Field of the subject matter

The disclosed subject matter relates to an adsorption-type refrigerating apparatus and a process of operating the apparatus to derive negative temperatures from low-grade heat.

Background

The present subject matter can be embodied as a technological part of refrigerating equipment, both mobile and stationary, used in the sectors of retail industry, public catering and food production, as example.

The frequently utilized adsorption-type refrigerating apparatuses are driven by mortar-substances of two components: coolant and adsorbent. The design of such apparatuses contains a generator, condenser, evaporator and adsorber, paired into the corresponding units: generator-condenser, evaporator-adsorber. Other integral functional parts are represented by a mortar recuperative heat exchanger, gas separator and circular pump.

The main shortcoming of the existing types of refrigerating apparatuses is the use of water as a coolant therein. This choice does not allow utilizing the apparatuses to derive negative temperatures. Furthermore, the complexity of the designs is a frequently recorded shortcoming of the above apparatuses. Such complexity is caused by the manifold of units and aggregates that are co-joint in an elaborate network of technological links. As a result, the production of negative temperatures is not facilitated, and this fact in turn, restricts the range of applications of the apparatuses.

There is knowledge of the four-component adsorption-type refrigerating apparatuses using adsorber, desorber, evaporator and condenser, wherein, water is used as a coolant and silica gel - as an adsorber (See the project by Mayekawa (http://www.mayekawa.com/)). In this publication, water, used as a coolant, does not facilitate deriving negative temperatures. Furthermore, separate locations of the above components increase hydrogasdynamic drag between them, which reflects into the decrease of cooling capacity of the kind of apparatuses. With relevance to the technical nature, a solar refrigerating apparatus of periodic operation seems as the closest prior art. This type of apparatus contains two adsorbers, enclosed in a single compartment therein, a condenser of the coolant and a cooling chamber with an encapsulated evaporator. (I. Samson On improving the characteristics and elaborating the method of analysis of a solar adsorption-type refrigerating apparatus or periodic operation. An abstract of the author seeking a postgraduate degree in Sector 05.04.03. Moscow, National Research University MPEI., - 2015, - 20p.-pp. 7, fig.3 Tekhnosfera.com/view/591322).

The adsorbent layer in the above-mentioned adsorption apparatus is too thick to result in noticeable increase of the time of the operation cycle. Further restrictions on the application of this type of apparatus are explained by a twenty-four hour period of the adsorption cycle.

There exist adsorption (absorbing)-type refrigerating apparatuses or thermal- pumps driven by methanol and various ad/absorbents. Due to high pressure of saturated vapor, methanol, when used as a coolant, allows overcoming transporting obstructions, cutting short the interval of temperatures of the operation of the apparatus, and deriving cold of temperatures of 0°C and lower. [Tchernev D. (1999) Int. Sorp. Heat Pump Conf., 24-26 March, Munich, Germany, pp.65-70., Meunier, F. Proceed. 20 ^th hit. Cong. Refrigeration, Sydney, vol III, p.522.] There have been utilized of both solid-bodied pore adsorbents, and liquid absorbents (mortars of inorganic salts and their mixtures).

The shortcomings of the first group described above are the following: low sorptive capacity in the operational cycle of the refrigerating apparatus, and high temperature of adsorbent regeneration. The aftermaths in this case are low values of the refrigeration coefficient. Transporting obstructions characterize the use of liquid absorbents. They are linked to the necessity of methanol vapor diffusion throughout the absorbent layer. This process leads to both an increase of the time of the cycle and low values of apparatus output.

The process of deriving cold with help of a refrigerating apparatus containing an evaporator filled with methanol, adsorber filled with methanol vapors, sorbent and condenser presumes the use of pore matrix in the function of the sorbent. The cycle of this type of apparatus is characterized with the following parameters: the temperature of the evaporator of 0 or 7°C, the temperature of the condenser ranging from 30 to 45°C, the temperature of desorption 85°C (See for example RU Patent no. 2,294,796 "Sorbent of methanol vapors and the process of deriving cold by utilizing a adsorption-type refrigerating apparatus", F25B 17, Published 10.03.2007).

In the presented process, it is shown that a solid-bodied adsorbent used as an adsorber causes effective reach of technological cold ranging from 0 to plus 7°C. At the same time, this solution does not allow reaching negative temperatures. This aftermath is the result of both insufficient level of vacuum in the operational chamber and the thickness of the layer of the adsorbent.

