the module according to the invention is linear. This implies that the flow regimen in the module is laminar flow. It makes that the air flow can be increased to commercially viable values without increasing the risk of carryover. Experiments were made with the module of the invention to detect the occurrence of carry-over. It was observed that carry-over occurred only at flow rates of approximately 4500 m ³ /h and higher. The striped area shown in Fig. 13 indicates the "forbidden" area of operation in the module of the invention, so as to prevent carry-over. This allows a very high air flow, and still at a pressure drop that is strongly reduced in comparison to the prior art. In fact, the pressure drop in the invention at 4000 m ³ /h is approximately the same as that in the prior art at 2000 m ³ /h.

Fig. 14 shows the drying effect obtained in accordance with the invention. Herein, the reduction in humidity was obtained in dependence of the temperature of the incoming air flow. The y-axis herein indicates humidity as g H ₂ 0 per kg of dry air. The upper line shows the relative humidity of the incoming air flow, when the relative humidity (RH) is 80%. The lower line shows the relative humidity of the air flow leaving the air-conditioner module. It turns out that for any temperature of the incoming air, the humidity in the reduced with at least 50%. At a high air temperature of 27°C, the air contains three times as much humidity as at 10°C. The reduction in humidity achieved with the module of the invention increases then to 75-80% reduction (from 18 g/kg to 4 g/kg). Fig. 15 shows a comparison of the drying efficiency (also known as dehydration effectiveness) of the modules of the prior art and the invention. This result was obtained for a high air temperature of 27.5°C and a humidity content of 12-13 g/kg. This corresponds to a lower relative humidity (RH) than the 80% line shown in Fig. 14. It is apparent from this Figure that the tested module of the invention (line A) gives a drying efficiency in the range of 70-80%. The prior art (line B) merely achieves 40-50%. This strong increase in drying efficiency is obtained at even lower ratios between the LiCl and the air mass flow, thus with less LiCl flow at a given air flow rate, or alternatively equal LiCl flow at a higher air flow rate. The drying efficiency is calculated as the ratio of the actual dehydration to the maximum possible dehydration of the air. The maximum possible is the difference between the water vapour content of humid air at the air inlet and the equilibrium water vapour content of air in contact with the liquid desiccant solution.

Fig. 16 shows a further embodiment of a module in accordance with the invention, in a diagrammatical cross-sectional view onto a sheet. In accordance with this embodiment, a first container 71, a second container 72, and a third container 73 are present and overlie the air channels 20 and the liquid channels 30. The three containers 71-73 are for instance embodied as a vessel subdivided into three sub-containers, with partitions in between. Alternatively, individual containers attached to one another or simple arranged adjacent to one another can also be employed. In the embodiment with one partitioned vessel, the partitions are preferably impermeable to the liquid desiccant. Fewer or more containers may also be used. In an implementation, each container 71, 72, 73 is provided with a separate entry 81, 82, 83 to the liquid channel. These entries may take the form of a manifold, of which different types are feasible. The manifold may comprise a porous material, through which the liquid desiccant may flow downwards. The manifold may alternately comprise a body of for instance rigid material with apertures. The manifold may also comprise a combination of a rigid body and a layer of porous material. A preferred version of the manifold is shown in Fig. 9 and lOa-lOb. The module may further be provided with a plurality of containers below an exit of the liquid channels 30, i.e. at the bottom of a module 10, so as to collect the liquid that has passed the liquid channels in a specific section separately. Typically, such section corresponds to the overlying containers 71-73, and any connections to the entry regions of the liquid channels. It has been found, in experiments with a first prototype of the module of the invention, that the liquid flows downwards without broadening of flow area.

In operation, the first, second and third containers 71-73 are typically provided with liquid that will flow into the liquid channels 30 of the module 10 from the containers 71-73. Suitably, the containers 71-73 are arranged such that each of them overlies a section of substantially all the liquid channels 30. More preferably, the intermediate manifold - which is particularly embodied in the form of strip wise extending distance holders as shown in Fig. 9, 10a and 10b - is configured such that the liquid in the first container 71 is distributed to all of the liquid channels 30. The same holds for the liquid in the second container 72 and in the third container 73. It is not excluded that the intermediate manifold distributes the liquid from any one of the containers 71-73 merely to selected (rather than to all) liquid channels.

