Abstract:
An air/refrigerant heat exchanger includes a plurality of coiled tubes. A first tube of the plurality of coiled tubes has a phase change material therein. A second tube of the plurality of coiled tubes has a flow of cooled refrigerant flowing therethrough and the first tube is in thermal contact with the second tube. A third tube of the plurality of coiled tubes has a flow of air flowing therethrough and the third tube is in thermal contact with the first tube and the second tube.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of and is a division of U.S. patent application Ser. No. 11/598,042, entitled “REFRIGERATION-TYPE DRYER APPARATUS AND METHOD,” filed Nov. 13, 2006, now U.S. Pat. No. 7,721,787, which claims priority to and is a division of U.S. patent application Ser. No. 10/670,213 entitled, “REFRIGERATION-TYPE DRYER APPARATUS AND METHOD,” filed Sep. 26, 2003, now U.S. Pat. No. 7,134,483, all of which are hereby incorporated by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to drying systems. More particularly, the present invention is directed to a refrigeration-type air dryer comprising a heat storage medium phase change material. 
     BACKGROUND OF THE INVENTION 
     Air dryers are generally utilized to remove water vapor typically from compressed air or gas. Where refrigerant-type air dryers are employed, a refrigerant system is used to lower the temperature of the air or gas being dried to a temperature at or below the condensation temperature of water therein. At such temperatures, water vapor in the undried air condenses on a surface within a condenser where it can be collected and purged from the system. 
     In order to sufficiently lower the temperature of the undried air or gas, many refrigerant systems comprise a heat exchanger where heat is drawn from the air or gas being dried to a refrigerant. Typically, heat from undried air is coupled to the evaporation of a colder refrigerant in an evaporator. In this case, as the liquid refrigerant is vaporized, it removes heat from the undried air or gas and cools the air in the process. When the air or gas reaches a temperature at or below the condensation temperature of water therein, the net result is that the water vapor therein begins to condense (or separate) from the air or gas and is collected in a condenser or separator. 
     In order to recycle the refrigerant in the system, a compressor and a chiller unit are often installed—the compressor compresses the gaseous refrigerant that has been vaporized in the chiller, and the condenser condenses the gaseous refrigerant into a high pressure liquid. The refrigerant is then ready for another cycle of vaporization. 
     A common problem with refrigeration-type dryers is determining how to suspend cooling (i.e., “de-energize” the system) during times of no load or low load conditions. For example, the demand for refrigeration is low or non-existent when little to no air is flowing through the refrigerator dryer or when the incoming air is already cool. Typically, it is desirable to reduce or discontinue cooling during such periods to avoid ice formation in the refrigerant system that could affect operation of the refrigeration air dryer. Ice can plug the system so that it does not continue drying the air, or it can plug the air passages stopping the flow of compressed air. 
     One way to prevent excessive cooling and the resulting problem, is to use a cycling-type refrigeration dryer. In a cycling refrigeration-type dryer system, a thermostatic temperature device causes de-energizing of a refrigerant compressor when the undried air has been cooled to a predetermined temperature. This can also be accomplished by measuring the evaporator pressure. The same device can then cause the compressor to be re-energized when the temperature in the evaporator elevates to a predetermined temperature, indicating further cooling is required to remove moisture from the incoming air. Thus, it has been found that between adequate load and low load conditions, a refrigeration compressor may cycle on and off about thirty to forty times per hour. 
     The number of cycles per hour is significant because frequent cycling adds costs associated with wear and tear on the compressor, control systems, and valves. As a result, the life without maintenance of the refrigeration system is drastically reduced. Accordingly, it would be desirable to provide a refrigerant air dryer system and method that extends the life of its refrigeration system. 
     Moreover, the greater the number of times a refrigeration system cycles, the greater the amount of energy that is consumed. Lower energy consumption has both cost and environmental benefits. Accordingly it would also be desirable to provide a refrigeration dryer system and method that reduces the amount of energy consumed. 
