De-superheated combined cooler/condenser

Abstract

A heat exchanger includes a first plurality of segments having a first plurality of tubes formed therein and a second plurality of segments having a second plurality of tubes formed therein. The first plurality of segments is coupled to the second plurality of segments such that the second plurality of tubes is fluidly coupled to the first plurality of tubes. The first plurality of tubes includes a greater cumulative cross-sectional area per segment than the second plurality of tubes per segment, and, as such, improves the overall heat transfer capability of the heat exchanger.

Description

FIELD OF THE INVENTION

The present invention relates to heat exchangers and more particularly to an improved structure for a heat exchanger.

BACKGROUND OF THE INVENTION

Heat exchangers, such as evaporators and condensers, are commonly used in refrigeration systems. Such refrigeration systems typically also include a compressor, an expansion valve, and fans, which operate together, and with the heat exchangers, to cool a refrigerated space.

The compressor, expansion valve, condenser, and evaporator are fluidly coupled such that a loop or a closed system exists for circulation of a refrigerant therein. The compressor receives the refrigerant in a gaseous form from the evaporator and pressurizes the gas in the condenser. As the gaseous refrigerant is received under pressure from the compressor, at least one fan circulates air through the condenser and around condenser coils such that heat associated with the gaseous refrigerant is absorbed by the passing air. The resultant drop in refrigerant temperature, combined with the increase in pressure imparted thereon by the compressor, causes the refrigerant to change from the gaseous state into a liquid state.

Once the refrigerant reaches the liquid state, the refrigerant is sent through the expansion valve before reaching the evaporator, which is held at a low pressure through operation of the expansion valve and condenser. The low pressure of the evaporator causes the refrigerant to change state back to a gas, and as it does so, absorb heat from an air stream moving through the evaporator. In this manner, the air stream flowing through the evaporator is cooled and the temperature of the refrigerated space is lowered.

In vehicle applications, refrigeration systems must be of sufficient cooling capacity to maintain a passenger cabin at a desired temperature. A condenser associated with such a vehicle refrigeration system is typically disposed within an engine compartment of the vehicle and positioned such that air caused by forward movement of the vehicle passes through the condenser and over condenser coils. The passing air flow reduces the necessity of continuous fan operation and facilitates dissipation of heat from the condenser to the atmosphere.

Refrigeration system cooling capacity is related to the ability of the condenser to reject heat from the system through conversion of gaseous refrigerant into liquid refrigerant. Therefore, larger condensers are generally able to dissipate more heat than smaller condensers, and thus, provide additional cooling capacity. As most vehicle condensers are disposed within a vehicle's engine compartment, the size of the condenser is often limited to that which can be packaged. Such packaging problems are further compounded when the condenser is combined with another heat exchanger such as a transmission or oil cooler in a so-called “combo-cooler.” In such situations, condenser size is limited not only by available packaging space within the engine compartment, but also by available air flow.

Therefore, a condenser that adequately converts gaseous refrigerant to liquid refrigerant to adequately cool a refrigerated space while concurrently meeting vehicle packaging and size requirements is desirable in the industry.

SUMMARY OF THE INVENTION

Accordingly, a heat exchanger is provided and includes a first plurality of segments having a first plurality of tubes formed therein and a second plurality of segments having a second plurality of tubes formed therein. The first plurality of segments is coupled to the second plurality of segments such that the second plurality of tubes is fluidly coupled to the first plurality of tubes. The first plurality of tubes includes a greater cumulative cross-sectional area per segment than the second plurality of tubes per segment, and, as such, improves the overall heat transfer capability of the heat exchanger.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a perspective view of a condenser in accordance with the principles of the present invention;

FIG. 2 is a cross-sectional view of the condenser of FIG. 1 taken along line 2-2;

FIG. 3 is a perspective view of a combined cooler/condenser in accordance with the principles of the present invention; and

FIG. 4 is a pressure-enthalpy (P-H) chart comparing a prior art refrigeration system to a refrigeration system incorporating the condenser of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

With particular reference to FIG. 1, a heat exchanger 10 is provided and includes an upper portion 12 fluidly coupled to a lower portion 14. The upper portion 12 includes a plurality of segments 16 fluidly coupled by a pair of end caps 18 while the lower portion 14 similarly includes a plurality of segments 20 fluidly coupled by end caps 18. The end caps 18 extend along a length of the heat exchanger 10 and fluidly couple not only the individual segments 16 and the individual segments 20, but also fluidly couple the upper portion 12 to the lower portion 14 such that fluid communication between segments 16 and segments 20 is provided.