The use of a plurality of containers 71-73 in combination with a single module 10 may be used for setting a flow profile along the width of the liquid channel 30. This is deemed beneficial to tune and optimize the flow. The use of a plurality of containers 71-73 in combination with a single module 10 may further be used so that different liquids will flow in different sections of the liquid channels 30. In one specific example, the liquid flowing from the first container 71 into the first section is an evaporative liquid, such as water, and the liquid flowing from the third container 73 into the third section is a liquid desiccant. The second container 72 is for instance kept empty. The functions of evaporative cooler and dehumidifier are therewith integrated into a single module. This significantly simplifies the overall design, since there is no need for any connection of modules. Still, the air flow is first cooled and thereafter dehumidified.

In another specific example, the first container 71 contains an evaporative liquid, particularly water, the second container 72 contains a liquid desiccant and the third container 73 contains a diluted solution of any desired additive, for instance a disinfectant, a fragrance or parfum. It will be understood that variations are feasible. A single module may contain merely two overlying containers or even more overlying containers. Furthermore, it may be feasible that the two of the containers contain the same liquid (water, liquid desiccant), but in a different state, so as to set a flow profile along the width of the liquid channel. Options for setting flow profiles are further specified in a co-pending and simultaneously filed application of the Applicant. Generally, the term 'state' of the liquid refers to temperature, (static) pressure, concentration and/or composition.

Fig. 17 shows a further implementation of the module of the invention, in again a very

diagrammatical view onto a sheet 10. In the shown implementation, a first container 71 and a second container 72 overlie the module 10. In addition, the liquid channels 30 are subdivided into a first section 30A and a second section 30B with an intermediate isolation area 33. Such subdivision is suitably achieved by provision of the layer of wicking material onto the sheet according to a predefined pattern. The subdivision into a first section 30A and a second section 30B will further prevent any mixing of the liquid from the first container 71 and the second container 72.

Furthermore collecting containers 91, 92 are shown for the two different liquids.

It will be understood that the subdivision into a first 30A and a second section 30B only is merely an example and that any desired number of sections may be present. Furthermore, in dependence of the overall width of the sheets, a further strengthening protrusion may be defined in the intermediate isolation area 33. Rather than implementing the first section 30A and the second section 30B onto a single sheet 10 by patterning the layer of wicking material 11, it is feasible that the first section 30A and the second section 30B are defined on separate sheets that are however integrated into a single module. Furthermore, though it is deemed beneficial for manufacturing reasons and for the avoidance of carry-over that the corrugation present in the first section 30A and the second section 30B is identical, this is not deemed strictly necessary.

Fig. 18(a) shows in a highly schematical, cross-sectional view a sheet 10. Fig. 18(b) shows the same sheet 10 in combination with a manifold 240. While merely one sheet 10 and one manifold 40 are shown, it is observed that these are deemed representative for a full module comprising a plurality of sheets adjacent from each other. Both the sheet 10 and the manifold 40 are herein preferably of the types as have been discussed with respect to preceding figures. In summary, the sheet is herein corrugated and particularly comprises a pattern of waves. The series of waves is arranged from the top to the bottom, such that when propagating from the top to the bottom, in accordance with a flow pattern that liquid will follow, the liquid will follow a path between its inlet 31 and its outlet 32 that is substantially sine -wave shaped. It is preferable in this configuration that the edges of the sheet 10 are planar, which facilitates assembly of the sheets into the module.

