US20120227949A1

US20120227949A1 - Aerodynamic heat exchange structure

Info

Publication number: US20120227949A1
Application number: US13/046,597
Authority: US
Inventors: Richard M. Weber; Gary Schwartz
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 2011-03-11
Filing date: 2011-03-11
Publication date: 2012-09-13

Abstract

The present invention relates to heat exchangers, and more particularly to a heat exchange structure configured to operate in an air stream. In one embodiment, a heat exchange structure configured to operate in an air stream includes coolant flow portions, each of the coolant flow portions having at least one substantially closed surface directed into the air stream; and air flow portions disposed between adjacent coolant flow portions for receiving air from the air stream, the air flow portions having air passages directed into the air stream; the substantially closed surface of the coolant flow portions having an aerodynamic shape.

Description

FIELD

The present invention relates to heat exchangers, and more particularly to a heat exchange structure configured to operate in an air stream.

BACKGROUND

Heat exchangers are devices used transfer heat from one medium to another. For example, in a heat exchanger, air may flow over a coil carrying hot engine coolant, and heat from the coil may be released into the air. Common applications for heat exchangers include air conditioning, refrigeration, space heating, power plants, chemical plants, sewage treatment, and car radiators.
Heat exchangers come in many forms, and can have different structures depending on the heat load to be transferred and the environment in which the heat exchanger is used. Efficient heat exchangers are able to transfer large amounts of heat from one medium to another. Typical heat exchange structures have surfaces such as walls separating heat transfer fluids from one another.
The flow paths of the heat transfer fluids can be arranged in various ways. Some heat exchangers have channels that carry the heat transfer fluids in two different directions that are substantially perpendicular to one another. For example, as shown in FIG. 1, a typical heat exchange structure 10 may have a plurality of air flow portions 12 disposed between a plurality of coolant flow portions 16. Air from the air stream 14 enters and exits the heat exchange structure 10 through the air flow portions 12, and the coolant fluid 18 enters and exits the heat exchange structure 10 in a substantially perpendicular direction through the coolant flow portions 16. Thus, coolant fluid 18 flows in one direction through the coolant flow portions 16, and air from the air stream 14 flows through the air flow portions 12 in a second direction that is substantially perpendicular to the coolant flow direction.
The coolant flow portions 16 have closed surfaces 17 that are broadside to the air stream 14, so that the coolant fluid 18 can flow through the coolant flow portions 16 in a direction perpendicular to the flow of the air stream 14. In typical heat exchangers, the closed surfaces 17 are blunt, flat-faced surfaces. As a result, when the air stream 14 enters the air flow portions 12, the air experiences a pressure drop due to flow separation occurring at the blunt closed surfaces 17 of the coolant flow portions 16. Therefore, typical heat exchangers may be inefficient for operation in an air stream, because the pressure of the air entering the heat exchanger may be reduced.
Accordingly, there is a need for a heat exchange structure that can transition air through a heat exchanger with less pressure drop.

SUMMARY

The present invention relates to heat exchangers, and more particularly to a heat exchange structure configured to operate in an air stream. The efficiency of a heat exchanger can be improved by decreasing the resistance to fluid flow through the heat exchanger. In one embodiment, a heat exchange structure includes coolant flow portions having a substantially closed surface directed into an air stream, and air flow portions having air passages directed into the air stream. The substantially closed surfaces of the coolant flow portions have aerodynamic shapes at their leading edges. The aerodynamic shapes of the closed surfaces facilitate the flow of air through the air flow portions and decrease the pressure drop of the air flowing through the heat exchanger.
In one embodiment, a heat exchange structure configured to operate in an air stream includes coolant flow portions, each of the coolant flow portions having at least one substantially closed surface directed into the air stream; and air flow portions disposed between adjacent coolant flow portions for receiving air from the air stream, the air flow portions having air passages directed into the air stream; the substantially closed surface of the coolant flow portions having an aerodynamic shape.
The substantially closed surface may be at a leading edge of the coolant flow portions directed into the air stream. The substantially closed surface may have a shape that is convex into the air stream. Each coolant flow portion may have a trailing edge at an end of the coolant flow portion opposite the leading edge. The trailing edge may have a shape that is tapered rearwardly away from the leading edge.
The heat exchange structure may be configured in a free air stream, in an air duct, or in an air plenum.
In another embodiment, a method of manufacturing a heat exchange structure configured to operate in an air stream includes providing coolant flow portions, each of the coolant flow portions having at least one substantially closed surface; arranging the coolant flow portions such that the substantially closed surface is directed into the air stream; providing air flow portions between adjacent coolant flow portions, the air flow portions having air passages for receiving air from the air stream; arranging the air flow portions such that the air passages are directed into the air stream; and configuring the substantially closed surface of the coolant flow portions to have an aerodynamic shape.
The step of configuring the substantially closed surface of the coolant flow portions to have an aerodynamic shape may further include designing the aerodynamic shape to be convex into the air stream. The method of manufacturing the heat exchange structure may further include designing each of the coolant flow portions to have a trailing edge at an end opposite the substantially closed surface, wherein the trailing edge has a shape that is tapered rearwardly away from the substantially closed surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a typical heat exchange structure.