With particular reference to FIG. 2, the upper portion 12 includes a plurality of upper tubes 22 formed within each segment 16 while the lower portion 14 includes a plurality of lower tubes 24 formed within each segment 20. The upper tubes 22 extend along a length of each segment 16 and are fluidly coupled to each end cap 18. Similarly, the lower tubes 24 extend along a length of each segment 20 and are fluidly coupled to each end cap 18. In this manner, the upper tubes 22 are fluidly coupled to the lower tubes 24 via end caps 18.

The upper and lower tubes 22, 24 are formed integrally with respective segments 16, 20 during an extrusion process performed during formation of segments 16, 20. Specifically, the segments 16, 20 are formed from a thermally conductive material, such as, but not limited to, aluminum, and are formed by passing a blank of aluminum through an extrusion die (Not shown). As the blank is fed through the extrusion die, an elongate, generally rectangular shape is produced having a plurality of cylindrical voids extending along its length.

The rectangular shape forms an outer surface of each segment 16, 20, while the cylindrical voids form respective tube structures 22, 24 therein. It should be noted that while an extrusion process is disclosed, that any suitable process for integrally forming tubes 22, 24 within respective segments 16, 20 should be considered within the scope of the present invention. Furthermore, while a rectangular shape is disclosed, it should be understood that the outer surface could include any geometric shape and may also include fins for increasing heat transfer capability of each segment 16, 20.

The upper segments 16 include a greater number of tubes 22 per segment 16 than the lower segments 20. Therefore, the cumulative surface area of the upper tubes 22, per segment 16, is greater than the cumulative surface area of the lower tubes 24, per segment 20. The increase in surface area allows the upper tubes 22 to transmit more heat per segment 16, as compared to the lower tubes 24, per segment 20.

The number of tubes 22, 24 per segment 16, 20, as well as the required number of upper and lower segments 16, 20, is governed by the overall heat transfer coefficient, given by the following equation where U is the overall heat transfer coefficient, A is the total heat transfer area, η is surface effectiveness of cooling fins, h_air is the air-side heat transfer coefficient, A_air is the air-side heat transfer area, R_wall is the thermal resistance of the respective segment 16, 20, h_tube is the refrigerant heat transfer coefficient, A_tube is the refrigerant heat transfer area:
1/UA=(1/ηh_airA_air)+(R_wall)+(1/h_tubeA_tube)

Generally speaking, when refrigerant is introduced at an inlet 26 of the heat exchanger 10, the refrigerant is in a high pressure, gaseous state. Heat transfer between the gaseous refrigerant and the upper segment 16 of the heat exchanger 10 is a so-called “gas-to-gas” heat exchange, as heat from the gaseous refrigerant is transferred to the atmosphere (i.e., a gas) by the upper segment 16. Such gas-to-gas heat exchanges include a low air-side heat transfer coefficient h_air as well as a low refrigerant heat transfer coefficient h_tube. Therefore, an increased surface area (i.e., A_air A_tube) is required to maintain the overall heat transfer coefficient (i.e., UA) of the system 10.

Once the high-pressure, gaseous refrigerant experiences a reduction in pressure, and begins to change state into a liquid, less surface area is required to maintain the overall heat transfer coefficient of the system 10, as the low air-side heat transfer coefficient h_air and the low refrigerant heat transfer coefficient h_tube are increased, as will be described further below.

