Patent Grant
7527089
This invention relates generally to heat exchangers having a plurality of parallel tubes extending between a first header and a second header, also sometimes referred to as manifolds, and, more particularly, to providing fluid expansion within the header of a heat exchanger for improving distribution of two-phase flow through the parallel tubes of the heat exchanger, for example a heat exchanger in a refrigerant compression system.
Refrigerant vapor compression systems are well known in the art. Air conditioners and heat pumps employing refrigerant vapor compression cycles are commonly used for cooling or cooling/heating air supplied to a climate controlled comfort zone within a residence, office building, hospital, school, restaurant or other facility. Refrigeration vapor compression systems are also commonly used for cooling air or other secondary fluid to provide a refrigerated environment for food items and beverage products within, for instance, display cases in supermarkets, convenience stores, groceries, cafeterias, restaurants and other food service establishments.
Conventionally, these refrigerant vapor compression systems include a compressor, a condenser, an expansion device, and an evaporator connected in refrigerant flow communication. The aforementioned basic refrigerant system components are interconnected by refrigerant lines in a closed refrigerant circuit and arranged in accord with the vapor compression cycle employed. An expansion device, commonly an expansion valve or a fixed-bore metering device, such as an orifice or a capillary tube, is disposed in the refrigerant line at a location in the refrigerant circuit upstream, with respect to refrigerant flow, of the evaporator and downstream of the condenser. The expansion device operates to expand the liquid refrigerant passing through the refrigerant line running from the condenser to the evaporator to a lower pressure and temperature. In doing so, a portion of the liquid refrigerant traversing the expansion device expands to vapor. As a result, in conventional refrigerant vapor compression systems of this type, the refrigerant flow entering the evaporator constitutes a two-phase mixture. The particular percentages of liquid refrigerant and vapor refrigerant depend upon the particular expansion device employed and the refrigerant in use, for example R12, R22, R134a, R404A, R410A, R407C, 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 therethrough provided by a plurality of tubes extending in parallel relationship between an inlet header and an outlet header. The inlet header receives the refrigerant flow from the refrigerant circuit and distributes it amongst the plurality of flow paths through the heat exchanger. The outlet header serves to collect the refrigerant flow as it leaves the respective flow paths and to direct the collected flow back to the refrigerant line for a return to the compressor in a single pass heat exchanger or through an additional bank of heat exchange tubes in a multi-pass heat exchanger.
Historically, parallel tube heat exchangers used in such refrigerant compression systems have used round tubes, typically having a diameter of ½ inch, ⅜ inch or 7 millimeters. More recently, flat, rectangular or oval shape, multi-channel tubes are being used in heat exchangers for refrigerant vapor compression systems. Each multi-channel tube has a plurality of flow channels extending longitudinally in parallel relationship the length of the tube, each channel providing a small cross-sectional flow area refrigerant path. Thus, a heat exchanger with multi-channel tubes extending in parallel relationship between the inlet and outlet headers of the heat exchanger will have a relatively large number of small cross-sectional flow area refrigerant paths extending between the two headers. In contrast, a parallel tube heat exchanger with conventional round tubes will have a relatively small number of large flow area flow paths extending between the inlet and outlet headers.
Non-uniform distribution, also referred to as maldistibution, of two-phase refrigerant flow is a common problem in parallel tube heat exchangers which adversely impacts heat exchanger efficiency. Among other factors, two-phase maldistribution problems are 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 as it traversed the upstream expansion device.
One solution to control refrigeration flow distribution through parallel tubes in an evaporative heat exchanger is disclosed in U.S. Pat. No. 6,502,413, Repice et al. In the refrigerant vapor compression system disclosed therein, the high pressure liquid refrigerant from the condenser is partially expanded in a conventional in-line expansion device upstream of the heat exchanger inlet header to a lower pressure refrigerant. Additionally, a restriction, such as a simple narrowing in the tube or an internal orifice plate disposed within the tube, is provided in each tube connected to the inlet header downstream of the tube inlet to complete the expansion to a low pressure, liquid/vapor refrigerant mixture after entering the tube.