FIG. 2 shows a profile of coolant flow portions of a heat exchange structure according to an embodiment of the present invention.

FIG. 3 shows a profile of coolant flow portions of a heat exchange structure according to another embodiment of the present invention.

FIGS. 4A and 4B show profiles of coolant flow portions of a heat exchange structure according to another embodiment of the present invention.

DETAILED DESCRIPTION

The present invention relates to heat exchangers, and more particularly to a heat exchange structure configured to operate in an air stream. The efficiency of a heat exchanger can be improved by decreasing the resistance to fluid flow through the heat exchanger. In one embodiment, a heat exchange structure includes coolant flow portions having a substantially closed surface directed into an air stream, and air flow portions having air passages directed into the air stream. The substantially closed surfaces of the coolant flow portions have aerodynamic shapes at their leading edges. The aerodynamic shapes of the closed surfaces facilitate the flow of air through the air flow portions and decrease the pressure drop of the air flowing through the heat exchanger.
FIG. 2 shows a profile of coolant flow portions of a heat exchange structure according to an embodiment of the present invention. Coolant fluid flows into the coolant flow portions 26 in a direction perpendicular to the air stream 24. For example, in FIG. 2 coolant fluid flows in a direction that is normal to the surface of the page. Adjacent coolant flow portions 26 define air flow portions 22 therebetween. The air flow portions 22 have air passages for air stream 24 to flow through the heat exchange structure 20. Each coolant flow portion 26 has a leading edge facing upstream at the entrance to an adjacent air flow portion 22, and a trailing edge on the downstream at an exit of the adjacent air flow portion 22. The coolant flow portions 26 may be constructed of any material suitable for heat transfer, such as aluminum fin stock.
As shown in FIG. 2, in one embodiment each coolant flow portion 26 has an additional shape 23 at a leading edge of the coolant flow portion 26. The shape 23 is pointed and tapered in an upstream direction. Each coolant flow portion 26 also has an additional shape 25 opposite the shape 23 at a trailing edge of the coolant flow portion 26, which is also pointed and is tapered in a downstream direction. That is, the shape 25 is tapered rearwardly away from (or relative to) the leading edge. The coolant flow portions 26 having additional shapes 23 and 25 at their leading and trailing edges, respectively, improve the flow of air through the air flow portions 22. The air flow through the heat exchange structure 20 is improved over the air flow through the heat exchange structure 10 shown in FIG. 1, because the added aerodynamic shapes reduce or eliminate the pressure drop experienced at the blunt closed surfaces 17.
In other words, in FIG. 2, air from the air stream 24 clings to the aerodynamic shapes 23 at the entrances of the air flow portions 22 such that the air is more easily pulled in, and therefore the air flow is not separated by blunt, flat-faced surfaces as in FIG. 1. Accordingly, the additional shapes 23 at the leading edges of the coolant flow portions 26 reduce the pressure drop encountered at the entrance to the air flow portions 22. Further, the aerodynamic shapes 25 at the trailing edges of the coolant flow portions 26 produce a companion decrease in the air pressure at the exit to the air flow portions 22. The pointed, tapered shape 25 of the trailing edge can provide a greater decrease in the air pressure at the exit than can the blunt trailing edges of the coolant flow portions 16 in FIG. 1. The resulting increase in a differential pressure between the entrance and exit to the air flow portions 22 improves the flow of air through the heat exchange structure 20.
The additional shapes 23 and 25 also increase the available surface area for heat transfer along the leading and trailing edges of the coolant flow portions 26. As a result, the coolant flow portions 26 in FIG. 2 have a higher heat transfer coefficient than the coolant flow portions 16 in FIG. 1. Therefore, a heat exchange structure according to the embodiment of FIG. 2 may have improved heat transfer efficiency.
FIG. 3 shows a profile of coolant flow portions of a heat exchange structure according to another embodiment of the present invention. In the embodiment shown in FIG. 3, each of the coolant flow portions 36 is formed in an elliptical shape. A rounded shape 33 at the leading edge of each coolant flow portion 36 is convex into the air stream 34. The aerodynamic surface of the shape 33 reduces the pressure drop at the entrance to the air flow portions 36, because air from the air stream 34 clings to the aerodynamic surfaces of the shapes 33, rather than separating at the entrance to the air flow portions 32. In addition, the aerodynamic shape 35 at the trailing edge of each coolant flow portion 36 creates a partial vacuum on the downstream, so that an increased differential pressure between the entrance and exit of each air flow portion 32 causes more air to be drawn into the heat exchange structure 30.
FIGS. 4A and 4B show profiles of coolant flow portions of a heat exchange structure according to another embodiment of the present invention. The shapes of the coolant flow portions 46 shown in FIGS. 4A and 4B are based on the shapes of select wings (or airfoils) developed by the National Advisory Committee for Aeronautics (NACA). The coolant flow portion 46 shown in FIG. 4A is based on the shape of an NACA 0009 airfoil, and the coolant flow portion 46 shown in FIG. 4B is based on the shape of an NACA 0006 airfoil.
Each of the coolant flow portions 46 has a rounded shape 43 at a leading edge followed by a sharp, tapered shape 45 at a trailing edge. The rounded shape 43 at the leading edge of each coolant flow portion 46 is convex into the air stream 44. As such, flow separation in the air stream 44 can be reduced, because the air clings to the aerodynamic surfaces of the rounded shapes 43, rather than separating. In addition, the tapered shape 45 at the trailing edge of each coolant flow portion 46 draws the air flowing into the air passage past the surface of the coolant flow portion 46, toward the exit of the air passage. Accordingly, the aerodynamic shapes 43 and 45 of the coolant flow portions 46 may facilitate the transition of air through the heat exchange structure. While in FIGS. 4A and 4B the upper and lower portions of the coolant flow portions 46 are asymmetrical about the x-axis, the present invention is not limited thereto, and in other embodiments the upper and lower portions of the coolant flow portions may be symmetrical. In addition, the coolant flow portions may be designed to have any suitable thickness, and the thickness is not limited to the sizes shown in FIGS. 4A and 4B.
A heat exchange structure according to embodiments of the present invention may be used in various types of heat exchangers, such as heat exchangers configured to operate in a duct or a plenum. In addition, a heat exchange structure according to embodiments of the present invention may be used in a heat exchange apparatus configured to operate in a free air stream, as described in U.S. Patent Application No. ______, filed concurrently with this application, which is incorporated herein by reference.
According to another embodiment of the present invention, a method of manufacturing a heat exchange structure configured to operate in an air stream includes providing coolant flow portions, each of the coolant flow portions having at least one substantially closed surface, arranging the coolant flow portions such that the substantially closed surface is directed into the air stream, providing air flow portions between adjacent coolant flow portions, the air flow portions having air passages for receiving air from the air stream, arranging the air flow portions such that the air passages are directed into the air stream, and configuring the substantially closed surface of the coolant flow portions to have an aerodynamic shape.
In one embodiment, the step of configuring the substantially closed surface of the coolant flow portions to have an aerodynamic shape further includes designing the aerodynamic shape to be convex into the air stream. The method may further include the step of designing each of the coolant flow portions to have a trailing edge at an end opposite the substantially closed surface, wherein the trailing edge has a shape that is tapered rearwardly away from the substantially closed surface.
As this invention has been described herein by way of exemplary embodiments, many modifications and variations will be apparent to those skilled in the art. Accordingly, it is to be understood that the invention described herein may be embodied other than as specifically described herein. For example, the leading and trailing edges of the coolant flow portions may have any aerodynamic shape, and are not limited to tapered, rounded, and elliptical shapes. Further, it is to be understood that the steps of the methods described herein are not necessarily in any particular order.