Furthermore, air is transmitted between its inlet 21 and its outlet 22. This air channel is effectively rather straight, at least for an infinitissimally small volume of air, and more particularly within the width of the liquid channel. The sheet may further be strengthened by means of additional protrusions running in a direction different and preferably substantially perpendicular to the series of waves. Preferably, these protrusions are themselves also wave-shaped and more preferably, they are located outside the liquid channel. The manifold 40 is herein most suitably embodied as a plurality of strips that simultaneously act as spacer between adjacent sheets.As shown in Fig. 18(a) and Fig. 18(b), the sheet 10 is provided with the same shape as the manifold 40. This may be suitable, but is not deemed necessary. It is however important that the manifold contains a first level 241 and a second level 242. There is furthermore shows a third level, but that is merely a side wall 51 to the container 50 for liquid that is defined in between of the manifold 40. Herein, the first level 241 and the second level 242 are provided with entry regions through which liquid may pass to a liquid channel defined at the surface of a sheet 10. These entry regions are suitable of the type as discussed with reference to Fig. 10 and 11, but other versions may well be feasible. Importantly, the reservoir 50 is provided with a first inlet 61 and a second inlet 62. As shown in this view, the first inlet 61 and the second inlet 62 are provided on top of each other at different levels: the first inlet 61 is configured for the provision of liquid on the first level 241. The second inlet 62 is configured for the provision of liquid on the second level 242. The final implementation may however be different, and the inlets 61, 62 could be arranged at the top. Furthermore the first inlet 61 could be designed for a different flow rate than the second inlet 62.

What matters, is that the first inlet 61 is designed for another type of liquid than the second inlet 62. In one most beneficial example, the first inlet 61 is configured for water and the second inlet 62 is configured for the provision of a cleaning disinfectant. The intention thereof is that the cleaning disinfectant will flow over a broader area than the water.

This principle is shown in Fig. 18(c) and 18(d). Fig. 18(c) shows herein the sheet 10 onto which water flows. The water is applied on the sheet 10 only via the first level 241 of the manifold. As a consequence of the flow profile of the water, it will have width W-l. This width is smaller than the width of the sheet and is typically equal to the width of the liquid channel as has been defined hereinabove. The water is supplied into the container 50 through the first inlet 61. The water level in the container is controlled such that it remains below the second level 242.

However, after a predefined time of operation, the module needs cleaning. This cleaning more particularly involves a disinfectant so as to remove any type of microbiological material. However, the cleaning may alternatively or additionally include a treatment with another type of solution. In accordance with this embodiment and as shown in Fig. 18(d), the cleaning disinfectant is supplied into the container 50 through the second inlet 62. The liquid level in the container 50 is then controlled so that the cleaning disinfectant is held above the second level 242. As a consequence, the cleaning disinfectant will not merely flow over the sheet 10 in an area with a width W-l, but also outside thereof. The cleaning disinfectant will flow over a width W-2, which is larger than W- 1 but suitably still smaller than the width of the sheet. In this way, it is ensured that the full sheet 10 in so far as there is the least chance that it will get into contact with liquid is appropriately cleaned. It may herewith be, that carry-over of the cleaning disinfectant in the air flow may occur. However, first of all, there does not appear a need that an air flow is provided during the incidental periods that the cleaning disinfectant is provided onto the sheet 10. Secondly, even if there would be some carry-over, this can be dealt with: the air flow during such cleaning operation can be considered as exhaust air.

It is added for sake of completeness that an aqueous solution could be applied as an alternative to water. Such aqueous solution is typically diluted, particularly in comparison to a liquid desiccant solution and suitably diluted to such an extent that a layman would consider the resulting liquid any kind of water.

This innovative design as shown in Fig. 18 is particularly intended for use in cooling towers, where air is cooled by evaporation of water. Such cooling towers however need to be cleaned regularly, so as to avoid microbiological growth to an undesirable level, and also to remove any other contaminants that are left behind in the module upon evaporation of the water. Regular cleaning is needed and are a particular concern for cooling towers. Because the cooling towers are often close to the public, the risk of infection from poorly maintained cooling towers is elevated. The stabilisation of contaminant concentrations is usually accomplished by blowdown, which is the constant discharge of a portion of the circulating water to waste, and its replacement by fresh water. In fact, in accordance with the shown design, the cleaning of cooling towers becomes more efficient and may be carried out with less delay and/or costs, therewith overall reducing the risk of growth of pathogenic bacteria, including for instance Legionella Pneumophila, possibly resulting in Legionella's disease. Furthermore, because the cleaning area has a larger width than the flow area of the water, the risk that bacteria remain behind is further reduced. It is additionally observed that the module of the invention is anyhow designed for minimum carry-over, and further achieves this in accordance with operation of the air flow in laminar flow regimen, resulting in a low pressure drop as compared to conventional modules. This already reduces the risk of carry-over of the pathogenic bacteria, even without the use of the preferred embodiment as shown in Fig. 18.