Heat Exchanger Arrangement

Abstract

A refrigeration system includes a compressor for driving a refrigerant along a flow path in at least a first mode of system operation; a first heat exchanger along the flow path downstream of the compressor in the first mode; a second heat exchanger along the flow path upstream of the compressor in the first mode; and a pressure regulator or expansion device in the flow path downstream of the first heat exchanger and upstream of the second heat exchanger in the first mode, wherein the first heat exchanger is positioned within a housing which defines a flow path for heat exchange fluid and the housing defines a zone of reduced flow area along the flow path, and wherein the first heat exchanger is positioned in the zone of reduced flow area.

Description

BACKGROUND OF THE INVENTION

The invention relates to a heat exchanger arrangement for a vapor compression system, especially a transcritical vapor compression system.

The heat rejection process in transcritical vapor compression refrigeration applications and systems occurs at a pressure above the critical pressure of the refrigerant. The refrigerant does not undergo a phase change during this process and the temperature of the refrigerant changes throughout the entire heat rejection process. The energy efficiency of the refrigeration system increases if the heat exchanger arrangement approaches an ideal counter flow arrangement with the heat sink.

It is therefore a primary object of the invention to provide a system having an efficient heat exchanger arrangement.

It is a further object of the invention to provide such a system which is readily incorporated into existing refrigeration systems.

Other objects and advantages will appear herein.

SUMMARY OF THE INVENTION

According to the invention, the foregoing objects and advantages have been attained.

According to the invention, a refrigeration system is provided which comprises a compressor for driving a refrigerant along a flow path in at least a first mode of system operation; a first heat exchanger along the flow path downstream of the compressor in the first mode; a second heat exchanger along the flow path upstream of the compressor in the first mode; and a pressure regulator or expansion device in the flow path downstream of the first heat exchanger and upstream of the second heat exchanger in the first mode, wherein the first heat exchanger is positioned within a housing which defines a flow path for heat exchange fluid and the housing defines a zone of reduced flow area along the flow path, and wherein the first heat exchanger is positioned in the zone of reduced flow area.

According to the invention, a refrigeration system is provided which includes a compressor for driving a refrigerant along a flow path in at least a first mode of system operation; a first heat exchanger along the flow path downstream of the compressor in the first mode; a second heat exchanger along the flow path upstream of the compressor in the first mode; and a pressure regulator or expansion device in the flow path downstream of the first heat exchanger and upstream of the second heat exchanger in the first mode, wherein the first heat exchanger comprises a plurality of substantially parallel refrigerant flow paths, and wherein heat exchange fluid for the first heat exchanger is directed in counter flow substantially transverse to the refrigerant flow paths.

A preferred embodiment is drawn to transcritical vapor compression operation using CO₂ refrigerant fluid. Serpentine and/or parallel modular refrigerant flow paths are provided. A particular environment of use for the invention is in connection with so-called bottle coolers, or cooling units for cooling and storing beverages. Such coolers can be in the form of vending machines are refrigerator cases, for example.

In one embodiment, the housing of the beverage cooler defines an internal flow area for heat exchange fluid such as air, and this flow area has a flow restriction which serves to speed flow of the heat exchange fluid therethrough. According to the invention, the refrigerant flow paths are positioned at the flow restriction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a counter flow heat exchanger arrangement according to the invention;

FIG. 2 is a schematic illustration of an alternate counter flow heat exchanger arrangement according to the invention;

FIG. 3 is an illustration of a preferred structure for a beverage cooler including the heat exchanger arrangement of the present invention;

FIG. 4 illustrates a preferred type of heat exchanger according to the invention; and

FIG. 5 illustrates a preferred embodiment of the structure shown in FIG. 3.

DETAILED DESCRIPTION

The invention relates to refrigeration systems and, more particularly, to systems operating in a transcritical vapor compression regime, one particular embodiment of which is a beverage cooler. According to this invention, a heat exchanger configuration is utilized which provides efficient exchange of heat between a refrigerant fluid and a heat exchange fluid.

