EP2165141A1

EP2165141A1 - Parallel flow heat exchanger with connectors

Info

Publication number: EP2165141A1
Application number: EP07795595A
Authority: EP
Inventors: Igor B. Vaisman; Michael F. Taras; Joseph J. Sangiovanni; Satyam Bendapudi
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2007-06-01
Filing date: 2007-06-01
Publication date: 2010-03-24
Also published as: WO2008147361A1; CN101772687A; CN101772687B; EP2165141A4; US20100170664A1; HK1145870A1

Abstract

A parallel flow heat exchanger includes a plurality of connector tubes which fluidly interconnect the individual flat heat exchange tubes to a refrigerant delivery member such that the refrigerant flows along the lengths of the connector tubes and then flows in a direction orthogonal thereto to enter the flat heat exchange tubes to thereby provide improved refrigerant distribution thereto. The refrigerant distribution member may be an inlet manifold or an entrance port or a refrigerant distributor. The connector tubes may be connected so as to conduct the flow in parallel or in series, and an orifice may be placed at the entrance end thereof to improve refrigerant distribution.

Description

Parallel Flow Heat Exchanger with Connectors

Background of the Invention

[0001] This invention relates generally to air conditioning and refrigeration systems and, more particularly, to parallel flow evaporators thereof. [0002] A definition of a so-called parallel flow heat exchanger, sometimes referred to as a flat tube heat exchanger, is widely used in the air conditioning and refrigeration industry now and designates a heat exchanger with a plurality of parallel passages, among which refrigerant is distributed to flow in an orientation generally substantially perpendicular to the refrigerant flow direction in the inlet and outlet manifolds.

[0003] Refrigerant maldistribution in refrigerant system evaporators is a well-known phenomenon. It causes significant evaporator and overall system performance degradation over a wide range of operating conditions. Maldistribution of refrigerant may occur due to differences in flow impedances within evaporator channels, non-uniform airflow distribution over external heat transfer surfaces, improper heat exchanger orientation or poor manifold and distribution system design. Maldistribution is particularly pronounced in parallel flow evaporators due to their specific design with respect to refrigerant routing to each evaporator circuit. Attempts to eliminate or reduce the effects of this phenomenon on the performance of parallel flow evaporators have been made with little or no success. The primary reasons for such failures have generally been related to complexity and inefficiency of the proposed technique or prohibitively high cost of the solution. [0004] In recent years, parallel flow heat exchangers, and brazed aluminum heat exchangers in particular, have received much attention and interest, not just in the automotive field but also in the heating, ventilation, air conditioning and refrigeration (HVAC&R) industry. The primary reasons for the employment of the parallel flow technology are related to its superior performance, high degree of compactness, good structural rigidity and enhanced resistance to corrosion. Parallel flow heat exchangers are now utilized in both condenser and evaporator applications for multiple products and system designs and configurations. The evaporator applications, although promising greater benefits and rewards, are more challenging and problematic. Refrigerant maldistribution is one of the primary concerns and obstacles for the implementation of this technology in the evaporator applications. 10005] As known, refrigerant maldistribution in parallel flow heat exchangers occurs because of unequal pressure drop inside the channels and in the inlet and outlet manifolds, as well as poor manifold and distribution system design. In the manifolds, the difference in length of refrigerant paths, phase separation and gravity are the primary factors responsible for maldistribution. Inside the heat exchanger channels, variations in the heat transfer rate, airflow distribution, manufacturing tolerances, and gravity are the dominant factors. Furthermore, the recent trend of the heat exchanger performance enhancement promoted miniaturization of its channels (so-called minichannels and microchannels), which in turn negatively impacted refrigerant distribution. Since it is extremely difficult to control all these factors, many of the previous attempts to manage refrigerant distribution, especially in parallel flow evaporators, have failed. [0006] If the two-phase flow enters the inlet manifold at a relatively high velocity, the liquid phase (droplets of liquid) is carried by the momentum of the flow further away from the manifold entrance to the remote portion of the header. Hence, the channels closest to the manifold entrance receive predominantly the vapor phase and the channels remote from the manifold entrance receive mostly the liquid phase. If, on the other hand, the velocity of the two-phase flow entering the manifold is low, there is not enough momentum to carry the liquid phase along the header. As a result, the liquid phase enters the channels closest to the inlet and the vapor phase proceeds to the most remote ones. Also, the liquid and vapor phases in the inlet manifold can be separated by the gravity forces, causing similar maldistribution consequences. In either case, maldistribution phenomenon quickly surfaces and manifests itself in evaporator and overall system performance degradation. [0007] While traditional round tube heat exchangers have a potential to feed each tube or circuit individually, flat tubes have not had such a capability and efforts to improve refrigerant distribution in such heat exchanger have included, for instance, the use of inserts and multiple inlet headers, all of which complicate the design and increase the manufacturing cost. Also, since large diameter headers are replaced with small diameter headers and connectors, operating pressures may be substantially elevated.