The upper segments 16 achieve an increased surface area by increasing the overall number of tubes 22 disposed within each upper segment 16, rather than increasing the overall number of segments 16. The increase number of tubes 22 per upper segment 16 not only maintains the overall heat transfer coefficient of the heat exchanger 10, but also optimizes the size of the heat exchanger 10 by minimizing the overall number of upper segments 16.

The lower segments 20 include a reduced number of tubes 24 disposed within each lower segment 20, and therefore reduce the air-side heat transfer coefficient (A_air) and the refrigerant heat transfer coefficient (A_tube). The decrease in the number of tubes 24 does not affect the overall heat transfer coefficient of the system 10, as the lower segments 20 receive refrigerant in a reduced-pressure state from the upper segments 16, and therefore do not require an increase in area to maintain the overall heat transfer coefficient.

The number of upper segments 16 can be varied depending on the particular system and will generally be governed by the pressure and state of the incoming refrigerant. For example, higher inlet pressures necessitate additional segments 16 to thereby extract a sufficient amount of heat prior to transferring the refrigerant to the lower segments 20. Conversely, lower inlet pressures allow for fewer segments 16, which are capable of extracting a sufficient amount of heat from the gaseous refrigerant prior to transferring the refrigerant to the lower segments 20. In either situation, the number of upper segments 16 must be sufficient in number and design (i.e., number of tubes 22 per segment 16) such that the lower segments 20 can completely convert the gaseous refrigerant to the liquid phase prior to the refrigerant exiting the heat exchanger at outlet 28. The number of lower segments 20 can also be varied in number and design (i.e., number of tubes 24 per segment 20) based on the number of upper segments 16. In other words, the system 10 can be optimized by adjusting not only the overall number of upper and lower segments 16, 20, but also by adjusting the respective number of tubes 22, 24 disposed within each segment 16, 20.

With particular reference to FIG. 3, the heat exchanger 10 is shown incorporated with another heat exchanger 30. Heat exchanger 30 is not fluidly coupled to heat exchanger 10, but is fixedly attached thereto near the inlet 26 to form a so-called “combo-cooler.” The combo-cooler allows vehicle designers, for example, to easily package multiple cooling units such as condensers and oil coolers in a single device. Even though the respective heat exchangers 10, 30 are not fluidly coupled, packaging of multiple components in a single unit is advantageous from a manufacturing and cost perspective.

As can be appreciated, the combo-cooler, while increasing productivity during assembly and reducing costs, requires a reduction in the overall size of at least one of the heat exchangers 10, 30 to adequately package the combo-cooler in a vehicle. The reduction in the number of upper segments 16, achieved by increasing the number of tubes 22 per segment 16, effectively reduces the overall size of the heat exchanger 10 and allows the heat exchanger 10 to be packaged with a second heat exchanger 30 without having to sacrifice performance.

With particular reference to FIGS. 1 and 4, operation of the heat exchanger 10 will be described in detail. For exemplary purposes, the heat exchanger 10 will be described as a condenser in a refrigeration system having an evaporator, a compressor, and an expansion valve (none shown). Operation of the refrigeration system will be described through use of an exemplary P-H diagram (FIG. 4), which compares a prior art plot “Z” associated with a prior art refrigeration system having a conventional condenser (i.e., a condenser with uniform segments from an inlet to an outlet) to a plot “Y” of a refrigeration system incorporating the condenser 10 of the present invention.

At the outset, the compressor receives low-pressure gaseous refrigerant from the evaporator generally at point A. The compressor pressurizes the gaseous refrigerant between points A and B prior to delivering the high-pressure, gaseous refrigerant to the condenser 10 at point B. The condenser 10 receives the high-pressure, gaseous refrigerant at inlet 26, with the refrigerant first encountering the upper segments 16 at tubes 22, as previously discussed.

The increased number of upper tubes 22 not only increases the heat transfer capability of the upper segments 16, but also decreases the head pressure of the incoming refrigerant, as the pressure of the incoming refrigerant is dissipated over a greater number of tubes 22. The reduction in pressure is achieved generally between points B and C when the refrigerant is roughly 30-80% superheated. Once the refrigerant reaches a sufficient pressure (i.e., point C), the gaseous refrigerant enters the lower segments 20. The refrigerant is maintained at a constant pressure between points C and D and is sub-cooled between points D and E.