A transcritical vapor compression system operates at pressures above the critical pressure of the refrigerant and, therefore, the refrigerant does not undergo a phase change during the process. Under these circumstances, it has been found that a counter flow arrangement of the heat rejection heat exchanger with respect to the heat exchange fluid provides better efficiency in operation, and this counter flow arrangement can be approached by a heat exchanger consisting of a single flow path of several parallel flow path segments.

It has also been found that the position of a heat exchanger within the housing is important, and positioning of a heat exchanger in an area of increased flow velocity has been found to make the heat exchange process more efficient.

FIG. 1 shows a refrigerant system 10 having a compressor 12, a first heat exchanger 14, a second heat exchanger 16, an expansion device 18 and refrigerant lines connecting these components in serial fashion as illustrated.

FIG. 3 further illustrates a beverage cooler 20 into which system 10 is positioned. FIG. 3 shows compressor 12 as well as first heat exchanger 14 and second heat exchanger 16. Cooler 20 has a housing which defines a first heat exchange fluid flow path (arrows 22) wherein external air is drawn from an inlet 24, past first heat exchanger 14, and to an outlet 26. A second fluid flow path (arrows 28) is also defined, and passes from within the space of the beverage cooler, past second heat exchanger 16, and back to the refrigerated space. As shown in FIG. 3, flow path 22 passes through the housing and passes through a zone 23 of reduced flow area. At zone 23, air flowing through the housing increases in velocity. According to the invention, it is preferred to position heat exchanger 14 at zone 23.

FIG. 1 shows a simplified configuration of first heat exchanger 14 in accordance with the invention, and shows the heat exchanger in the form of a single refrigerant flow path or tube formed into a series of substantially parallel flow path segments. In this embodiment, the segments are serially fed with refrigerant fluid from compressor 12 such that the flow path segments include an upstream flow path segment 30 and a downstream flow path segment 32. In the embodiment shown in FIG. 1, all flow path segments are part of a single serpentine path and, thus, each segment is progressively further downstream as it relates to flow of refrigerant, when considered from upstream segment 30 to downstream segment 32. First heat exchanger 14 is positioned within the housing of beverage cooler 20 such that incoming heat exchange fluid 22 first passes the downstream refrigerant flow path segment 32, and then passed increasingly over the next flow path segments in order until finally passing upstream flow path 30. This configuration has been found, according to the invention, to provide for good heat exchange between the heat exchange fluid and the refrigerant. particularly when the system defined is a transcritical vapor compression system.

FIG. 2 shows an alternative embodiment wherein the flow path segments are broken up into two main groups or components of the heat exchanger, and wherein the groups are positioned so as to define an upstream and a downstream component. Within each component, segments are defined in parallel. Incoming heat exchange fluid, as shown, passes first over the downstream component and then over the upstream component.

It should be appreciated that the configurations of FIGS. 1 and 2 are examples of the counter flow arrangement of the present invention, and that alterations to these specific structures could of course be made by a person of skill in the art, well within the broad scope of the present invention. Further, one preferred embodiment of a heat exchanger for use in accordance with the invention is a wire-on-tube heat exchanger, an example of which is illustrated in FIG. 4. FIG. 4 shows a portion of a heat exchanger 50 defined by a single flow tube 52 which has a serpentine flow configuration as illustrated in FIG. 1 and which also is configured to have a vertical structure as well. Specifically, heat exchanger 50 is shaped to have alternating angled sections 54, 56 when considered in the direction of air flow as shown by arrow 58. A series of wires 60 are positioned along heat exchanger 50 in a substantially transverse direction to the paths defined by tube 52, and wires 60 preferably follow tube 52 along the sections 54, 56. Wires 60 can advantageously be positioned on both sides of tube 52 as shown in FIG. 4. FIG. 4 illustrates several turns of a wire-on-tube heat exchanger. It should be appreciated that the actual heat exchanger could continue for one or more additional angled sections 54, 56, to provide for the desired flow length of the heat exchanger.

As set forth above, FIG. 3 shows a further embodiment of the present invention wherein system 10 is incorporated into a beverage cooler 20. In this system, the beverages would be stored in a refrigerated area positioned above the portion illustrated, and communicated with the flow of air along path 28.