Summary of the Invention

[0008] Briefly, in accordance with one aspect of the invention, the individual flat heat exchange tubes of an evaporator are interconnected to a refrigerant delivery member by way of connector tubes such that the two phase refrigerant flows first from the refrigerant delivery member into the connector tubes and then into the individual flat heat exchange tubes to thereby obtain improved distribution of refrigerant flow.

[0009] In accordance with another aspect of the invention the connector tubes are connected to a common inlet manifold and extend generally orthogonally therefrom.

[0010] In accordance with another aspect of the invention, the connector tubes are cylindrical in shape, and the flat heat exchange tubes are inserted into longitudinal slots formed in the connector tubes to form tee joints.

[0011] By yet another aspect of the invention, the connector tubes have orifices at their one end such that the refrigerant entering the connector tube is expanded in the process to thereby improve uniform refrigerant distribution.

[0012] In accordance with another aspect of the invention, each of the connector tubes is fluidly connected directed to a traditional refrigerant distributor by way of an inlet tube.

[0013] In the drawings as hereinafter described, preferred and alternative embodiments are depicted; however, various other modifications and alternate constructions can be made thereto without departing from the spirit and scope of the invention.

Brief Description of the Drawings

[0014] FIG. 1 is a schematic illustration of the present invention as incorporated into a parallel flow evaporator.

[0015] FIG. 2 is a side view thereof.

[0016] FIG. 3 is an end view thereof. [0017] FIG. 4 is an enlarged view of a portion thereof.

[0018] FIG. 5 is a sectional view as seen along lines 5-5 of Fig. 4.

[0019] FIGS. 6A and 6B are respective front and top view of a tee connector.

[0020] FIGS. 7 A and 7B are schematic illustrations of an alterative embodiment thereof.

[0021] FIGS. 8 and 9 are schematic illustrations of another alternative embodiment thereof.

[0022] FIG. 10 is a schematic illustration of another alternative embodiment thereof.

[0023] FIG. 11 is a schematic illustration of another alternative embodiment thereof.

[0024] FIG. 12 is a schematic illustration of another alternative embodiment thereof.

[0025] FIGS. 13A and 13B are schematic illustrations of another alternative embodiment thereof.

[0026] FIGS. 14 and 15 are schematic illustrations of another alterative embodiment thereof.

[0027] FIG. 16 is a schematic illustration of yet another embodiment thereof.

Description of the Preferred Embodiment

[0028] Referring to Figs. 1-3, the invention is shown generally at 10 as incorporated into a parallel flow heat exchanger 11 which includes an inlet manifold 12, a plurality of flat heat exchange tubes 13 and an outlet manifold 14. [0029] Each of the flat heat exchange tubes 13 is fluidly connected to a respective connecting tube as shown at 16, 17, 18 and 19 which are, in turn, fluidly connected to the inlet manifold 12.

