US3602298A

US3602298A - Heat exchanger

Info

Publication number: US3602298A
Application number: US819345A
Authority: US
Inventors: Mecislaus Joseph Ciesielski
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-04-25
Filing date: 1969-04-25
Publication date: 1971-08-31
Anticipated expiration: 1988-08-31

Abstract

A heat exchanger is disclosed which includes a first fluid conveying conduit for carrying a fluid which is to give up heat. Positioned beneath the first fluid conveying conduit and in heat transferring relationship therewith is a second fluid conveying conduit which carries a fluid which is to receive heat given up by the fluid carried by the first conduit. Because the receiving fluid receives heat from above, convection currents, which are normally generated when a fluid is heated from underneath, are eliminated. In this manner, heat transfer is maximized.

Description

United States Patent 1,803,586 6/1932 Wilke 3,220,472 11/1965 Raskin Inventor Mecishus Joseph Ciesielsld 239 Broad SL, Keyport, NJ. 07735 Appl. No. 819,345 Filed Apr. 25, 1969 Patented Aug. 31, 1971 HEAT EXCHANGER 2 Claims, 9 Drawing Figs.

11.8. CI 165/164, 165/135 Int. Cl F281 13/00 Field oiSearch l65/46, 164,166,168,154,158,171,172,134,135

References Cited 1 UNITED STATES PATENTS 3,490,523 1/1970 Esmond 165/46 X FOREIGN PATENTS 1,040,245 5/1953 France 165/164 539,529 9/1941 Great Britain 165/172 Primary Examiner-Frederick L. Matteson Assistant Examiner-Theophil W. Streule Anomey-Jerry M. Presson ABSTRACT: A heat exchanger is disclosed which includes a first fluid conveying conduit for carrying a fluid which is to give up heat. Positioned beneath the first fluid conveying conduit and in heat transferring relationship therewith is a second fluid conveying conduit which carries a fluid which is to receive heat given up by the fluid carried by the first conduit. Because the receiving fluid receives heat from above, convection currents, which are normally generated when a fluid is heated from underneath, are eliminated. in this manner, heat transfer is maximized.

HEAT EXCHANGER BACKGROUND OF THE INVENTION This invention relates to heat exchangers, and more particularly to a highly efficient heat exchanger in which undesirable convection currents are avoided.

In the quest for more efficient heat exchangers, designers and engineers have turned to more and more sophisticated arrangements in an effort to maximize heat transfer between a fluid giving up its heat and a fluid receiving such heat. In addition to being extremely expensive, such systems do not achieve the thermal efficiency which is thought possible from pure theoretical considerations. For some heretofore unexplained reason, there occurs an unrecovered loss of energy in virtually every heat exchanger of the prior art.

SUMMARY OF THE INVENTION The instant inventor, after having done much experimentation with basic heat exchange systems, has discovered a very fundamental reason that heat exchangers do not produce the thermal exchange efficiency which is theoretically possible from mathematical calculations. Thus, after consideration and analysis of a variety of prior art heat exchange devices, the inventor has appreciated a fundamental phenomenon which gives rise to an unrecoverable loss of energy when one fluid is utilized to give up its heat to another fluid. The instant inventor has designated this phenomenon convection currents" and can be explained as follows.

Considering the most basic type of heat exchanger in which a first duct or conduit carries a fluid which-is to give up heat, and a second conduit or duct is positioned in heat contacting relationship therewith and carries a second fluid which is to receive the heat given up by the first fluid; virtually all such prior art units examined position the duct which carries the giving" fluid beneath the duct which carries the receiving" fluid. In other words, the transfer of heat is affectuated by positioning the heat source beneath the fluid which is to be heated.

The instant inventor, in studying the above defined orientation of the respective fluid carrying ducts, has noted that when a fluid is heated from beneath," there is substantial turbulence in the fluid being heated. This turbulence which the inventor designates convection current," can be appreciated on an even more elementary level and to a somewhat exaggerated degree by considering what happens when water or any other fluid approaches its boiling point as it is heated on a common range or stove. As the boiling point is approached, one will observe, in addition to rising air bubbles, substantial currents of turbulence seemingly originating near the bottom of the fluid and emanating toward the top.

