HK1117894B - Heat exchanger with fluid expansion in header - Google Patents

Description

Heat exchanger with fluid expansion in header

Cross Reference to Related Applications

The present invention claims priority from U.S. provisional patent application No. 60/649422, filed on 2/2005 entitled "microchannel heat exchanger with fluid expansion in the space between the tubes and header," which is incorporated herein by reference in its entirety.

Technical Field

The present application relates generally to refrigerant vapor compression system heat exchangers having a plurality of parallel tubes extending between a first header and a second header and, more particularly, to providing expansion of a coolant in an inlet header for improving distribution of two-phase refrigerant flow through the parallel tubes of the heat exchanger.

Background

Refrigerant vapor compression systems are well known in the art. Air conditioners and heat pumps employing refrigerant vapor compression cycles are commonly used to cool or cool/heat air to control the ambient climate in dwellings, office buildings, hospitals, schools, restaurants or other facilities to a comfortable range. Refrigerant vapor compression systems are also commonly used to cool air, or other secondary media such as water or glycol solutions, to provide a refrigerated environment for food and beverage products in display cases of supermarkets, convenience stores, groceries, cafeterias, restaurants and other food service establishments.

Typically, these refrigerant vapor compression systems include a compressor, a condenser, an expansion device, and an evaporator in fluid communication with a refrigerant. The aforementioned basic refrigerant system components are interconnected by refrigerant lines in a closed refrigerant circuit and are arranged in accordance with the vapor compression cycle employed. An expansion device, typically an expansion valve or a fixed orifice metering device (e.g., a metering orifice or a capillary tube), is disposed in the refrigerant conduit at a location in the refrigerant circuit upstream of the evaporator and downstream of the condenser with respect to refrigerant flow. The expansion device operates to expand the liquid refrigerant flowing through the refrigerant line extending from the condenser to the evaporator to a lower pressure and temperature. Thus, a portion of the liquid refrigerant passing through the expansion device expands to a vapor. As a result, in such conventional refrigerant vapor compression systems, the refrigerant flow entering the evaporator constitutes a two-phase mixture. The specific percentages of liquid refrigerant and vapor refrigerant depend on the specific expansion device employed, the operating conditions, and the refrigerant used, e.g., R-12, R-22, R-134A, R-404A, R-410A, R-407C, R717, R744, or other compressible fluid.

In some refrigerant vapor compression systems, the evaporator is a parallel tube heat exchanger. Such heat exchangers have a plurality of parallel refrigerant flow paths provided by a plurality of tubes extending in parallel between an inlet header or inlet header and an outlet header or outlet header. The inlet header receives a refrigerant flow from the refrigerant circuit and distributes the refrigerant flow to a plurality of flow paths through the heat exchanger. The outlet header serves to collect the refrigerant flow leaving the respective flow paths and direct the collected flow back into the refrigerant lines for return to the compressor of the single-pass heat exchanger or to another set of heat exchange tubes of the multi-pass heat exchanger. In the latter case, the outlet header is an intermediate header or header chamber and serves as the inlet header for the next downstream group of tubes.

Historically, parallel tube heat exchangers for such refrigerant vapor compression systems have employed round tubes, typically 3/8 inches or 7 millimeters in diameter. More recently, multichannel tubes that are flat in cross-section, typically rectangular or oval, have been used in heat exchangers for refrigerant vapor compression systems. Each multi-channel tube typically has a plurality of flow channels extending longitudinally parallel to the length of the tube, each channel providing a refrigerant flow path having a relatively small flow area. Thus, a heat exchanger having multi-channel tubes extending in parallel between the heat exchanger inlet and outlet headers will have a relatively large number of small flow area refrigerant flow paths extending between the two headers. In contrast, a conventional heat exchanger with conventional circular tubes will have a relatively small number of large flow area flow paths extending between the inlet and outlet headers.

Non-uniform distribution of two-phase refrigerant flow, also referred to as maldistribution, is a common problem in parallel heat exchangers and can negatively impact heat exchanger efficiency. The problem of two-phase maldistribution is often caused by the difference in density of the vapor phase refrigerant and the liquid phase refrigerant present in the inlet header due to the expansion of the refrigerant through the upstream expansion device.

One solution for controlling the distribution of refrigerant flow through parallel tubes in an evaporative heat exchanger is disclosed in U.S. patent No.6502413 to Repice et al. In the refrigerant vapor compression system disclosed therein, high pressure liquid refrigerant from the condenser is partially expanded in a conventional in-line expansion valve upstream of the evaporative heat exchanger inlet header to a lower pressure liquid refrigerant. A throttling element, such as a simple constriction in the tube or an internal orifice plate disposed within the tube, is disposed in each tube connected to the inlet header downstream of the tube inlet to allow the refrigerant to complete its expansion to a low pressure liquid/vapor refrigerant mixture upon entering the tube.