[0030] In operation, two-phase refrigerant flow enters an inlet port 21 of the inlet manifold 12 and flows toward both ends of the inner manifold 12. It then flows to the individual connector tubes 16, 17, 18 and 19 and then to the respective flat heat exchange tubes 13, after which it passes to the outlet manifold 14 and exits from the outlet port 22. [0031] Such a design configuration allows for sufficiently small diameters of the inlet manifold 12 and connecting tubes 16-19, which are favorable for refrigerant distribution among the flat heat exchange tubes 13.

[0032] As is seen in Figs. 4 and 5, the connector tubes 16, 17 and 18 are v cylindrical in a cross-section and have linear slots 23, 24 and 26, respectively formed therein for receiving the respective flat heat exchange tubes 13 therein. The degree of the penetration of the fiat heat exchange tubes 13 into the respective connector tubes 16, 17 and 18 is a matter of a design choice and may be selected to have a significant penetration as shown, or they may have little or no penetration such that the ends of the heat exchange tubes 13 are substantially flush with the inner walls of the connector tubes. Alternatively, the flat heat exchange tubes 13 may have different penetration depths, which may be selected depending on the position of the inlet port 21 to provide substantially equal inlet refrigerant flow impedances among the heat exchange tubes 13. The flat heat exchange tubes 13 are then fixed in their positions by a process such as welding, furnace brazing or the like.

[0033] As is seen in Fig. 5, the flat heat exchange tubes 13 may include a plurality of spaced ports 27 of any suitable cross section and have an overall height of H and an overall width of W. One end 28 of each connector tube, e.g. 17, is open and connected to the inlet manifold 12 as indicated above. The other end 29 can be sealed as shown in Fig. 5, or it may be interconnected to another connector tube as will be described hereinafter.

[0034] As should be understood, the relative sizes of the flat heat exchange tubes 13 and their respective connector tubes 16-19 are such that the diameter of the connector tubes is sufficient to allow for the height of the slot 24 to accommodate the height H of the flat heat exchange tube. Similarly, the length of the connector tube, i.e. the distance between the two ends 28 and 29, should be sufficient to accommodate the width W of the heat exchange tube 13. [0035] Figs. 4 and 5 show connectors 16, 17, and 18 as tubes with a cylindrical cross-section. As should be understood, the connectors may have elliptical, square, rectangular, triangular, or of any other possible shape. Also, the shape of the cross-section and the area may be different along the centerline of the connectors.

[0036] Figs.4 and 5 imply one connector per one flat heat exchange tube. As should be understood, a number of adjacent flat heat exchange tubes may be connected to one connector. In this case, multiple slots have to be made in the connectors to accommodate multiple flat heat exchange tubes.

[0037] Further, it may be beneficial to have flat heat exchange tubes of different sizes. For instance, the height or the width of the flat heat exchange tube may be varied. The corresponding slot dimensions of the respective connectors then need to be adjusted accordingly to accept the flat heat exchange tube of different sizes. As one example, the parallel flow heat exchanger may include sections with flat heat exchange tubes of different width to accommodate substantially different airflow amounts passing over these sections.

[0038] Figs. 4 and 5 show connectors 16, 17, and 18 as straight tubes. Such connectors are called two-end connectors. As should be understood, the connectors may be fabricated as triple-end connectors, particularly as a tee connector shown on

Figs. 6 A and 6B. The tee connector has a first side end 101, a second side end 102, and a central end 103. As should be also understood, each end may have a plurality of ends. Such connectors are called multiple-end connectors. It is obvious that at least one end of the connectors must be active. All remaining ends, if there are any, are inactive and sealed.

[0039] Figs. 6A and 6B show the ends 101, 102, and 103 having their centerline in one plane and shaped as the letter T. As should be understood, each end of the two-end, triple-end, and multiple-end connectors may have any possible shape of their centerlines.

[0040] Although the outlet header 14 has been shown as being directly connected to the flat tube channels 13, it should be understood that connector tubes similar to the connector tubes 16-19 may be used to interconnect the flat heat exchange tubes 13 to the outlet manifold 14.

