The invention relates to the field of cooling towers such as are used, for example, in power stations or industrial plants. In particular, it relates to counter- flow thermal exchange installations fitted inside so-called wet or hybrid cooling towers.

Background of the invention

Waste heat from power stations or large industrial plants may be dissipated to the atmosphere by means of natural draught cooling towers, or by mechanical draught coolers with sucking or blowing fans. In so-called wet cooling towers, the waste heat is normally extracted from the plant as heated water which is subsequently sprayed on to the so-called "fill" of the cooling tower. The heat-exchange fill typically comprises many counter-flow fill modules which are generally manufactured as a matrix comprising many vertical or near- vertical surfaces which the coolant (typically water) can flow as a downward- flowing film, while large volumes of air flow up through air channels between the vertical liquid-flow surfaces. The air current may be generated by fans and/or by the natural chimney effect of a high tower, which may have the outline of a hyperbola. The heat transfer from the water to the upward-flowing air takes place mainly through evaporation from the film of water, which is flowing down the liquid flow surfaces, into the passing upward airflow. Coolant fluids other than water may also be used.

In hybrid cooling towers, the "wet" fill arrangement described above is supplemented by a "dry" heat-exchange system in which coolant flows through a closed heat-exchange circuit. Dry heat-exchange units typically comprise radiating fins or a matrix of surfaces which are arranged to conduct heat away from the coolant and which provide a large dry heat-exchange surface to environmental air flowing over the fins or matrix. In such hybrid heat-exchange systems, the dry air warmed by the dry heat-exchange units is mixed with the wet air warmed by the wet fill modules in the space above the fill, so as to reduce the amount of visible vapour plume which issues from the top of wet (counter-flow) cooling towers. Dry heat-exchange units require dry cooling air, and hybrid cooling towers typically require many large, powerful fans and special ducting in order to draw dry environmental air in from the tower's surroundings, and thereby generate the required airflow over the dry heat- exchange modules.

Such counter-flow and hybrid cooling systems are still far from achieving the cooling efficiency which may be achieved with direct cooling, for example, in which coolant from a body of water such as a river, lake or sea is pumped through the plant's condensers or coolers and then, after heating, back out into the body of water. The performance of the cooling system may be expressed in terms of the temperature of the coolant (eg water), and it typically influences the overall efficiency of the power station or plant. The lower the temperature of the coolant, the more output (ie work or electrical energy) is obtained per unit of primary energy source (coal, gas, uranium, etc.) used. Efficient cooling is thus important for reducing CO2 emissions and other environmental impacts.

Related prior art

Prior art counter-flow fill modules are typically manufactured as large rectangular blocks, each comprising many liquid flow surfaces, and the module blocks may be fitted such that they abut each other to form a layer of modules occupying all or most of the cross-sectional area of a wet cooling tower. Multiple layers of blocks may be used, one layer above another, to increase the counter- flow heat-exchange surface area. An example of a prior art cooling tower 1 is shown in schematic cross-section in figure 1 . In this example, two layers of counter-flow fill modules are shown. In operation, water which has been heated by the power station or plant is sprayed on to the top of the fill 2 by nozzles 3 and flows down the liquid flow surfaces of the modules 5. The upward-flowing air 9 cools the downward-flowing water. Once it reaches the bottom of the liquid flow surface of the bottom-most fill module 5, the cooled water 10 falls to a collecting pool 20 below, from where it is pumped back into the cooling cycle. The space between the fill and the pool below is referred to as the rain room. The amount of "rain" 10 falling from the fill into the pool 20 may be large; in a wet cooling tower of a medium-sized nuclear power station, for example, the rain may fall at a rate of thirty to fifty tonnes per second. The rain room is typically open at the sides, so that the required large volumes of air can be drawn from outside the tower 1 and up through the counter-flow fill 2 via the rain room.