Summary

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

Objectives of the disclosed subject matter are to increase the cooling efficiency and to simplify the design of the adsorption-type refrigerating apparatus.

According to one aspect of the disclosed subject matter, it is provided a refrigerating apparatus capable of producing heat carrier of negative temperatures, comprising:

at least one first heat exchanger unit and at least one second heat exchanger unit wherein the first unit and the second unit are enclosed within a single chamber, wherein the first and the second heat exchanger units comprises at least one tube through which heat carrier can flow from an inlet to an outlet and heat sinks made of substantially parallel layers having surfaces that are perpendicular to at least a portion of the tubes, wherein the tubes pass through the surfaces of the heat sinks;

an absorbent capable of reversibly entrapping a coolant is coating the at least one first heat exchanger unit;

wherein the heat carrier can be of high, medium, or low temperatures and wherein the inlets of the heat exchanger units can alternately receive the heat carrier in an appropriate temperature so that when high temperature heat carrier passes through the first heat exchanger unit, said coolant escapes from the absorbent to the single chamber and condenses onto the second heat exchanger unit through which medium temperature heat carrier flows, and wherein when medium temperature heat carrier flows through the first heat exchanger unit so as to cool the absorbent and cause a pressure drop within the single chamber, and low temperature flows through the second heat exchanger unit so that the coolant boils, re-absorbed within the absorbent, and cools the heat carrier in the tube of the second heat exchanger to negative temperatures.

In accordance with another embodiment, a plurality of basins made of bent portions of the surfaces adjacent to the tube are provided to said at least one second heat exchanger unit, wherein the basins are capable of accumulating the coolant in liquid state.

In accordance with another embodiment, said coolant can be selected from a group of coolants such as methanol and ammonia.

In accordance with another embodiment, said absorbent can be selected from a group of absorbents such as silica gel or activated carbon.

In accordance with another embodiment, the heat carrier is a fluid.

In accordance with another embodiment, said absorbent is a thin layer of two or three granules of silica gel.

In accordance with another embodiment, a distance L between the first and the second heat exchanger units is designed to be minimal.

In accordance with another embodiment, the single chamber is provided with an outlet and a valve.

In accordance with another embodiment, the tube is configured with portions that are descending and portion that are ascending.

In accordance with another embodiment, the tube is configured to be a plurality of substantially parallel tubes having a distributing portion that distribute the heat carrier to within the parallel tubes and a collecting portion that collects the heat carrier from the tubes.

In accordance with another aspect, a method of refrigerating a heat carrier to negative temperatures is provided that comprises: providing a module comprising at least two heat exchangers, each heat exchanger has at least one tube configured to let heat carrier flow within from an inlet to an outlet and heat sinks, wherein the module is enclosed within a single chamber; coating one of the at least two heat exchangers with an absorbent so as to form a coated heat exchanger;

providing coolant to within the single chamber wherein said coolant is capable of being reversible absorbed in said absorbent;

inserting relatively hot temperature heat carrier to the inlet of said coated heat exchanger;

inserting relatively medium temperature heat carrier to the inlet of another heat exchanger that was not coated;

inserting relatively medium temperature heat carrier to the inlet of said coated heat exchanger;

inserting relatively low temperature heat carrier to the inlet of another heat exchanger that was not coated;

wherein negative temperature heat carrier will come out of the outlet of the another heat exchanger that was not coated.

In accordance with another embodiment, said heat sinks are substantially parallel riffles that are positioned substantially perpendicular to the tube.

In accordance with another embodiment, the method further comprises providing a plurality of basins made of bent portions of the riffles that are adjacent to the tube.

In accordance with another embodiment, said coolant can be selected from a group of coolants such as methanol and ammonia.

In accordance with another embodiment, said absorbent can be selected from a group of absorbents such as silica gel or activated carbon.

In accordance with another embodiment, the heat carrier is a fluid.

In accordance with another embodiment, said absorbent is a thin layer of two or three granules of silica gel.

Brief Description of the Drawings

Embodiments are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the embodiments. In this regard, no attempt is made to show structural details in more detail than is necessary for a fundamental understanding, the description taken with the drawings making apparent to those skilled in the art how several forms may be embodied in practice.

Figure 1 depicts a design of a refrigerating module in accordance with a preferred embodiment.

Figure 2 depicts an enlarged cross- sectional view of the evaporator-condenser of the heat exchanger shown in Figure 1.

Figure 3 depicts a design of a refrigerating module in accordance with another preferred embodiment.