[0041] The embodiment as described above shows the individual connector tubes 16-19 (which are of the two-end connector type) being aligned in parallel arrangement and extending orthogonally from the inlet manifold 12. It also shows them as being connected such that the flow of refrigerant therein is parallel. It should be understood that, the connector tubes 16-19 may be interconnected in serial flow relationship and may be further connected directly to the inlet port, without the need for an inlet manifold 12. Such an embodiment is shown in Figs. 7A and 7B wherein an elbow 28 interconnects the ends of connector tubes 16 and 17, an elbow 32 interconnects the ends of connector tubes 17 and 18, and an elbow 33 interconnects the ends of connector tubes 18 and 19 as shown. [0042] The refrigerant flow then enters the inlet port 34, passes through the connector tube 16, one flat heat exchange tube 13, the elbow 31 , the connector tube 17, another flat heat exchange tube 13, the elbow 32, the connector tube 18, the elbow 33 and the connector tube 19. Eventually, the refrigerant flows out of the outlet port 36.

[0043] Figs. 7A and 7B demonstrate a heat exchanger having tee connectors

16, 17, 18, and 19 on one end of the heat transfer tubes 13 and tee-connectors 116, 117, 118 and 119 on the other end thereof. The connectors each have one active end and two inactive ends. Ultimately, any described connector type is applicable. [0044] Figs. 8 and 9 show a heat exchanger having one circuit and four passes. As should be understood, any number of passes per circuit is possible, whatever is appropriate for a particular application. Also, it may be appropriate to have multiple circuits.

[0045] Fig. 10 shows a heat exchanger having three equal parallel circuits.

Each circuit has its own inlet port 34a, 34b, and 34c and its own outlet port 36a, 36b, and 36c, respectively. The refrigerant flow in the Fig.10 embodiment is generally downward, as it enters at the top and flows down to the bottom. However, it is possible to have a reversed generally upward (refrigerant enters at the bottom and flows up to the top) or a mixed flow arrangement. The heat exchanger design in Fig. 10 provides two-end connectors, for the top circuit, 116, 16, 17, 117, 118, 18, 19, and 119, and each connector has one active end and one inactive end. [0046] The heat exchanger design in Fig. 11 demonstrates a three-circuit, four-pass heat exchanger with tee connectors 116, 16, 17, 117, 118, 18, 19, and 119. Each tee connector has one active end and two inactive ends. 10047] Figs. 10 and 11 demonstrate the embodiments having the same number of passes in each circuit. As should be understood, the number of passes for each circuit may be different.

[0048] The heat exchangers described above may operate as condensers and evaporators. Usually, condensers have vapor at the inlet and liquid at the outlet. Due to the difference in densities of liquid and vapor phases, the condensers are typically more efficient if they have more inlets and fewer outlets. Fig. 12 shows a three- circuit heat exchanger having three inlets 34a, 34b, and 34c; one outlet 36; tee- connectors 116, 16, 17, 117, 118, 18, 119; and four-end connector 19 with two sealed side ends. Figs. 13 A and 13B show a similar heat exchanger where the four- end connector 19 has one sealed side end.