It is to be appreciated that to generate this turbulence requires substantial amounts of energy-energy which, but for the generation of these currents, could be efficiently absorbed by the fluid whose temperature was to be raised. The fact that these convection currents steal" energy from the.heat transferring process can be appreciated from a simple analogy such as appreciating the amount of work (energy) expended by a man attempting to generate turbulence in a body of water by mechanical energy such as by a paddle.

In accordance with the instant invention, the above described phenomena has not only been recognized, but there has been provided a basic heat exchanger unit which eliminates such convection currents and thereby materially increases the thermal efficiency of the heat transferring process taking place'therein. Thus, in its most basic form, the heat exchanger of the instant invention includes a first fluid conveying conduit for carrying a fluid which is to give up heat; and a second fluid conveying conduit positioned beneath the first conduit in heat transferring relationship therewith. The second conduit carries the fluid which is to receive heat from the first fluid. Since the heat being supplied to the receiving fluid enters from the top surface thereof, all convection currents are eliminated and thennal efficiency is increased.

As a particularly advantageous feature of the instant invention, the lower conduit which carries the receiving fluid is constructed -of a nonheat conductive material. In this manner, there is no possibility of heat from the upper duct following the path established by the side and bottom walls of the lower duct such thateven the remote possibility of convection currents being established by the walls of the lower duct is eliminated.

in an alternative embodiment, the lower duct may be constructed of a heat conducting material, such as a metal, but suitable insulation is provided to prevent thermal communication between the walls of the upper duct and the walls of the lower duct.

As a further particularly advantageous feature of the invention, at least one side of the wall or walls which establish the heat transferring relationship between the first and second duct is provided with an irregular cross section. In this manner, the planar surface area available for establishing heat transfer is maximized.

As a further feature of the instant invention, it is to be appreciated that the basic teachings outlined above can be physically embodied in a variety of shapes and materials and has basic application in any environment where heat exchange between any types of fluids (liquid or gas) is necessary or desirable.

Accordingly, it is an object of the instant invention to provide a heat exchanger which eliminates convection current.

It is another object of the instant invention to provide such a heat exchanger which includes a first duct for carrying a fluid which is to give up heat and a second duct positioned beneath the first ductin heat contacting relationship therewith, aid second duct carrying a fluidwhich is to receive heat given up by the fluid carried by the first duct.

.Another object of the instant invention is to provide a heat exchanger wherein the aforementioned second or lower duct is constructed of nonheat conductive material.

Still another object of the instant invention is to provide such a heat exchanger wherein the aforementioned second or lower duct is constructed of a heat conducting material that is insulatingly supported beneath the aforementioned first duct.

Yet another object of the instant invention is to provide such a heat exchanger wherein a common surface which establishes a heat transferring relationship between the aforementioned first and second ducts is provided with at least one irregular surface.

Yet another object of the instant invention is to provide such a heat exchanger which can be embodied in a variety of different shapes; may be constructed of-various materials; and

which has basic application in a variety of environments where it is desirable to exchange heat between any two fluids, liquid or gas.

These and other objects of the instant invention may be had by referring to the following specification and drawing in which:

FIG. 1 is a cross-sectional view of a heat exchanger exemplifying the prior art over which the instant invention is an improvement;

FIG. 2 is a perspective view of a basic heat exchanger constructed in accordance with the teachings of the instant invention; and

FIGS. 3-9 are cross-sectional views of various alternative embodiments of the instant invention.

Turning to the Figures and with specific reference to FIG. 1 there is illustrated a basic heat exchanger exemplary of the prior art over which the instant invention is intended to be an improvement. Thus, the heat exchanger 10 of FIG. 1 includes a first generally rectangular duct or conduit 12 which carries a fluid, generally indicated at 14, which is to give up its heat to a second fluid, generally indicated at 16, carried in a second generally rectangular duct 18 positioned above the first duct 12 and in heat transferring relationship therewith. The heat exchange is established in the prior art device of FIG. 1 by heat, indicated by the arrows 20, passing through the upper wall 22 of the lower duct 12, the lower wall 24 of the upper duct 18 and into the fluid l6.