Figure 4 depicts routing of coolants in the two modules, according to Figure 1.

Figure 5 represents routing of coolants, according to Figure 3.

Description of the Preferred Embodiments

Before explaining at least one embodiment in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. In discussion of the various figures described herein below, like numbers refer to like parts. The drawings are generally not to scale.

For clarity, non-essential elements were omitted from some of the drawings.

As mentioned herein before, it is an objective of the disclosed subject matter to increase the cooling efficiency and to simplify the design of the adsorption-type refrigerating apparatus.

This can be achieved by using an adsorption-type refrigerating apparatus that is capable of producing carriers with negative temperatures from low-grade heat. The apparatus has two modules, alternately operating as an evaporator-adsorber and desorber-condenser, respectively. The latter are connected to systems of heating and cooling mediums preferably via a three-way spiral automatic ball valve gate, allowing heat intake and withdrawal on the respective steps of desorption and adsorption to the system of operational cold connected to the evaporator.

According to the disclosed subject matter, the two modules or units of heat- exchangers alternately functioning as an evaporator-absorbent and condenser- desorbent are enclosed in a minimal distance L between them and within a single chamber, wherein, the tubes of the heat-exchangers have heat sinks in the form of riffles that are made of layers of one-piece surface in each layer. The elements of the layers are placed horizontally, in parallel to each other. More than two modules can be used and more than one unit of heat exchanger can be utilized.

To enhance efficiency, the surfaces of the heat-exchangers riffles are designed with circular bends in the areas adjoining the tubes to form basins for the liquid coolant to accumulate.

A process of deriving negative temperatures from low-grade heat by an adsorption-type refrigerating apparatus is an integral part of the disclosed subject matter. The process stipulates the use of a solid-bodied coolant-adsorbent, wherein, methanol is used as a coolant, and adsorption takes place in the at least two independent modules consisting of a pair of heat-exchangers that act as an adsorber- desorber and evaporator-condenser, respectively. Needless to mention that more heat exchangers can be used. Methanol, when in the phase of adsorption of the process is subjected to pressure of about 0,007 - 0,03 bars. This approach enables boiling temperature to range from about 0°C to minus 20°C.

Alternatively and additionally, ammonia can be used as a coolant, with a pressure , when in the phase of adsorption ranges from 0,4294 to 0,04082 mPa and the temperature from 0°C to minus 50°C.

In addition, to increase efficiency of the presented process, silica gel or activated carbon, as example, can be used as a solid-bodied adsorbent applied in a thin layer over the outer surface of the heat exchanger, which acts as an adsorber-desorber.

These criteria determine effective behavior of heat mass exchange in the apparatus and increase its cooling capacity.

Provided each module is designed as at least two heat exchangers, enclosed within a single pressure controlled chamber and functioning by turns as an evaporator-adsorber and condenser-desorber, the hydrodynamic resistance is minimized and the two phases of the operational cycle in each unit are joined by turns. As a result, the cooling capacity increases, the overall design of the refrigerant is simplified, and the quality of the apparatus is enhanced.

The alternating mode of operation of the modules when functioning in the cycles of evaporation-adsorption and condensing-desorption, supports continuity of the cooling process and faultless operation of the adsoption-type refrigerating apparatus as a technological mechanism.

The design of the heat exchanger configured as tubes, which have single forming of heat sinks representing a one-piece surface in each layer, the elements of which are placed horizontally in parallel to each other, increases the efficiency of heat and mass transfer by a more even distribution of coolant in the apparatus. This effect is further supported by designing circular bends in the areas of riffles adjacent the tubes. This form determines an increase of the heat gradient and, correspondently, an enhancement of stability of the heat exchanger operation as well as an increase of the coefficient of heat emission.

Creation of vacuum in the phase of adsorption under the condition of coolant optimization in the operational volume determines the process of deriving negative temperatures, wherein, methanol is used as a coolant, and adsorption takes place by turns in the two independent modules, wherein, methanol when in the phase of adsorption in the operational chamber is subjected to pressure of about 0,007 - 0,03 bars, which is the precondition for the boiling temperature to range from 0°C to minus 20°C.

Ammonia, when used as a coolant, with the pressure in the operational chamber in the phase of adsorption ranging from 0,4294 to 0,04082 mPa, determines the temperature to fall in the range from 0°C to minus 50°C. This approach broadens the technological span of the apparatuses, and allows using them, for example, against technological cold of the range from 0°C to minus 20°C or low-temperature cold of the range from minus 20°C to minus 50°C.

