US20090139702A1

US20090139702A1 - Heat exchanger

Info

Publication number: US20090139702A1
Application number: US12/292,880
Authority: US
Inventors: Gordon Hogan
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-11-30
Filing date: 2008-11-28
Publication date: 2009-06-04
Also published as: CA2645462A1

Abstract

A heat exchanger element for a heat exchanger includes a curved thermally conductive sheet having a curved end and a pair of legs extending contiguously from the curved end. The sheet has a substantially horizontal base edge along a lower edge of the sheet when, in an operational position, the curved end and the pair of legs are substantially horizontally aligned relative to one another. The base edge lays on a horizontal floor surface of a fluid filled cavity in a fluid reservoir when the sheet is operably positioned in the operational position in the cavity. The curved end and the pair of legs form substantially vertically extending walls. A plurality of horizontal tubes are mounted in the sheet so as to extend substantially horizontally in a vertically spaced apart array of tubes spaced apart along a height of the walls when the sheet is in the operational position. Each tube is mounted in a corresponding sleeve formed in the sheet. Each sleeve is sized to snugly encase a corresponding tube in heat conducting contact between the tube and the sleeve.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional Patent Application No. 61/004,696 filed Nov. 30, 2007 entitled Heat Exchanger.

FIELD OF THE INVENTION

This invention relates to heat exchanges designed to efficiently transfer heat energy from one medium to another in an isolated manner so as to avoid mixing the two media. The media may include water and/or refrigerant. In particular the present invention relates to heat exchangers where the heat exchanger is immersed in a reservoir of heat transfer fluid that has no forced circulation of heat transfer fluid but relies on convective circulation.

BACKGROUND OF THE INVENTION

It is known that there are many methods for exchanging heat between two media. Applicant is aware of patents regarding such beat exchange methods including:
U.S. Pat. No. 4,998,584 titled “Heat Exchanger” issued to Foglesonger, et al. on Mar. 12, 1991., teaches a method of ensuring good thermal conductivity between a heat exchange tube and a body of aluminum alloy by filling the interfacing space between the tube and the body with thermal conductor boron nitride. This is accomplished by forming a cavity in at least one side of a body of aluminum alloy for inserting heat exchange tubing of a dimension less than the cavity and coating the tubing and cavity with boron nitride powder in a carrier, placing the heat exchange tubing in the cavity, filling the space between the wall of the cavity and the tubing with boron nitride powder in a solvent such as alcohol and bonding the two sides together. The present invention achieves good thermal conductivity between the tube and aluminum sheet by crimping and welding the sheet around the tube, eliminating the need for a thermally conductive material in between.
U.S. Pat. No. 6,026,890 titled “Heat Transfer Device having metal band formed with longitudinal holes” issued to Akachi on Feb. 22, 2000, teaches a heat passive heat transfer device in which the phase change from liquid to gas and back again transfers heat from a hot section to a cold section. This is achieved using a sealed metal heat pipe unit partially filled, in a partial vacuum, with a predetermined amount of working fluid capable of condensation and vaporization around a working temperature range of interest. The metal heat pipe unit has a heat absorbing section for absorbing heat in a high temperature region, and a heat releasing section for releasing heat in a low temperature region. The metal heat pipe is made of a flexible plate like light metal band extending along a longitudinal direction from a first longitudinal end to a second longitudinal end, formed with a plurality of longitudinal holes being connected with one another to form said sealed inside cavity. The metal band is bent in a sinuous manner such that the band extends back and forth between the high temperature region and the low temperature region. In operation streams of a heat medium fluid flow substantially parallel to the side faces of the plate like metal band in the regions between the bends. This differs from the present invention in that this prior art is a closed and passive heat exchanger. The present invention is an active flow through heat exchanger.
U.S. Pat. No. 7,131,288 titled “Heat Exchanger” issued to Toonen, et al. on Nov. 7, 2006, teaches a heat exchanger for transferring heat from one fluid to another with one using porous metal foam that lets a fluid pass through, and is in contact with one or more tubes or flow passages for the other fluid to pass through and exchange heat via the passage wall and porous metal foam. Toonen also teaches a heat pump for energy conversion, comprising a motor for compressing and displacing a gaseous second fluid, and a heat exchanger for transferring heat from a first fluid to the second fluid, and a heat exchanger for transferring heat from the second fluid to a third fluid, a regenerator being arranged between the beat exchangers, as seen in the direction of flow of the gas. The present invention uses a solid thin sheet of thermally conductive material immersed in one fluid, while the second fluid flows through tubes that have been embedded in the sheet, with the sheet wrapped about the tubes and welded.

