Patent Application
20050279127
This invention relates to refrigeration systems and to an integrated heat exchanger for use in such systems.
Most refrigeration systems (which term, as used herein, is intended to include air conditioning systems) operate on the vapor compression cycle. In such a cycle, a refrigerant is compressed and then the compressed refrigerant cooled before being expanded in an evaporator to cool a heat exchange fluid. The heat exchange fluid may be used to cool various objects, such as the contents of a refrigerator or the occupants of a space. Until relatively recently, common refrigerants were chloro-fluoro carbons (CFC's) or hydro-chloro-fluoro carbons (HCFC's) because of their non combustibility and relatively easy cycling through the system. However, many such systems have been prone to refrigerant leakage, particularly those in vehicular applications. The escaping refrigerant, depending upon the type, is believed to damage the ozone layer surrounding the earth in varying degrees. Consequently, certain refrigerants such as CFC 12 are no longer manufactured and resort has been made to more environmentally friendly refrigerants such as HFC 134a. The search continues for even more environmentally friendly refrigerants.
With the new refrigerants that are being utilized, changes are required in many of the refrigeration systems in which they are used to achieve optimum efficiency. And this is true whether one is employing some of the newer refrigerants which still actually physically condense from the gaseous phase to the liquid phase in the system condenser or whether one is employing a so-called transcritical refrigerant, such as CO2 which does not truly condense during typical system operation but nonetheless requires cooling after compression in a so-called gas cooler.
Some of these systems utilize a multiple-stage compressor for increased efficiency, usually a two stage compressor, to compress the expanded refrigerant after it is passed through the evaporator to an elevated pressure at which it enters the system condenser or gas cooler. For brevity, both condensers for true condensing refrigerants and gas coolers used in transcritical refrigerant systems will hereinafter be referred to as gas coolers.
In any event, when multiple-stage compressors are utilized, some means of cooling the refrigerant between stages is often needed. This is typically accomplished using an air cooled intercooler.
In common refrigeration systems, the gas cooler and intercooler are typically separate components in the system loop. Where there are few space constraints in the system, the use of separate components is not a major concern. However, in applications where space constraints are significant, it would be desirable to have an integrated gas cooler/intercooler component which functions with an efficiency that will match that of a system utilizing separate components.
For example, in vehicular applications, available space for air conditioning units is at a premium. Large components limit the ability of the designer of the vehicle to achieve aerodynamic slipperiness which, of course, affects fuel economy as well as the ability to achieve a pleasing appearance. Further, a weight saving may be achieved in an integrated unit over a system utilizing separate components which similarly contributes to the fuel economy. Thus, there is a real need for a refrigeration system employing a multistage compressor that avoids the problems associated with separate gas coolers and intercoolers.
The present invention is directed to fulfilling that need.
It is the principal object of the invention to provide a new and improved refrigeration system of the multistage compressor type. It is also an object of the invention to provide a new and improved integrated heat exchanger which may find use in such a system as an integrated gas cooler and intercooler.
According to one aspect of the invention, a refrigeration system having a multistage compressor with at least two stages for sequentially compressing a refrigerant is provided. A gas cooler is connected to the compressor for receiving compressed refrigerant from the last stage of the compressor to cool the same. After an expansion device, an evaporator is connected to the gas cooler to receive compressed, cooled refrigerant therefrom and expand the same to cool a fluid stream passing through the evaporator. A return passage is provided and connects the evaporator to a first stage of the compressor to return expanded refrigerant thereto to be compressed therein and an intercooler is connected between the first stage and the last stage of the compressor to cool refrigerant compressed by the first stage and direct the refrigerant cooled thereby to the last stage for further compression in the compressor. The intercooler and the gas cooler are integrated into a single unit to receive a single cooling heat exchange fluid. The gas cooler has a larger heat transfer area than that of the intercooler, the heat transfer area being the area of the respective coolers through which heat transfer between the refrigerant and the single cooling heat exchange fluid occurs.
In a preferred embodiment, the gas cooler is a cross-counter flow heat exchanger having plural tube or passage rows through which the refrigerant serially passes from back to front in relation to the direction of flow of the single cooling heat exchange fluid through the gas cooler.
According to one embodiment of the invention, the gas cooler and the intercooler are in side-by-side abutting relation to define a single, split face through which the single cooling heat exchange fluid enters the unit and includes common header assemblies extending between remote sides of the gas cooler and the intercooler. Baffles are located in the header assemblies to isolate the refrigerant flow paths in the intercooler from refrigerant flow paths in the gas cooler.
In the embodiment described in the preceding paragraph, the intercooler has plural tubes or passage rows through which the refrigerant serially passes and the number of tubes or passage rows in the intercooler is less than the number of tubes or passage rows in the gas cooler.
Preferably, the number of rows in the gas cooler is at least twice the number of rows in the intercooler.
In a highly preferred embodiment, the rows in the gas cooler are defined by aligned runs of serpentine tubes and the rows in the intercooler are defined by U-shaped or serpentine tubes.
In another embodiment of the invention, the gas cooler and intercooler are interleaved with the tubes or passages of the gas cooler being located between adjacent tubes or passages of the intercooler.
