US20110120177A1

US20110120177A1 - Heat exchanger for shedding water

Info

Publication number: US20110120177A1
Application number: US12/674,971
Authority: US
Inventors: Allen C. Kirkwood
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2007-12-18
Filing date: 2007-12-18
Publication date: 2011-05-26
Also published as: CN101903736A; WO2009078869A1; EP2235467A4; EP2235467A1

Abstract

A microchannel heat exchanger includes a two headers and tubes that extend between the headers. Each tube has an elongated cross-section, the cross-section having a first end and an opposing second end. In one example, each tube is angled such that a line defined between the ends of each tube is angled relative to the horizontal. As the tubes are angled, water that collects on the tubes is directed away from the tubes. In another example, a plate fin directs water away from the tubes. The plate fin includes openings, and a louver including parallel vertical slots is located between each of the openings. Each tube is interference fit in one of the openings of the plate fin, positioning a louver between each tube.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to a microchannel heat exchanger that improves water shedding from a surface of tubes.
Microchannel heat exchangers (MCHX) can be used as a condenser in a refrigeration system. The microchannel heat exchanger includes horizontal tubes with a flattened surface that extend between two vertical headers. The flattened surface of the tubes is substantially horizontal, and water does not shed from fins effectively. Water sits on the tubes, decreasing heat transfer performance, causing an increase in pressure drop, and allowing the gradual build up of ice under frosting conditions. For this reason, microchannel heat exchangers have not been widely applied as evaporators or as outdoor coils for heat pumps.
In another prior microchannel heat exchanger, the tubes are oriented vertically to prevent the accumulation of water on the tubes. Any condensate that forms gradually drains through louvers in the fins of the microchannel heat exchanger. However, this is not optimal as the louvers are blocked by the water, reducing heat transfer performance. Additionally, for a residential heat pump application, the length of the horizontal headers could be eight feet in length and must be bent several times to fit into a chassis. This creates manufacturing difficulties and reliability concerns and is more expensive than the vertical header/horizontal tube configuration.

SUMMARY OF THE INVENTION

A heat exchanger includes a two headers and tubes that extend between the headers. Channels are defined in each of the tubes. Refrigerant flows through the channels of the tubes, and air that passes over the tubes exchanges heat with the refrigerant. In one example, the heat exchanger is a microchannel evaporator. Each tube has an elongated cross-section taken perpendicular to a length of the tubes, the cross-section of the tubes having a first end and an opposing second end.
In one example, each tube is angled relative to the horizontal such that a line defined between the ends of each tube is angled relative to the horizontal. As the tubes are angled, water that collects on the tubes is directed away from the tubes.
In another example, a plate fin directs water away from the tubes. The plate fin includes openings, and a louver including parallel vertical slots is located between each opening. Each tube is interference fit in one of the openings of the plate fin, positioning a louver between each of the tubes.
These and other features of the present invention will be best understood from the following specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:

FIG. 1 illustrates a prior art refrigeration system;

FIG. 2 illustrates a microchannel heat exchanger;

FIG. 3 illustrates a cross-section of a tube of the microchannel heat exchanger;

FIG. 4 illustrates a header of the microchannel heat exchanger;

FIG. 5 illustrates a plate fin of the microchannel heat exchanger;

FIG. 6 illustrates a cross-sectional view of a portion of the plate fin of FIG. 5 showing a louver and a v-shaped channel;

FIG. 7 illustrates an alternate plate fin of the microchannel heat exchanger;

FIG. 8 illustrates a cross-sectional view of the microchannel heat exchanger; and

