US20170343288A1

US20170343288A1 - Multi-pass and multi-slab folded microchannel heat exchanger

Info

Publication number: US20170343288A1
Application number: US15/526,917
Authority: US
Inventors: Arindom Joardar
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2014-11-17
Filing date: 2015-11-13
Publication date: 2017-11-30
Also published as: WO2016081306A1; RU2722930C2; RU2017118516A; EP3221656B1; ES2831020T3; CN107110568A; RU2017118516A3; EP3221656A1

Abstract

A heat exchanger is provided including a first manifold and a second manifold separated from one another. A plurality of tube segments arranged in a spaced parallel relationship fluidly couple the first and second manifold. The plurality of tube segments includes a bend defining a first slab and a second slab. The second slab is arranged at an angle to the first slab. The heat exchanger has a multi-pass configuration relative to an air flow including at least a first pass and a second pass. The first pass has a first flow orientation and the second pass has a second flow orientation. The second flow orientation is different from the first flow orientation.

Description

BACKGROUND

This invention relates generally to heat pump and refrigeration applications and, more particularly, to a microchannel heat exchanger configured for use in a heat pump or refrigeration system.
Heating, ventilation, air conditioning and refrigeration (HVAC&R) systems include heat exchangers to reject or accept heat between the refrigerant circulating within the system and surroundings. One type of heat exchanger that has become increasingly popular due to its compactness, lower weight, structural rigidity, and superior performance, is a microchannel or minichannel heat exchanger. As compared to conventional plate-and-fin heat exchangers, microchannel heat exchangers are also more environmentally friendly as they utilize less refrigerant charge which typically are synthetic fluids with high GWP (global warming potential). A microchannel heat exchanger includes two or more containment forms, such as tubes, through which a cooling or heating fluid (i.e. refrigerant or a glycol solution) is circulated. The tubes typically have a flattened cross-section and multiple parallel flow channels. Fins are typically arranged to extend between the tubes to augment efficient exchange of thermal energy between the heating/cooling fluid and the surrounding environment. The fins have a corrugated pattern, incorporate louvers to further enhance heat transfer, and are typically secured to the tubes via controlled atmosphere brazing.
In the heat pump and refrigeration applications, when the microchannel heat exchanger is utilized as an evaporator, moisture present in the airflow provided to the heat exchanger for cooling may condense and then freeze on the external heat exchanger surfaces. The ice or frost formed may block the flow of air through the heat exchanger, thereby reducing the efficiency and functionality of the heat exchanger and HVAC&R system. Microchannel heat exchangers tend to freeze faster than the round tube and plate fin heat exchangers and therefore require more frequent defrosts, reducing useful heat exchanger utilization time and overall performance. Consequently, it is desirable to construct the microchannel heat exchanger with improved frost tolerance and enhanced performance.

SUMMARY OF THE INVENTION

According to one embodiment of the invention, a heat exchanger is provided including a first manifold and a second manifold separated from one another. A plurality of tube segments arranged in a spaced parallel relationship fluidly couple the first and second manifold. The plurality of tube segments includes a bend defining a first slab and a second slab. The second slab is arranged at an angle to the first slab. The heat exchanger has a multi-pass configuration relative to an air flow including at least a first pass and a second pass. The first pass has a first flow orientation and the second pass has a second flow orientation. The second flow orientation is different from the first flow orientation.
In addition to one or more of the features described above, or as an alternative, in further embodiments the first pass has a cross parallel flow orientation.
In addition to one or more of the features described above, or as an alternative, in further embodiments the second pass has a cross counter flow orientation.
In addition to one or more of the features described above, or as an alternative, in further embodiments a first portion of the plurality of tube segments forms the first pass and a second portion of the plurality of tube segments forms the second pass.
In addition to one or more of the features described above, or as an alternative, in further embodiments a number of tube segments arranged within each of the first pass and the second pass is selected to reduce the formation of frost on the heat exchanger.
In addition to one or more of the features described above, or as an alternative, in further embodiments the second portion has a greater number of tube segments than the first portion.
In addition to one or more of the features described above, or as an alternative, in further embodiments a ratio of tube segments in the first portion to the second portion is 20:80.
In addition to one or more of the features described above, or as an alternative, in further embodiments a ratio of tube segments in the first portion to the second portion is 40:60.
In addition to one or more of the features described above, or as an alternative, in further embodiments a divider is arranged within the first manifold to define a first section and a second section. The first section is fluidly coupled to the first portion of the plurality of tube segments, and the second section is fluidly coupled to the second portion of the plurality of tube segments.
In addition to one or more of the features described above, or as an alternative, in further embodiments a distributor is arranged within the first section of the first manifold.
In addition to one or more of the features described above, or as an alternative, in further embodiments a distributor is provided between the first pass and the second pass.
In addition to one or more of the features described above, or as an alternative, in further embodiments the bend is formed about an axis arranged perpendicular to a longitudinal axis of the plurality of tube segments.
In addition to one or more of the features described above, or as an alternative, in further embodiments the bend of each tube segment includes a ribbon fold.
In addition to one or more of the features described above, or as an alternative, in further embodiments wherein the angle between the second slab and the first slab is about 180 degrees.
In addition to one or more of the features described above, or as an alternative, in further embodiments each of the plurality of tube segments is a microchannel tube having a plurality of discrete flow channels formed therein.
A heat exchanger is provided including a first manifold and a second manifold separated from one another. A plurality of tube segments arranged in a spaced parallel relationship fluidly couple the first and second manifold. The plurality of tube segments includes a bend defining a first slab and a second slab. The second slab is arranged at an angle to the first slab. The heat exchanger has a multi-pass configuration relative to an air flow including at least a first pass and a second pass. An inlet of the heat exchanger and an outlet of the heat exchanger are both formed in the first slab.
In addition to one or more of the features described above, or as an alternative, in further embodiments a first portion of the plurality of tube segments forms the first pass and a second portion of the plurality of tube segments forms the second pass. The first portion has fewer tube segments than the second portion.
In addition to one or more of the features described above, or as an alternative, in further embodiments each of the plurality of tube segments is a microchannel tube having a plurality of discrete flow channels formed therein.
In addition to one or more of the features described above, or as an alternative, in further embodiments a distributor is arranged adjacent an inlet of each pass of the heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of an example of a vapor refrigeration cycle of a refrigeration system;

