Heat exchanger core

Abstract

A heat exchanger core is fabricated from plastic sheets with a flat side and a corrugated side. The plastic sheets are stacked so that the corrugated sheets define two flow paths. The plastic sheets is held in a stacked position by a retaining member.

Description

RELATED APPLICATION

The present application claims the benefit of U.S. Provisional Application No. 60/682,134 filed May 18, 2005, which is incorporated herein in its entirety by reference.

FIELD OF THE INVENTION

The present invention relates generally to a heat exchanger core. More particularly, the present invention relates to a heat exchanger core fabricated from single-face corrugated plastic, or laminated corrugated plastic.

BACKGROUND OF THE INVENTION

To enhance the efficiency of many processes, it is desirable to use heat exchangers that permit the exchange of heat from a gas or liquid at a first temperature to a gas or liquid at a second temperature, which is different than the first temperature. The heat exchanger reclaims energy from a material that is being discarded while raising the energy in a material that is being input into the system, or vice versa.

For example, heating and air conditioning systems often include a heat exchanger. Many manufacturing processes utilize heat exchangers to reclaim energy from waste materials and thereby reduce the costs associated with heating or cooling new materials.

A heat exchanger core is the part of a heat exchanger where materials at different temperatures are brought into proximity with each other. Existing heat exchanger cores are generally made of conductive materials, such as metal or plastic. Metallic heat exchangers, such as those made from aluminum, are commonly used but are much costlier to construct than ones made from plastic and consequently are much more expensive for consumers.

U.S. Pat. No. 5,474,639 describes a double wall heat exchanger made of polypropylene. The single die manufacturing process used for this heat exchanger requires that two walls be extruded for every flow path section. This double wall construction reduces the amount of heat transfer available. Further, the particular structure of the heat exchanger in U.S. Pat. No. 5,474,639, with its direction-dependent resistance to flow, causes potential flow balancing problems.

Although plastic offers the advantages of lower cost and lighter weight for the construction of heat-exchanger cores, plastic does not generally offer the same high level of conductivity that metal does. Existing plastic heat exchanger cores, which use plastic sheets that are less conductive than metal and stacked less efficiently, make plastic heat exchanger cores generally less efficient than metal ones. What is needed is an efficient plastic heat exchanger core that is relatively simple to construct using inexpensive plastic sheets.

SUMMARY OF THE INVENTION

The problems outlined above are solved in part by a heat-exchanger core made from single-wall corrugated plastic sheets. The use of single-wall plastic sheets retains the advantages of low cost and light weight offered by plastic while also providing improved efficiency. The heat exchanger core includes layers of plastic sheets with a generally planar side and a corrugated side defining a plurality of channels, the channels defining a flow path having a direction. The sheets are disposed in layers and oriented so that two flow path directions are created. The device includes a top layer and a bottom layer and a retaining member for retaining the plurality of plastic sheets in a stacked configuration between the top and bottom layers. Retention of the plastic sheets may be facilitated by channels in the top and bottom layers that receive straps. Or the plastic sheets may be mounted in a frame between the top and bottom layers. The plastic sheets may be provided with notches to facilitate framing. A method of layering the plastic sheets so that two flow paths are created is also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a heat exchanger core of the present invention.

FIG. 2 is a an enlarged, fragmentary, perspective view of the heat exchanger core.

FIG. 3 is a perspective view of a first side of one of the corrugated plastic sheets.

FIG. 4 is a perspective view of a second side of the corrugated plastic sheet in FIG. 3.

FIG. 5 is a perspective view of an alternative configuration of the heat exchanger core.

FIG. 6 is a plan view of a corrugated plastic sheet designed for use in the embodiment shown in FIG. 5.

FIG. 7 is an enlarged, fragmentary, plan view of the corrugated plastic sheet in FIG. 6.

FIG. 8 is a perspective view of a stack of the corrugated plastic sheets shown in FIG. 6.

FIG. 9A is a perspective cross-sectional view of a heat exchanger including the heat exchanger core.

FIG. 9B is an elevational cross-sectional view of the heat exchanger showing the flow paths in the heat exchanger core.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention is a heat exchanger core as illustrated at 10 in FIG. 1. The heat exchanger core 10 in accordance with the present invention broadly includes a plurality of corrugated plastic sheets 20 that are mounted in a frame 22.