Another method for controlling the distribution of refrigerant flow through parallel tubes in an evaporative heat exchanger is disclosed in japanese patent No. jp4080575 to Kanzaki et al. In the refrigerant vapor compression system disclosed therein, the high pressure liquid refrigerant from the condenser is also partially expanded in a conventional in-line expansion valve into a lower pressure liquid refrigerant upstream of the distribution chamber of the heat exchanger. A plate having a plurality of holes therein extends in the cavity. As the lower pressure liquid refrigerant passes through the holes, it expands into a low pressure liquid/vapor mixture downstream of the plate and upstream of the inlet to the respective conduit leading to the chamber.

Japanese patent No.6241682, Massaki et al, discloses a parallel flow tube heat exchanger for a heat pump in which the inlet end of each multi-channel tube connected to an inlet header is crushed to form a partial restriction in the tube downstream of each tube inlet. Japanese patent No. jp8233409 to Hiroaki et al discloses a parallel flow tube heat exchanger in which a plurality of flat, multi-channel tubes are connected between a pair of headers each having an interior with a reduced flow area in the direction of refrigerant flow as a means of uniformly distributing refrigerant to the respective tubes. Japanese patent JP2002022313 to Yasushi discloses a parallel tube heat exchanger in which refrigerant is supplied to a header through an inlet tube extending along the axis of the header without terminating the end of the header, the two-phase refrigerant flow not being separated when entering an annular channel between the outer surface of the inlet tube and the inner surface of the header from the inlet tube. The two-phase refrigerant flow thus flows into each of the tubes leading to the annular channel.

Obtaining uniform refrigerant flow distribution in a relatively large number of small flow area refrigerant paths is even more difficult than in conventional round tube heat exchangers and can significantly reduce heat exchanger efficiency and cause serious reliability problems due to compressor flooding.

Disclosure of Invention

It is a general object of the present invention to mitigate maldistribution of refrigerant flow in a heat exchanger of a refrigerant vapor compression system having a plurality of multi-channel tubes extending between a first header and a second header.

It is an object of one aspect of the invention to distribute refrigerant as a single phase liquid refrigerant to individual channels in an array of multi-channel tubes.

It is an object of another aspect of the invention to delay expansion of refrigerant in a heat exchanger of a refrigerant vapor compression system having a plurality of multi-channel tubes until the refrigerant flow has been distributed as a single phase liquid refrigerant to individual channels in a row of multi-channel tubes.

In one aspect of the invention, a heat exchanger is provided having a header defining a chamber for receiving primarily liquid refrigerant from a refrigerant cycle, and at least one heat exchange tube defining a refrigerant flow path therethrough and having an inlet opening into the refrigerant flow path at an inlet end thereof. The inlet end of the heat exchange tube extends into the chamber of the header and is positioned such that the inlet to the refrigerant flow path is spaced apart and disposed facing the opposite interior surface of the header thereby defining a relatively narrow expansion gap between the inlet to the refrigerant flow path to the heat exchange tube and the inward surface of the header. The gap may have a width in the range of 0.01-0.5 mm. In one embodiment, the gap has a width of about 0.1 millimeters. In one embodiment of the heat exchanger, the at least one heat exchange tube has a plurality of channels extending longitudinally in parallel relationship through the refrigerant flow path, each channel defining a separate refrigerant flow path through the at least one heat exchange tube. The flow path defined by the plurality of channels may have a circular cross-section, a rectangular cross-section, a triangular cross-section, a trapezoidal cross-section, or other non-circular cross-section. The heat exchanger of the present invention may be implemented as a single pass or a multiple pass arrangement.

In one particular embodiment, a heat exchanger has a first header, a second header, and a plurality of heat exchange tubes extending between the first and second headers. Each header defines a chamber for collecting refrigerant. Each tube of the plurality of heat exchange tubes has an inlet end opening into the chamber of one of the headers and an outlet end opening into the other header. Each tube of the plurality of heat exchange tubes has a plurality of channels extending longitudinally in parallel relationship from the inlet end to the outlet end with each channel defining a discrete refrigerant flow path. The inlet end of each heat exchange tube extends into the chamber of at least one header and is positioned such that the inlet to the channel is spaced from and disposed against the inner surface of the header thereby defining a relatively narrow gap between the inlet to the channel and the opposite inner surface of the header which serves as an expansion gap.