FIG. 2 is a side view of a microchannel heat exchanger according to an embodiment of the invention prior to a bending operation;

FIG. 3 is a cross-sectional view of a tube segment of a microchannel heat exchanger according to an embodiment of the invention;

FIG. 4 is a perspective of a microchannel heat exchanger according to an embodiment of the invention;

FIG. 5 is a front view of a microchannel heat exchanger according to another embodiment of the invention;

FIG. 6 is a side view of a microchannel heat exchanger according to an embodiment of the invention;

FIG. 7 is a perspective view of a microchannel heat exchanger according to yet an embodiment of the invention; and

FIG. 7a is a cross-sectional view of the microchannel heat exchanger of FIG. 6 taken along line X-X according to yet an embodiment of the invention; and

FIG. 7b is a cross-sectional view of the microchannel heat exchanger of FIG. 6 taken along line Y-Y according to yet an embodiment of the invention.

The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.

DETAILED DESCRIPTION

Referring now to FIG. 1, a vapor compression refrigerant cycle 20 of an air conditioning or refrigeration system is schematically illustrated. Exemplary air conditioning or refrigeration systems include, but are not limited to, split, packaged, chiller, rooftop, supermarket, and transport refrigeration systems for example. A refrigerant R is configured to circulate through the vapor compression cycle 20 such that the refrigerant R absorbs heat when evaporated at a low temperature and pressure and releases heat when condensed at a higher temperature and pressure.
Within this cycle 20, the refrigerant R flows in a counterclockwise direction as indicated by the arrow. The compressor 22 receives refrigerant vapor from the evaporator 24 and compresses it to a higher temperature and pressure, with the relatively hot vapor then passing to the condenser 26 where it is cooled and condensed to a liquid state by a heat exchange relationship with a cooling medium (not shown) such as air. The liquid refrigerant R then passes from the condenser 26 to an expansion device 28, wherein the refrigerant R is expanded to a low temperature two-phase liquid/vapor state as it passes to the evaporator 24. The low pressure vapor then returns to the compressor 22 where the cycle is repeated. The vapor compression cycle 20 described herein is a heat pump cycle operating in a heating mode. As a result, the outdoor coil of the cycle 20 is configured as the evaporator 24 and the indoor coil is configured as the condenser. When configured as a heat pump, the vapor compression cycle additionally includes a four-way valve 29 disposed downstream of the compressor 22 with respect to the refrigerant flow that reverses the direction of refrigerant flow through the cycle 20 to switch between the cooling and heating mode of operation. It should be understood that the refrigeration cycle 20 depicted in FIG. 1 is a simplistic representation of an HVAC&R system, and many enhancements and features known in the art may be included in the schematic.
Referring now to FIG. 2, an example of a heat exchanger 30 configured for use in the vapor compression system 20 is illustrated in more detail. The heat exchanger 30 may be used as either a condenser 24 or an evaporator 28 in the vapor compression system 20. The heat exchanger 30 includes at least a first manifold or header 32, a second manifold or header 34 spaced apart from the first manifold 32, and a plurality of tube segments 36 extending in a spaced, parallel relationship between and connecting the first manifold 32 and the second manifold 34. In the illustrated, non-limiting embodiments, the first header 32 and the second header 34 are oriented generally horizontally and the heat exchange tube segments 36 extend generally vertically between the two headers 32, 34. However, other configurations, such as where the first and second headers 32, 34 are arranged substantially vertically are also within the scope of the invention.
Referring now to FIG. 3, an example of a cross-section of a heat exchange tube segment 36 is illustrated. The tube segment 36 includes a flattened microchannel heat exchange tube having a leading edge 40, a trailing edge 42, a first surface 44, and a second surface 46. The leading edge 40 of each heat exchanger tube 36 is upstream of its respective trailing edge 42 with respect to an airflow A passing through the heat exchanger 36. The interior flow passage of each heat exchange tube segment 36 may be divided by interior walls into a plurality of discrete flow channels 48 that extend over the length of the tubes 36 from an inlet end to an outlet end and establish fluid communication between the respective first and second manifolds 32, 34. The flow channels 48 may have a circular cross-section, a rectangular cross-section, a trapezoidal cross-section, a triangular cross-section, or another non-circular cross-section. The heat exchange tubes 36 including the discrete flow channels 48 may be formed using known techniques and materials, including, but not limited to, extruded or folded.
The heat exchange tube segments 36 disclosed herein further include a plurality of fins 50. In one embodiment, the fins 50 are formed of a single continuous strip of fin material tightly folded in a ribbon-like serpentine fashion thereby providing a plurality of closely spaced fins that extend generally orthogonal to the heat exchange tube segments 36. Heat exchange between the one or more fluids within the heat exchange tube segments 36 and an air flow, A, occurs through the outside surfaces 44, 46 of the heat exchange tube segments 36 collectively forming a primary heat exchange surface, and also through the heat exchange surface of the fins 50, which forms a secondary heat exchange surface.
