DESIGN CHARACTERISTICS FOR HEAT EXCHANGERS DISTRIBUTION INSERT

Info

Publication number: 20110127023
Type: Application
Filed: Jun 10, 2009
Publication Date: Jun 2, 2011
Inventors: Michael F. Taras (Fayetteville, NY), Satyam Bendapudi (Manchester, CT), Yirong Jiang (Ellington, CT)
Application Number: 12/994,236

Abstract

A heat exchanger includes heat exchange tubes, a manifold, and a distribution insert incorporating orifices that communicate a fluid into the manifold for distribution into the heat exchange tubes. A design characteristic of the distribution insert and another design characteristic of at least one of the distribution insert, the manifold and the heat exchange tubes are employed to determine an essential design relationship. The essential design relationship defines a design parameter, the value of which falls within a determined range of values.

Description

Description

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 61/079,521, which was filed Jul. 10, 2008.

BACKGROUND OF THE INVENTION

Microchannel or minichannel heat exchangers of a refrigeration system or an air conditioning system include a plurality of parallel flat heat exchange tubes through which refrigerant is distributed. An inlet manifold is in fluid communication with the heat exchange tubes, and the heat exchange tubes are substantially perpendicular to the direction of refrigerant flow through the inlet manifold. The heat exchanger may have a multi-pass configuration to improve performance by balancing and optimizing heat transfer and pressure drop characteristics, typically by employing a plurality of parallel heat exchange tubes within each refrigerant pass. Single-pass configurations are typically more desirable in evaporator applications as the refrigerant pressure drop plays a dominant role in the evaporator performance.

Maldistribution of refrigerant into the heat exchange tubes can occur, which can cause the performance of the heat exchanger to decrease as compared to the performance achievable if the refrigerant is uniformly distributed through the heat exchange tubes. Maldistribution typically occurs when the two-phase refrigerant enters the inlet manifold. A vapor phase of the two-phase refrigerant has significantly different properties, moves at different velocities and is subjected to different effects of internal and external forces than a liquid phase refrigerant. The vapor phase separates from the liquid phase and flows independently, causing maldistribution of the refrigerant.

A distribution insert can be employed inside the inlet manifold of the heat exchanger to improve the distribution of the refrigerant. The refrigerant enters the heat exchanger through the distribution insert and flows into the inlet manifold through orifices in the distribution insert. Due to the nature of two-phase refrigerant flow, it is difficult to design a distribution insert.

SUMMARY OF THE INVENTION

A heat exchanger includes heat exchange tubes, a manifold, and a distribution insert including orifices that communicate a fluid into the manifold for distribution into the heat exchange tubes. A design characteristic of the distribution insert and another design characteristic of at least one of the distribution insert, the manifold and the heat exchange tubes are employed to determine an essential design relationship. The essential design relationship defines a design parameter that falls within a determined range of values.

In still another exemplary embodiment, a method of designing a heat exchanger includes the steps of determining a range of values and selecting at least one design characteristic of a distribution insert. The distribution insert includes orifices, and the distribution insert is received in a manifold. A fluid is communicated through the plurality of orifices and into the manifold for distribution into heat exchange tubes. The method further includes the step of determining a relationship between the at least one design characteristic of the distribution insert and another characteristic of at least one of the distribution insert, the manifold and the heat exchange tubes. The essential design relationship defines a design parameter that falls within the range of values.

These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary refrigeration system;

FIG. 2 illustrates a side view of an inlet portion of a manifold of a heat exchanger; and

FIG. 3 illustrates a perspective view of the inlet portion of the manifold of the heat exchanger showing various dimensions.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 illustrates a basic refrigeration or air conditioning system 20 including a compressor 22 that compresses a refrigerant and delivers it downstream to a condenser 24. In the condenser 24, the refrigerant rejects heat to a secondary fluid. From the condenser 24, the refrigerant passes through an expansion device 26 and is expanded to a low pressure. The expanded refrigerant flows into an inlet refrigerant pipe 28 leading into an evaporator 30. In the evaporator 30, the refrigerant accepts heat from another secondary fluid. From the evaporator 30, the refrigerant is returned to the compressor 22, completing the closed-loop refrigerant circuit.

The air conditioning system 20 can include a refrigerant flow control device, such as a four-way reversing valve, shown schematically at 35, to reverse the direction of refrigerant flow throughout the refrigerant circuit, in order to accommodate heat pump configurations and applications. When the refrigeration system 20 is operating in a cooling mode, the four-way reversing valve 35 directs the refrigerant from the compressor 22 to the condenser 24. When the refrigeration system 20 is operating in a heating mode, the four-way valve 35 directs the refrigerant from the compressor 22 to the evaporator 28 (which operates as a condenser, in the heating mode).