It has hitherto been assumed that the cooling performance of such counter-flow systems can best be optimized by maximizing the heat-exchange surface area, ie the phase boundary, of the coolant liquid (usually water) flowing down through the fill, and by maximizing the volume of the air flowing up through the fill. To this end, prior art cooling installations have been designed to maximize the airflow and to maximize the heat-exchange surface area between the water and the air. In PCT application WO2012059496, it was proposed to improve the efficiency of a cooling tower by improving the aerodynamic flow characteristics of the cooling air around the periphery of the rain room. It was also proposed to remove the rain at the periphery of the rain room in order to improve airflow into the rain room. However, these measures were only designed to affect the aerodynamic characteristics at the outer periphery of the rain room, by reducing air flow resistance at the critical air inlet zone where air velocity, and thus losses, are highest. As will be explained in more detail below, new experimental measurement data has now been obtained which shows that the radial heat exchange which occurs between the rain 10 and the cross- flowing air 9 in the rain room may have a negative effect on the overall thermodynamic performance of the cooling tower 1 .

As mentioned above, prior art rain rooms involve a large amount (thirty to fifty tonnes per second, for example) of water 10 falling into the collection pool 20. A prior art rain room is thus an extremely noisy and hostile environment, into which humans and machines cannot safely be deployed. This means that the cooling tower 1 , and therefore the power station or plant, must be shut down for any cleaning, maintenance or repair work which involves entering the rain room beneath the counter-flow fill 2. The high noise levels also impose significant constraints on the environs of the tower 1 ; a significant area around the tower 1 may be deemed unsuitable for building homes, or even workplaces, because of the noise from the rain room. Alternatively, extensive noise abatement measures, such as raised earth banks or sound screening around the tower may be required in order to deflect or mitigate the noise.

Brief description of the invention

The present invention aims to address the above and other

disadvantages of prior art counter-flow cooling systems. In particular, it aims to provide a counter-flow fill module according to claim 1 , a cooling tower according to claim 9 and a method according to claim 11 . Other variants of the invention are set out in dependent claims 2 to 8, 10 and 12 to 15. By integrating the function of rain collection and disposal into the bottom-most counter-flow fill modules, it is possible to eliminate or significantly reduce the rain density in the the rain room without the need for the large, unwieldy and vulnerable structures which have hitherto been proposed. The combination of heat-exchange and coolant collection and conveying functions into one counter-flow module means that the counter-flow modules can easily be fitted to existing counter-flow fill installations, thereby improving thermodynamic efficiency of the cooling tower. An additional advantage is that the noise of the falling rain in the rain room may also be significantly reduced, and the rain room may be rendered more accessible, even during operation of the tower, to humans or machines. Features of the counter-flow modules of the invention are such that they are less susceptible to fouling. If fouling does occur, the fouling may be more easily cleaned, even during operation of the tower, for example by pressure-washing from below.

Furthermore, since the use of counter-flow modules according to the invention allows the amount of rain in the rain room to be eliminated or greatly reduced, the air which enters the bottom of the heat-exchange fill region 2 of the tower may be substantially dry. This makes it possible to fit dry heat-exchange modules in the fill 2 among the wet (counter-flow) heat-exchange modules, with both types of modules sharing the same source of upwardly flowing dry air. The counter-flow modules can still function as usual, generating a strong natural updraught 9 by the chimney effect and thereby drawing in dry environmental air through the bottom of heat-exchange fill 2. In this case, the same updraught 9 also flows up through the dry heat-exchange modules. The advantages of a hybrid cooling system (eg reduced plume) may thus be achieved without the need for powerful fans and/or separate dry-air ducting.

The inventor of the present invention carried out extensive experimental measurements of conditions in the rain room of a conventional counter-flow cooling system, and discovered that, in a narrow volume below the main counter-flow fill modules 5, there was a significant surface of heat exchange as a result of the rain droplets leaving the fill. These droplets have a broad spectrum in terms of size and corresponding fall velocities. An intensive cooling effect was detected in this zone, and may be explained by considering the three types of raindrops which fall from the lower edge of a conventional counter-flow fill module. Firstly, very small droplets issuing below the counter-flow fill 2 are likely to be carried back upwards to the fill 2 after they have transferred part of their heat to the air. They offer a large surface to mass ratio and are quickly cooled.