Once all of the refrigerant is in the liquid phase (i.e., point E), the refrigerant exits the condenser 10 and encounters the expansion valve. The expansion valve decreases the pressure of the liquid refrigerant between points E and F prior to the refrigerant entering the evaporator at point F. The refrigerant enters the evaporator and reverts back to the gaseous state between points F and A due to absorption of heat from the space to be cooled. Once the refrigerant has fully achieved the gaseous state (i.e., point A), the compressor receives the refrigerant to begin the cycle anew.

As can be seen from FIG. 4, the condenser 10 of the present invention reduces the overall pressure of the system, and therefore reduces energy costs associated with operation of the compressor. Furthermore, due to the geometry of the upper segments 16, the overall size and weight of the condenser is reduced, thereby allowing the condenser 10 to be packaged with additional heat exchangers and providing an opportunity for material savings and increased efficiency.

The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

Claims

1. A heat exchanger comprising:

a first plurality of segments having a first plurality of tubes formed therein; and

a second plurality of segments having a second plurality of tubes formed therein, said second plurality of tubes fluidly coupled to said first plurality of tubes;

wherein said first plurality of segments includes a different internal geometry than said second plurality of segments.

2. The heat exchanger of claim 1, wherein said first plurality of segments is disposed proximate an inlet of the heat exchanger.

3. The heat exchanger of claim 1, wherein said second plurality of segments is disposed proximate an outlet of the heat exchanger.

4. The heat exchanger of claim 1, wherein said first series of tubes is integrally formed within each of said first plurality of segments and said second series of tubes is integrally formed within each of said second plurality of segments.

5. The heat exchanger of claim 4, wherein each segment of said first plurality of segments includes more tubes per segment than each segment of said second plurality of segments.

6. The heat exchanger of claim 1, wherein said second series of tubes includes a larger diameter than said first series of tubes.

7. The heat exchanger of claim 1, wherein the heat exchanger is a condenser.

8. A heat exchanger comprising:

a first plurality of segments having a first plurality of tubes formed therein; and

a second plurality of segments having a second plurality of tubes formed therein, said second plurality of tubes fluidly coupled to said first plurality of tubes;

wherein said first plurality of segments includes a greater number of tubes per segment than each of said second plurality of segments.

9. The heat exchanger of claim 8, wherein said first plurality of segments is disposed proximate an inlet of the heat exchanger.

10. The heat exchanger of claim 8, wherein said second plurality of segments is disposed proximate an outlet of the heat exchanger.

11. The heat exchanger of claim 8, wherein said first plurality of segments and said second plurality of segments are extruded.

12. The heat exchanger of claim 8, wherein said first plurality of tubes includes a greater cumulative cross-sectional area per segment than said second plurality of tubes per segment.

13. The heat exchanger of claim 8, wherein each tube of said second series of tubes includes a larger diameter than each tube of said first series of tubes.

14. The heat exchanger of claim 8, wherein the heat exchanger is a condenser.

15. A heat exchanger comprising:

a first plurality of segments having a first plurality of tubes formed therein; and

a second plurality of segments having a second plurality of tubes formed therein, said second plurality of tubes fluidly coupled to said first plurality of tubes;

wherein said first plurality of tubes includes a greater cumulative cross-sectional area per segment than said second plurality of tubes per segment.

16. The heat exchanger of claim 15, wherein said first plurality of segments includes more tubes per segment than said second plurality of segments.

17. The heat exchanger of claim 15, wherein said first plurality of segments and said second plurality of segments are extruded.

18. The heat exchanger of claim 15, wherein said second series of tubes includes a larger diameter than said first series of tubes.

19. The heat exchanger of claim 15, wherein the heat exchanger is a condenser.

20. The heat exchanger of claim 15, wherein said first series of tubes is integrally formed within each of said first plurality of segments and said second series of tubes is integrally formed within each of said second plurality of segments.