Another solution to control refrigeration flow distribution through parallel tubes in an evaporative heat exchanger is disclosed in Japanese Patent No. JP4080575, 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 device to a lower pressure refrigerant upstream of a distribution chamber of the heat exchanger. A plate having a plurality of orifices therein extends across the chamber. The lower pressure refrigerant expands as it passes through the orifices to a low pressure liquid/vapor mixture downstream of the plate and upstream of the inlets to the respective tubes opening to the chamber.
Japanese Patent No. 6241682, Massali et al., discloses a parallel flow tube heat exchanger for a heat pump wherein the inlet end of each multichannel tube connecting to the inlet header is crushed to form a partial throttle restriction in each tube just downstream of the tube inlet. Japanese Patent No. JP8233409, Hiroaki et al., discloses a parallel flow tube heat exchanger wherein a plurality of flat, multi-channel tubes connect between a pair of headers, each of which has an interior which decreases in flow area in the direction of refrigerant flow as a means to uniformly distribute refrigerant to the respective tubes. Japanese Patent No. JP2002022313, Yasushi, discloses a parallel tube heat exchanger wherein refrigerant is supplied to the header through an inlet tube that extends along the axis of the header to terminate short of the end the header whereby the two phase refrigerant flow does not separate as it passes from the inlet tube into an annular channel between the outer surface of the inlet tube and the inside surface of the header. The two phase refrigerant flow thence passes into each of the tubes opening to the annular channel.
Obtaining uniform refrigerant flow distribution amongst the relatively large number of small cross-sectional flow area refrigerant flow paths is even more difficult than it is in conventional round tube heat exchangers and can significantly reduce heat exchanger efficiency.
It is a general object of the invention to reduce maldistribution of fluid flow in a heat exchanger 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 reduce maldistribution of refrigerant flow in a refrigerant vapor compression system heat exchanger 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 to the individual channels of an array of multi-channel tubes in a relatively uniform manner.
It is an object of another aspect of the invention to provide for distribution and expansion of the refrigerant in a refrigerant vapor compression system heat exchanger having a plurality of multi-channel tubes as the refrigerant flow passes from a header to the individual channels of an array of multi-channel tubes.
In one aspect of the invention, a heat exchanger is provided having a header defining a chamber for receiving a fluid and at least one heat exchange tube having a plurality of fluid flow paths therethrough from an inlet end to an outlet end of the tube and having an inlet opening to the plurality of fluid flow paths. A connector is provided having an inlet end and an outlet end and defining an inlet chamber at its inlet end in fluid flow communication with the fluid chamber of the header, an outlet chamber at its outlet end in fluid communication with the inlet opening of the at least one heat exchange tube, and an intermediate chamber defining a flow path between said inlet chamber and said outlet chamber. The flow path has a plurality of flow restriction ports disposed therein in a spaced series arrangement. Fluid flow passing from the header to the flow channels of the at least one heat exchange tube will undergo a series of fluid expansions in passing through the flow restriction ports provided in the flow path through the connector. In an embodiment, each flow restriction port is a straight walled, cylindrical opening. In another embodiment, each flow restriction port is a contoured opening.
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 passes from the compressor to the condenser, high pressure refrigerant liquid passes from the condenser to the evaporative heat exchanger, and low pressure refrigerant vapor passes from the evaporative heat exchanger to the compressor. The evaporative heat exchanger includes an inlet header and an outlet header, and a plurality of heat exchange tubes extending between the headers. The inlet header defines a chamber for receiving liquid refrigerant from a refrigerant circuit. Each heat exchange tube has an inlet end, an outlet end, and a plurality of fluid flow paths extending from an inlet opening at the inlet end to an outlet opening at the outlet end of the tube. A connector is provided having an inlet end and an outlet end and defining an inlet chamber at its inlet end in fluid flow communication with the fluid chamber of the inlet header, an outlet chamber at its outlet end in fluid communication with the inlet opening of the at least one heat exchange tube, and an intermediate chamber defining a flow path between said inlet chamber and said outlet chamber. The flow path has a plurality of flow restriction ports disposed therein in a spaced series arrangement. Fluid flow passing from the header to the flow channels of the heat exchange tube will undergo a series of fluid expansions in passing through the flow restriction ports provided in the flow path through the connector. In an embodiment, each flow restriction port is a straight walled, cylindrical opening. In another embodiment, each flow restriction port is a contoured opening.