The corrugated plastic sheets 20 are fabricated from a single-face configuration having a substantially flat (planar) first section or liner 30 and a corrugated (fluted) second section 32 that is affixed to the liner 30, as most clearly illustrated in FIGS. 3 and 4. The fluting or corrugation of second section 32 together with liner 30 define a series of channels through which a material, such as air, may flow.

The corrugated plastic sheets 20 are stacked so that corrugations on adjacent corrugated plastic sheets are oriented substantially transverse to each other, although other orientations may also be used. Within the stack, each corrugated plastic sheet is a layer. As shown in FIG. 1, corrugated plastic sheets 20 are stacked in layers and the corrugations 32 of each alternating sheet are oriented at 90-degree angles to define a first flow path and a second flow path.

In the stack, liner 30 of each sheet 20 is oriented the same way throughout so that liner 30 of one corrugated plastic sheet 20 contacts the corrugation 32 of adjacent sheets. As shown in FIG. 1, the uppermost sheet 21 is oriented with liner 30 facing up. The sheets below have the same orientation as the top sheet, so that liner 30 of the bottom sheet 23 faces up and corrugation 32 faces down. Alternatively, uppermost sheet 20 may be oriented with corrugated surface 32 facing up. In this configuration (which can be achieved simply by turning the previously described stack upside down) the bottom sheet will also have corrugated surface 32 facing up and liner 30 facing down. The designations “top” and “bottom” are for convenience only, as it can be appreciated that inverting the stack or corrugated plastic sheets 20 does not affect the function of the heat exchanger core.

In addition to the corrugated plastic sheets 20, the heat exchanger core 10 includes a top plate 40, a bottom plate 42, and may include a plurality of mounting straps 44 as most clearly illustrated in FIGS. 1 and 2. The top plate 40, the bottom plate 42, and the plurality of mounting straps 44 facilitate maintaining the heat exchanger core 10 in a substantially rigid configuration.

The top plate 40 and the bottom plate 42 each include channels 46 formed in their exterior surfaces. The channels 46 are sized to receive the mounting straps 44 and geometrically spaced to prevent the mounting straps 44 from moving laterally on the top plate 40 and the bottom plate 42. As shown in FIG. 1, when mounting straps 44 are secured in channels 46 on top plate 40 and bottom plate 42, and positioned securely around the stack of corrugated plastic sheets 20, they collectively form frame 22.

In an embodiment, the corrugated plastic sheets 20 are fabricated from high-density polyethylene (HDPE), or other synthetic resins. HDPE is more flexible than other commercial plastics, which makes the sheets less expensive to construct and transport. Other plastic materials, such as polypropylene, may also be used to manufacture corrugated plastic sheets 20. The heat-transfer coefficient of the sheet material should be 60% or better. In alternative embodiments, various dopants may be added to the synthetic resin to improve the conductive properties of the material.

To facilitate good heat transfer in the heat exchanger core 10, liner 30 and corrugation 32 are fabricated with a relatively small thickness. Preferably, liner 30 and corrugation 32 each have a wall thickness of less than 0.25 inches and greater than 0.0001 inches.

The corrugated plastic sheets 20 have a thickness of less than 1 inch and greater than 0.001 inches. Spacing between individual corrugations 34 is less than 1 inch and greater than 0.001 inches. In some embodiments, the thickness of corrugation 32 and liner 30 may be different from each other. In these embodiments, the thickness of liner 30 may be reduced to improve thermal transfer.

The corrugated plastic sheets 20 are molded of synthetic resin in a two-part die where one part of the die extrudes liner 30 and a second die extrudes corrugation 32. The materials extruded from the first die and the second die are placed in contact with each other when in a slightly molten form so that the liner 30 and corrugation 32 bond together.

The corrugated plastic sheets 20 are fabricated with a length and width that are selected based upon the desired use of the heat exchanger core 10. For most applications, the corrugated plastic sheets 20 would include an equilateral rectangle or parallelogram. The width and length of the corrugated plastic sheets are each between about three inches and eight feet.

As an example, when the heat exchanger core 10 is fabricated with a width and length that are both about 12 inches and there are 42 corrugated plastic sheets in the first direction and 41 corrugated plastic sheets in the second direction, the heat exchanger core 10 provides a total contact area for the first material of approximately 25,000 square inches and a total contact area for the second material of approximately 25,000 square inches.