     SUMMARY OF THE INVENTION 
     The foregoing needs are met, to an extent, by the present invention, wherein in one embodiment an air drying apparatus is provided that comprises a refrigerant system and a heat exchanger further comprising a phase change material, wherein the refrigerant system is adapted for cooling the heat exchanger. The air dryer may dry air or gas which may optionally be compressed air or gas. In some embodiments, air dryers of the present invention may comprise a condensate separator, preferably including a wire mesh. The phase change material can change between solid and liquid phases. In some embodiments the phase change material is an organic paraffin. 
     In other embodiments, a method of drying air is provided which comprises providing a refrigerant system and a heat exchanger comprising a phase change material and using the refrigerant system to cool the heat exchanger. The method may be used to dry air or gas which may optionally be compressed air or gas. In some embodiments, method of air drying of the present invention may comprise a condensate separator, preferably including a wire mesh. The phase change material can change between solid and liquid phases. In some embodiments the phase change material is an organic paraffin. 
     In yet other embodiments, a means for drying air is provided, comprising a refrigeration means and a heat exchanger means comprising a phase change material, wherein the refrigeration means is adapted for cooling the heat exchanger means. The air drying means may dry air or gas which may optionally be compressed air or gas. In some embodiments, air dryer means of the present invention may comprise a condensate separator means, preferably including a wire mesh. The phase change material can change between solid and liquid phases. In some embodiments the phase change material is an organic paraffin. 
     There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto. 
     In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
     As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cut-away of an evaporator of a refrigerated air dryer in accordance with the present invention. 
         FIG. 2  is a cut-away of refrigeration chiller of a refrigerated air dryer in accordance with the present invention. 
         FIG. 3  is a cut-away of refrigeration chiller of a refrigerated air dryer in accordance with the present invention. 
         FIG. 4  is cut-away of refrigeration chiller of a refrigerated air dryer in accordance with the present invention, in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. An embodiment in accordance with the present invention provides a refrigeration system  10  operationally coupled to a heat exchanger  20  to cool undried compressed air to a temperature sufficient to separate and remove any water therein by virtue of its condensation at such sufficient temperature. The heat exchanger  20  may be of multiple embodiments, some of which will be described below. In the schematic shown in  FIG. 1 , the heat exchanger  20  comprises an air-to-air (“air/air”) exchanger  30  and an air-to-refrigerant (“air/refrigerant”) exchanger  40 . The exchanger  40  further comprises a thermal jacket  50 , which in the embodiment shown, is directly cooled by the refrigerant system  10 . The exchanger  30  is shown with co-current flow in  FIG. 1 , but in some embodiments can also comprise counter-current flow. 
     Broadly speaking, air, gas, including compressed air and gas, or generally, any vapor in need of drying, is injected into the heat exchanger  20  through an inlet  60 . The term “air” has been used herein to encompass all of the above fluids and should not be construed or limited to any one particular embodiment. The air then travels through the exchanger  30  to the exchanger  40 . Preferably, the air traverses a path  61  through the exchanger  30 , adapted in a manner such that heat from the hotter, undried air entering the inlet  60  can be transferred to the cooler, dried air exiting an outlet  70 . By way of example, air entering the inlet  60  may be 40 to 70 degrees Fahrenheit hotter than air exiting the outlet  70 . Such a temperature differential can provide motive for significant heat transfer without the need for further mechanical intervention. 
     Once the air has traversed the exchanger  30 , it enters the exchanger  40 . The exchanger  40  is designed to draw heat from the incoming air to the refrigerant  11  supplied by the refrigerant system  10 . In the embodiment shown, the refrigerant  11  cools the thermal jacket  50 . Contents of the thermal jacket may comprise any material known and present in the art that can be cooled to a temperature at or lower than the dew point of the vapor (i.e., water) being condensed. Suitable materials include, but are not limited to, glycols and mixtures thereof. 
     In some embodiments, the thermal jacket  50  may comprise a phase change material (PCM). PCMs are heat storage media that can absorb or diffuse heat by changing from a solid to a liquid, or vice versa. In the instant invention, for example, as the phase change material absorbs heat from the undried air, it begins to change phase from a solid to a liquid. However, without being limited by or held to scientific theory, because of the constant temperature behavior of PCM technology, the thermal jacket  50  can maintain a constant temperature during the transition. The process can take minutes to hours depending on the PCM, ambient temperature of the air, and workload. 