The heat exchanger 30 has a multi-pass configuration relative to airflow A, To achieve a multi-pass configuration, in one embodiment illustrated in FIGS. 4-6, the multi-pass configuration is achieved by forming at least one bend 60 in each tube segment 36 of the heat exchanger 30. The bend 60 is formed about an axis extending substantially perpendicular to the longitudinal axis of the tube segments 36. In the illustrated embodiment, the bend 60 is a ribbon fold (see FIG. 6) formed by bending and twisting the heat exchange tube segments 36 about a mandrel (not shown); however other types of bends are within the scope of the invention. In one embodiment, a plurality of bends 60 may be formed at various locations along a length of the plurality of the heat exchange tube segments 36.
Bend 60 at least partially defines a first section 62 and a second section 64 of each of the plurality of tube segments 36, wherein in the bent configuration, the first section 62 forms a first slab 66 of the heat exchanger 30 relative to airflow A and the second section 64 forms a second slab 68 of the heat exchanger 30 relative to airflow A. In the illustrated, non-limiting embodiment, the bend 60 is formed at an approximate midpoint of the tube segments 36 between the opposing first and second manifolds 32, 34 such that the first and second sections 62, 64 are generally equal in size. However, other embodiments where the first section 62 and the second section 64 are substantially different in length are within the scope of the invention.
As shown in the FIGS. the heat exchanger 30 can be formed such that the first slab 66 is positioned at an obtuse angle with respect to the second slab 68. Alternatively, or in addition, the heat exchanger 30 can also be formed such that the first slab 66 is arranged at either an acute angle or substantially parallel (FIG. 5) to the second slab 68. As a result of the bend 60 between the first and second slabs 66, 68, the heat exchanger 30 may be formed having a conventional A-coil or V-coil shape. Forming the heat exchanger 30 by bending the tube segments 36 results in a heat exchanger 30 having a reduced bending radius, such as when configured with a 180° bend for example. As a result, the heat exchanger 30 may be adapted to fit within the sizing envelopes defined by existing air conditioning and refrigeration systems.
Referring again to FIGS. 2, a plurality of first fins 50 a extend from the first slab 66 and a plurality of second fins 50 b extend from the second slab 68 of the heat exchanger 30. In embodiments where the heat exchanger 30 is formed by bending the plurality of tube segments 36. no fins are arranged within the bend portion 60 of each tube segment 36. The first fins 50 a and the second fins 50 b may be substantially identical, or alternatively, may vary in one of size, shape, and density.
Conventional heat exchangers configured as evaporators of a heat pump typically have a parallel flow configuration to achieve a desired efficiency. However, parallel flow orientation leads to poor frost tolerance in microchannel heat exchangers. The heat exchanger 30 may have any of a variety of multi-pass configurations such that the refrigerant passes through the heat exchanger 30 in one or more of a parallel flow orientation, a cross flow orientation, and a counter flow orientation for example. In one embodiment, a divider 38 may be arranged within one or both of the first and second headers 32, 34 to increase the number of passes, and therefore the length of the flow path, within the heat exchanger 30.
In the embodiment illustrated in FIG. 7, a divider 38 is arranged within the first header 32 to form a first section 32 a and a second section 32 b. As a result, refrigerant supplied to an inlet (not shown) of the first header 32 is only configured to flow through the portion 36 a of the tube segments 36 fluidly connected to the first section 32 a. After passing through a first portion 36 a of the tube segments 36, the refrigerant is received in the second header 34. Within the second header 34, the refrigerant flows away from the first portion 36 a of tube segments 36, towards a second, adjacent portion 36 b of tube segments 36. The second portion 36 b may include the same number or a different number of tube segments 36 as the first portion 36 a. In one embodiment, the ratio of tube segments in the first portion 36 a to the second portion 36 b is 20:80, or alternatively, 40:60.
The second header 34 may similarly include a divider 38 to define a fluidly coupled first and second section 34 a, 34 b thereof. The refrigerant is configured to flow from the second header 34 through the second portion 36 b of tube segments 36 fluidly connected to the second section 32 b of the first header 32 and to an outlet (not shown) formed therein. Though the illustrated heat exchanger 30 includes two distinct portions of heat exchanger tube segments 36, heat exchangers 30 having any number of portions of tube segments 36 that form discrete passes through the heat exchanger 30 are within the scope of the invention.