Secondly, droplets of intermediate size, up to a diameter of around 1 mm, are likely to stay suspended in the air within this narrow zone for a while due to their fall velocity being comparable to the velocity of the up-draught air 9; they are also likely to cool down substantially before they rain down out of the zone, and they contribute further to the cooling of the water.

Thirdly, larger drops of up to 6mm in diameter are quickly accelerated by gravity, leaving the lower edge of the counter-flow fill modules with relatively little heat exchange to the air due to their smaller surface in relation to their mass. Such larger droplets may also create a down drag on the surrounding air, thereby slowing the upwards airflow, which can also be detrimental to the tower's cooling performance.

While the understanding of the thermodynamic processes in the rain room of the towers has progressed, and calculation tools have improved, an apparent paradox has been observed, namely that an improvement in the radial component of the heat exchange between the vertically falling rain and the cross-flow (the horizontally flowing air) may reduce the overall performance of prior art cooling towers.

The cooling performance gains which can be made as a result of aerodynamic improvements at the periphery of the rain room may be more than offset by performance losses due to cross-flow heat exchange with the air flowing to the inner areas of the rain room. These losses arise because the air which reaches the inner areas of the rain room has already been significantly warmed by the rain through which it has passed. Since it is already warm, its cooling capacity in the central areas of the counter-flow fill 2 is significantly reduced.

Further efficiency losses are incurred in the tower updraught 9 due to heterogeneous radial air temperature distribution as it issues upwards from the counter-flow fill system of the tower and into the tower chimney. This also contributes to a reduction in the overall tower performance.

A further effect arises as a result of the relatively high fall velocity of the droplets in the lower zone of the rain room. This generates a down drag, high turbulence and vertical mixing of the airflow laminae, which is detrimental to the thermodynamic performance of the tower.

As a result of these insights, the inventor has now recognised that it is beneficial to reduce the amount of radial cross-flow heat transfer in the lower areas of the rain room, and to increase the upwards counter-flow heat transfer in the narrow upper part of the rain room. The particular dimensional

parameters of the counter-flow modules of the invention, and their position in the rain room, can be optimised for the particular requirements of a particular tower design based on field measurements and analysis/modelling tools.

Detailed description of the invention

The invention will be described with reference to the appended drawings, in which:

Figure 1 , as described above, illustrates a schematic cross-section of a cooling tower having a counter-flow fill system as known in the prior art. Figure 2 shows a simplified schematic representation of the function of counter-flow fill modules.

Figure 3a shows a schematic end-view of an example of a counter-flow fill module according to a first embodiment of the present invention.

Figure 3b shows a schematic end-view of an example of a counter-flow fill module according to a second embodiment of the present invention.

Figure 4 shows a schematic side-view of an example of one of the liquid flow surfaces 7 shown in figure 3a or 3b.

Figure 5 shows a schematic side-view of an example of a composite liquid flow surface combining features from figure 3a and 3b.

Figure 6 shows a schematic side-view of a liquid flow surface of a counter-flow module according to a variant of the present invention.

Figures 7a and 7b show schematic representations of two examples of counter-flow fill modules, fitted and in operating, according to two variants of the present invention.

Figure 8 shows a schematic side view of a hybrid cooling arrangement according to a variant of the present invention.

The drawings are provided as an aid to understanding certain underlying principles of the invention, and are not intended to indicate any particular limitations of the claimed scope of protection. Where the same reference signs have been used in different drawings, these are intended to refer to the same or corresponding features. However, the use of different reference signs should not be taken as indicating a particular difference between features. References in this text to the "fill 2" of a cooling tower are intended to refer to the heat- exchange zone as a whole, while the term "counter-flow fill module (5)" refers to a single constituent block of the fill 2.