Flow path 22 represents flow of outside or ambient air which enters through an inlet 24 located at the front 34 of cooler 20 and passes a first component 14a of first heat exchanger 14 and then a second component 14b of first heat exchanger 14, and then to an outlet 26 preferably at the rear 36 of cooler 20.

An inner housing wall 38 separates the area of flow path 22 from the area of flow path 28. This wall also serves to define a zone along flow path 22 where the cross sectional area, or flow area, is constricted. This reduction in flow area along path 22 serves to increase the velocity of flow through same. For this reason, second component 14b of first heat exchanger 14 is preferably positioned at the zone of restricted flow as shown so that the increased flow velocity of heat exchange fluid passes over this heat exchanger. It has been found, according to the invention, that this positioning helps to further increase the efficiency in heat exchange between the heat exchange fluid and the refrigerant. Reduced flow area zone 23 is in this embodiment shown toward the rear of path 22, and is substantially completely filled with heat exchanger component 14b.

In further accordance with the invention, and as shown in FIG. 5, a heat exchanger such as the wire-on-tube heat exchanger of FIG. 4 can advantageously be positioned at the zone 23 of increased flow velocity, and this heat exchanger is particularly efficient in exchanging heat with the flow of air passing through zone 23. In this configuration, it is possible to completely eliminate the heat exchanger from the location occupied by heat exchanger 14a in FIG. 3, and thereby provide this space for other uses. Thus, in one aspect of the present invention, a heat exchanger is advantageously positioned within the housing at a zone 23 where there is a decreased air flow area and a resulting increase in air flow velocity, and it is further preferred to position a wire on tube heat exchanger in zone 23. As used herein, a wire-on-tube heat exchanger is considered to be a heat exchanger defined by one or more tubes, preferably a single tube, which has wires positioned for interaction with a passing air flow to increase heat exchange efficiency. Such a heat exchanger is particularly desirable for positioning in a zone such as zone 23 since most heat exchangers would have too great of a resistance to air flow to position in such a location. However, a wire-on-tube heat exchanger has sufficiently low resistance to air flow that positioning of such a heat exchanger in zone 23 does not significantly interfere with the flow dynamics of the system, and further the wire-on-tube heat exchanger is particularly efficient at heat exchange under such flow conditions.

As set forth above, FIG. 3 shows one embodiment of structure used to generate flow along paths 22 and path 28. Flow along flow path 22 can be generated using a fan 40 driven by a motor 42 as shown. In similar fashion, flow along path 28 can be generated by a fan 44 driven by a motor 46 as shown. Other structures for generating the desired flows would be well known to a person of skill in the art and are well within the scope of the present invention.

It should be appreciated that the refrigerant flow paths represented by first heat exchanger 14 and its components 14a, 14b, can be formed as tubes, micro-channels or mini-channels, or the like. The secondary fluid surface area of the tube can be increased, for example with fins attached to the tube. The fins can be of any type, and can be in the shape of plates, wires, louvered fins or any other shape. One preferred embodiment is that referred to as a “wire-on-tube” configuration as described above and illustrated in FIG. 4.

In bottle cooler applications and other small refrigeration applications with carbon dioxide (CO₂) as refrigerant this invention offers particular benefits. This invention allows utilizing the space in a volume available for the heat exchanger most effectively. Additionally, the high operating pressure of CO₂ refrigeration applications reduces the effect of pressure drop on the system performance. Therefore, the high pressure drop in a single-tube serpentine arrangement of the heat exchanger as shown in FIG. 1 does not reduce the system performance significantly, while the effective utilization of the volume available for the heat exchanger paths maximizes the system performance. Specifically, the volume normally occupied by a heat exchanger 14a (FIG. 3) can be utilized for other system components, or to make existing components larger and/or more efficient.

The system according to the invention is discussed herein in terms of having upstream and downstream relationship with various components of the refrigerant circuit in at least one mode of operation. This takes into account that a device such as a beverage cooler utilizing the apparatus of the present invention could have more than one mode of operation, and/or intermittent modes of operation, aside from the “normal” cooling mode wherein the first heat exchanger gives off heat and the second heat exchanger cools air within a refrigerated space.