Evenly distributing refrigerant within a header, such as header 32 or 34 or an intermediate header for example, is a common problem of microchannel heat exchangers. It is generally easy to distribute the refrigerant evenly for small manifold lengths, but mal-distribution becomes a more significant problem as the length of the manifold increases.
The heat exchanger 30 disclosed herein has improved refrigerant distribution by partitioning at least one of the first and second headers 32, 34, with a divider 38. As a result, the lengths of the manifold in which refrigerant must be evenly distributed is decreased. In addition, by bending the heat exchanger 30, the need for an intermediate header, and therefore the distribution problems associated with such a header, is eliminated. In one embodiment, a longitudinally elongated distributor insert 70, as is known in the art, may be arranged within one or more of the sections of either the first header 32 or the second header 34 of the heat exchanger 30. The distributor insert 70 is arranged generally centrally within the interior volume of the header and is configured to evenly distribute the flow of refrigerant between the plurality of heat exchanger tubes 36 fluidly coupled thereto. In the illustrated, non-limiting embodiment, a first distributor insert 70 is arranged within the first section 32 a of the header 32. The distributor insert 70 arranged within the first section 32 of the first header 30 generally over a portion or the full length of the section 32 such that the refrigerant provided thereto will be more evenly distributed over the length of the first section 32, thereby improving the heat transfer of the heat exchanger 30. Alternatively, or in addition, another distributor 70 may similarly be positioned within the second section 34 b of the second header 34.
Because the direction of the air flow A is the same relative to the first and second portions 36 a, 36 b of the tube segments 36, the refrigerant within each of these portions has a different flow-orientation. For example, in the illustrated, non-limiting embodiment, the air A flows from the first header 32 towards the second header 34. By supplying the refrigerant to an inlet of the first section 32 a of the first header 32, refrigerant flowing through the first portion 36 a of the tube segments 36, shown in detail in FIG, 7 a, has a cross-parallel flow orientation. In addition, the refrigerant flowing through the second portion 36 b of the tube segments 36. shown in more detail in FIG. 7b , has a cross-counter flow orientation.
In conventional heat exchangers having a parallel flow configuration, two phase refrigerant enters the first section 32 with low-vapor quality wherein it is configured to absorb heat from the air A and starts to boil. Because the boiling takes place at a constant temperature, the temperature difference between the air and the refrigerant reduces progressively as the air flows through the heat exchanger 30, reducing the heat transfer that occurs, particularly in the downstream slab 68. This behavior reduces the overall effectiveness of the heat exchanger and also results in lower evaporating temperatures, which is detrimental to both system efficiency and frost tolerance.
By dividing the plurality of heat exchange tube segments 36 of a heat exchanger 30 configured as an evaporator into a first portion 36 a and a second portion 36 b to form two sequential passes, partially evaporated refrigerant is supplied from the first pass to the second pass. In the second pass, the refrigerant is fully boiled and the superheated vapor leaves the upstream face of the heat exchanger 30. By configuring the second pass to have a refrigerant flow cross-counter to the air flow A, the temperature difference between the air and the refrigerant is move favorable. In addition, the presence of superheated vapor on the upstream face of the heat exchanger 30 prevents excessive frost accumulation and improves frost tolerance.
A heat exchanger 30 having a multi-pass, multi-slab, folded construction allows for optimization of the refrigerant pressure drop, thereby improving performance. As the refrigerant flows through the heat exchange tube segments 36, the vapor quality continuously increases, leading to increased volumetric flow and therefore increased pressure drop. By allocating progressively greater internal flow area as the refrigerant moves from one pass to the next, it is possible to greatly improve the pressure drop performance compared to conventional heat exchangers. Improvement in the operational efficiency of the heat exchanger 30 may allow the size of the heat exchanger 30 required for a desired application to be reduced. Alternatively, size of other system components, such as a compressor for example, may be reduced which in turn would cause even higher evaporation temperature and further reduction of defrost cycles as well as the system performance boost.
While the present invention has been particularly shown and described with reference to the exemplary embodiments as illustrated in the drawing, it will be recognized by those skilled in the art that various modifications may be made without departing from the spirit and scope of the invention. Therefore, it is intended that the present disclosure not be limited to the particular embodiment(s) disclosed as, but that the disclosure will include all embodiments falling within the scope of the appended claims. In particular, similar principals and ratios may be extended to the rooftops applications and vertical package units.