     In some embodiments, PCMs that can absorb the greatest amount of heat over the smallest temperature range are preferred. In other words, PCMs that remain in the solid phase longer for a given amount of heat are desirable. Scientifically, the thermal conductivity of a fluid increases significantly when in a solid phase as opposed to a liquid. Water, for example, has a thermal conductivity of 0.326 BTU/hr-ft-° F. at 32° F., whereas ice has a thermal conductivity of 1.18 BTU/hr-ft-° F. at the same temperature. Because of their ability to absorb heat at both a solid state (high thermal conductivity) and a liquid state (lower thermal conductivity), PCMs can more rapidly and efficiently absorb the heat of condensation than materials that do not undergo a phase change. Therefore, much more heat can be stored in a much smaller volume of medium using the latent heat of freezing (solid→liquid) rather than the heat associated with changing temperatures, allowing for the development of much smaller heat exchangers. 
     During standard operation of one embodiment of the instant invention, the refrigerant  11  cools (or “charges”) the thermal jacket  50  so that the PCM therein becomes solid, thereby allowing the thermal jacket  50  to draw heat from the incoming air  61 . The heat from the incoming air  61  is transferred through the PCM/thermal jacket  50  to the heat absorbing refrigerant  11 . 
     When the temperature or pressure of return refrigerant  12  reaches a pre-determined temperature or pressure, the refrigerant system  10  can shut off. The pre-determined temperature or pressure may be chosen to signal that no further cooling by the refrigerant system  10  is needed, for example, at times when the temperature or pressure of refrigerant  11  entering the thermal jacket  50  nears the temperature or pressure of the refrigerant  12  exiting the jacket  50 . 
     During such periods of little to no load, when the compressor is deenergized, the PCM can continue to absorb heat from the undried air. In other words, the PCM can supply the necessary cooling by absorbing heat in the solid phase while maintaining a low constant temperature before changing to liquid. In such a manner, this invention can allow for the extension of time periods where the refrigerant system  10  may remain deenergized 
     When the temperature of return refrigerant  12  or the thermal jacket  50  reaches a pre-determined temperature, the refrigerant system  10  can re-energize and the PCM can be relatively quickly recharged (i.e., solidified) by the refrigerant system  10 . The net effect of this system is that the cycle periods can be extended and less energy can be consumed than convention refrigeration-type air dryers that do not use PCMs. The compressor cycling rate can be reduced from thirty or forty times per hour to, for example, less than six per hour. 
     Heat storage mediums can be developed to change state at a chosen temperature. For example, a medium can be of a composition to freeze at +4° C. that would preclude water freezing, or icing, in the exchanger  40 . PCMs which change states between liquid and solid are manufactured by many companies, for example PCM Thermal Solutions of Naperville, Ill. The PCM A4 is an organic paraffin which freezes at +4° C. and is composed of a blend of heavy cut hydrocarbons. The types E7 and E8 that change state at +7° C. and +8° C., respectively, are composed of ammonia and sodium sulfate salts. For low dew point services, such as refrigeration systems with reversing regenerative heat exchangers, low temperature PCMs can be used including TEA-29 that freezes at −29° C. The TEA media are composed of inorganic hydrated salt solutions, such as calcium chloride in water. 
     Returning to  FIG. 1 , the cooled air  62  exiting the thermal jacket  50 , should be cooled enough to initiate condensation of the water therein. The use of “water” herein is merely exemplary, and is intended to include any and all vaporous fluids that are chosen for condensation. The condensed water, then, is collected and removed in a condensate separator  80 . Condensate separators are known in the art and any such separator may be used with the present invention. 
     As shown in  FIG. 1 , the return path for cooled air  62  may optionally be adapted in the exchanger  30  such that heat may be transferred from the incoming air  61  to the exiting air  62 . In such a way, not only is the exiting air heated closer to the temperature of the air  61  as it enters the exchanger  20 , but the air  61  entering the exchanger  20  is precooled before entering exchanger  40 . 