SUMMARY OF THE INVENTION

The heat exchanger of present invention serves to cost effectively and efficiently transfer heat from one medium or fluid to another when the heat exchanger is immersed into one fluid, and a the second fluid is passed through the heat exchanger. The heat exchanger consists of a thin sheet of thermally conductive material, such as aluminum, with tubes, such as copper tubes, pressed into the sheet. The sheet is crimped around the tubes and then the crimps welded closed to tighten contact between the tube and sheet. The tubes ends are connected to create one flow through path through the heat exchanger. The tubes are plumbed to communicate the heat transfer fluid to a beat pump or a second heat exchanger. The sheet may be formed into a U shape. In use the heat exchanger is immersed into the first heat transfer fluid.
In summary, the heat exchanger according to one aspect of the present invention may be characterized as including at least one heat exchanger element, where each element includes a curved thermally conductive sheet having a curved end and a pair of legs extending contiguously from the curved end. The sheet has a substantially horizontal base edge along a lower edge of the sheet when, in an operational position, the curved end and the pair of legs are substantially horizontally aligned relative to one another. The base edge lays on a horizontal floor surface of a fluid filled cavity in a fluid reservoir when the sheet is operably positioned in the operational position in the cavity, the curved end and the pair of legs forming a substantially vertically extending wall extending substantially vertically upwardly from the base edge.
A plurality of horizontal tubes are mounted in the sheet so as to extend substantially horizontally in a vertically spaced apart array of tubes spaced apart along a height of the walls when the sheet is in the operational position. Each tube is mounted in a corresponding sleeve formed in the sheet. Each sleeve is sized to snugly encase a corresponding tube in heat conducting contact between the tube and the sleeve.
The array of tubes are interconnected by interconnecting tubes at adjacent ends of the plurality of horizontal tubes so as form a substantially spiraling flow path for a heat exchanger fluid flowing through the array and the interconnecting tubes.
With the sheet in the operational position, heat energy is exchanged between the array and the sheet via the sleeves. The heat energy from the sleeves and the sheet is exchanged between a first heat exchange fluid flowing down along the flow path through the array and the interconnecting tubes, and a passive second heat exchange fluid in which the heat exchanger is immersed. The passive second heat exchange fluid is thereby circulated over the sheet by convection up along the surfaces the walls of the sheet.
In one embodiment the interconnecting tubes are substantially horizontal and the sheet is substantially U-shaped in plan view. The interconnecting tubes may also be inclined or vertical.
The heat exchanger may further include inlet and outlet headers in fluid communication with a plurality of the heat exchanger elements mounted in a parallel gang to the headers.
Advantageously the sheet is made substantially of aluminum. The sleeves maybe formed by crimping the sheet around the tubes so as to closely conformally wrap sleeve forming segments of the sheet around the tubes in close contact therewith. Seams are formed along the sleeves where the sleeve forming segments of the sheet are crimped closed about the tubes. The seams are sealed closed by heat conductive sealant. Advantageously the seams are sealed by welding the seams closed so as to further tighten the contact between the tubes and sleeves. That is, following welding, the liquid aluminum from the weld shrinks as it cools from the liquefying temperature of aluminum to the ambient temperature of the surrounding aluminum.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying figures like characters of reference denote corresponding parts in each view, wherein:

FIG. 1 is, in front perspective view, one embodiment of the heat exchanger of the present invention having four folded sheet heat exchanger elements plumbed in parallel to headers with three tubes in each element plumbed in series between the headers.

FIG. 2 is a plan view of the heat exchanger of FIG. 1.

FIG. 3 is a side-on perspective view of the heat exchanger of FIG. 1.

FIG. 4 is a rear perspective view of the heat exchanger of FIG. 1.

FIG. 5 is, in perspective view, one of the heat exchanger elements of FIG. 1.

FIG. 6 is, in perspective view, a u-shaped sheet portion of the heat exchanger element of FIG. 1.

FIG. 7 is an enlarged partially cutaway portion of FIG. 6 illustrating in greater detail the tube and sheet of a heat exchanger element of the present invention showing the tube pressed into the sheet metal, with the sheet metal crimped and welded around the tube.