In this embodiment as well, the gas cooler runs are defined by serpentine tubes and the intercooler runs are defined by U-shaped or serpentine tubes.
In a preferred embodiment, there are more tubes or passages in each row of the gas cooler than in each row of the intercooler and the tubes or passages of the intercooler are substantially uniformly distributed between tubes or passages of the gas cooler.
According to another facet of the invention, an integrated, interleaved heat exchanger is provided which includes a first plurality of tubes bent to define a plurality of parallel runs. A second plurality of tubes bent to define a plurality of parallel runs is also provided. First header assemblies are connected to the ends of the tubes in the first plurality and are in fluid communication with the interiors thereof while second header assemblies are connected to the ends of the tubes of the second plurality and are in fluid communication with the interiors of the second plurality. The tubes of the first plurality are located between the tubes of the second plurality in a substantially uniformed manner and in spaced relation to one another. The parallel runs of the tubes in each plurality defines rows, and fins extend between adjacent tubes in the rows.
In one embodiment, the tubes of both of the pluralities have the same number of runs while in another embodiment, the number of runs defined by each tube in the first plurality is greater than the number of runs defined by each tube of the second plurality.
In preferred embodiment, the first and second plurality of tubes and the fins define a generally rectangular heat exchanger core and the header assemblies are all on one side of the core.
A preferred embodiment again contemplates that the tubes of the first plurality be serpentine tubes and that the tubes of the second plurality be U-shaped or serpentine tubes.
In one embodiment of the heat exchanger, the second plurality of tubes have corresponding ends located inwardly of the ends of the first plurality and the second header assemblies are located between the first header assemblies. In another embodiment, the second plurality of tubes have corresponding ends located outwardly of the ends of the first plurality and the first header assemblies are located between the second header assemblies.
Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings.
Before proceeding to the detailed description of the various embodiments, it is to be understood that the term “refrigeration system” as used herein is used in a broad sense to include any vapor compression based system utilized for cooling other objects. It is intended to include not only refrigeration systems in the narrow sense, such as refrigerators, refrigerated vehicles, etc. but also to include systems utilized for cooling spaces and/or occupants of such spaces, more narrowly understood to refer to air conditioning systems.
It is also to be noted that the invention is applicable to systems employed with refrigerants that in fact substantially fully change from the vapor phase to the liquid phase in a heat exchanger typically termed a condenser as well as in the systems utilizing so called transcritical refrigerants, such as carbon dioxide, wherein true condensation does not fully occur but nonetheless require a gas cooler for cooling the refrigerant after it has been compressed. Thus, the term gas cooler, as used herein, and as alluded to previously, is intended to be generic to both gas coolers in transcritical systems as well as to condensers in subcritical systems.
It is also to be noted that the integrated gas cooler and intercooler described herein is not restricted to use as an integrated intercooler and gas cooler. It may be utilized in systems wherein a single heat exchange fluid at two different stages in its processing, may be heated or cooled by a single stream of a heat transfer medium or where two different heat exchange fluids can be advantageously heated or cooled by a single stream of a heat transfer medium.
Consequently, no restriction to particular types of refrigeration systems is intended except insofar as expressly stated in the appended claims. Similarly, no restriction to a specific use of the embodiments of heat exchanger described herein in refrigeration systems is intended except insofar as specified in the appended claims.
With the foregoing in mind, the system in
The system is based on a multi-stage compressor, generally designated 10 which typically will be a two stage compressor. Thus, a first stage is shown at 12 and a second stage is shown at 14. An inlet 16 to the compressor is connected to the outlet of an evaporator 18 through which a heat exchange fluid is driven by a fan 19 to be cooled, the heat exchange fluid typically being air but in some instances could be another gas or even a liquid.
The compressor 10 includes an outlet 20 from the second stage 14 which is connected to the gas cooler part 21 of an integrated gas cooler, intercooler unit, generally designated 22. The unit 22 is adapted to receive a heat exchange fluid, again typically air, but which could be another gas or even a liquid, driven by a fan 24 in a single stream through the gas cooler part 21 and through an intercooler part 26 of the unit 22.
The outlet 28 of the first compressor stage 12 is connected to the intercooler part 26 to provide refrigerant compressed by the first stage to the intercooler part 26. From the intercooler part 26, the refrigerant compressed by the first stage 12 is directed to an inlet 30 to the second stage 14 of the compressor unit 10.
Compressed refrigerant cooled in the gas cooler part 21 exits the unit 22 and is directed through an expansion device (EXP DEVICE) and then passed to the evaporator 18 where it cools the heat exchange fluid directed through the evaporator 18 by the fan 19.
Other components may optionally be included in the system of
Turning now to
The intercooler part 26 includes spaced flow passages 40 also typically tubes or tube runs separated by fins 38 in the usual case. As it will be explained in greater detail hereinafter, in a preferred embodiment, the flow passages 27 and 40 are made up of flattened tubes. However, other types of flow passages could be provided, including those of the so called “drawn-cup” type.