Figure 2 shows in greatly simplified, schematic form, an example counter-flow fill structure 2 of two layers of counter-flow fill modules; an upper layer of first modules 5 and a lower layer of second modules 6. Each module is denoted by a dashed outline and comprises many liquid-flow surfaces 7, down which the coolant 10 can flow while being cooled by the upward-flowing air 9. The liquid flow surfaces 7 are shown as parallel planar surfaces, inclined at an angle from the vertical, in which case they may be arranged to catch free-falling coolant falling from above. However, the liquid flow surfaces 7 may in practice be oriented vertically, for example if the falling coolant is flowing directly off a liquid flow surface of the module 5 above and on to the liquid flow surface 7 in question. Both sides of each heat-exchange sheet or plate preferably serve as a liquid flow surface 7. The arrangement shown in figure 2 is highly simplified. In practice, the arrangement of liquid flow surfaces 7 in such modules may be more complicated, and the liquid flow surfaces 7 may be formed as a complex matrix of vertical or near-vertical surfaces, arranged for example in an intersecting pattern, or sometimes with corrugations, to give structural strength to the module as a whole, and to maximise the magnitude of the surface area down which the coolant liquid can flow. In contrast to former practice, in which asbestos cement plates were usually used, counter-flow fill modules are manufactured and supplied as a single integral structure, typically a rectangular block, so that they can be easily transported, handled and fitted. The matrix of liquid flow surfaces may be made of a thin plastics material such as polyvinyl chloride (PVC or uPVC), polypropylene (PP) or acrylonitrile butadiene styrene (ABS), with a wall thickness of 0.3mm or 0.5mm, for example. Alternatively, some modules are manufactured as grid structures or similar. The liquid flow surfaces 7 may for example be 2 or 3cm apart when plates of films are used. Large modules, for example of 2m x 0.5m x 0.5m, may thus be manufactured as strong, lightweight blocks. In figure 2, the lower modules 6 are shown as less tall than the upper blocks. The lower edges of the lower modules 6 are indicated by the reference 8. In prior art counter-flow fill modules, the coolant 10 would simply flow down and fall off the lower edge 8 to the collection pool 20 below. As will be discussed in relation to the invention, by contrast, the lower edges 8 of the liquid flow surfaces 7 of the lower modules 6 are adapted to convey the coolant 10 laterally to a drop-off point (not shown), without falling directly off the lower edge 8.

Figures 3a and 3b show two example embodiments of modules according to the invention. In both cases, the liquid flow surfaces 7 are illustrated from an end-view, and are shown as parallel, planar sheets or plates, set at an angle 4 from the vertical. The angle 4 may be between 0 and 30 degrees, for example. In some configurations, the angle 4 may be significantly greater than 30 degrees, even approaching 90 degrees (see for example the non-linear lower edges 8 illustrated in figure 6, which will be described below). The liquid flow surfaces 7 may typically have more complex forms and arrangements, and they may be equipped with intermediate structural members (not shown) for strengthening the module 6 and/or for holding the liquid flow surfaces 7 in position in the module 6 and in relation to each other. The materials of the liquid flow surfaces 7 may also be chosen to be more robust (eg a thickness of 1 mm) in the counter-flow modules 6 of the invention than in conventional counter-flow fill modules 5, in order to permit a more open structure, and so that the lower edges 8 can be formed as lateral flow guides 14, 15.

In some applications, for example where the liquid flow surfaces of the upper counter-flow fill modules 5 are vertical, and both sides of the sheets or plates which form the liquid flow surfaces 7 may function equally well as liquid- flow surfaces 7, it may be advantageous to set the liquid flow surfaces 7 of the counter-flow modules 6 also to be vertical or near vertical (ie angle 4 of the liquid flow surfaces 7 from the vertical is zero or less than 5 degrees), and to set the separation pitch and the positions of the liquid flow surfaces 7 of the counter-flow modules 6 to be the same as those of the liquid flow surfaces of the counter-flow fill modules 5 above them.