One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, when implemented as a remanufacturing of an existing system or reengineering of an existing system configuration, details of the existing configuration may influence details of the implementation. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. A refrigeration system comprising: a compressor for driving a refrigerant along a flow path in at least a first mode of system operation;a first heat exchanger along the flow path downstream of the compressor in the first mode;a second heat exchanger along the flow path upstream of the compressor in the first mode; anda pressure regulator or expansion device in the flow path downstream of the first heat exchanger and upstream of the second heat exchanger in the first mode,wherein the first heat exchanger is positioned within a housing which defines a flow path for heat exchange fluid and the housing defines a zone of reduced flow area along the flow path, and wherein the first heat exchanger is positioned in the zone of reduced flow area.

2. The system of claim 1, wherein the first heat exchanger comprises a wire-on-tube heat exchanger.

3. The system of claim 1, wherein the heat exchanger comprises a plurality of substantially parallel refrigerant flow path segments, and wherein the heat exchange fluid is directed in counter flow with respect to refrigerant in the first heat exchanger, and substantially transverse to the refrigerant flow path segments.

4. A refrigeration system comprising: a compressor for driving a refrigerant along a flow path in at least a first mode of system operation;a first heat exchanger along the flow path downstream of the compressor in the first mode;a second heat exchanger along the flow path upstream of the compressor in the first mode; anda pressure regulator or expansion device in the flow path downstream of the first heat exchanger and upstream of the second heat exchanger in the first mode,wherein the first heat exchanger comprises a plurality of substantially parallel refrigerant flow path segments, and wherein heat exchange fluid for the first heat exchanger is directed in counter flow substantially transverse to the refrigerant flow path segments.

5. The system of claim 4 wherein the refrigerant flow paths have an upstream end and a downstream end with respect to refrigerant flow from the compressor, and wherein the heat exchange fluid is directed from the downstream end to the upstream end of the refrigerant flow path segments to provide the counter flow.

6. The system of claim 4, further comprising structure for guiding flow of the heat exchange fluid substantially transverse to the refrigerant flow path segments.

7. The system of claim 4 wherein the refrigerant flow path segments are defined by at least one refrigerant flow path in a serpentine arrangement.

8. The system of claim 4 wherein the refrigerant flow path segments are defined by a plurality of heat exchange modules arranged in series with respect to refrigerant flow and in counter flow with the heat exchange fluid.

9. The system of claim 8 wherein each heat exchange module comprises a plurality of substantially parallel refrigerant flow path segments.

10. The system of claim 4 wherein: the refrigerant comprises, in major mass part, CO2; andthe first and second heat exchangers are refrigerant-air heat exchangers.

11. The system of claim 4, wherein the system is adapted to operate in a transcritical vapor compression mode.

12. A beverage cooling device comprising the system of claim 4.

13. The device of claim 12, wherein the beverage cooling device comprises a housing having an inlet and an outlet for the heat exchange fluid, wherein the housing defines a flow restriction between the inlet and the outlet, and wherein the first heat exchanger is positioned at the flow restriction.

14. A method for exchanging heat between a refrigerant and a heat exchange fluid, comprising: operating a compressor to drive a refrigerant from the compressor to a heat exchanger in a housing which defines a flow path for heat exchange medium, wherein the housing defines a zone of decreased flow area for the heat exchange medium, and wherein the heat exchanger is positioned in the zone; andpassing a heat exchange fluid over the heat exchanger in the zone in a direction which is substantially transverse to the substantially parallel flow paths.

15. The method of claim 14, wherein the heat exchanger comprises a plurality of substantially parallel flow path segments.

16. The method of claim 15, further comprising feeding the substantially parallel flow path segments sequentially so as to define at least one upstream flow path and at least one downstream flow path with respect to refrigerant flow from the compressor, andwherein the passing step comprises passing heat exchange fluid over the substantially parallel flow path segments from the downstream flow path to the upstream flow path.