FIG. 9 illustrates a cross-sectional view of another configuration of the microchannel heat exchanger.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a refrigeration system 20 including a compressor 22, a first heat exchanger 24, an expansion device 26, and a second heat exchanger 28. Refrigerant circulates through the closed circuit refrigeration system 20.
When the refrigeration system 20 is operating in a cooling mode, the refrigerant exits the compressor 22 at a high pressure and a high enthalpy and flows through the first heat exchanger 24, which acts as a condenser. In the first heat exchanger 24, the refrigerant rejects heat to air and is condensed into a liquid that exits the first heat exchanger 24 at a low enthalpy and a high pressure. A fan 30 directs the air through the first heat exchanger 24. The cooled refrigerant then passes through the expansion device 26, expanding the refrigerant to a low pressure. After expansion, the refrigerant flows through the second heat exchanger 28, which acts as an evaporator. In the second heat exchanger 28, the refrigerant accepts heat from air, exiting the second heat exchanger 28 at a high enthalpy and a low pressure. A fan 32 blows air through the second heat exchanger 28. The refrigerant then flows to the compressor 22, completing the cycle.
When the refrigeration system 20 is operating in a heating mode, the flow of the refrigerant is reversed with a four-way valve 34. The first heat exchanger 24 accepts heat from the air and functions as an evaporator, and the second heat exchanger 28 rejects heat to the air and functions as a condenser.
The heat exchangers 24 and 28 are microchannel heat exchangers 38. The microchannel heat exchanger 38 can be part of a refrigeration system 20 used with a microdevice or an automobile air conditioner.
FIG. 2 shows the microchannel heat exchanger 38. The microchannel heat exchanger 38 includes two headers 40 and 42 that extend along an axis Y, and tubes 44 having a length that extend between the two headers 40 and 42 along an axis X. The tubes 44 include channels or openings 46 (shown in FIG. 3). The headers 40 and 42 are substantially vertical, and the tubes 44 extend substantially horizontally between the headers 40 and 42. The refrigerant flows through the tubes 44 and exchanges heat with the air that flows over the tubes 44. The openings 46 can be substantially circular, rectangular, or have any shape or geometry.
In one example, as shown in FIG. 3, a cross-section of the tubes 44 taken perpendicular to the axis X has an elongated shape, such as a rectangle or oval. For example, the tubes 44 can include an outer surface 36 with a flattened portion. Each tube 44 include a first end 48 and an opposing second end 50, and a line A extends between the ends 48 and 50.
The line A defined between the ends 48 and 50 of the tubes 44 extends at an angle B° relative to the horizontal. The first end 48 is a distance S from the ground G, and the opposing second end 50 is a distance R from the ground G. That is, the first end 48 is farther from the ground G than the opposing second end 50 is from the ground G (the first end 48 is higher than the second end 50). The tubes 44 are optimally angled to balance the competing effects of shedding water and airside pressure drop.
FIG. 4 shows the header 40. Although only the header 40 is illustrated and described, the header 42 also includes the same features. The tubes 44 extend into and out of the page along the axis X.
FIG. 5 shows a plate fin 52 including c-shaped collars 54 that each define an opening 64. The collars 54 create various different fin densities required for different applications. The collars 54 include a V-shaped channel 68 (shown in FIG. 6) that surrounds and defines the opening 64. The openings 64 and the collars 54 extend at the angle B° relative to the horizontal.
The plate fin 52 includes a first edge 70 and a second edge 72 that extend along the axis Y. The first edge 70 is continuous, and the second edge 72 is interrupted by the openings 64. An elongated surface 74 is defined between the first edge 70 and the openings 64. In one example, the elongated surface 74 is located on the side 70 near the second end 50 of the tubes 44 (the lower end of the tubes 44).
The plate fin 52 also includes at least one louver 56 having parallel slots 58. In one example, the parallel slots 58 are vertical and extend along the axis Y. A louver 56 is located between each of the openings 64 and extend at the angle B° relative to the horizontal. That is, the louvers 56 and the openings 64 alternate along the axis Y.
In another example plate fin 52 shown in FIG. 7, the second edge 72 is continuous and not interrupted by the openings 64. In this example, the material of the plate fin 52 completely surrounds the openings 64, and the collars 54 can have an oval or rectangular shape. The tubes 44 are laced in the openings 64 and received in the openings 64 with an interference fit. The tubes 44 are then brazed to the plate fin 52.
In the example shown in FIGS. 8 and 9, the louvers 56 extend upwardly relative to the first edge 70. In another example shown in FIG. 8, the louvers 56 extend downwardly relative to the first edge 70.
Each tube 44 is received in one of the openings 64 of the plate fin 52 with an interference fit, positioning a louver 56 between adjacent tubes 44 to improve heat transfer. The plate fin 52 is then brazed to the tubes 44.
As refrigerant flows through the openings 46 in the tubes 44, it exchanges heat with the air that flows over the tubes 44. If the refrigerant is accepting heat from the air, the microchannel heat exchanger 38 is acting as an evaporator, and condensate can form on the surface of the tubes 44. As the tubes 44 are angled relative to the horizontal, water sheds from the tubes 44 and does not collect on the tubes 44. The collars 54 and the v-shaped channels 68 allow the water to flow towards the first edge 70 and then downwardly towards the bottom of the microchannel heat exchanger 38 along the elongated surface 74. The parallel slots 58 also direct water downwardly. Shedding water or condensate from the surface of the tubes 44 increases heat performance, does not cause an increase in pressure drop, and prevents the accumulation of ice.
The foregoing description is only exemplary of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.