In a further aspect of the invention, a refrigeration vapor compression system is provided having a compressor, a first heat exchanger and a second heat exchanger connected in fluid flow communication in a refrigerant circuit. When the system is operated in a cooling mode, refrigerant circulates in a first direction from the compressor through the first heat exchanger, functioning as a condenser, thence through the second high exchanger, functioning as an evaporator, and back to the compressor. When the system is operated in a heating mode, refrigerant circulates in a second direction from the compressor through the second heat exchanger, now functioning as a condenser, thence through the first heat exchanger, now functioning as an evaporator, and back to the compressor. Each heat exchanger has a first header, a second header, and at least one beat exchange tube defining a plurality of discrete fluid flow paths extending between a first end of the tube and a second end of the tube.
In an embodiment, the second heat exchanger includes a connector having an inlet end and an outlet end and defining an inlet chamber at its inlet end, an outlet chamber at its outlet end, and an intermediate chamber defining a flow path between the inlet chamber and the outlet chamber. The inlet chamber of the connector is in fluid flow communication with the first header and the outlet chamber is in fluid flow communication the plurality of discrete fluid flow paths of the heat exchange tube. The flow path includes a plurality of flow restriction ports disposed therein in a spaced series arrangement and adapted to create a relatively large pressure drop in refrigerant flow passing in the first direction and a relatively small pressure drop in refrigerant flow passing in the second direction.
In an embodiment, the first heat exchanger includes a connector having an inlet end and an outlet end and defining an inlet chamber at its inlet end in fluid flow communication with the fluid chamber of the second header, an outlet chamber at its outlet end in fluid communication with the plurality of discrete fluid flow paths of the at least one heat exchange tube, and an intermediate chamber defining a flow path between the inlet chamber and the outlet chamber. The flow path includes a plurality of flow restriction ports disposed therein in a spaced series arrangement and adapted to create a relatively small pressure drop in refrigerant flow passing in the first direction and a relatively large pressure drop in refrigerant flow passing in the second direction.
For a further understanding of these and objects of the invention, reference will be made to the following detailed description of the invention which is to be read in connection with the accompanying drawing, where:
The heat exchanger 10 of the invention will be described in general herein with reference to the illustrative single pass, parallel-tube embodiment of a multi-channel tube heat exchanger as depicted in
The heat exchanger 10 includes an inlet header 20, an outlet header 30, and a plurality of longitudinally extending multi-channel heat exchanger tubes 40 thereby providing a plurality of fluid flow paths between the inlet header 20 and the outlet header 30. Each heat exchange tube 40 has an inlet at one end in fluid flow communication to the inlet header 20 through a connector 50 and an outlet at its other end in fluid flow communication to the outlet header 30. Each 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 multiple, independent, parallel flow paths between the inlet of the tube and the outlet of the tube. Each multi-channel heat exchange tube 40 is a “flat” tube of, for instance, rectangular or oval cross-section, defining an interior which is subdivided to form a side-by-side array of independent flow channels 42. The flat, multi-channel tubes 40 may, for example, have a width of fifty millimeters or less, typically twelve to twenty-five millimeters, and a height of about two millimeters or less, as compared to conventional prior art round tubes having a diameter of ½ inch, ⅜ inch or 7 mm. The tubes 40 are shown in drawings hereof, for ease and clarity of illustration, as having twelve channels 42 defining flow paths having a circular cross-section. However, it is to be understood that in commercial applications, such as for example refrigerant vapor compression systems, each multi-channel tube 40 will typically have about ten to twenty flow channels 42, but may have a greater or a lesser multiplicity of channels, as desired. Generally, each flow channel 42 will have a hydraulic diameter, defined as four times the flow area divided by the perimeter, in the range from about 200 microns to about 3 millimeters. Although depicted as having a circular cross-section in the drawings, the channels 42 may have a rectangular, triangular, trapezoidal cross-section or any other desired non-circular cross-section.