Finally, the use of silica gel as a solid-bodied adsorbent in the presented process enhances both the cooling capacity and the service-time of the apparatus. When applied in a thin layer of two or three granules over the outer surfaces of the heat exchanger, including the tubes and the riffles, silica gel reduces noticeably the time of the operational cycle and facilitates heat mass transfer. Similar indicators can be reached when activated coal is used as solid-bodied adsorbent. The drawings included herein reflect the specific features of both the design of the adsorption-type refrigerating apparatus and the process of deriving negative temperatures.

Reference is now made to Figure 1 illustrating a design of a refrigerating module in accordance with a preferred embodiment. The configuration of a refrigerating module is preferably as follows:

Two heat exchangers, a first heat exchanger unit 2 and a second heat exchanger unit 4, are enclosed in a single chamber 1 and alternately operate as an adsorber-desorber and condenser-evaporator. The heat exchanger 2 comprises of tube 5 having descending and ascending portions with riffles 6 through which the ascending and descending portions of the pipe 5 passes. . The outer surface of the heat exchanger 2 is covered with a thin layer of an adsorbent 3 that can reversibly absorb a coolant that is presented within the chamber 1. The heat exchanger 4 comprises in a similar manner tube 7, configured with ascending and descending portions that passes through riffles 8. The heat exchangers are enclosed within a single chamber 1 with a partition 10, at a minimal distance L from one another. The outlet branch 9 with a valve 11 fitted to it is used to form vacuum in an operational chamber 12 formed between the heat exchanges. The pipe of the heat exchanger 2 has an input 13 and an output 14. In a same manner, an outlet 16 and an inlet 15 of the heat exchanger's 4 pipe 7 are shown. The directions, indicated with arrows in Figures 1, 3, 4, and 5, represent the direction of the coolant flow.

Reference is now made to Figure 2 depicting an enlarged cross- sectional view of the evaporator-condenser of the heat exchanger shown in Figure 1. In the areas in which the tube 7 pass through the riffles 8 in the heat-exchanger 4, circular downward bends 21 are formed about the tubes . The circular bends 21, designed as relatively small basins, are adjacent to the tubes 7. The size of the basins and the curvature can be determined according to need.

Reference is now made to Figure 3 depicting a design of a refrigerating module in accordance with another preferred embodiment. Heat exchanger 2 now comprises a plurality of pipes 5 having a distributor 19 and a collector 20 that are connected to an inlet 13 and outlet 14, respectively. At a similar manner, the second heat exchange 4 comprises a plurality of pipes 7 and an inlet 15 fluidically connected to a distributer 18 that is connected to the plurality of pipes on one side and a collector 17 that collects the fluids from the pipes 7 and is connected to an outlet 17. Collectors and distributers 17, 18, 19, and 20 are functional parts of the design that form uniform flow heat exchangers. Both heat exchangers 2 and 4 are provided with riffles 6 and 8, respectively, that are placed vertically relative to the pipes 5 and 7, respectively. Other portions of the system are the same as previously disclosed.

The operation of the adsorption-type refrigerating aggregate is characterized as follows:

At Phase 1, hot heat-carrier is discharged from the source of low-grade heat into the tubes 5 of the heat-exchanger 2 via the inlet 13. Hot air, steam, waste gas etc. can be the sources of low-grade heat and the heat carrier is preferably an aqueous solution of ethylene glycol. The heat-carrier heats the thin layer of adsorbent 3 that is located on the outer surfaces of the tubes 5 and the riffles 6 and is saturated with the coolant (methanol, in this case). As a result, the coolant is heated and escapes the adsorbent as vapor that flows within the single chamber 1. At the same time, the tube 7 of the heat exchanger 4 is fed with the medium-heated heat-carrier via the inlet 15. This heat-carrier cools down the tubes 7 and the riffles 8, wherein, the coolant, which evaporated from the heat-exchanger 2, starts condensing onto heat exchanger 4. The first phase finishes once the coolant is fully condensed.

At Phase 2, the three-way ball valve gate (not shown in the figures) switches to let the medium-heated heat-carrier pass through the tube 5 of the heat-exchanger 2, which cools down the layer of the adsorbent 3. This process results in the latter adsorbing the vapor of the coolant in the operational chamber 12, and by turn in dropping the pressure in the chamber. The tube 7 of the heat-exchanger 4 are fed with the low-heat heat-carrier, which causes the coolant to boil and evaporate in the low pressure and temperature. The low-heat heat-carrier in tube 7 cools down, as a result, to negative temperatures.