     A conventional refrigeration system  10  is depicted in the embodiment of  FIG. 1 . Refrigerant gas  12  is pressurized by a compressor  13 . The compressor  13  compresses the refrigerant gas  12 . The compression process raises the refrigerant  12  pressure and also the temperature. In order to cool the temperature, the refrigerant  12  is channeled through a condenser  14 , which is a heat exchanging means that allows the refrigerant  12  to dissipate the heat of pressurization. As it cools, the refrigerant gas  12  cools into a refrigerant liquid  11 . The refrigerant  11  is then dried and/or filtered of contaminants by a filter/dryer means  15 . 
     The liquid refrigerant  11  is then passed through an expansion device  16  which transfers the liquid refrigerant  11  from a high pressure zone to a low pressure zone, thereby vaporizing the refrigerant  11 . In evaporating, the refrigerant  11  draws heat, preferably from the thermal jacket  50  and/or the undried air  61 . Typically, refrigeration systems will also comprise a sensing bulb  17 . The sensing bulb  17  is generally a temperature sensing device that can regulate the flow of the return refrigerant  12 . Preferably, the sensing bulb  17  is able to compare the temperature of the cooled refrigerant  11  with the return refrigerant  12  and has the means to regulate the system  10  when a pre-determined superheat is reached. 
     Shown in  FIG. 2  is an embodiment of a heat exchanger  120  in accordance with the present invention. The heat exchanger  120  comprises an air/air heat exchanger  130 , an air/refrigerant heat exchanger  140 , and a condensate separator  180 . The air/refrigerant exchanger  140  is known as a “brazed plate” heat exchanger and comprises a series of stacked plates. The plates may be comprised of any materials that are sturdy when pressurized, heated, and cooled, and can conduct heat efficiently. Preferably metal plates are used, and more specifically, stainless steel or copper plates. 
     A brazed plate exchanger comprises alternating stainless steel and copper plates fused together creating “gaps” or “slits” between the plates. In some embodiments of the present invention, at least three such gaps are envisioned. A first of the gaps is utilized to contain an incoming flow of air to be dried. A second of the gaps can contain a refrigerant and a third one of the gaps may contain a PCM. Preferably, the refrigerant plate contacts the PCM plate which contacts the air plate, however, alternate combinations are also possible. 
     As shown in  FIG. 2 , an inlet pipe  160  may be attached to the air/air exchanger  130  evaporator to allow incoming air to flow into any chamber designated to hold incoming air. Preferably, as described above, the incoming air follows a course counter-flow to the outgoing air. This adaptation functions as an air/air heat exchange thereby pre-cooling the incoming air before it enters exchanger  140 . The incoming air then moves through the braized plate heat exchanger  150 . 
     The brazed plate heat exchanger  150  comprises a series of stacked plates creating chambers therefrom. For the reasons mentioned above, the incoming air preferably traverses the heat exchanger  140  counter-flow to the refrigerant. A probe  155  may also be incorporated in the exchanger  150  to sense and/or report a status of the refrigerant and/or the PCM therein. Preferably, in some embodiments, the probe  155  is a phase change temperature sensing probe and is located at a location within exchanger  150  where the PCM would be warmest. However, probe  155  may be adapted for use in any location within heat exchanger  120 . In any event, once having traversed the heat exchanger  140 , the exiting air is cooled to permit condensation of the water. 
     A condensate separator  180  may be coupled to the exchanger  120  via an outlet port  190 . The separator  180  separates the condensed water from the air stream. In some embodiments, a mesh  181  may be introduced into the separator  180  to aid condensation. The mesh  181  may comprise any material, preferably materials that will not rust or fail when wet, and need not be limited to any one particular design. Stainless steel wire meshes may be utilized in some embodiments. A drain  182  may be provided to allow the condensate to exit the separator  180 . 
     Piping  100  may be coupled to the separator  180  to allow dried air to re-enter the exchanger  130 , and exit through an outlet port  170 . An air/air exchanger  130  is provided to allow the outgoing cool dry air to pre-cool incoming warm air. 