In another aspect of the invention, a refrigerant vapor compression system includes a compressor, a condenser and an evaporative heat exchanger connected in refrigerant flow communication, whereby high pressure refrigerant vapor enters the condenser from the compressor, high pressure refrigerant liquid enters the evaporative heat exchanger from the condenser, and low pressure refrigerant vapor enters the compressor from the evaporative heat exchanger. An evaporative heat exchanger includes at least an inlet header and an outlet header, and at least one heat exchange tube extending between the inlet and outlet headers. The inlet header defines a chamber for receiving liquid refrigerant from the refrigerant circuit. Each heat exchange tube has an inlet end opening into an inlet header and an outlet end opening into an outlet header. Wherein the tubes of each heat exchange tube have a plurality of channels extending longitudinally in parallel relationship from the inlet end to the outlet end with each channel defining a discrete refrigerant flow path. The inlet end of each heat exchange tube extends into the chamber of the inlet header and is positioned such that the inlet to the channels is spaced from and disposed against the inner surface of the header thereby defining an expansion gap between the inlet to the channels and the opposed surface of the inlet header. In refrigerant vapor compression systems incorporating the heat exchanger of the invention, such as an evaporator, the expansion gap may be used as the only expansion device or the primary expansion device in the system, or as an auxiliary expansion device in series with an upstream expansion device in the refrigerant line leading to the system evaporator.

In a further aspect of the invention, a method is provided for operating a refrigerant vapor compression cycle. The method comprises the following steps: providing a compressor, a condenser and an evaporative heat exchanger connected in a refrigerant circuit; passing high pressure refrigerant vapor from the compressor to the condenser; passing high pressure refrigerant liquid from the condenser to an inlet header of the evaporative heat exchanger; providing at least one heat exchange tube defining a plurality of refrigerant flow paths for passing refrigerant from an inlet header to an outlet header of an evaporative heat exchanger; distributing the high pressure fluid collected in the inlet header into and through each of the plurality of refrigerant flow paths by passing the high pressure liquid refrigerant through an expansion gap formed between the inner surface of the inlet header and the outlet to the at least one heat exchange tube, whereby the liquid refrigerant is substantially uniformly distributed into the plurality of refrigerant flow channels and expanded into a low pressure mixture of liquid refrigerant and vapor refrigerant; and returning the low pressure refrigerant vapor from the outlet header of the evaporative heat exchanger to the compressor.

Drawings

These and other objects of the present invention will be further understood from the following detailed description of the invention, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of an embodiment of a heat exchanger according to the present invention;

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

FIG. 3 is a perspective view of another embodiment of a heat exchange tube and inlet header assembly;

FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 3;

FIG. 5 is a perspective view of another embodiment of a heat exchange tube and inlet header assembly;

FIG. 6 is a cross-sectional view taken along line 6-6 of FIG. 5;

FIG. 7 is a perspective view of another embodiment of a heat exchange tube and inlet header assembly;

FIG. 8 is a cross-sectional view taken along line 8-8 of FIG. 7;

FIG. 9 is a schematic view of a refrigerant vapor compression system incorporating the heat exchanger of the present invention;

FIG. 10 is a schematic view of a refrigerant vapor compression system incorporating the heat exchanger of the present invention;

FIG. 11 is a front view, partially in section, of one embodiment of a multi-channel evaporator according to the invention; and

FIG. 12 is a front elevation view, partially in section, of one embodiment of a multi-channel condenser according to the present invention.

Detailed Description

Referring to various exemplary single pass embodiments of the multichannel tube heat exchanger shown in fig. 1-8, the parallel tube heat exchanger 10 of the present invention will be generally described herein. The heat exchanger 10 includes an inlet header 20, an outlet header 30, and a plurality of multi-channel heat exchange tubes 40 extending longitudinally between the inlet header 20 and the outlet header 30 to provide a plurality of refrigerant flow paths between the inlet header 20 and the outlet header 30. Each heat exchange tube 40 has an inlet 43 in refrigerant flow communication at one end with the inlet header 20 and an outlet in refrigerant flow communication at the other end with the outlet header 30.

In the exemplary embodiment of the heat exchanger 10 depicted in fig. 1, 3, 5 and 7, the heat exchange tubes 40 are shown arranged in a parallel fashion, extending generally vertically between a generally horizontally extending inlet header 20 and a generally horizontally extending outlet header 30. The illustrated embodiments, however, are exemplary and not limiting of the invention. It should be understood that the invention described herein may be implemented on a variety of other configurations of the heat exchanger 10. For example, the heat exchange tubes are arranged in a parallel fashion, extending generally horizontally between a generally vertically extending inlet header and a generally vertically extending outlet header. As a further example, the heat exchanger may have annular inlet and outlet headers of different diameters with the heat exchange tubes extending slightly radially inwardly or slightly radially outwardly between the annular headers. The heat exchange tubes may also be provided in a multi-pass embodiment, as will be described in more detail below.