Since the heat transfer coefficient of plastic is greater than the heat transfer coefficient of some materials, such as air, increase of the surface area of the heat exchanger core 10 enables more heat to be extracted from the materials flowing through the heat exchanger core 10.

Because of the structure of the heat exchanger core 10, the heat exchanger core 10 also exhibits a low resistance. As a result of the low velocity in the channels or flutes and the low resistance, a low driving force is needed to move materials through the heat exchanger core 10.

The heat exchanger core 10 of the present invention provides good heat transfer characteristics when used in a variety of applications such as heating, ventilation and air conditioning. The heat exchanger 10 resists corrosion because the corrugated sheets are fabricated from plastic.

Forming the heat exchanger core 10 from plastic corrugated sheets 20 also reduces the cost associated with manufacturing the heat exchanger core when compared with heat exchanger cores that are fabricated from metallic materials such as aluminum. Although the heat-transfer properties of plastics are generally less desirable than those of metallic materials, the use of single-face corrugated sheets offsets this in part.

Single-face corrugated plastic sheets 20 can be stacked so that liner 30 of one sheet does not rest on liner 30 of an adjacent sheet 20 Corrugation 32 of each sheet contacts liner 30 of an adjacent sheet. Likewise, liner 30 of each plastic sheet contacts corrugation 32 of an adjacent sheet. In such a configuration, adjacent liners 30 do not touch, thus preventing the formation of a double thickness of liners 30 in the stack of plastic corrugated sheets 20 and ensuring that each liner 30 is exposed to flow directly on either side through channels defined by corrugation 32.

In an alternate configuration shown in FIG. 5, heat exchanger core 80 includes top member 81, a plurality of corrugated plastic sheets 82, and bottom member 83 in a frame 84 that extends along each of the edges of the device. The frame 84 generally includes L-shaped pieces 85 that prevent the corrugated plastic sheets 82 from moving. Frame 84 also includes fasteners 86 that connect L-shaped pieces 85 to top frame members 87, which enclose top member 81. Bottom frame members 88 are similarly joined to L-shaped pieces 85 and enclose bottom member 83. The frame 84 may be fabricated from plastic or a metallic material such as aluminum. As in the embodiment of FIG. 1, the heat exchanger core 80 includes a plurality of corrugated plastic sheets 82 that are arranged so that adjacent corrugated plastic sheets 82 are oriented substantially transverse to each other, although other orientations may also be used. Corrugated plastic sheet 82 is constructed like corrugated plastic sheet 20.

In a variation of the embodiment shown in FIG. 5, a modified corrugated plastic sheet 120 is adapted to receive side frame elements (not shown), as illustrated in FIGS. 6 and 7. Proximate intersection of sides 122 of the corrugated sheet 120 a notch 124 is formed in the corrugated sheet 120.

The notch 124 includes a pair of side walls 130 and a base wall 132 that extends between the side walls 130 so that the notch 124 has a U-shaped configuration. Forming the notch 124 with this configuration prevents the side frame elements from moving out of the notch 124 by sliding laterally. In other respects, corrugated plastic sheet 120 is constructed like corrugated plastic sheets 20 and 82.

Corrugated plastic sheets 120 are used to construct a heat exchanger core that includes a top plate (not shown) and a bottom plate (not shown) that are both attached to the side frame elements. Using this configuration of the corrugated sheet 120 enables the heat exchanger core to have outer dimensions that are approximately the same as the dimensions of the corrugated sheet. This can be seen from FIG. 8, which shows how a stack of corrugated plastic sheets 120 facilitates framing. The choice of frame members could be either a rigid frame member similar to that shown in FIG. 5 or bands as shown in FIG. 1.

Heat exchanger core 10 may be used as part of a heat exchanger 140 as shown in FIGS. 9A-9B. Heat exchanger 140 generally comprises a housing 142 sized to receive heat exchanger core 10. A flow path in housing 142 in a first direction 144 is formed by aperture 146 and aperture 148. A flow path in housing 142 in a second direction 150 is formed by aperture 152 and aperture 154. As shown in FIG. 9A-9B, heat exchanger core 10 is angularly disposed inside housing 142 so that the geometry of heat exchanger core 10 contributes to the formation of two distinct flow paths. The angle and disposition of heat exchanger core 10 inside housing 142 may be varied. Apertures 146, 148, 152, and 154 may have a variety of shapes and be positioned at other positions in housing 142.