Referring now to
Each connector 50 defines a flow path comprising the inlet chamber 51, the outlet chamber 53, and an intermediate section extending from the inlet chamber 51 at the inlet end 52 of the connector to the outlet chamber 53 at the outlet end 54 of the connector. Fluid collecting in the fluid chamber 25 of the header 20 passes therefrom into the inlet chamber 51, thence through the intermediate section and through the outlet chamber 53 to be distributed to the individual channels 42 of the heat exchange tubes 40. The intermediate section of the flow path through each connector 50 is provided with at least two flow restriction ports 56 that serve as expansion orifices. The at least two flow restriction ports 56 are arranged in series with respect to fluid flow through the intermediate section. An expansion chamber 57 is disposed between each pair of sequentially arrayed flow restriction ports 56. The expansion chamber 57 may have a cross-sectional flow area that is approximately equal to or at least on the same order as the cross-sectional flow area of the inlet chamber 51. The flow restriction ports 56, on the other hand, have a cross-section flow area that is relatively small in comparison to the cross-section flow area of the expansion chamber 57.
As the fluid flowing from the chamber 25 of the header 20 flows through the intermediate section, the fluid undergoes an expansion as it passes through each of the flow restriction ports 56. Thus, the fluid undergoes multiple expansions commensurate with the number of flow restriction orifices provided in the flow path through the connector 50 before the fluid passes into the outlet chamber 53 of the connector for distribution to the channels 42 of the heat exchange tube 40 associated with the connector. Inasmuch as the pressure drop produced in a fluid flow by an orifice restriction is created as a result of momentum exchange in the fluid at the inlet and at the outlet of the orifice, the fluid pressure drop created by an orifice restriction is inversely proportional to the orifice size or dimension, a larger port will produce a lower pressure drop. Since the fluid undergoes multiple stages of expansion, at least two expansions in accord with the invention, the individual flow restriction ports 56 may be sized somewhat larger than would be necessary if the same degree of expansion were to be obtained through a single orifice. Further, with a connector 50 operatively associated with each heat transfer tube 40, the flow restriction ports 56 provide relative uniformity in pressure drop in the fluid flowing from the chamber 25 of the header 20 into the outlet chamber 53 within each connector 50, thereby ensuring a relatively uniform distribution of fluid amongst the individual tubes 40 operatively associated with the header 20.
In the embodiments depicted in
In the embodiments depicted in
To provide the series arrangement of alternate flow restriction ports 56 and expansion chambers 57 between the inlet chamber 51 and the outlet chamber 53 in the embodiments of the connector 50 depicted in
Referring now to
The condensed refrigerant liquid passes from the condenser 10A directly to the evaporator 10B without traversing an expansion device. Thus, in this embodiment, the refrigerant typically enters the header 20 of the evaporative heat exchanger 10B as a high pressure, liquid-phase only refrigerant. Expansion of the refrigerant will occur only within the evaporator 10B of the invention as the refrigerant passes through the flow restriction ports 56, and the inlet ports 58 if provided, thereby ensuring that expansion occurs only after the refrigerant has been distributed amongst the heat exchange tubes 40 opening into the header 20 in a substantially uniform manner as a single-phase, liquid.
Referring now to
Referring now to
It is to be understood that although an equal number of heat exchange tubes is shown in
In the embodiments of the heat exchanger of the invention depicted and described herein, the inlet header 20 comprises a longitudinally elongated, hollow, closed end pipe having either a circular cross-section or a rectangular cross-section. However, neither the inlet header, nor the outlet header, is limited to the depicted configuration. For example, the headers might comprise longitudinally elongated, hollow, closed end pipes having an elliptical cross-section, a hexagonal cross-section, an octagonal cross-section, or a cross-section of other shape.