Each multi-channel heat exchange tube 40 has a plurality of parallel flow channels 42 extending longitudinally, i.e. along the axis of the tube, the length of the tube, thereby providing a plurality of independent parallel flow paths between the inlet and outlet of the tube. Each multi-channel heat exchange tube 40 is a "flat" tube, e.g., of rectangular cross-section, defining an interior which is divided to form a side-by-side array of independent flow channels 42. The flat multichannel tubes 40 may have a width of, for example, 50 millimeters or less, typically 12 to 25 millimeters, and a height of about 2 millimeters or less, as compared to conventional prior art circular tubes having a diameter of 1/2 inches, 3/8 inches, or 7 millimeters. For simplicity and clarity of illustration, the conduit 40 shown in fig. 1-8 has twelve channels 42 that define a flow path having a circular cross-sectional area. However, it should be understood that in an application, each multi-channel tube 40 will typically have about ten to twenty flow channels 42. Typically, each flow channel 42 will have a hydraulic diameter, defined as four times the cross-sectional flow area divided by the perimeter, in the range of about 200 microns to about 3 millimeters. Although shown as circular in cross-section in the figures, the channels 42 may have a rectangular, triangular or trapezoidal cross-section, or other desired non-circular cross-section.

Referring now particularly to fig. 2, 4, 6 and 8, each heat exchange tube 40 of the heat exchanger 10 is inserted into one side of the inlet header 20 with the inlet end 43 of the tube extending into the interior 25 of the inlet header 20. Each heat exchange tube 40 is inserted to a sufficient length to juxtapose the respective openings 41 of the channels 42 at the inlet end 43 of the heat exchange tube 40 in relatively close proximity to the inside surface 22 of the opposite side of the header 20 to provide a relatively narrow gap G between the opening 41 at the inlet end 43 of the heat exchange tube 40 and the inside surface 22 of the header 20. The gap G must be small enough relative to the flow area of the opening 41 in each channel 42 of the heat exchange tube 40 to ensure that the expansion of the high pressure liquid refrigerant to the low pressure liquid and vapor refrigerant mixture reaches the desired level as the refrigerant flows through the gap G into the opening 41 of each channel 42. Typically, the gap G should have a width, measured from the opening 41 at the inlet end 43 of the tube 40 to the opposite inner surface of the header, on the order of one tenth (0.1 mm) of 1 mm for a heat exchanger 40 having a channel with a nominal 1 mm square internal flow cross-sectional area. Of course, it will be understood by those skilled in the art that the degree of expansion can be adjusted by varying the width of the gap G by selectively positioning the inlet end of the tube 40 relative to the inner surface 22 of the header 20.

In the embodiment shown in fig. 1 and 2, headers 20 and 30 comprise longitudinally extending, hollow, closed-ended cylinders having a circular cross-section. In the embodiment shown in fig. 3 and 4, headers 20 and 30 comprise longitudinally extending, hollow, closed-ended cylinders having an oval cross-section. In the embodiment illustrated in fig. 5 and 6, headers 20 and 30 comprise longitudinally extending, hollow, closed-ended containers having a D-shaped cross-section. In the embodiment illustrated in fig. 7 and 8, headers 20 and 30 comprise longitudinally extending, hollow, closed-ended containers having a rectangular cross-section. In each embodiment, high pressure liquid refrigerant entering the inlet header 20 through the refrigerant line 14 flows along the interior 25 of the header 20 and, due to its uniform density and high pressure, is automatically distributed among each of the heat exchange tubes 40 and undergoes expansion as it enters the opening of each channel through the gap G between the respective opening 41 of the channel 42 and the interior surface 22 of the header 20.

Referring now to fig. 9 and 10, there is schematically illustrated a refrigerant vapor compression system 100 comprising a compressor 60, a heat exchanger 10A, which functions as a condenser, and a heat exchanger 10B, which functions as an evaporator, connected in a closed-loop refrigerant circuit by refrigerant lines 12, 14 and 16. As in conventional refrigerant vapor compression systems, the compressor 60 causes hot, high pressure refrigerant vapor to flow through the refrigerant line 12 into the inlet header 120 of the condenser 10A, and thence through the heat exchanger tubes 140 of the condenser 10A, wherein the hot refrigerant vapor condenses to a liquid as it passes in heat exchange relationship with a cooling fluid, such as ambient air passing over the heat exchange tubes 140 by the condenser fan 70. High pressure liquid refrigerant collects in the outlet header 130 of the condenser 10A and thence passes through refrigerant line 14 to the inlet header 20 of the evaporator 10B. The refrigerant thus passes through the heat exchanger tubes 40 of the evaporator 10B, wherein the refrigerant is heated as it passes in heat exchange relationship with the air to be cooled passing over the heat exchange tubes 40 by the evaporator fan 80. The refrigerant vapor collects in the outlet header 30 of the evaporator 10B and from there is returned through refrigerant line 16 to the compressor 60 through the suction port. While the exemplary refrigerant vapor compression cycle illustrated in fig. 9 and 10 is a simplified air conditioning cycle, it should be understood that the heat exchanger of the present invention may be employed in refrigerant vapor compression systems of various designs, including but not limited to heat pump cycles, economized cycles, cycles having components in series (e.g., a compressor and a heat exchanger), refrigerant circuits, and many other cycles including various options and features.