The circular bends 21 are configured to provide the increase of the temperature gradient and intensification of the heat mass transfer, resulting in enhanced refrigerating capacity of the apparatus.

Phase 2 finishes with substantially all the coolant adsorbed by the adsorber 3.

This process is cyclical, hence, the use of the two modules provides continuity of the refrigerating process: when Module 1 is operating in Phase 1 (desorbtion- condensation), Module 2 is operating the Phase 2 (evaporation-adsorption). Alternating mode of operation provides faultless and continuous work of the refrigerating apparatus. Reference is now made to Figure 4 and 5, illustrating routing of coolants in the two modules, according to Figure 1 and routing the coolants according to Figure 3, respectively. According to Figures 4 and 5, the inlet and outlet 13 and 14 of Module 1 are connected to the hot heat-carrier (HT), the inlet and outlet 15 and 16 of Module 1 are connected to the medium-heat heat-carrier, the inlet and outlet 13 and 14 of Module 2 are connected to the medium-heat heat-carrier (MT) and the inlet and outlet 15 and 16 of Module 2 are connected to the low-heat heat-carrier (LT). With every switch of the phases of the operational cycle, module 1 is connected as module 2, and module 2 as module 1.

The technological parameters of the adsorption-type refrigerating apparatus are controlled by increasing the temperature of the hot heat-carrier and decreasing the temperature of the medium-heat heat-carrier. This approach enhances refrigerating capacity of the adsorption-type apparatus and lowers the temperature, produced in the system of the low-heat heat-carrier.

Alternatively, the control of the adsorption-type apparatus can be performed by varying the intensity of the heat-carriers discharge in the three systems.

In practice, the design of the adsorption-type refrigerating apparatus can be realized with varied spatial location of the inlets and outlets of the heat-exchangers, as show in Figure 1 and 3.

AN EXAMPLE OF PRACTICAL IMPLEMENTATION OF THE PROCESS OF DERIVING NEGATIVE TEMPERATURES IN THE DESCRIBED EMBODIMENT

An adsorption-type refrigerating apparatus of cooling capacity of 7 kW was designed and built in accordance with the description herein. Water-based ethylene glycol solution (40%) of temperature of about 70°C was used as a primary source of low-grade heat. The solution was discharged into the heat exchanger of Module 1, wherein, the outer surface was coated with 2-4 mm thick of silica gel granules. Dehydrated methanol was utilized as a coolant that is initially adsorbed within the silica gel coating.

Ethylene glycol aqueous solution was utilized also as the medium-heat carrier, which was cooled down in the outer heat-exchanger with forced air cooling up to temperature of about 32-34 °C. As a result of the full cycle of the refrigerating apparatus operation, the low-temperature heat carrier was cooled down to the temperature of substantially minus 8-9°C, providing, thereby, high cooling capacity of the present design of the adsorption-type refrigerating apparatus. This embodiment has proved to be a highly effective energy-saving technological apparatus.

Compared to other known refrigerating apparatuses, utilization of the described apparatus enhances cooling capacity, which reflects in reduced consumption of primary low-grade heat as well as in potential for noticeable decrease of the temperature as the output of the system.

The important feature of the disclosed adsorption-type refrigerating apparatus is absence of any shifting or moving parts or those, connected by any actuating mechanisms. This approach simplifies the design of the apparatus, increases its reliability, and facilitates maintenance.

Further or complimentary advantages of the present adsorption-type refrigerating apparatus include reduced labor input and cost of manufacturing. Alongside the enhanced cooling capacity, this fact provides high market competitiveness.

It is suggested that the most efficient utilization of the adsorption-type refrigerating apparatuses as disclosed herein have derivative sources of low-grade heat of 50-80°C and the cooling capacity of all single modules ranging from 10 to 150kW.

The prospective way of utilization of the present type of an apparatus is disclosed in effective derivation of technological cold with temperatures from minus 5 to minus 20°C. The highest efficiency of utilizing of the present type of an apparatus is considered to be gained when installed within mobile refrigerators, or either sea or river vessels. The embodiment of the present invention within a mobile refrigerator, for example, may save up to 7 - 8 liters of diesel for every 100 kilometers.

It is appreciated that certain features of the subject matter, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the subject matter, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub combination.

Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.