As noted previously, this arrangement (wherein the fluid giving up the heat is positioned beneath the fluid receiving the heat), gives rise to turbulence, designated convection currents and illustrated by the wavy arrows 26 which require and in effect steal thermal energy which would otherwise be available for raising the temperature of the fluid 16.

Turning to FIG. 2, there is illustrated the basic heat exchanger 28 of the instant invention which is so designed as to eliminate the convection currents" designated 26 in the prior art device FIG. 1. Thus the heat exchanger 28 of FIG. 2 includes a first upper generally rectangular conduit 30 which carries a fluid 32 which is to give up its heat to a fluid 34 carried by a second generally rectangular conduit 36. In accordance with a primary aspect of the instant invention, the second conduit 36 carrying the fluid which is to receive heat, is positioned beneath the conduit 30 (carrying the fluid which gives up its heat) and is positioned in heat transferring relationship therewith.

Thus heat (designated by the arrows 37) given up by the fluid 32 passes downwardly through the lower wall 38 of the upper conduit 30, through the upper wall 40 of the lower conduit 36 and into the fluid 34 whose temperature is to be raised. Because the heat enters the lower fluid 34 from its upper surface thereof, convection currents are eliminated and thermal efficiency is materially increased.

Turning to FIG. 3, there is shown in cross section an altemative embodiment 42 of the heat exchanger of the instant invention in which the upper duct 44 is generally rectangular four sided conduit while the lower duct 46 which carries the fluid which receives the heat is a generally U-shaped trowel having a lower bite portion 48 and a pair of

upstanding side walls

50 and 52 respectively. In the embodiment of FIG. 3, it will be appreciated that heat designated by the arrows 54 passes directly through the lower wall 56 of the upper duct 44 and into the fluid (not shown) carried by the lower duct 46. In a sense, it might be said that the two ducts 44 and 48 are sharing the common wall 56.

Turning to FIG. 4, there is illustrated an embodiment similar to the embodiment of FIG. 3. Thus the heat exchanger 58 of FIG. 4 includes a generally rectangular upper duct 60 for carrying the fluid which is to give up heat and a substantially U-shaped trowel 62 secured therebeneath. The primary difference between the embodiment of FIG. 4 and that of FIG. 3 is that the lower wall 64 of the upper duct 60 includes an irregular cross section indicated at 66 which increases the planar area available to afiectuate the heat transfer between the upper and lower ducts.

Turning to FIG. 5, there is illustrated a heat exchanger 68, again similar to the embodiments of FIGS. 3 and 4, with the exception that the so called common wall 64 includes irregular surfaces 70 and 72 to increase the planar surface available on both sides of the common wall 64 to thereby maximize heat transfer.

As indicated by the drawing symbols for metallic cross-sectioning, both the upper and lower ducts of the various embodiments of FIGS. 2-5 are constructed of generally heat conducting material and might consist for example of any commonly available metal or alloy. However, when the lower duct (such as the rectangular duct 36 of FIG. 2 or the trowel like ducts of FIG. 3, 4, and are constructed of a heat conductive material; it is possible, that heat from the upper duct could follow the path established by the heat conductive material of the side and bottom walls of the lower ducts. This is illustrated in FIG. 4 by the arrows 74 depicting the flow of heat from the upper duct along the side and bottom walls of the lower duct 62. It will be appreciated therefore, that the utilization of heat conductive material for the lower duct could have the effect of establishing an undesirable heat source below the fluid which is to receive the heat which source could generate undesirable convection current.

Thus, in the preferred embodiment of the instant invention, illustrated in FIG. 6 for example, the lower duct 76 is constructed of a nonheat conductive material such as asbestos, extruded plastic, etc. In this manner, heat from the upper duct 78 does not follow the path of the side and bottom walls of the lower duct 76 and the possibility of convection currents being established thereby is eliminated.