In the embodiment shown in fig. 9, the condensed refrigerant liquid does not pass through the expansion device from condenser 10A directly into evaporator 10B. Thus, in this embodiment, the refrigerant enters the inlet header 20 of the evaporative heat exchanger 10B as a high pressure liquid refrigerant, rather than as a fully expanded low pressure refrigerant liquid/vapor mixture as in conventional refrigerant vapor compression systems. Thus, in this embodiment, expansion of the refrigerant occurs in the evaporator 10B of the present invention at the gap G, thereby ensuring that expansion occurs only after the distribution is completed in a substantially uniform manner.

In the embodiment shown in fig. 10, as the condensed refrigerant liquid passes from the condenser 10A to the evaporator 10B, the condensed refrigerant liquid passes through an expansion device 90 operatively associated with the refrigerant conduit 14. In the expansion device 90, the high pressure liquid refrigerant is partially expanded to a low pressure liquid refrigerant or liquid/vapor refrigerant mixture. In this embodiment, expansion of the refrigerant is accomplished in the evaporator 10B of the present invention at the gap G. When the gap G cannot be made small enough to ensure full expansion of the liquid as it flows through the gap G, or when a thermostatic expansion valve or electronic expansion valve 90 is used as the flow control device, partial expansion of the refrigerant in the expansion device 90 may be beneficial, the expansion device being upstream of the inlet header 20 of the evaporator 10B.

The embodiments of the heat exchanger of the invention shown in figures 1, 3, 5, 7 are described as single pass heat exchangers. However, the heat exchanger of the present invention may also be a multi-pass heat exchanger. Referring now to fig. 11, a heat exchanger 10 is shown in a multi-pass evaporator embodiment. In the multi-pass embodiment shown, the inlet header is divided into first chamber 20A and second chamber 20B, the outlet header is also divided into first chamber 30A and second chamber 30B, and the heat exchange tubes 40 are divided into three groups 40A, 40B and 40C. The heat exchange tubes of the first tube bank 40A have inlets opening into the first chamber 20A of the inlet header 20 and outlets opening into the first chamber 30A of the outlet header 30. The heat exchange tubes of the second tube bank 40B have inlets opening into the first chamber 30A of the outlet header 30 and outlets opening into the second chamber 20B of the inlet header 20. The heat exchange tubes of the third tube bank 40C have inlets opening into the second chamber 20B of the inlet header 20 and outlets opening into the second chamber 30B of the outlet header 30. In this manner, refrigerant entering the heat exchanger from refrigerant line 14 exchanges heat with air passing over the exterior of the heat exchange tubes 40 three times, rather than once as in the case of a single pass heat exchanger. In accordance with the present invention, the inlet end of each heat exchange tube of the first, second and third tube banks is disposed within the associated header chamber with the inlet openings to the plurality of flow channels being positioned in spaced, confronting relationship with the opposite interior surface of the respective header so as to define an expansion gap G between the inlet to the channels and the opposite interior surface of the respective header. Expansion therefore also occurs in the header between passes, thereby ensuring a more uniform distribution of refrigerant liquid/vapor upon entry into the tube flow channels of each tube pass.