     Shown in  FIG. 3  is an embodiment of a heat exchanger  220  in accordance with the present invention. The heat exchanger  220  comprises an air/air heat exchanger  230 , an air/refrigerant heat exchanger  240 , and tubes  221  and  222  that permit that transfer of air between the exchangers  230  and  240 . 
     In greater detail, the heat exchanger design of  FIG. 3  comprises an inlet port  260  that receives an incoming flow of a fluid, for example, compressed air. The inlet  260  is coupled to tubing  231  within exchanger  230  that is adapted for air/air heat exchange between the warmer, undried air entering the exchanger  220  and the cooler, dried air exiting the exchanger  220 . For example, air entering may be designed to flow through the tubes  231  through the center or periphery of exchanger  230 , the sum of the tubes  231  being surrounded by cooler air exiting an outlet  270 . As with the other embodiments described herein, preferably, the entering air and the exiting air are arranged in a counter-flow arrangement so as to maximize heat transfer. Such designs are commonly referred to as “shell-and-tube” or “multitube-in-tube” heat exchangers in the art. 
     Once the incoming air has traversed the air/air exchanger  230 , it may move through a connecting tube  221  into the air/refrigerant exchanger  240 . The exchanger  240  can be constructed with three concentric tubes such that the refrigerant flows through the inner-most tube, a PCM is retained between the first and second tube, and the air passes through the annular space between the third and second tubes. The triple tube design can be constructed in a coiled manner, or it can be designed as a straight tube construction as shown. Refrigerant is circulated through the exchanger  240  through inlet/outlet ports  241 . The refrigerant, in turn, cools a jacket  245  containing the PCM and/or the undried air traversing the exchanger  240 . 
     As heat is drawn from the incoming air to the refrigerant and/or the PCM, the air is cooled to or below its dew point and moisture (e.g., water) begins to condense. The condensed water is collected within the exchanger  240  and can be drained from the system though a condensate drain  242 . The exchanger  240  may also include a fluid fill/vent  243 . The fill/vent  243  may be adapted to allow filling or refilling of PCM as is required, and also allow for venting of gases or heat contained therein. 
     Preferably, in some embodiments, a probe  243  is incorporated into the air/refrigerant exchanger  240 . Preferably, the probe  243  is a phase change temperature sensing probe and is located at a location within the exchanger  240  where the PCM would be warmest. However, the probe  243  may be adapted for use in any location within heat exchanger  120 . The probe  243  may also signal shut-off or operation of the refrigerant system in some embodiments. 
     In the embodiment shown in  FIG. 3 , once dried, the cooled air may be directed by another connecting tube  222  back to the exchanger  230 . In the arrangement shown, the cooled air is fed counter-flow to the incoming air in tubes  231  within the exchanger  230 . This process not only cools air within the tubes  231 , but also warms the dried air exiting the exchanger  220  though the outlet  270 . 
       FIG. 4  depicts a heat exchanger  320 . The heat exchanger  320  comprises an air/refrigerant exchanger  340  and a separator  380 , and may optionally include an air/air exchanger as well. The exchanger  340  can be constructed with three coiled tubes bundled together as illustrated in the figure. One of the three tubes  361  passes the air as it enters the exchanger  320  and exits drier. The air may enter/exit the exchanger  320  via an inlet/outlet  365  which can comprise a tube within a tube design. 
     In addition, there are at least two other tubes  311  and  351  positioned/nested around the air tube  361 . One of the other tubes,  351 , contains a PCM, and the other of the two tubes,  311 , contains a refrigerant. In the preferred embodiment of the present invention, the tubes  311 ,  351 , and  361  are made from copper, and all three tubing lines are positioned such that one line of tubing does not overlap another line of material. 
     However, it should be understood by one of ordinary skill in the art that the three lines of tubing may all be made from any other material, or each of the three lines of tubing may be made from different materials. It should also be understood by one of ordinary skill in the art that the positioning of the three lines of tubing may also vary. 
     The exchanger  320  embodied in  FIG. 4  additionally comprises a separator  380  to mechanically separate the condensed moisture from the dried air. A probe  355  may also be installed in the exchanger  320  as indicated in the embodiments above. 
     The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.