Although the exemplary refrigerant vapor compression cycle illustrated in
With respect to heat exchanger 10A, which would be the outdoor heat exchanger in a heat pump application, the refrigerant will flow through the flow restriction ports in the direction 4 when the heat pump cycle is operating in the cooling mode and heat exchanger 10A is functioning as a condenser, and in the direction 2 when the heat pump cycle is operating in a heating mode and the heat exchanger 10A is functioning as an evaporator. Conversely, with respect to heat exchanger 10B, which would be the indoor heat exchanger in a heat pump application, the refrigerant will flow through the flow restriction ports in the direction 2 when the heat pump cycle is operating in the cooling mode and the heat exchanger 10B is functioning as an evaporator, and in the direction 4 when the heat pump cycle is operating in a heating mode and the heat exchanger 10B is functioning as a condenser. Therefore, when either heat exchanger 10A, 10B is functioning as an evaporator, the refrigerant is flowing in the direction 2 through the flow restriction orifices and will pass through a pair of sharp edge orifices, which will result in a relatively large pressure drop. However, when either heat exchanger 10A, 10B is functioning as a condenser, the refrigerant is flowing in the direction 4 through the flow restriction orifice and will pass through a pair of contoured orifices, which will result in a relatively small pressure drop. Further, when a heat exchanger functions as an evaporator, the expansion occurs before the refrigerant pass through the heat exchange tubes, while when a heat exchanger functions as a condenser, the expansion occurs after the refrigerant has passed through the heat exchange tubes.
While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one 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.
Reference is made to and this application claims priority from and the benefit of U.S. Provisional Application Ser. No. 60/649,268, filed Feb. 2, 2005, and entitled MINI-CHANNEL HEAT EXCHANGER WITH MULTI-STAGE EXPANSION DEVICE, which application is incorporated herein in its entirety by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2005/047362 | 12/28/2005 | WO | 00 | 9/27/2006 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2006/083448 | 8/10/2006 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 1340153 | Cardwell | May 1920 | A |
| 2297633 | Philipp | Sep 1942 | A |
| 2591109 | Wade | Apr 1952 | A |
| 3920069 | Mosier | Nov 1975 | A |
| 4088182 | Basdekas et al. | May 1978 | A |
| 4202182 | Kawashima et al. | May 1980 | A |
| 4334554 | Geiger et al. | Jun 1982 | A |
| 4382468 | Hastwell et al. | May 1983 | A |
| 4497363 | Heronemus | Feb 1985 | A |
| 4524823 | Hummel et al. | Jun 1985 | A |
| 4607689 | Mochida et al. | Aug 1986 | A |
| 4724904 | Fletcher et al. | Feb 1988 | A |
| 5320165 | Hughes | Jun 1994 | A |
| 5341870 | Hughes et al. | Aug 1994 | A |
| 5415223 | Reavis et al. | May 1995 | A |
| 5517757 | Hayashi et al. | May 1996 | A |
| 5632329 | Fay | May 1997 | A |
| 5743329 | Damsohn et al. | Apr 1998 | A |
| 5826649 | Chapp et al. | Oct 1998 | A |
| 5934367 | Shimmura et al. | Aug 1999 | A |
| 5941303 | Gowan et al. | Aug 1999 | A |
| 5967228 | Bergman et al. | Oct 1999 | A |
| 5971065 | Bertilson et al. | Oct 1999 | A |
| 6340055 | Yamauchi et al. | Jan 2002 | B1 |
| 6546998 | Oh et al. | Apr 2003 | B2 |
| 6564863 | Martins | May 2003 | B1 |
| 6688137 | Gupte | Feb 2004 | B1 |
| 6688138 | DiFlora | Feb 2004 | B2 |
| 20010004935 | Sanada et al. | Jun 2001 | A1 |
| 20030116308 | Watanabe et al. | Jun 2003 | A1 |
| 20030155109 | Kawakubo et al. | Aug 2003 | A1 |
| 20050051318 | Fujita et al. | Mar 2005 | A1 |
| Number | Date | Country |
|---|---|---|
| 1611907 | May 2005 | CN |
| 0228330 | Jul 1987 | EP |
| 1258044 | Apr 1961 | FR |
| 2777645 | Oct 1999 | FR |
| 62147296 | Jul 1987 | JP |
| 2217764 | Aug 1990 | JP |
| 4080575 | Mar 1992 | JP |
| 6241682 | Sep 1994 | JP |
| 7301472 | Nov 1995 | JP |
| 8233409 | Sep 1996 | JP |
| 11351706 | Dec 1999 | JP |
| 2002022313 | Jan 2002 | JP |
| WO-0242707 | May 2002 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20080251245 A1 | Oct 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60649268 | Feb 2005 | US |