In FIG. 7 is illustrated an alternative embodiment of the instant invention which eliminates convection currents generated by heat paths established in the lower duct, but at the same time permits the lower duct to be constructed of a heat conductive material. Thus in FIG. 7, the lower metallic trowel like duct 80 is positioned beneath the upper duct 82 but is separated therefrom by elongated insulating strips 84 again constructed of suitable nonheat conductive material such as plastic, asbestos etc. Thus the sidewalls 86 and bottom wall 88 of the lower duct 80 are not in thermal communication with respect to the upper duct 82 but yet the fluid (not shown) carried by the lower duct 80 is still in heat transferring relationship with respect to the lower wall 90 of the upper duct 82 to receive heat therefrom.

Although not illustrated in either FIGS. 6 or 7, it is to be appreciated that the

lower walls

92 and 90 of the

upper ducts

78 and 82 respectively could, if desired, be provided with one or more irregular surfaces such as illustrated in FIGS. 4 or 5 to increase the planar area established by these surfaces and thereby increase the heat transfer between the upper and lower ducts. FIG. 8 is an alternative embodiment of the instant invention in which the upper duct 94 is generally circular cross section while the lower duct 96, preferably of nonheat conducting material (for reasons discussed with respect to the embodiments of FIGS. 6 and 7) is similarly of generally circular cross section with an arcuate upper portion thereof removed. As in the other embodiments, the upper duct 94 carries the fluid which gives up heat, which heat passes through the lower arcuate portion 98 to the heat receiving fluid carried by the lower duct 96. Although not shown in the Figures, it is to be appreciated that the lower arcuate portion 98 of the upper duct 94 could similarly be provided with one or more irregular surfaces to maximize the planar surface available for heat transfer. Such an irregular surface area over the particular arcuate portion 98 might be provided for example by an extrusion process.

It will be appreciated that the various ducts illustrated throughout the Figures may be secured to one another in any convenient manner such as by adhesives, or mechanical means such as suggested by the band 100in FIG. 2 or a combination or both. I

In FIG. 9 there is illustrated yet another embodiment of the instant invention in which an outer duct 100 carries a fluid (not shown) which is to give up its heat to fluid or fluids carried by one or more inner ducts such as 102 and 104 respectively. Each inner duct is constructed of heat insulating material as illustrated at 106 with the exception that their upper surfaces 108 are constructed of heat conductive material such as commonly available metal alloy. In this manner, heat given up by the fluid in duct 100 will always be transferred down through the surfaces 108 to the fluid being carried by the

ducts

102 and 104. Since heating takes place from the top, convection currents will be eliminated.

Thus it will be appreciated that the instant invention provides a basic heat exchanger unit which increases thermal efficiency by eliminating energy absorbing convection currents normally generated in prior art devices. It is to be understood that the term fluid, used throughout this specification, is intended to mean all types of fluids in liquid or gaseous form.

Although this invention has been described with respect to its preferred embodiments, it should be understood that many variations and modifications will now be obvious to those skilled in the art, and it is preferred, therefore, that the scope of the invention be limited, not by the specific disclosure herein, only by the appended claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. A heat exchanger comprising: first liquid conveying means for conveying a first heated liquid, and second fluid conveying means positioned beneath said first conveying means for conveying a second fluid which is to receive heat conducted downwardly from the first liquid, said first conveying means including an enclosed, first elongated duct of generally rectangular cross section formed by a top wall, a first pair of parallel side walls, and a first bottom wall, said second conveying means including a second, elongated duct formed by a second pair of parallel sidewalls and a second bottom wall joined to said second pair of sidewalls such that said second duct has an essentially U-shaped cross section with the free edges defined by said second pair of sidewalls facing upwardly, said first bottom wall, said second duct having good thermal conductivity, the spacing between said first and second pairs of sidewalls being substantially equal, and a plurality of elongated strips of rectangular crosssection having good thermal insulative characteristics, the longitudinal axes of said strips extending parallel to and joining different ones of said free edges to said first conveying means with said first bottom wall serving as a continuous heat-conducting interface common to fluid in both of said ducts with the first liquid in direct contact therewith, said strips isolating said first duct from said second sidewalls so as to inhibit the production of thermal convection currents between second sidewalls and the fluid conveyed by said second duct.