The refrigerant, which is a high pressure liquid, or a partially expanded liquid/vapor mixture, enters the first chamber 20A of the header 20 of the heat exchanger 10 from refrigerant line 14. The refrigerant thus passes from the chamber 20A through the gap G into each of the flow channels 42 associated with the heat exchange tubes of the first tube bank 40A, which constitute the rightmost four tubes shown in fig. 11. As the refrigerant passes through the gap G, the refrigerant expands as previously described. The refrigerant liquid/vapor mixture passes from the flow channels of the first tube bank 40A into the first chamber 30A of the outlet header 30 and is distributed therein into the heat exchange tubes of the second tube bank 40B which make up the central four tubes shown in fig. 11. In order to enter the flow tubes of the heat exchange tubes of the second tube bank 40B from the first chamber 30A of the outlet header 30, the refrigerant must again pass through the narrow gap G, resulting in further expansion of the refrigerant. The refrigerant liquid/vapor mixture passes from the flow tubes of the second tube bank 40B into the second chamber 20B of the inlet header 20 and is distributed therein into the heat exchange tubes of the third tube bank 40C which make up the left-most four tubes shown in fig. 11. In order to enter the flow channels of the heat exchange tubes of the third tube bank 40C from the second chamber 20B of the inlet header 20B, the refrigerant must again pass through the narrow gap G, resulting in further expansion of the refrigerant. The refrigerant liquid/vapor mixture passes from the flow channels of the third tube bank 40C into the second chamber 30B of the outlet header 30 and thence into the refrigerant tubes 16.

Referring now to fig. 12, a heat exchanger 10 in a multi-pass condenser embodiment is shown. In the illustrated multi-pass embodiment, the inlet header 120 is divided into first and second chambers 120A, 120B, the outlet header 130 is also divided into first and second chambers 130A, 130B, and the heat exchange tubes 140 are divided into three tube banks 140A, 140B, and 140C. The heat exchange tubes of the first tube bank 140A have inlets opening into the first chamber 120A of the inlet header 120 and outlets opening into the first chamber 130A of the outlet header 130. The heat exchange tubes of the second tube bank 140B have inlets opening into the first chamber 130A of the outlet header 130 and outlets opening into the second chamber 120B of the inlet header 120. The heat exchangers of the third tube bank 140C have inlets opening into the second chamber 120B of the inlet header 120 and outlets opening into the second chamber 130B of the outlet header 130. In this manner, refrigerant entering the condenser from refrigerant line 12 exchanges heat with air passing over the exterior of the heat exchange tubes 140 three times, rather than once as in the case of a single pass heat exchanger. The refrigerant entering the first chamber 120A of the inlet header 120 is entirely high pressure refrigerant vapor directed from the compressor outlet through refrigerant line 14. However, the refrigerant entering the second tube set and the third tube set will be a liquid/vapor mixture because the refrigerant partially condenses as it passes through the first and second tube sets. In accordance with the present invention, the inlet end of each heat exchange tube of the second and third tube banks is disposed within the associated header chamber with the inlets to the plurality of flow channels being positioned in spaced and facing relationship with the opposite inside surface of the respective header so as to define a relatively narrow gap G between the inlets to the channels and the opposite inside surface of the respective header. This gap G provides fluid throttling to ensure more uniform distribution of the refrigerant liquid/vapor mixture as it enters the heat exchange tube flow channels of each subsequent pass.

Hot, high pressure refrigerant vapor from the compressor 60 enters the first chamber 120A of the inlet header 120 of the heat exchanger 10 from refrigerant line 12. From the chamber 120A, the refrigerant thus enters each of the flow channels 42 associated with the heat exchange tubes of the first tube bank 140A, which constitute the left-most four tubes shown in fig. 12. As the refrigerant passes through the flow channels of the first tube bank 140A, a portion of the refrigerant vapor condenses into a liquid. The refrigerant liquid/vapor mixture passes from the flow channels of the first tube bank 140A into the first chamber 130A of the outlet header 130 and is distributed there into the tubes of the second tube bank 140B, which make up the central four tubes shown in fig. 12. The refrigerant liquid/vapor must now pass through the narrow gap G in order to enter the flow tubes of the heat exchange tubes of the second tube bank 140B from the first chamber 130A of the outlet header 130. The refrigerant liquid/vapor mixture passes from the flow tubes of the second tube bank 140B into the second chamber 120B of the inlet header 120 and is distributed therein into the heat exchange tubes of the third tube bank 140C which make up the rightmost four tubes shown in fig. 12. In order to enter the flow tubes of the heat exchange tubes of the third tube bank 140C from the second chamber 120B of the inlet header 120B, the refrigerant must again pass through the narrow gap G. The refrigerant liquid/vapor mixture passes from the flow tubes of the third tube bank 140C into the second chamber 130B of the outlet header 130 and thence into the refrigerant tubes 14.

It should be understood that while fig. 11 and 12 illustrate the same number of heat exchange tubes in each tube bank of the multi-pass heat exchanger 10, this number may vary depending on the relative amounts of vapor and liquid refrigerant flowing through the respective tube banks. Generally, the higher the vapor content of the refrigerant mixture, the more heat exchange tubes are included in the associated refrigerant tube bank to ensure a suitable pressure drop through the tube bank. Further, as is well known to those skilled in the art, the heat exchange tubes extending within the header should not create excessive hydraulic resistance to the refrigerant flowing around the tubes within the header, which can be readily accomplished by the opposing header and heat exchange tube design.