FIG. 2 illustrates a portion of the evaporator 30. The evaporator 30 includes a manifold 34. In one example, the manifold 34 is an inlet manifold or an intermediate manifold of the evaporator 30. In the below examples, an inlet manifold of an evaporator 30 is described. In one example, the evaporator 30 is a microchannel heat exchanger.

However, the features of the invention can extend to other types of heat exchangers, such as round tube and plate fin heat exchangers, and to other applications, such as condensers and reheat heat exchangers. Further, although the invention will be disclosed with reference to a manifold 34 of an evaporator 30, an intermediate manifold of a condenser 24 also falls within the scope of the invention. The condenser 24 can also be a microchannel heat exchanger. Additionally, although the benefits of the invention will be disclosed with reference to a two-phase refrigerant flow passing through the evaporator 30, single-phase refrigerant flows and refrigerant-oil mixtures are also within the scope and can benefit from the invention.

The inlet refrigerant pipe 28 fluidly communicates with a distribution insert 32 received within the manifold 34, which provides a refrigerant flow path along a longitudinal axis X. The distribution insert 32 fluidly communicates with a plurality of heat exchange tubes 36 positioned generally perpendicular to the manifold 34. The inlet refrigerant pipe 28 may be positioned at the end of the manifold 34, in the middle of the manifold 34, or at any intermediate location in between, and may have a single or multiple connections to the distribution insert 32. Each heat exchange tube 36 can be a flat tube, and may have several ports for refrigerant to flow through. In one example, each port has a hydraulic diameter of less than 1 mm.

A plurality of heat transfer fins 38 can be disposed between and rigidly attached to the heat exchange tubes 36 to enhance external heat transfer and provide structural rigidity for the evaporator 30. In one example, the plurality of heat transfer fins 38 are attached to the heat exchange tubes 36 by a furnace braze process.

The distribution insert 32 includes a plurality of refrigerant distribution orifices 42 to provide a refrigerant path from an internal cavity 50 of the distribution insert 32 to the manifold 34. The distribution orifices 42 can have any shape. For example, the distribution orifices 42 can have a round shape, a rectangular shape, an oval shape or any other suitable shape.

The distribution insert 32 receives the two-phase refrigerant from the inlet refrigerant pipe 28 and uniformly delivers the refrigerant through the plurality of distribution orifices 42 and into the manifold 34 for distribution to the heat exchange tubes 36. Typically, the relatively small size of the distribution insert 32 provides significant momentum for the refrigerant flow, preventing the phase separation of the two-phase refrigerant or promoting annual (in contrast to stratified) refrigerant flow pattern.

FIG. 3 shows various design characteristics, such as diameters, lengths, positions and other dimensions of components of the evaporator 30. The evaporator 30 is designed for optimal refrigerant distribution. At least one design characteristic of the distribution insert 32 is selected. An essential design relationship between the at least one design characteristic of the distribution insert 32 and another design characteristic of at least one of the distribution insert 32, the manifold 34 and the heat exchange tubes 36 is determined and defines a design parameter. If the design parameter falls within a pre-determined range of values, this indicates that the evaporator 30 is designed for optimal refrigerant distribution to the heat exchange tubes 36 and to prevent or significantly reduce refrigerant maldistribution amongst the heat exchange tubes 36.

In one example, the essential design relationship is a ratio of a first design characteristic to a second design characteristic, that is, a first design characteristic divided by a second design characteristic. Optimal effectiveness of refrigerant distribution through the distribution insert 32 is achieved if the non-dimensional design parameter defined by essential design relationship falls within the given pre-determined range. At least one of the first design characteristic and the second design characteristic is associated with the distribution insert 32.