Claims

1. A heat exchange structure configured to operate in an air stream, the heat exchange structure comprising:

coolant flow portions, each of the coolant flow portions having at least one substantially closed surface directed into the air stream; and

air flow portions disposed between adjacent coolant flow portions for receiving air from the air stream, the air flow portions having air passages directed into the air stream;

the substantially closed surface of the coolant flow portions having an aerodynamic shape.

2. The heat exchange structure of claim 1, wherein the substantially closed surface is at a leading edge of the coolant flow portions directed into the air stream.

3. The heat exchange structure of claim 2, wherein the substantially closed surface has a shape that is convex into the air stream.

4. The heat exchange structure of claim 2, wherein each coolant flow portion has a trailing edge at an end of the coolant flow portion opposite the leading edge.

5. The heat exchange structure of claim 4, wherein the trailing edge has a shape that is tapered rearwardly away from the leading edge.

6. The heat exchange structure of claim 1, wherein the heat exchange structure is configured in a free air stream.

7. The heat exchange structure of claim 1, wherein the heat exchange structure is configured in an air duct.

8. The heat exchange structure of claim 1, wherein the heat exchange structure is configured in an air plenum.

9. A method of manufacturing a heat exchange structure configured to operate in an air stream, comprising:

providing coolant flow portions, each of the coolant flow portions having at least one substantially closed surface;

arranging the coolant flow portions such that the substantially closed surface is directed into the air stream;

providing air flow portions between adjacent coolant flow portions, the air flow portions having air passages for receiving air from the air stream;

arranging the air flow portions such that the air passages are directed into the air stream; and

configuring the substantially closed surface of the coolant flow portions to have an aerodynamic shape.

10. The method of claim 9, wherein configuring the substantially closed surface of the coolant flow portions to have an aerodynamic shape further comprises designing the aerodynamic shape to be convex into the air stream.

11. The method of claim 10, further comprising designing each of the coolant flow portions to have a trailing edge at an end opposite the substantially closed surface, wherein the trailing edge has a shape that is tapered rearwardly away from the substantially closed surface.