FIG. 8 is, in perspective view, one alternative embodiment of the present invention configured as an evaporator for a refrigerant based heat exchanger.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Heat exchanger 1 includes u-shaped elements 2, each having two or more tubes 7 embedded within a thermally conductive sheet 8. A first heat transfer fluid is passed through the tubes. Elements 2 are immersed in a second heat transfer fluid. The first and second heat transfer fluids do not commingle or mix.
Sheet 8 of thermally conductive material may be advantageously made of aluminum sheet, for example, having a thickness of 22 gauge. The dimensions of the sheets depend on the available space in the body of fluid in wherever the heat exchanger is immersed. During manufacturing, fluid conducting tubes 7 are pressed into the sheet 8. Sheet 8 conformally encases tubes 7 in crimped sleeve 8 a. The edges 8 b of the sleeve are closed by a welded seam 11 along opposed facing parallel fold lines of sheet 8 where the edges of the seam are formed. The welding may be continuous welding of seam 11, or may be stitch welding spaced along the seam. The welding causes the sleeves 8 a to tighten firmly around the tubes 7 as the molten metal in the weld cools and contracts. In one method the crimping is formed by the constant applied pressure from jaws forming the crimp, in which case, as the metal of the sleeve expands during welding, the jaws are able to tighten the crimp further. As the sleeve cools it also contracts down onto the tube. Shrinkage of the weld can be of about one half of a millimeter. The tension in the aluminum, when stitch welded, is clearly visible.
The tubes 7 are typically copper, steel, or generally metallic tubing capable of handling pressures up to several hundred PSI for solar applications using fluids ranging from water to liquid/vapor phase change materials. For example the tubing may be quarter inch diameter tubing.
The heat exchanger 1 of the present invention is constructed in a modular fashion by ganging, for example in parallel, a number of heat exchanger elements 2 to inlet header 3 and outlet header 4. The first heat transfer fluid flows into elements 2 via inlet header 3, and exits via outlet header 4. Headers 3 and 4 are capped at their end by caps ends 5. In this way more than one heat exchanger element 2 may be ganged or arrayed inside a heat reservoir containing the second heat transfer fluid thereby increasing the heat exchange capacity.
Welding the edges 8 b of sleeve 8 a together along seam 11 while the conformally encasing tube 7 while it is pressed and held in sleeve 8 a results in a tensioned contact between the interior surface of sleeve 8 a and the outer surface of tube 7. This provides a good thermal connection between the two that will be maintained over the life of the heat exchanger despite thermal expansion and shrinkage. In the instance of the sheet 8 being of aluminum, once the aluminum is work hardened through the pressing and crimping process it is less likely to move as much with thermal expansion and shrinkage, which also helps maintain the integrity of the thermal conduction between the tube 7 surface and sleeve 8 a.
During manufacturing, after inserting tubes 7 in sleeves 8 a and welding seam 11, the sheet heat exchanger element 2 is then formed into a U-shape, or other curved space saving shape that optimizes the fit of the elements 2 in the available space in the reservoir of the second beat transfer and allows the elements to be free standing.
The U-Shaped beat exchanger elements 2 may in one embodiment also be twisted in directions A and B so as to approximately align the outlet of one tube 7′ with the inlet of an adjacent tube 7″ on the opposite leg of the u-shaped element as seen in FIG. 5. The aligned tube ends 7′ and 7″ are interconnected by being extended and formed to join the two tube ends together, or may be joined by a short interconnecting tube 6. Collectively herein, the interconnecting of ends of the tubes is referred to by use of the term “interconnecting tubes” whether separate tubes are used, or whether the tubes are merely extended to provide the interconnection. Connecting ends 7′ to 7″ creates a single serial spiraling flow path through the circuit of the heat exchanger element 2 that will drain with gravity to the outlet 10.
In other embodiments, tubing 7′ and 7″ remain parallel and inter connecting tubes 6′ are angled so as to complete the approximation of a downwardly spiraled flow path. In yet a further embodiment short interconnecting tubes 6″ (shown in dotted outline in FIG. 6) interconnect the vertically adjacent pairs of tubes 7′ and the vertically adjacent pair of tubes 7″ to approximate the downwardly spiraled flow path in each element 2. Supporting members (not shown) may be extended through the vertical apertures defined by tubes 6″ to help stabilize the structure in large heat exchangers.
Multiple such heat exchanger elements 2 may be configured in parallel in a gang to increase the thermal transfer capacity. The inlet 9 and outlet 10 of the heat exchanger is plumbed in fluid communication with headers 3 and 4 respectively. Thus in flow of the first heat transfer fluid in direction C in header 3 feeds flow in directions C′ into inlets 9, and outflow in direction D′ feed flow in direction D from header.4. The headers may be plumbed directly to a heat pump or another heat exchanger along with their associated reservoir and pump for along the corresponding first heat transfer fluid flow path. In operation heat exchanger 1 may be merely placed into the heat reservoir containing the second heat transfer fluid and thereafter fluid flow simply commenced. The u-shaped elements may merely sit on the floor of the reservoir without any further supporting structure, as the u-shaped elements 2 are self supporting.
An alternative embodiment of the present invention illustrated in FIG. 8 is configured as an evaporator in a refrigerant based heat exchanger. Inlet header 3 is segmented into five segments. Liquid refrigerant is introduced by inlet 36 to inlet header 3 a and then by tubes 16 to the corresponding five headers and 3. Metering header 3 a is conventional. Refrigerant then flows from the metering header 3 a through the five metering tubes 16 of equal length to corresponding segments of header 3. The inlet header 3 a, headers 3, and equal length metering tubes 16 extending therebetween balance the pressure load across the refrigerant heat exchanger array 15. The heated refrigerant gas is returned to the circuit by outlet header 4 and refrigerant outlet 18 in a balanced configuration similar to the inlet.
In each embodiment of the present invention the header caps 5 typically shown on one end of each header 3 and 4, are optional as the headers 3 and 4 may be configured to flow through to additional sets of headers, or may be fed and discharged from both sides to achieve more balanced flow through the heat exchanger elements arrayed along the headers.
Applicant has observed that efficiency is increased using the present invention for a certain length of tubing as compared to the equivalent length of tubing without the benefit of being embedded in conductive sleeves 8 a in parallel array formed in a thin, for example 22 gauge, aluminum conductive sheet 8. In particular, although not wishing to be bound by any particular theory of operation, applicant has observed convection currents flowing over sheet 8 and believes these upward convection currents increase the heat transfer rate as between the two heat transfer fluids. Applicant believes that approximately one hundred feet of one quarter inch diameter copper tubing used in accordance with the present invention has a greater heat transfer rate that approximately one hundred and twenty five feet of one half inch diameter copper tubing when used alone. In many instances applicant has observed a seven degree drop in temperative from the hot fluid inlet side to the cold fluid outlet of the heat exchanger according to the present invention.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.

