Heat exchange – Flow passages for two confined fluids
Reexamination Certificate
1999-12-02
2001-07-24
Leo, Leonard (Department: 3743)
Heat exchange
Flow passages for two confined fluids
C165SDIG003
Reexamination Certificate
active
06263961
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a National Stage Application of International Application PCT/BE97/00088, filed on Jul. 28, 1997.
FIELD OF THE INVENTION
The present invention relates to coiled heat exchangers having a spiral configuration. In these types of heat exchangers, heat transfer fluids enter, circulate, and exit the heat exchanger in a counterflow manner in a direction substantially parallel to the coil's longitudinal axis.
BACKGROUND OF THE INVENTION
Though numerous applications utilize coiled heat exchangers, the gas turbine recuperator is among the most demanding. In any application, and especially when used as a gas turbine recuperator, the heat exchanger should be compact, efficient, reliable, and relatively inexpensive to manufacture. By designing the primary heat transfer surface with small hydraulic diameters and counterflow circulation of heat transfer fluids, a relatively compact and efficient heat exchanger can be obtained. Furthermore, providing the heat exchanger with relatively large cross-sectional flow areas reduces load losses. Achievement of large cross-sectional flow areas in coiled heat exchangers requires circulating heat transfer fluids in the axial, as opposed to tangential, direction. Additionally, production costs can be lowered by minimizing the number of elements used to make the heat exchanger and by forming and coiling the heat exchanger in a continuous process. Another design consideration, especially when used as a gas turbine recuperator, includes resistance to thermal shock. Heavy thermal loads often result from the transient operation of turbines. Therefore, to ensure reliable performance and operation, the heat exchanger should have high resistance to thermal shock.
Various known heat exchangers are made from coiling a pair of sheets between which heat transfer fluids circulate in a counterflow manner in directions substantially parallel to the longitudinal axis of the coil. For example, U.S. Pat. No. 5,797,449 pertains to an annular heat exchanger formed by a pair of sheets welded together and coiled, with openings cut through the sheets through which heat transfer fluid passes.
German patents DE 1121090 and DE 3234878 describe spiral heat exchangers having axially circulated fluid flows, in which the fluids enter and exit through alternating angular sectors. In DE 1121090, sectors for circulating the heat transfer fluids are formed by cutting evenly-spaced openings in borders that close the edges of a pair of sheets coiled to form the heat exchanger. After the borders are cut, the two sheets are coiled to form the heat exchanger. DE 1121090 additionally discloses the fabrication of the spiral heat exchangers with external headers.
In DE 3234878, the sectors are formed by glueing blocking segments on the two faces of the coiled heat exchanger.
Finally, in French patent document FR-A-2319868, borders are closed by the direct welding of adjacent sheets.
A particular difficulty in heat exchangers having a coiled configuration includes the distribution of the single incoming flow into the myriad of small heat transfer passages and the collection of the same into a single outgoing flow after the heat transfer has taken place. Preferably, this distributing and collecting should not result in excessive head losses, nor should it cause mechanical stresses due to large thermal gradients. Another difficulty arises from blockages to the heat transfer fluids that exist on the core face as the result of the particular construction used for the heat exchanger. For instance, in one known example, the sheets are constructed and cut such that one sheet has openings only for one fluid and the other has openings only for the other fluid. This leads to a relatively high amount of fluid being blocked at the core faces, thus reducing gas flow passage and overall efficiency of the heat exchanger.
Stacked plate heat exchangers often include openings cut in the plates to distribute and collect the heat transfer fluids. The edges of these openings generally are either brazed or welded together during assembly of the heat exchanger (for example in U.S. Pat. No. 4,073,340) or are fitted with a gasket (for example in Alfa-Laval plate heat exchangers). Other stacked plate heat exchangers do not include such openings (see SAE 851254: “Development, Fabrication, and Application of a Primary Surface Gas Turbine Recuperator”, E.L. Parsons), but the sides of the plates must be provided with sealing bars.
SUMMARY OF THE INVENTION
The invention relates to a heat exchanger formed by coiling a pair of sheets. According to an aspect of the invention a coiled heat exchanger comprises a first sheet having at least one edge extending substantially coplanar with the first sheet and a second sheet having at least one edge with alternating portions along a length of the edge being respectively raised and unraised with respect to a plane of the second sheet. The at least one edge of the second sheet is configured to abut portions of the at least one edge of the first sheet at locations corresponding to the alternating raised portions when the first and second sheets are coiled together.
According to another aspect of the invention, a cylindrical heat exchanger made by coiling a pair of sheets includes a pair of adjacent sheets coiled together so as to form angular sectors on opposite faces of the cylindrical heat exchanger, said angular sectors being formed by alternating raised portions disposed along the edge of one sheet abutting portions along the edge of the other sheet. The pair of sheets further includes ripples extending substantially parallel to the longitudinal axis of the cylindrical heat exchanger on one sheet of the pair of sheets and ripples extending substantially perpendicular to the longitudinal axis of the cylindrical heat exchanger on the other sheet of the pair of sheets. A sum of the heights of corresponding ripples on each sheet is a constant along an axial length of the heat exchanger from one face to the other and the constant is equal to a height of the alternating raised portions on the edge of the second sheet, as measured from a plane of the second sheet. The two sheets are one of joined and brazed at contact points of crests of the respective ripples of each sheet.
According to yet another aspect of the invention, a cylindrical heat exchanger made by coiling a pair of sheets comprises essentially the same elements as those listed in the preceding paragraph except that fins extend on the sheets rather than ripples.
Yet another aspect of the invention includes a heat exchanger formed by coiling a pair of sheets comprising a cylindrical core having two opposite faces with a plurality of openings in the form of angular sectors around a longitudinal axis of the core. The core is formed by coiling a first sheet having at least one edge extending substantially coplanar with the first sheet with a second sheet having at least one edge with alternating portions along the edge being respectively raised and unraised with respect to the plane of the second sheet. The raised portions of the edge of the second sheet abut portions of the edge of the first sheet and the angular sector openings are partially defined by the abutting portions of the edges of the first and second sheets.
According to yet another aspect of the invention, a method of forming a coiled heat exchanger includes providing a first sheet having at least one edge extending substantially coplanar to the first sheet and providing a second sheet having at least one edge with alternating portions along the edge being respectively raised and unraised with respect to a plane of the second sheet. The method further includes placing the first and second sheets together such that their edges are substantially aligned with one another and coiling the first and second sheets together such that the alternating raised portions of the edge of the second sheet abut portions of the edge of the first sheet.
REFERENCES:
patent: 2663549 (1953-12-01), Otten
patent: 3854530 (1974-12
Ateliers de Construction de Thermo Echangeurs S.A.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Leo Leonard
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