Various characteristics of the evaporator 30 are defined as below:

D_ins inner diameter of the distribution insert 32 D_man inner diameter of the manifold 34 D_orifice hydraulic diameter of the distribution orifices 42 of the distribution insert 32 D_tube hydraulic diameter of the heat exchange tubes 36 L_ins length of the distribution insert 32 L_man length of the manifold 34 L_orifice axial separation between centers of the distribution orifices 42 of the distribution insert 32 A_{insert, surf} external surface area of the distribution insert 32 A_{insert, cross} cross-sectional area of the distribution insert 32 in the plane perpendicular to the axis X and based on the diameter D_ins A_orifice total cross-sectional area of all the distribution orifices 42 of the distribution insert 32 A_{man, dia} cross-sectional area of the manifold 34 in the plane perpendicular to the axis X and based on the diameter D_man A_{man, long} cross-sectional area of the manifold 34 in the plane of the longitudinal axis X M number of the heat exchange tubes 36 N number of the distribution orifices 42

By employing these design characteristics within the below defined relationships/ratios, several non-dimensional design parameters can be defined. A list of these design parameters and the desired pre-determined ranges of their values are defined below:

Relationship Lower Upper No. Relationships limit limit 1 (D_ins/D_man)² 0.02 0.95 2 A_orifice/A_{insert, surf} 50 5000 3 A_orifice/A_{insert, cross} 0.01 100 4 D_orifice/L_orifice 0.01 35 5 (D_orifice²/A_{insert, surf})/ 0.01 25 (D_tube²/A_{man, long}) 6 [(N* D_orifice)²]/[(M* D_tube)²] 0.1 100 7 (D_man/D_orifice²)/(L_ins/D_ins)² 0.01 20 8 D_man/L_ins 1 1000

Using Relationship 1, the characteristic of the distribution insert 32 is the inner diameter of the distribution insert 32 (D_ins). The relationship is defined as a ratio of the inner diameter of the distribution insert 32 (D_ins) to the inner diameter of the manifold 34 (D_man), and the ratio is then squared to define a non-dimensional design parameter. This non-dimensional design parameter represents the flow momentum within the distribution insert 32 versus the flow momentum within the manifold 34 without the distribution insert 32. For optimal performance, the value of the design parameter should be in the range of 0.02 to 0.95.

Using Relationship 2, the characteristics of the distribution insert 32 are the total cross-sectional area of all the distribution orifices 42 of the distribution insert 32 (A_orifice) and the external surface area of the distribution insert 32 (A_insert,surf). The relationship is defined as a ratio of the total cross-sectional area of all the distribution orifices 42 of the distribution insert 32 (A_orifice) to the external surface area of the distribution insert 32 (A_insert,surf), which defines a non-dimensional design parameter. This non-dimensional design parameter represents the density of the distribution orifices 42 of the distribution insert 32. For optimal performance, the value of the design parameter should be in the range of 50 to 5000.

Using Relationship 3, the characteristics of the distribution insert 32 are the total cross-sectional area of all the distribution orifices 42 of the distribution insert 32 (A_orifice) and the cross-sectional area of the distribution insert 32 in the plane perpendicular to the axis X and based on the diameter (A_insert,cross). The relationship is defined as a ratio of the total cross-sectional area of all distribution orifices 42 of the distribution insert 32 (A_orifice) to the cross-sectional area of the distribution insert 32 in the plane perpendicular to the axis X and based on the diameter D_ins(A_insert,cross) which defines a non-dimensional design parameter. This non-dimensional design parameter represents the flow momentum through the distribution orifices 42 of the distribution insert 32 versus the flow momentum through the distribution insert 32. For optimal performance, the value of the design parameter should be in the range of 0.01 to 100.

Using Relationship 4, the characteristics of the distribution insert 32 are the hydraulic diameter of the distribution orifices 42 of the distribution insert 32 (D_orifice) and the axial separation between centers of the distribution orifices 42 of the distribution insert 32 (L_orifice). The relationship is defined as the ratio of the hydraulic diameter of the distribution orifices 42 of the distribution insert 32 (D_orifice) to the axial separation between centers of the distribution orifices 42 of the distribution insert 32 (L_orifice), which defines a non-dimensional design parameter. This non-dimensional design parameter represents the density of the distribution orifices 42 of the distribution insert 32. For optimal performance, the value of the design parameter should be in the range of 0.01 to 35.

Using Relationship 5, the characteristics of the distribution insert 32 are the hydraulic diameter of the distribution orifices 42 of the distribution insert 32 (D_orifice) and the external surface area of the distribution insert 32 (A_insert,surf). The relationship is defined as the ratio of a first design characteristic to a second design characteristic. The first design characteristic is defined as the hydraulic diameter of the distribution orifices 42 of the distribution insert 32 (D_orifice) squared divided by external surface area of the distribution insert 32 (A_insert,surf). The second design characteristic is defined as the hydraulic diameter of the heat exchange tubes 36 (D_tube) squared divided by the cross-sectional area of the manifold 34 in the plane of the longitudinal axis X (A_man,long). The ratio of the first design characteristic to the second design characteristic determines a non-dimensional design parameter. This non-dimensional design parameter represents the flow momentum through the heat exchange tubes 36 versus the flow momentum through the distribution orifices 42. For optimal performance, the value of the design parameter should be in the range of 0.01 to 25.