[0049] The heat exchangers shown on Figs. 12, 13 A and 13B may be applied as components of a heat pump system and operate as condensers and evaporators. Evaporators have a two-phase refrigerant at their inlet and typically vapor at the outlet. Due to the differences in densities of liquid and vapor phases, the evaporators may be more efficient if they have fewer inlets and more outlets. Since the operation as a condenser and the operation as an evaporator are reversed, with respect to the refrigerant flow direction, the embodiments in Figs. 12, 13A and 13B should have an appropriate number of inlets and outlets for both operational modes. [0050] Heat exchangers operating as evaporators should have means for distribution of the two-phase refrigerant. Another embodiment which is applicable for evaporators wherein an inlet manifold is not used is that shown in Figs. 14 and 15, wherein a traditional distributor 40 is fluidly connected to the individual connector tubes 16-19 by way of small diameter distributor tubes 38, 39, 41 and 42 respectively. In this case, an expansion device (not shown) is provided upstream of the distributor 40 such that the two-phase refrigerant flow is passed from the distributor 40 to the individual small diameter distributor tubes 38, 39, 41 and 42. The two-phase refrigerant flow then passes to the individual connector tubes 16-19 and is further distributed in the manner described hereinabove. [0051] Figs. 14 and 15 imply that the number of distributor tubes corresponds to the number of flat heat exchange tubes. It should be understood that, in general, each circuit may have a number of passes with the number of distributor tubes corresponding to the number of circuits. Also, as before with the connector tubes, there is an option to use one distributor for several circuits. [00S2] A variation of the Figs. 1-5 embodiment is shown in Fig. 16 wherein, rather than having an open-end connection between the connector tube 17 and the inlet manifold 12, as shown in Fig. 5, both ends 28 and 29 of the connector tube 19 are closed, and an orifice 42 is provided in the end 28 as shown. Thus, as the refrigerant passes from the inlet manifold 12 through the orifice 42, expansion occurs so as to provide two-phase lower pressure and temperature refrigerant to the connector tube 19. The flow of refrigerant from that point is the same as described hereinabove. It should be understood that the orifice 42 may have a plurality of orifices arranged in parallel and/or in series.

[0053] Fig 16 shows that the number of orifices 42 (or their pluralities) corresponds to the number of flat heat exchange tubes. It should be understood that, in general, each circuit may have several passes with the number of the orifices 42 (or their pluralities) corresponding to the number of circuits. Also, there is an option to use one orifice 42 (or its plurality) for several circuits.

[0054] There are two possible designs. One configuration implies that the manifold 12 operates as a receiver, and the orifices 42 along the manifold 12 operate as expansion devices, providing isenthalpic expansion from a condenser pressure to the evaporator pressure. Another arrangement includes an expansion device attached to the manifold 12. The expansion device provides isenthalpic expansion from the condenser pressure to a pressure which is higher than the evaporator pressure and lower than the condenser pressure. The orifices 42 function as a refrigerant distributor of the two-phase refrigerant providing single, double, or multiple expansions from the pressure downstream of the expansion device to the evaporator pressure.

[0055] In addition to the advantages discussed hereinabove, the present design features allow for the use of substantially wider heat exchange tubes, reduced fin density and/or increased fin height, without comprising performance characteristics and cost of the heat exchanger.

[0056] It should be understood that the present invention is intended for use with a heat exchanger that can be oriented horizontally, vertically, or inclined. That is, although the flat heat exchange tubes are shown as being horizontally oriented, the present invention would also be useful with vertically oriented and inclined flat heat exchange tubes.

[0057] While certain preferred embodiments of the present invention have been disclosed in detail, it is to be understood that various modifications in its structure may be adopted without departing from the spirit of the invention or the scope of the following claims.

Claims

We Claim:

1. A parallel flow heat exchanger of the type having a plurality of flat heat exchange tubes aligned in substantially parallel relationship, comprising: a plurality of connector tubes, each connector tube being fluidly connected to at least one of said plurality of said heat exchange tubes for conducting the flow of refrigerant therein; and a refrigerant delivery member for delivering refrigerant to each of said plurality of connector tubes.

2. A parallel flow heat exchanger as set forth in claim 1 wherein each of said plurality of connector tubes includes a linear slot into which a flat heat exchange tube is inserted.

3. A parallel flow heat exchanger as set forth in claim 2 wherein said flat heat exchange tubes extend inside said respective connector tubes.

4. A parallel flow heat exchanger as set forth in claim 3 wherein the protrusion depth of said flat heat exchange tubes into respective connector tubes is not uniform.

5. A parallel flow heat exchanger as set forth in claim 2 wherein said flat heat exchange tubes are inserted into said respective connector tubes such that the respective ends of said flat heat exchange tubes are substantially flush with the inner walls of said respective connector tubes.