Claims

1. A heat exchanger apparatus comprising:

at least one heat exchanger element, each element including a curved thermally conductive sheet having a curved end and a pair of legs extending contiguously from said curved end, said sheet having a substantially horizontal base edge along a lower edge of said sheet when, in an operational position, said curved end and said pair of legs are substantially horizontally aligned relative to one another so that said base edge lays on a horizontal floor surface of a fluid filled cavity in a fluid reservoir when said sheet is operably positioned in said operational position in the cavity, said curved end and said pair of legs forming substantially vertically extending walls extending substantially vertically upwardly from said base edge,

a plurality of horizontal tubes mounted in said sheet so as to extend substantially horizontally, in a vertically spaced apart array of tubes spaced apart along a height of said walls when said sheet is in said operational position,

wherein each tube of said plurality of tubes is mounted in a corresponding sleeve formed in said sheet, each said sleeve sized to snugly encase a corresponding said tube in heat conducting contact between said tube and said sleeve,

wherein said array of tubes are interconnected by interconnecting tubes at adjacent ends of said plurality of horizontal tubes so as form a substantially spiraling flow path for a heat exchanger fluid flowing through said array and said interconnecting tubes,

wherein, with said sheet in said operational position, heat energy is exchanged between said array and said sheet via said sleeves, and wherein the heat energy from said sleeves and said sheet is exchanged between a first heat exchange fluid flowing down along said flow path through said array and said interconnecting tubes, and a passive second heat exchange fluid in which said apparatus is immersed, and wherein said passive second heat exchange fluid is thereby circulated over said sheet by convection along the surfaces said walls of said sheet.

2. The apparatus of claim 1 wherein said interconnecting tubes are substantially horizontal and said sheet is substantially u-shaped in plain view.

3. The apparatus of claim 1 wherein said interconnecting tubes are inclined and said sheet is substantially U-shaped.

4. The apparatus of claim 1 wherein said interconnecting tubes are substantially vertical and said sheet is substantially u-shaped.

5. The apparatus of claim 1 further comprising inlet and outlet headers, and wherein said at least one heat exchanger element is a plurality of said heat exchanger elements mounted in a parallel gang to said headers in fluid communication therewith.

6. The apparatus of claim 5 wherein said array includes at least three said tubes in said array.

7. The apparatus of claim 1 wherein said sheet is substantially aluminum sheet.

8. The apparatus of claim 7 wherein said sleeves are formed by crimping said sheet around said tubes so as to closely conformally wrap sleeve forming segments of said sheet around said tubes in close contact therewith.

9. The apparatus of claim 8 wherein seams are formed along said sleeves where said sleeve forming segments of said sheet are crimped so as to be substantially closed about said tubes, and wherein said seams are sealed closed by heat conductive sealant.

10. The apparatus of claim 9 wherein said seams are sealed by welding said seams closed.