The liquid flow surfaces 7 of the counter-flow modules 6 may preferably have hydrophilic properties for promoting a homogeneous water film at its surface. This may be achieved by means of a hydrophilic coating applied to the liquid flow surfaces 7, for example. The lower edge 8 may be provided with a hydrophilic coating in order to increase the volume of water which may be conveyed along the lower edge 8.

In the first embodiment, shown in figure 3a, each of the lower edges 8 is provided with a runnel 15 for collecting coolant flowing down the liquid flow surface 7 and diverting it laterally to a drop-off point, as will be discussed below. In the case where the liquid flow surfaces 7 are vertical (ie angle 4 is zero), separate runnels 15 may be provided for each opposing liquid flow surface 7 of the vertical sheet or plates of the counter-flow modules 6. Alternatively, a single runnel may be formed at the lower edge 8 such that the single runnel collects water from both of the opposed liquid flow surfaces 7 of each sheet/plate (not illustrated).

In the second embodiment, shown in figure 3b, each of the lower edges 8 is provided with an edge portion 14 which serves as a surface on which the downward-flowing coolant (typically water) can collect and be retained by its own surface tension, while flowing laterally to a drop-off point. The edge portions 14 may optionally be shaped to be thicker than the material of the liquid flow surfaces 7, as depicted in figure 3b, depending on the geometry of the lower edges 8. A greater coolant volume or a slower coolant flow rate would require a larger surface area on which the coolant can collect. It has been found that the coolant 10 may accumulate to a maximum stream depth of

approximately 7mm on the lower edge 8 before its weight causes it to separate from the lower edge 8 if relying on surface tension only. A thickened portion 14 of the lower edge 8 thus results in a greater volume of water which can be conveyed laterally along the lower edge 8. Additional measures can be used to increase the transport capacity of the lower edge 8, such as increasing the angle from the horizontal (and thereby also the flow velocity). Upwards wind drag also helps to increase the transport capacity beyond that which is achieved by surface tension alone. The lower edge flow path may also be shaped and directed (for example by including a curvature to provide a centrifugal force assisting retention of the flowing water on the lower edge). Such measures can help to stabilise the flow and to retain the coolant water on the lower edge, and thereby further increase the lateral coolant transport capacity of each liquid flow surface element 7.

The surface-tension type flow guides 14 may be treated or coated to promote their hydrophilic properties sufficient for keeping the water flow attached to the lower edge 8 by surface tension, thereby maximising water transport capacity. They may optionally be equipped with pins, textured surfaces, edge duplication or multiplication, treads or other fouling-resistant features. Fouling may occur as a result of slime generated by bacteria, for example, by chemical processes (scaling) or as a build-up of foreign matter deposited from the flowing water.

The runnel 15 or (thickened) edge portion 14 (referred to collectively as the lateral flow guide) provides extra strength to the lower edge 8, and has a width which is minimised in order to maximise the distance 12 between adjacent lower edges 8, and thereby minimise the obstructive effect of the lateral flow guides 14,15 to the air flowing upwards between the liquid flow surfaces 7. The lower edges 8 of alternate liquid flow surfaces 7 may be set higher or lower in order to increase the effective width of the airflow inlet between the adjacent liquid flow surfaces 7. For the same reason, the pitch 11 of the liquid flow surfaces 7 of the lower modules 6 according to the invention may be chosen to be larger than the liquid flow surface separation distance of conventional modules 5. A pitch 11 of 3cm to 7cm or more may be used, for example.

Figures 4 to 6 show three different examples of geometries of liquid flow surfaces which may be used to implement the invention. In each case, a liquid flow surface 7 is depicted, with a lower edge 8 and a lateral flow guide 14, 15 for conveying coolant laterally along the lower edge to a drop-off point 13, where the coolant falls from the liquid flow surface.