Common headers 42 (only one of which is shown) are connected to and in fluid communication with the interior of the flow passages 27 and 40 and extend basically from the remote side 32 of the intercooler to the remote side 34 of the gas cooler. In the ususal case, the headers 42 will be tubes but they could consist of a header plate and attached tank if desired. A baffle 46 is located along the interface 30 in each of the headers 42 to isolate refrigerant flow within the gas cooler from refrigerant flow within the intercooler 26. One of the headers 42 includes an inlet 48 for the gas cooler part 21 and, on the opposite side of the baffle 46, an inlet 50 for the intercooler part 26. Similarly, the other header 42, specifically the header 42, illustrated in
In
It will also be appreciated that in the embodiment shown in
The ends of the flow passages 27 and 40 end in first and second sets of headers which may be in the form of tubes or in the form of header plates and separate tanks. In the embodiment illustrated in
The illustration in
The forward most header 58 includes an outlet 66 for the flow paths 27 while an inlet 68 in the rearmost one of the headers 58 provides an inlet for the passages 27.
Scrutiny of
Turning now to
On the other hand, the passages 40 in a highly preferred embodiment, are formed of a flattened tube having a single bend to define a U-shaped tube having two straight, elongated, parallel runs 82 and 84. The runs 82 and 84 are in two rows of runs with individual fins 38 extending just slightly more than the major dimension of the corresponding tube runs 82, 84.
Thus, in the embodiment of
If desired, the passages 40, rather than being U-shaped as shown in
In both of the embodiments shown in
In the embodiments shown in both
Referring specifically to
In both embodiments, the headers 56 and 58 are on the same side of the rectangular core defined by the passages 27, 40 and fins 38 and in the embodiment illustrated in
In the embodiment illustrated in
The principal difference between the embodiments of
Either header arrangement may be employed, depending upon the spacial constraints of any particular system installation.
On some instances, the fins 38, where they extend between passages 27 on the one hand and passages 40 on the other may be so called split or slit fins wherein the slits minimize heat conduction through the fins between the passages 27 and the passages 40. Various constructions for achieving this are well known and form no part of the present invention. Alternatively, conventional fins, including louver fins could be used throughout.
In the most preferred and optimal embodiment of the invention, of which, is mentioned previously, is a cross-counter flow construction, there can be any number of rows for the gas cooler part 21 as desired. In general, the number of rows in the intercooler part 26 will be less than the number of rows in the gas cooler. This type of arrangement is preferred when the unit is used as a integral gas cooler and intercooler unit. In such a case, the ratio of the heat transfer area of the gas cooler to that of the intercooler is typically somewhat greater than 2:1. By heat transfer area, it is meant that area of each unit which transfers heat from a refrigerant stream, typically the exposed area of the passages 27, 40 and fins 38, to the fluid stream passing through the unit as provided by, for example, the fan 24 shown in
In a refrigeration system, it will be recognized that the mass flow rate through both the gas cooler part 21 and the intercooler part 26 will be the same. If the same size of tubes are used for the passages 27, 40, while maintaining the above mentioned heat transfer surface ratio, the pressure drop of refrigerant could reach excessively high levels in the intercooler part 26. The reason for this is that the number of passages in the intercooler part 26 is relatively small and pressure drop can become too high because of increasing fluid velocity. For gas cooler parts 21 that require four or more rows of runs than the passages 27, the situation intensifies and the intercooler part 26 pressure drop becomes too high.
Accordingly, It is desirable that the pressure drop in both parts be at similar levels. To achieve this desire, one embodiment of the invention contemplates the use of fewer of the rows of the flow paths 40 in the intercooler part 26 than the number of rows of the passages 27 and the gas cooler part 21. In the described embodiments, because the length of the flow paths 40 for the intercooler part 26 is approximately half of that of the flow paths 27 for the gas cooler part 21, the pressure drop in the intercooler section 26 will be less in spite of the fact that fewer of the flow paths 40 exists in the intercooler part 26 in comparison to the number of flow paths 27 in the gas cooler 21. That is to say, the reduced intercooler part pressure drop will be directly linked to the reduction in length of the flow paths 40.
Another possibility is to increase the number of flow paths 40 in the intercooler part 26. The use of a lesser fin height in the intercooler part 26 will allow the use of more tubes or flow paths 40 in the intercooler part 26, although at the expense of frontal free flow air for the coolant.
Alternatively, tubes with different internal cross sectional areas may be employed in making up the flow paths 27 and 40. By using a larger cross sectional area in the tubes making up the flow paths 40, a reduction in pressure drop within the intercooler part 26 will result.
Most desirably, however, from the manufacturing standpoint, one would use the same tubes and rely on changes in the number of tubes or the number of runs or both to achieve the desired similarity in pressure drop in both section in the unit 22.
From the foregoing, it will be appreciated that the invention provides an improved refrigeration system by integrating an intercooler between the stages of a multi-stage compressor with the system gas cooler to achieve a significant spacial savings. Similarly, a heat exchanger made according to the invention is ideally suited for use in refrigeration systems but may be used with efficacy in other systems where spacial requirements are of concern.