It should be noted here that although the invention has been described with respect to the inlet end of the heat exchange tube, it can also be applied to the outlet end, although with only a slight benefit of pressure drop equalization between the heat exchange tubes in the relevant flow path. Further, the width of the gap G, which may vary between heat exchange tubes or groups of heat exchange tubes to further improve refrigerant distribution, is typically greater for heat exchange tubes disposed closer to the header inlet and smaller for heat exchange tubes disposed further away from the header inlet.

Further, the width of the gap G may vary along the span of an individual heat exchange tube 40 to ensure uniform distribution among the channels 42 of the tube or to vary the distribution of flow among the channels 42 of the tube. In general, gaps of larger dimensions are used in association with channels 42 disposed proximate the outer edges of the heat exchange tube 40, while gaps of slightly smaller dimensions are used in association with channels 42 proximate the middle portion of the heat exchange tube 40. However, in some heat exchanger applications, it may be desirable to vary the gap between the leading edge and trailing edge channels to selectively distribute flow between the channels 42 of the heat exchange tubes 40. For example, in some heat exchangers, it may be desirable to increase the efficiency of the heat exchanger by providing a slightly smaller gap relative to the channels at the leading edge of the heat exchange tubes (which is the edge of the tubes facing the air flow) and a slightly larger gap relative to the channels at the trailing edge of the heat exchange tubes. By varying the width of the gap G along the span between the leading and trailing edges of the heat exchange tube 40, the flow of liquid can be selectively distributed into the various channels 42 of the heat exchange tube 40 as desired.

While the present invention has been particularly shown and described with reference to the preferred examples illustrated in the drawings, it will be understood by those skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.

Claims (33)

1. A heat exchanger, comprising:

a header having an inner surface defining a chamber for collecting refrigerant; and

at least one heat exchange tube defining a refrigerant flow path therethrough and having an inlet opening to said refrigerant flow path at an inlet end thereof, said at least one heat exchange tube having an inlet end thereof extending into said chamber of said header and positioned such that the inlet opening to the refrigerant flow path is spaced from and faces an opposite inner surface of said header, thereby defining a relatively narrow gap between the inlet opening to said refrigerant flow path to said heat exchange tube and the opposite inner surface of said header, said gap serving as an expansion gap, and said gap having a width in the range of 0.01 to 0.5 mm.

2. The heat exchanger of claim 1, wherein the gap has a width on the order of 0.1 mm.

3. A heat exchanger as recited in claim 1 wherein said gap has a width which varies with respect to the inlet end of the at least one heat exchange tube.

4. The heat exchanger of claim 1, wherein the at least one heat exchange tube has a plurality of channels extending longitudinally in parallel relationship across its refrigerant flow path, each of the plurality of channels defining a separate refrigerant flow path through the at least one heat exchange tube.

5. The heat exchanger of claim 4, wherein each of the plurality of channels defines a flow path having a non-circular cross-section.

6. The heat exchanger of claim 5, wherein each of the plurality of channels defines a flow path having a rectangular, triangular, or trapezoidal cross-section.

7. The heat exchanger of claim 4, wherein each of the plurality of channels defines a flow path having a circular cross-section.

8. The heat exchanger of claim 1, wherein the heat exchanger is an evaporator.

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

10. The heat exchanger of claim 1, wherein the heat exchanger is a single pass heat exchanger.

11. The heat exchanger of claim 1, wherein the heat exchanger is a multi-pass heat exchanger.

12. A heat exchanger as recited in claim 1 wherein said at least one heat exchange tube has a generally rectangular cross-section.

13. A heat exchanger as recited in claim 1 wherein said at least one heat exchange tube has a generally oval cross-section.

14. A heat exchanger, comprising:

a first header and a second header, each header defining a chamber for collecting refrigerant; and

a plurality of heat exchange tubes extending between said first and second headers, each of said plurality of heat exchange tubes having an inlet end opening into one of said first and second headers and an outlet end opening into the other of said first and second headers, each of said plurality of heat exchange tubes having a plurality of channels extending longitudinally in parallel from its inlet end to its outlet end, each of said channels defining a separate refrigerant flow path, the inlet end of each of said plurality of heat exchange tubes extending into said chamber of said one of said first and second headers and being positioned so that the inlets to said channels are spaced apart and face an opposite inner surface of said one of said first and second headers to define a relatively narrow gap between the inlet to said channels and the opposite inner surface of said one of said first and second headers, the gap serves as an expansion gap, and the gap has a width in the range of 0.01 to 0.5 mm.