Figure 4 shows a liquid flow surface 7 in which the lower edge 8 is substantially straight, and angled at an angle 16 from the horizontal. The angle 16 may be chosen to suit the coolant flow rate and liquid flow surface geometry in a particular application. A value of angle 16 may be chosen between 5 and 30 degrees, for example, or it may need to be greater than 30 degrees in some configurations. The lower edge 8 of the counter-flow modules 6 need not be straight. The angle 16 may be varied along the length of the lower edge 8. It may for example be increased towards the drop-off point 13 in order to provide increasing coolant-conveying capacity towards the drop-off point 13. Similarly, the dimensions of the lateral flow guide 14, 15 may increase towards the dropoff point 13 in order to provide increased carrying capacity.

Figure 5 shows a second example of a liquid flow surface 7 according to the invention, in which the lower edge 8 comprises two lower edge portions 8' and 8". Portion 8' is shown angled at angle 16 to the horizontal, while portion 8" is angled at angle 17 to the horizontal . As with figure 4, the angles 16 and 17 may be varied (eg increased) along the edge portions 8' and 8" respectively in the direction of the drop-off point 13. The two edge portions 8' and 8" may be equipped with different types of lateral flow guide. In the illustrated example, a surface-tension-type lateral flow guide 14 is shown feeding into a runnel-type lateral flow guide 15.

Figure 6 shows an example of a lower module 6 in which the liquid flow surfaces 7 each have two lower edge portions, angled oppositely from the horizontal, and conveying the coolant laterally to two different drop-off points 13' and 13". Alternatively, the two edge portions could be arranged to convey the coolant to a single, common drop-off point, for example in the middle of the lower edge 8. Figure 6 also shows how the lower counter-flow fill modules 6 may be suspended from the counter-flow fill modules 5 above, for example using support elements 18. The length of support elements 18, and therefore the height of the vertical separation distance between the upper 5 and lower 6 modules, may be varied to suit different conditions in different parts of the rain room, as will be discussed in more detail below. The lower edge 8 shown in figure 6 has an angle from the horizontal which increases towards the drop-off point 13' or 13". In this case, the angle varies as a second-order function of the position along the lower edge 8, ie the increase in the angle increases at an increasing rate towards the drop-off point 13', 13".

The different parts of the counter-flow module 6 may be designed for minimising the effects of fouling on their performance. The liquid flow surface 7 may be rendered self-cleaning by setting its angle from the vertical at between 5 and 10 degrees so that droplets impinging on the surface have a cleaning effect on the liquid flow surface 7. The runnel type lateral guide 15 may be angled sufficiently from the horizontal so that liquid flow velocity is enough to avoid sedimentation of particles. The surface-tension type lateral guide 14 may be protected by selecting surface properties which avoid fouling, as discussed above.

Counter-flow modules 6 according to the invention may advantageously be fitted so that they are accessible for cleaning from below, for example by means of water jets. Cleaning, if required, may be accomplished during plant operation.

Figures 7a and 7b show two arrangements by which the coolant can be collected from the drop-off points 13 of the lower edges 8 of the liquid flow surfaces 7 of the lower modules 6. In both examples, gutters or channels 19 may be configured so that they occupy less than 8%, for example, of the combined plan view area of the counter-flow modules 6. The example gutters or channels 19 are used to collect the falling coolant 10 from multiple drop-off points 13, before delivering the coolant to the collection pool 20 below, either as free-falling streams, as shown in figure 7a, or through downpipes 21 , as shown in figure 7b.

The downpipes 21 may be arranged to feed the collected water down into the pool 20 below the water level in the pool 20, so as to reduce the level of the noise in the rain room. The water outlet into the rain room or into the pool 20 may be directed in such a way as to promote circulation within the pool 20 and thereby promote a homogeneous cooling water temperature.

Alternatively, the downpipes 21 may be arranged for leading the collected water to a pressure header for further applications, such as further energy recuperation.