6. A parallel flow heat exchanger as set forth in claim 1 wherein said connector tubes are cylindrical in shape and have a diameter which is larger than the height of said flat heat exchange tubes.

7. A parallel flow heat exchanger as set forth in claim 1 wherein said connector tubes have a length which is greater than the width of said flat heat exchange tubes.

8. A parallel flow heat exchanger as set forth in claim 1 wherein said refrigerant delivery member comprises an inlet manifold.

9. A parallel flow heat exchanger as set forth in claim 8 wherein said inlet manifold is connected at one end of said connector tubes.

10. A parallel flow heat exchanger as set forth in claim 1 wherein adjacent connector tubes are fluidly interconnected at their ends such that the refrigerant flows serially through the plurality of connector tubes.

11. A parallel flow heat exchanger as set forth in claim 1 wherein said refrigerant delivery member comprises a refrigerant distributor fluidly connected to the respective connector tubes.

12. A parallel flow heat exchanger as set forth in claim 1 and including an orifice disposed in one end of each of the plurality of connector tubes such that the refrigerant from the refrigeration delivery member flows first through the orifice and then into the respective connector tubes.

13. A parallel flow heat exchanger as set forth in claim 1 and including an outlet manifold fluidly connected at an end of each of said flat heat exchange tubes.

14. A parallel flow heat exchanger as set forth in claim 1 wherein at least one dimension of said flat heat exchange tube is not the same for said plurality of said flat heat exchange tubes.

15. A parallel flow heat exchanger as set forth in claim 14 wherein said dimension of said heat exchange tube is at least one of the tube width and the tube height.

16. A method of promoting uniform refrigerant flow into a plurality of parallel flat heat exchange tubes, comprising the steps of: providing a plurality of connector tubes, each connector tube being fluidly connected to at least one of said parallel flat heat exchanger tubes for conducting the flow of refrigerant therein; and providing a refrigerant flow delivery apparatus for delivering refrigerant to each of said of plurality of flat heat exchange tubes.

17. A method as set forth in claim 16 and including the step of providing in each of said plurality of connector tubes a linear slot into which a flat heat exchanger tube is inserted.

18. A method as set forth in claim 17 wherein said flat heat exchange tubes extend inside said respective connector tubes.

19. A method as set forth in claim 18 and the protrusion depth of said flat heat exchange tubes into respective connector tubes is not uniform.

20. A method as set forth in claim 17 wherein said flat heat exchange tubes are inserted into said respective connector tubes such that the respective ends of said flat heat exchange tubes are substantially flush with the inner walls of said respective connector tubes

21. A method as set forth in claim 16 wherein said connector tubes are cylindrical in shape and have a diameter which is larger than the height of said flat heat exchange tubes.

22. A method as set forth in claim 16 wherein said connector tubes have a length which is greater than the width of said flat heat exchange tubes.

23. A method as set forth in claim 16 wherein said refrigerant delivery member comprises an inlet manifold.

24. A method as set forth in claim 23 and including the step of connecting said inlet manifold to at one end of said connector tubes.

25. A method as set forth in claim 16 and including the step of fluidly interconnecting adjacent connector tubes at their ends such that the refrigerant flows serially through the plurality of connector tubes.

26. A method as set forth in claim 16 wherein said refrigerant delivery member comprises a refrigerant distributor fluidly connected to- the respective connector tubes.

27. A method as set forth in claim 16 and including the step of providing an orifice in one end of each of the plurality of connector tubes such that the refrigerant from the refrigeration delivery member flows first through the orifice and then into the respective connector tubes.

28. A method as set forth in claim 16 and including the step of fluidly connecting an outlet manifold to an end of each of said flat heat exchange tubes.

29. A method as set forth in claim 16 wherein at least one dimension of said flat heat exchange tube is not the same for said plurality of said flat heat exchange tubes.

30. A method as set forth in claim 29 wherein said dimension of said heat exchange tube is at least one of the tube width and the tube height.