15. A heat exchanger according to claim 14, wherein each gap has a width in the order of 0.1 mm.

16. A heat exchanger as recited in claim 14 wherein each gap has a width which can vary with respect to the corresponding inlet end of the plurality of heat exchange tubes.

17. A heat exchanger as recited in claim 14 wherein each gap has a width which can vary with respect to the corresponding channel of at least one of the plurality of heat exchange tubes.

18. The heat exchanger of claim 14, wherein each of the plurality of channels defines a flow path having a non-circular cross-section.

19. The heat exchanger of claim 14, wherein each of the plurality of channels defines a flow path having a circular cross-section.

20. The heat exchanger of claim 14, wherein the plurality of heat exchange tubes have a generally rectangular cross-section.

21. The heat exchanger of claim 14, wherein the plurality of heat exchange tubes have a generally oval cross-section.

22. A refrigerant vapor compression system comprising:

a compressor, a condenser and an evaporative heat exchanger connected in refrigerant flow communication whereby high pressure refrigerant vapor enters the condenser from the compressor, high pressure refrigerant liquid enters the evaporative heat exchanger from the condenser, and low pressure refrigerant vapor enters the compressor from the evaporative heat exchanger, characterized in that the evaporative heat exchanger comprises:

an inlet header having an inner surface defining a chamber for receiving liquid refrigerant from the refrigerant circuit and an outlet header; and

at least one heat exchange tube extending between said inlet and outlet headers, said at least one heat exchange tube having an inlet end opening into said inlet header and an outlet end opening into said outlet header, wherein said at least one heat exchange tube has a plurality of channels extending longitudinally in parallel relationship from said inlet end to said outlet end, each of said channels defining a discrete refrigerant flow path, the inlet end of said at least one heat exchange tube extending into the chamber of said inlet header and being positioned with the inlets to said channels spaced apart and facing the opposite inside surface of said header thereby defining an expansion gap between the inlets to said channels and the opposite inside surface of said inlet header.

23. The refrigerant vapor compression system of claim 22, wherein the expansion gap has a width on the order of 0.1 mm.

24. A refrigerant vapor compression system as recited in claim 22 wherein said expansion gap has a width, the width of said gap being variable relative to the inlet end of said at least one heat exchange tube.

25. The refrigerant vapor compression system of claim 22, wherein the expansion gap is a primary expansion device in the refrigerant vapor compression system.

26. The refrigerant vapor compression system of claim 22, wherein the expansion gap is an auxiliary expansion device in the refrigerant vapor compression system.

27. A refrigerant vapor compression system as recited in claim 22 wherein said evaporative heat exchanger is a single pass heat exchanger.

28. A refrigerant vapor compression system as recited in claim 22 wherein said evaporative heat exchanger is a multi-pass heat exchanger.

29. A method of operating a refrigerant vapor compression cycle comprising the steps of:

providing a compressor, a condenser and an evaporative heat exchanger connected in a refrigerant circuit;

passing high pressure refrigerant vapor from the compressor into the condenser;

passing high pressure refrigerant liquid from the condenser into an inlet header of the evaporative heat exchanger;

providing at least one heat exchange tube having a plurality of flow channels defining a plurality of refrigerant flow paths for passing refrigerant from an inlet header to an outlet header of said evaporative heat exchanger;

distributing high pressure liquid collected in the inlet header to and through each of the plurality of refrigerant flow paths by passing the high pressure liquid refrigerant through an expansion gap formed between the inlet header inner surface and the inlet end leading to the at least one heat exchange tube, the expansion gap having a width as measured between the inlet header inner surface and the inlet end leading to the at least one heat exchange tube, and

returning low pressure refrigerant vapor from an outlet header of the evaporative heat exchanger to the compressor.

30. The method as set forth in claim 29, wherein said expansion gap is provided as a primary expansion device in said refrigerant vapor compression cycle.

31. The method as set forth in claim 29, wherein said expansion gap is provided as an auxiliary expansion device in said refrigerant vapor compression cycle.

32. The method of claim 29, further comprising the steps of: the width of the expansion gap is varied relative to the inlet end of the at least one heat exchange tube whereby liquid refrigerant is substantially uniformly distributed into the plurality of refrigerant flow paths of the at least one heat exchange tube and expanded to a low pressure mixture of liquid refrigerant and vapor refrigerant.

33. The method of claim 29, further comprising the steps of: the width of the expansion gap is varied relative to the inlet end of the at least one heat exchange tube between a flow channel at a leading edge of the heat exchange tube, which is the edge of the tube facing the air flow, and a flow channel at a trailing edge of the heat exchange tube, whereby liquid refrigerant is selectively distributed between the plurality of refrigerant flow paths of the at least one heat exchange tube.