Claims

1. A heat exchanger comprising:

a first header and a second header; and

a plurality of tubes extending along an axis between the first header and the second header, wherein each of the plurality of tubes has an elongated cross-section taken substantially perpendicular to the axis, a first end and an opposing second end, and each of the plurality of tubes are angled relative to a horizontal such that the first end is higher than the opposing second end.

2. The heat exchanger as recited in claim 1 wherein the heat exchanger is an evaporator.

3. The heat exchanger as recited in claim 1 wherein the heat exchanger is a microchannel heat exchanger.

4. The heat exchanger as recited in claim 1 wherein each of the plurality of tubes includes an outer surface having a flattened portion.

5. The heat exchanger as recited in claim 1 wherein the first header and the second header are substantially vertical, each of the plurality of tubes are substantially horizontal, refrigerant flows through a plurality of channels in the plurality of tubes, and air flows over the plurality of tubes in a direction substantially perpendicular to a flow of the refrigerant through the plurality of tubes.

6. The heat exchanger as recited in claim 1 further including a plate fin including a plurality of collars each defining an opening, and each of the plurality of tubes is received in one of the plurality of openings.

7. The heat exchanger as recited in claim 6 wherein the plate fin includes a louver located between each of the plurality of openings, each of the louvers is located between two of the plurality of tubes, and each of the louvers includes a plurality of parallel vertical slots.

8. The heat exchanger as recited in claim 6 wherein each of the plurality of collars includes a v-shaped channel that surrounds each of the plurality of openings.

9. A refrigeration system comprising:

a compressor for compressing a refrigerant;

a condenser for cooling a refrigerant;

an expansion device for expanding the refrigeration; and

an evaporator for heating the refrigerant, wherein the evaporator includes a first header and a second header and a plurality of tubes extending along an axis between the first header and the second header, wherein each of the plurality of tubes have an elongated cross-section taken substantially perpendicular to the axis, a first end and an opposing second end, each of the plurality of tubes include a plurality of channels, and each of the plurality of tubes are angled relative to a horizontal such that the first end is higher than the opposing second end.

10. The refrigeration system as recited in claim 9 wherein each of the plurality of tubes includes an outer surface having a flattened portion.

11. The refrigeration system as recited in claim 9 wherein the first header and the second header are substantially vertical, each of the plurality of tubes are substantially horizontal, refrigerant flows through a plurality of channels in the plurality of tubes, and air flows over the plurality of tubes in a direction substantially perpendicular to a flow of the refrigerant through the plurality of tubes.

12. The refrigeration system as recited in claim 9 further including a plate fin including a plurality of collars each defining an opening, and each of the plurality of tubes is received in one of the plurality of openings.

13. The refrigeration system as recited in claim 9 wherein the plate fin includes a louver located between each of the plurality of openings, each of the louvers is located between two of the plurality of tubes, and each of the louvers includes a plurality of parallel vertical slots.