Using Relationship 6, the characteristics of the distribution insert 32 are the hydraulic diameter of the distribution orifices 42 of the distribution insert 32 (D_orifice) and the number of the distribution orifices 42 (N). The relationship is defined as the ratio of a first design characteristic to a second design characteristic. The first design characteristic is defined as the number of distribution orifices 42 (N) multiplied by the hydraulic diameter of the distribution orifices 42 of the distribution insert 32 (D_orifice), which is then squared. The second design characteristic is defined as the number of heat exchange tubes 36 (M) multiplied by the hydraulic diameter of the heat exchange tubes 36 (D_tube), which is then squared. The ratio of the first design characteristic to the second design characteristic defines a non-dimensional design parameter. This design parameter represents the flow momentum through the heat exchange tubes 36 versus the flow momentum through the distribution orifices 42. For optimal performance, the value of the design parameter should be in the range of 0.01 to 100.

Using Relationship 7, the characteristics of the distribution insert 32 are the hydraulic diameter of the distribution orifices 42 of the distribution insert 32 (D_orifice), the length of the distribution insert 32 (L_ins), and the inner diameter of the distribution insert 32 (D_ins). The relationship is defined as the ratio of a first design characteristic to a second design characteristic. The first design characteristic is defined as the inner diameter of the manifold 34 (D_man) divided by the hydraulic diameter of the distribution orifices 42 of the distribution insert 32 (D_orifice) squared. The second design characteristic is defined by the length of the distribution insert 32 (L_ins) divided by the inner diameter of the distribution insert 32 (D_ins) squared. The first design characteristic is divided by the second design characteristic to obtain the ratio. The ratio of the first design characteristic to the second design characteristic determines a non-dimensional design parameter. This non-dimensional design parameter represents the pressure differential across the manifold 34 versus the pressure differential along the manifold 34. For optimal performance, the value of the design parameter should be in the range of 0.01 to 20.

Using Relationship 8, the characteristic of the distribution insert 32 is the length of the distribution insert 32 (L_ins). The relationship is defined as the inner diameter of the manifold 34 (D_man) divided by the length of the distribution insert 32 (L_ins), which defines a non-dimensional design parameter. This non-dimensional design parameter represents the traveled distance along the distribution insert 32 compared to the distance across the manifold 34. For optimal performance, the value of the design parameter should be in the range of 1 to 1000.

By calculating a relationship or ratio employing at least one essential design characteristic of the distribution insert 32 and determining if the calculated value of a defined non-dimensional design parameter falls within a pre-determined range of values, it can be determined if the distribution effectiveness of the distribution insert 32 and the evaporator 30 is optimized.

The foregoing description is only exemplary of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.

Claims

1. A heat exchanger comprising: a distribution insert at least partially received in the manifold, wherein the distribution insert includes a plurality of orifices that can distribute a fluid into the manifold for distribution into the plurality of heat exchange tubes, wherein at least one design characteristic of the distribution insert and another design characteristic of at least one of the distribution insert, the manifold and the plurality of heat exchange tubes are employed to determine an essential design relationship, and the essential design relationship defines a design parameter with a value that falls within a determined range of values.

a plurality of heat exchange tubes;

a manifold; and

2.-3. (canceled)

4. The heat exchanger as recited in claim 1 wherein the heat exchanger is a microchannel heat exchanger.

5. The heat exchanger as recited in claim 1 wherein the essential design relationship is a non-dimensional ratio.

6. The heat exchanger as recited in claim 1 wherein the at least one design characteristic of the distribution insert is one of a length of the distribution insert, a diameter of the distribution insert, a hydraulic diameter of the plurality of orifices of the distribution insert, a separation distance between centers of the plurality of orifices of the distribution insert, a surface area of the distribution insert, a cross-sectional area of the distribution insert, a total cross-sectional area of the plurality of orifices of the distribution insert, and a number of the distribution orifices.

7. The heat exchanger as recited in claim 1 wherein the at least one design characteristic is an inner diameter of the distribution insert and the another design characteristic is an inner diameter of the manifold, and the essential design relationship is defined by a ratio of the inner diameter of the distribution insert to the inner diameter of the manifold, wherein the ratio is squared to define the design parameter.

8. The heat exchanger as recited in claim 7 wherein the range of values for the design parameter is between 0.02 and 0.95.