The inclusion of specially-adapted counter-flow modules 6 with integrated coolant-collection elements 14, 15 helps to reduce the rain density in the rain room, and thereby reduces the pre-heating of the air so that the temperature differential between the air 9 flowing up into the counter-flow fill 2 and the air flowing out of the top of the of the counter-flow fill 2 as large as possible, and so that variance in the the air temperatures across the counter- flow fill 2 is greatly reduced. When modelling the thermodynamic design of a counter-flow cooling system, the geometry of the lower edge of the inventive counter-flow modules 6 offers extra parameters which can be varied to optimise the overall

thermodynamic performance of the counter-flow system.

A similar advantage is to be achieved when designing a hybrid system.

Figure 8 illustrates an example of how a dry heat-exchange module 30 may be fitted among counter-flow fill modules 5, taking advantage of the relatively dry airflow 9 entering the fill from below. The example dry heat-exchange module 30 is shown with coolant feed and return pipes 32, and with a radiating part 31 , which may for example be a radiator-like structure having fins or a matrix of heat-sink surfaces. As discussed earlier, such a combination of dry heat- exchange modules 30 and counter-flow modules 6, sharing the same in-flowing airflow 9 can help to achieve the advantages of a hybrid cooling system, but without the need for powerful fans or separate ducting for routing dry air to the dry heat-exchange modules. The dry heat-exchange module 30 and counter- flow modules 6 may be combined in any proportion and distribution to suit the thermodynamic characteristics of the particular tower 1 or fill installation 2.

The liquid flow surfaces 7 with flow guides 14, 15 at their lower edges 8 may be assembled or manufactured as integrated structural modules, such as large rectangular blocks which may be 30cm to 1 m wide, for example, 20cm to 50cm tall, and 50cm to 2m long, which can be individually handled and fitted in position under the main counter-flow fill 2 of the cooling tower 1 .

Since the counter-flow modules 6 of the invention are fitted as the lowest level of the counter-flow fill 2, they can be retrofitted to existing counter-flow installations 2, and, because of their light weight, supported on the existing counter-flow fill modules 5 or on the support structure of the existing counter- flow fill modules 5 or other available support structures depending on the particular installation. The height of the counter-flow modules 6 of the invention should preferably be kept as small as possible, in order not to impede the radial flow of air. They may for example be between 150mm and 350mm in height - significantly less tall than the main counter-flow modules above them. However, it may be advantageous in some circumstances for the counter-flow modules 6 of the invention to be suspended such that there is a significant separation distance between the bottom face of the counter-flow modules above and the top face of the counter-flow modules 6 below. This separation distance can be varied depending on the desired effect, and may typically be increased towards the centre of the rain room, where the horizontal component of the air flow is less dominant.

The area below the counter-flow fill 2 can thus be rendered practically rain free, thereby enhancing the flow of air 9 from the tower inlet through the area of the rain room without any significant preheating, to the central region of the tower 1 . The colder, dryer environmental air thus offers improved cooling. Coolant-collecting counter-flow modules 6 according to the invention may be installed under the whole counter-flow cooling system 2 (ie across the whole area of the tower), or they may be installed under the majority (ie at least 50%) of the base area of the cooling tower 1 . Alternatively, the coolant-collecting counter-flow modules 6 may be installed selectively; for example, rain-free corridors may be formed through the rain room by judicious placing of the coolant-collecting counter-flow modules 6 of the invention, thereby enabling fresh, dry air to be provided laterally to rain zones equally throughout the tower. Thus, the modular construction of the coolant-collecting counter-flow modules 6 of the invention affords significant freedom for designing the airflow in the rain room.

Due to the relatively modest height (eg 150mm to 350mm) of the counter-flow modules 6, and the vertical or near-vertical orientation of the liquid flow surfaces 7, and their position immediately below the counter-flow fill modules 5, the operational performance of the counter-flow modules 6 may be largely independent of the orientation of the modules relative to the local direction of the horizontal air flow in the rain room below. The options for installing the counter-flow modules 6 above the rain room may thus be simplified, since it is less critical to make sure that the liquid flow surfaces 7 are aligned with the flow direction of the incident airflow. Counter-flow modules 6 may thus be positioned at whatever location in the rain room at which it is desired to reduce or eliminate the rainfall.