In operation, the heat exchanger core 10 is used with a first material flowing in a first direction (as indicated by arrow 100 in FIG. 1) and a second material flowing in a second direction (as indicated by arrow 102 in FIG. 1). The heat exchanger core 10 thereby permits heat to be transferred from the first material to the second material.

In an embodiment, the first material and the second material are both air. One or both of the materials, however, may be another fluid or gas.

The heat exchanger core 10 of the present invention is suited for use in a variety of heat transfer applications. One application for which the heat exchanger core 10 is particularly suited is heat-recovery ventilators or energy-recovery ventilators that are commonly used in residential dwellings. The heat exchange core 10 is suitable for use in both of these applications, as it is airtight and water tight even though, in an embodiment, adjacent corrugated sheets need not be bonded to each other. In alternative embodiments, the sheets may secured to each other or the frame in a variety of ways, such as by any combination of ultrasonic or thermal bonding, mechanical fasteners, adhesives or sealants.

It is contemplated that features disclosed in this application, as well as those described in the above applications incorporated by reference, can be mixed and matched to suit particular circumstances. Various other modifications and changes will be apparent to those of ordinary skill.

Claims

1. A heat exchanger core comprising a plurality of synthetic resin layers, each layer having a liner member presenting a liner member thickness, and a fluting member, the liner member and the fluting member of each layer cooperatively defining a plurality of fluid receiving channels presenting a fluid flow path along a fluid flow path direction, at least some of said synthetic resin layers oriented with each other such that said heat exchanger core presents first and second fluid flow paths in different fluid flow path directions, and at least some of said oriented layers positioned adjacent each other with said first and second flow paths being separated by a thickness of less than twice said liner member thickness

2. The device of claim 1, wherein some of the layers are rectangular.

3. The device of claim 1, wherein the plurality of synthetic resin layers are stacked in a frame.

4. The device of claim 1, wherein the first and second fluid flow path directions are generally transverse.

5. The device of claim 1, wherein one or more layers include notches for receiving a retaining member.

6. The device of claim 1, further comprising a top member and a bottom member including channels sized to receive a retaining member.

7. The device of claim 6, wherein the retaining member comprises a strap.

8. A heat exchanger comprising:

a plurality of synthetic resin layers, each layer having a liner member presenting a liner member thickness, and a fluting member, the liner member and the fluting member of each layer cooperatively defining a plurality of fluid receiving channels presenting a fluid flow paths along a fluid flow path direction, at least some of said synthetic resin layers oriented with each other such that said heat exchanger core presents first and second fluid flow paths in different fluid flow path directions, and at least some of said layers positioned adjacent each other with said first and second flow paths being separated by a thickness of less than twice said liner member thickness

a retaining member for retaining the plurality of layers in a stacked configuration; and

a housing comprising a first aperture and second aperture in communication with the first fluid flow path and a first aperture and a second aperture in communication with the second flow path.

9. The device of claim 8, wherein some of the layers are rectangular.

10. The device of claim 8, further comprising a top member and a bottom member having exterior surfaces with channels for receiving the retaining member.

11. A method of making a heat exchanger core comprising the steps of:

providing a plurality of synthetic resin layers, each layer having a liner member presenting a liner member thickness, and a fluting member, the liner member and the fluting member of each layer cooperatively defining a plurality of fluid receiving channels presenting a fluid flow paths along a fluid flow path direction,

layering the plastic sheets so that at least some of said synthetic resin layers are oriented with each other such that said heat exchanger core presents first and second fluid flow paths in different fluid flow path directions, and at least some of said oriented layers positioned adjacent each other with said first and second flow paths being separated by a thickness of less than twice said liner member thickness; and

retaining the plastic sheets in a stacked configuration with at least one retaining member.

12. The method of claim 11, wherein some of the layers are rectangular.

13. The method of claim 12, further comprising the step of providing a top member and a bottom member, wherein the step of retaining the plastic sheets in a stacked configuration comprises securing the plurality of plastic sheets between the top member and the bottom member.

14. The method of claim 13, wherein the top member and bottom member comprise exterior surfaces having channels for receiving the retaining member.

15. The method of claim 14, wherein the retaining member comprises a strap.

16. The method of claim 12, wherein the retaining member comprises a rectangular frame.