Heat exchange – Flow passages for two confined fluids – Interdigitated plural first and plural second fluid passages
Reexamination Certificate
1999-11-04
2001-09-25
Lazarus, Ira S. (Department: 3743)
Heat exchange
Flow passages for two confined fluids
Interdigitated plural first and plural second fluid passages
C165S167000, C165S170000, C060S039512, C060S039520
Reexamination Certificate
active
06293338
ABSTRACT:
The recuperator of a gas turbine engine transfers heat from the relatively hot, low pressure engine exhaust gas to incoming, relatively cold, high pressure compressed air. The recuperator enables the gas turbine engine to approach the fuel economy of a diesel engine as well as to exhibit emission levels below ULEV standards. Moreover, such relatively low emission levels can be achieved by recuperator equipped gas turbine engines without the use of a catalytic converter.
However, known recuperators, particularly metallic plate-and-fin recuperators of the type disclosed in U.S. Pat. No. 3,507,115, are one of the most expensive components of a gas turbine engine. In addition, known recuperators exhibit a relatively high temperature and pressure gradient across the high pressure air side of the recuperator which causes poor flow distribution which compromises efficiency. Yet another deficiency of known gas turbine engine recuperators, is that conventional seals are often employed between the hot and cold sections of the recuperator which rapidly degrade in the gas turbine engine environment.
SUMMARY OF THE INVENTION
The aforesaid problems are solved by the gas turbine engine recuperator of the present invention. The recuperator comprises an annular matrix of cells, each of which comprises a ribbed high pressure plate that is welded to a ribbed low pressure plate. In an exemplary constructed embodiment, the cells are orientated in an annular array having an inside diameter of 10.00 inches, an outside diameter of 16.12 inches, and an overall axial length of 6.30 inches. Both the high and low pressure plates of the cells are formed from, for example, 0.003-inch thick stainless steel sheet material. Ribs are stamped in the plates to a height of, for example, 0.024 inches to define fluid flow channels between the plates.
After welding of a high pressure plate to a low pressure plate to form a cell, the cell is formed to the involute curve having a base circle diameter equal to or somewhat less than the inner diameter of the annular recuperator matrix. Thereafter, the radially inner edges of the cells are welded to one another. The cells are restrained at the radially outer edges thereof, in free floating relation, by an outer shell.
In operation, relatively cold, high pressure air follows a “C” shaped flow path through the recuperator. Initial flow of air is radially outwardly from the engine compressor into a compressed air intake manifold, thence axially through the recuperator matrix, thence radially inwardly through a compressed air exit manifold to the engine combustor.
Low pressure, relatively high temperature exhaust gas flows radially outwardly from the engine turbine, thence axially through the recuperator matrix in counterflow relation to the flow of cold, high pressure combustion air, thence radially outwardly to atmosphere.
The inventive concept underlying the recuperator of the present invention is that each ribbed plate forms a high aspect ratio primary heat transfer element that is in direct contact with both fluids. The ribs control the spacing between the plates of each cell as well as the spacing between adjacent cells. In addition, the ribs accept fluid pressure loads between the counterflow passages. The ribs follow an undulating path arranged so that ribs in adjacent plates prevent nesting. Each low pressure plate has a rib pattern on the exterior thereof that, in combination with the high pressure plate of an adjacent cell, defines a low pressure exhaust gas flow path between the cells.
In accordance with one feature of the invention, spacing of the radially extending ribs on the high pressure plate of each cell varies longitudinally so as to define radially extending channels of different width. The different widths of the radial channels renders flow in each complete passage, namely, two radial channels plus an axial channel, equal at design conditions. Stated in another manner, the longer, radially outer, axially extending channels connect to the wider, radially extending channels thereby equalizing total flow resistance through the recuperator. This equality of flow in the channels at design conditions results in uniform heat transfer from the low pressure, high temperature, exhaust gas to the lower temperature compressed air which, in turn, permits the heat exchanger to more nearly approach its theoretical optimum heat transfer rate.
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Chapman William I.
Williams Samuel B.
Dinnin & Dunn P.C.
Lazarus Ira S.
McKinnon Terrell
Williams International Co. L.L.C.
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