Heat exchange – Flow passages for two confined fluids – Interdigitated plural first and plural second fluid passages
Patent
1980-01-14
1982-08-10
Scott, Samuel
Heat exchange
Flow passages for two confined fluids
Interdigitated plural first and plural second fluid passages
F28F 300
Patent
active
043433553
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates generally to a low stress heat exchanger module for use in devices such as gas turbines which use recuperators and a method for forming the same, and more particularly to a module formed from one or more single sheet, primary surface heat exchanger core units .
2. Background Art
U.S. Pat. No. 3,759,323 issued to Harry J. Dawson et al describes an important prior art primary surface heat exchanger for use as a recuperator core of a gas turbine. Dawson et al discloses a heat exchanger core made from a multiplicity of thin metal sheets which have been corrugated or folded in a wavy pattern to provide fluid passages on opposite sides of the sheet. A large number of these metal sheets are stacked on top of each other, and the edges of the sheets are crushed to form the flat sections necessary to encase the assembly and to allow the attachment of suitable manifolding for conveying hot and cold fluid to the passages.
In the Dawson et al structure, it is necessary to weld the crushed ends of the thin metal sheets to thicker metal members such as spacer bars, header plates, etc. Other known heat exchanger structures have used welding to selectively close the ends of fluid passages formed in thin metal heat exchange sheets. In all of these prior known heat exchange structures, the welds have often occured at the end of what, in effect, constitutes a prebuilt crack.
It is well established that welds must not be located in regions of high stress, and this automatically means that welds must not be placed so that they constitute the end of a prebuilt crack where the stress concentration is upredictably high. However, in prior heat exchange structures, it has not been possible to effectively place the welds in low stress areas, so that core failures, which would not otherwise have occurred, were often initiated at a weld.
Preformed cracks and other high stress areas arise when a thin metal or ceramic material is welded or bonded to a thicker support member. Also the failure of a weld to penetrate at certain junctions within the heat exchange core results in a preformed crack. The effect of crushing the corrugated edges of the Dawson et al heat exchange plate has been that of producing a multiplicity of cracks.
While the stress concentration factors present at the welds in prior heat exchange structures may not be significant when the assembly is preloaded in compression, as intended, and when the transients are not steep, high stresses which lead to premature failures may appear under severe operating conditions and after prolonged periods of operation during which the preload is likely to be relaxed.
The present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the present invention, a novel method is provided for making a junction within a heat exchanger by wrapping a thin metallic member around a thicker metallic member so that the thin member extends off tangentially from the thick member. A weld is then placed away from the point where the thin member tangentially leaves the thick member.
In another aspect of the present invention, a low stress single sheet primary surface heat exchanger core unit is provided which is formed from a single sheet of thin material pleated to any depth desired. Before pleating, the longitudinal edges of the thin sheet are provided with tabs which selectively close end sections of the completed core. These tabs are curled so that when the pleated sheet is compressed to form a pleated assembly, adjacent tabs overlap and may be welded together in a region of relatively low stress.
These and other objects of the present invention will be more readily apparent from a consideration of the following description taken together with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a section of single sheet of heat exchange material employed to form a heat exchange core for the heat exchanger of the present invention;
FIG
REFERENCES:
patent: 2143269 (1939-01-01), Hubbard
patent: 2400617 (1946-05-01), Wheller
patent: 2953110 (1960-09-01), Etheridge
patent: 3552488 (1971-01-01), Grill
patent: 3759323 (1973-09-01), Dawson et al.
Goloff Alexander
Grim George B.
Caterpillar Tractor Co.
Scott Samuel
Streule, Jr. Theophil W.
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