9. The heat exchanger as recited in claim 1 wherein the another design characteristic is a characteristic of the distribution insert, and the at least one design characteristic is a total cross-sectional area of the plurality of distribution orifices of the distribution insert and an external surface area of the distribution insert, and the essential design relationship is defined by a ratio of the total cross-sectional area of the plurality of distribution orifices of the distribution insert to the external surface area of the distribution insert, wherein the ratio defines the design parameter.

10. The heat exchanger as recited in claim 9 wherein the range of values for the design parameter is between 50 and 5000.

11. The heat exchanger as recited in claim 1 wherein the another design characteristic is a characteristic of the distribution insert, and the at least one design characteristic is a total cross-sectional area of the plurality of distribution orifices of the distribution insert and a cross-sectional area of the distribution insert, and the essential design relationship is defined by a ratio of the total cross-sectional area of the plurality of distribution orifices of the distribution insert to the cross-sectional area of the distribution insert, wherein the ratio defines the design parameter.

12. The heat exchanger as recited in claim 11 wherein the range of values for the design parameter is between 0.01 to 100.

13. The heat exchanger as recited in claim 1 wherein the another design characteristic is a characteristic of the distribution insert, and the at least one design characteristic is a hydraulic diameter of the plurality of distribution orifices of the distribution insert and a separation between centers of the plurality of distribution orifices of the distribution insert, and the essential design relationship is defined by a ratio of the hydraulic diameter of the plurality of the distribution orifices of the distribution insert to the separation between the centers of the plurality of distribution orifices of the distribution insert, wherein the ratio defines the design parameter.

14. The heat exchanger as recited in claim 13 wherein the range of values for the design parameter is between 0.01 to 35.

15. The heat exchanger as recited in claim 1 wherein the at least one design characteristic is a hydraulic diameter of the plurality of distribution orifices of the distribution insert and a surface area of the distribution insert, the another design characteristic is a hydraulic diameter of the plurality of heat exchange tubes and a cross-sectional area of the manifold, and the essential design relationship is defined as a first design characteristic divided by a second design characteristic,

wherein the first design characteristic is a ratio of the hydraulic diameter of the plurality of distribution orifices of the distribution insert squared to the external surface area of the distribution insert, and the second design characteristic is a ratio of the hydraulic diameter of the plurality of heat exchange tubes squared to the cross-sectional area of the manifold, and the ratio of the first design characteristic to the second design characteristic defines the design parameter.

16. The heat exchanger as recited in claim 15 wherein the range of values for the design parameter is 0.01 to 25.

17. The heat exchanger as recited in claim 1 wherein the at least one design characteristic is a hydraulic diameter of the plurality of distribution orifices of the distribution insert and a number of the plurality of distribution orifices of the distribution insert, the another design characteristic is a number of the plurality of heat exchange tubes and a hydraulic diameter of the plurality of heat exchange tubes, and the essential design relationship is defined as a first design characteristic divided by a second design characteristic,

wherein the first design characteristic is defined by the number of the plurality of distribution orifices of the distribution insert multiplied by the hydraulic diameter of the plurality of distribution orifices of the distribution insert, which is then squared, and the second design characteristic is the number of the plurality of heat exchange tubes multiplied by the hydraulic diameter of the plurality of heat exchange tubes, which is then squared, and the ratio of the first design characteristic to the second design characteristic defines the design parameter.

18. The heat exchanger as recited in claim 17 wherein the range of values for the design parameter is 0.01 to 100.

19. The heat exchanger as recited in claim 1 wherein the at least one design characteristic is a hydraulic diameter of the plurality of distribution orifices of the distribution insert, a length of the distribution insert and an inner diameter of the distribution insert, the another design characteristic is a diameter of the manifold, and the essential design relationship is defined as a first design characteristic divided by a second design characteristic,

wherein the first design characteristic is the diameter of the manifold divided by the hydraulic diameter of the plurality of distribution orifices of the distribution insert squared divided by the length of the distribution insert divided by the diameter of the distribution insert squared, and the ratio of the first design characteristic to the second design characteristic defines the design parameter.

20. The heat exchanger as recited in claim 19 wherein the range of values for the design parameter is 0.01 to 20.

21. The heat exchanger as recited in claim 1 wherein the at least one design characteristic is a length of the distribution insert, the another design characteristic is an inner diameter of the manifold, and the essential design relationship is defined as a ratio of the inner diameter of the manifold to the length of the distribution insert, wherein the ratio defines the design parameter.

22. The heat exchanger as recited in claim 21 wherein the range of values for the design parameter is 1 to 1000.

23.-25. (canceled)