Claims

1. A heat exchanger comprising:

a first manifold;

a second manifold separated from the first manifold;

a plurality of tube segments arranged in spaced parallel relationship and fluidly coupling the first manifold and the second manifold, the plurality of tube segments including a bend defining a first slab and a second slab, the second slab being arranged at an angle to the first slab;

wherein the heat exchanger has a multi-pass configuration relative to an air flow including at least a first pass and a second pass, the first pass having a first flow orientation and the second pass having a second flow orientation, the second flow orientation being different than the first flow orientation.

2. The heat exchanger according to claim 1, wherein the first pass has a cross parallel flow orientation.

3. The heat exchanger according to claim 2, wherein the second pass has a cross counter flow orientation.

4. The heat exchanger according to claim 1, wherein a first portion of the plurality of tube segments forms the first pass and a second portion of the plurality of tube segments forms the second pass.

5. The heat exchanger according to claim 4, wherein a number of tube segments arranged within each of the first pass and the second pass is selected to reduce the formation of frost on the heat exchanger.

6. The heat exchanger according to claim 4, wherein the second portion has a greater number of tube segments than the first portion.

7. The heat exchanger according to claim 6, wherein a ratio of tube segments in the first portion to the second portion is 20:80.

8. The heat exchanger according to claim 6, wherein a ratio of tube segments in the first portion to the second portion is 40:60.

9. The heat exchanger according to claim 4, wherein a divider is arranged within the first manifold to define a first section and a second section, the first section being fluidly coupled to the first portion of the plurality of tube segments, and the second section being fluidly coupled to the second portion of the plurality of tube segments.

10. The heat exchanger according to claim 9, wherein a distributor is arranged within the first section of the first manifold.

11. The heat exchanger according to claim 9, wherein a distributor is provided between the first pass and the second pass.

12. The heat exchanger according to claim 1, wherein the bend is formed about an axis arranged perpendicular to a longitudinal axis of the plurality of tube segments.

13. The heat exchanger according to claim 1, wherein the bend of each tube segment includes a ribbon fold.

14. The heat exchanger according to claim 1, wherein the angle between the second slab and the first slab is about 180 degrees.

15. The heat exchanger according to claim 1, wherein each of the plurality of tube segments is a microchannel tube having a plurality of discrete flow channels formed therein.

16. A heat exchanger comprising:

a first manifold;

a second manifold separated from the first manifold;

wherein the heat exchanger has a multi-pass configuration relative to an air flow including at least a first pass and a second pass, an inlet of the heat exchanger and an outlet of the heat exchanger both being formed in the first slab.

17. The heat exchanger according to claim 16, wherein a first portion of the plurality of tube segments forms the first pass and a second portion of the plurality of tube segments forms the second pass, the first portion having fewer tube segments than the second portion.

18. The heat exchanger according to claim 16, wherein each of the plurality of tube segments is a microchannel tube having a plurality of discrete flow channels formed therein.

19. The heat exchanger according to claim 16, wherein a distributor is arranged adjacent an inlet of each pass of the heat exchanger.