2. A heat exchanger comprising: first horizontal fluid conveying means for conveying a first hot fluid, and second horizontal fluid conveying means positioned beneath said first conveying means for conveying a second cold fluid, said first fluid conveying means in thermal contact only with the fluid in the second fluid conveying means, the. said cold fluid to receive heatdownward only by conduction from the first hot fluid, said first conveying means including an enclosed, first elongated duct formed by a top wall, a first pair of parallel sidewalls, and a first bottom wall, said second conveying means including a second, elongated duct formed by a second pair of parallel sidewalls and a second bottom wall joined to said second pair of sidewalls so that said second duct has an essentially U-shaped cross section with the free edges defined by said second pair of sidewalls facing upwardly toward'the said first bottom wall, said second duct having good thermal conductivity, the spacing between said first and second pairs of sidewalls being substantially equal, and elongated strips having good thermal insulative characteristics, the longitudinal axes of said strips extending parallel to and joining different ones of said free edges to said first conveying means with said first bottom wall serving as a continuous heat-conducting partition common to fluids in both of said duets with the hot fluid in direct thermal contact therewith, said strips thermally isolating said first duct from said second sidewalls so as to inhibit the production of thermal convection currents along second sidewalls and the second bottom wall in the fluid conveyed by said second duct to enable said fluid in the said second cut to receive heat energy only by conduction.

Claims

1. A heat exchanger comprising: first liquid conveying means for conveying a first heated liquid, and second fluid conveying means positioned beneath said first conveying means for conveying a second fluid which is to receive heat conducted downwardly from the first liquid, said first conveying means including an enclosed, first elongated duct of generally rectangular cross section formed by a top wall, a first pair of parallel side walls, and a first bottom wall, said second conveying means including a second, elongated duct formed by a second pair of parallel sidewalls and a second bottom wall joined to said second pair of sidewalls such that said second duct has an essentially U-shaped cross section with the free edges defined by said second pair of sidewalls facing upwardly, said first bottom wall, said second duct having good thermal conductivity, the spacing between said first and second pairs of sidewalls being substantially equal, and a plurality of elongated strips of rectangular cross section having good thermal insulative characteristics, the longitudinal axes of said strips extending parallel to and joining different ones of said free edges to said first conveying means with said first bottom wall serving as a continuous heatconducting interface common to fluid in both of said ducts with the first liquid in direct contact therewith, said strips isolating said first duct from said second sidewalls so as to inhibit the production of thermal convection currents between second sidewalls and the fluid conveyed by said second duct.

2. A heat exchanger comprising: first horizontal fluid conveying means for conveying a first hot fluid, and second horizontal fluid conveying means positioned beneath said first conveying means for conveying a second cold fluid, said first fluid conveying means in thermal contact only with the fluid in the second fluid conveying means, the said cold fluid to receive heat downward only by conduction from the first hot fluid, said first conveying means including an enclosed, first elongated duct formed by a top wall, a first pair of parallel sidewalls, and a first bottom wall, said second conveying means including a second, elongated duct formed by a second pair of parallel sidewalls and a second bottom wall joined to said second pair of sidewalls so that said second duct has an essentially U-shaped cross section with the free edges defined by said second pair of sidewalls facing upwardly toward the said first bottom wall, said second duct having good thermal conductivity, the spacing between said first and second pairs of sidewalls being substantially equal, and elongated strips having good thermal insulative characteristics, the longitudinal axes of said strips extending parallel to and joining different ones of said free edges to said first conveying means with said first bottom wall serving as a continuous heat-conducting partition common to fluids in both of said ducts with the hot fluid in direct thermal contact therewith, said strips thermally isolating said first duct from said second sidewalls so as to inhibit the production of thermal convection currents along second sidewalls and the second bottom wall in the fluid conveyed by said second duct to enable said fluid in the said second cut to receive heat energy only by conduction.