Heat exchange – Regenerator – Movable heat storage mass with enclosure
Reissue Patent
1995-03-23
2001-04-17
Atkinson, Christopher (Department: 3743)
Heat exchange
Regenerator
Movable heat storage mass with enclosure
C165S010000, C165S008000
Reissue Patent
active
RE037134
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to regenerative heat exchangers.
BACKGROUND OF THE INVENTION
Heat exchangers are devices used to transfer heat between a hot fluid stream and a cold fluid stream. In conventional heat exchangers the heat is transferred from one stream to another through a wall and the heat transfer is limited by the conductivity of the material of which the wall is made.
Regenerative heat exchangers typically are capable of achieving higher heating temperatures. Regenerative heat exchangers expose a heat-absorbing mass or matrix alternately to a hot stream and to a cold stream. In general, therefore, regenerative heat exchangers have periodic flow.
Periodic-flow exchangers operate differently from conventional fixed-surface heat exchangers in that heat is transferred from the hot fluid to the cold fluid by alternatively heating and cooling a high surface area matrix material. This matrix or core is either rotated through or shuttled back and forth between the hot and cold fluid streams of the fluid streams are switched between or among two or more stationary matrices. One type of periodic flow regenerative heat exchanger is the rotary regenerative heat exchanger in which a heat-absorbing matrix is rotated relative to streams of hot and cold fluids. The matrix generally comprises a disk or drum-shaped body having a plurality of internal passageways oriented axially. The fluid streams flow through these passageways alternately heating the matrix body or extracting heat therefrom. Such rotary heat exchangers are particularly useful as air preheaters in boiler plants and in gas turbine engines. Seals are provided that either have rubbing contact or maintain a very small gap with the matrix and serve to separate the hot and cold streams thereby reducing leakage losses that occur between the hot and cold fluid streams.
Rotary regenerators have advantages that make them well suited for gas-turbine engines. One of these advantages is compactness. In laminar flow of the fluid streams, the volume needed for a given quantity of heat to be transferred is proportional to the square of the hydraulic diameter of the passage used (Wilson,
The Design of High Efficiency Turbomachinery and Gas Turbines,
MIT Press, Cambridge, Mass., 1984). The passages in rotary regenerators for gas-turbine applications can be made much smaller than those of conventional tubular or plate fin type heat exchangers. In tubular or plate fin type heat exchangers, problems can be encountered if the passages are small because deposits from the hot and cold fluids can accumulate and block the small passages. This problem is alleviated or reduced in rotary regenerators because the fluid streams alternate and reverse flow direction in each passage, thereby removing deposits and reducing blockage. In addition, because hot and cold-stream separation is controlled by the seals rather than by complex ducts that are required in recuperators, the cost of making many small passages is low.
Another desirable feature of rotary and other regenerators is low pressure drop. The pumping power required to force gas through a heat exchanger is directly proportional to the square of the Mach number and is rather independent of matrix geometry (Wilson, 1984, cited supra. Therefore, large face areas must be used to minimize fluid velocity. In the rotary and other regenerators, elaborate manifold schemes to interleave the fluids are unnecessary, so a large flow area is practical. In contrast, with fixed surface heat exchangers, achieving both compactness and large, interleaved flow areas simultaneously is more difficult.
A problem encountered with conventional rotary regenerators is leakage of fluid from the exchanger which decreases its efficiency. Leakage occurs either through the seals that separate the high and low-pressure chambers or through void-volume carryover. Void volume carryover occurs because hot high pressure fluid trapped in the matrix is carried through the seals during rotation of the matrix to the cool, low pressure side. This leakage, although relatively small, worsens as the speed of rotation of the matrix increases.
SUMMARY OF THE INVENTION
According to the invention the seal leakage rate of a heat exchanger is reduced by discontinuously moving either the matrix or ducting while releasably isolating portions of the matrix with sealing members. In one embodiment of the invention a regenerative heat exchanger for transferring heat between a hot fluid stream and a cold fluid stream has a matrix defining a first group of passageways for fluid to flow therethrough. A seal means is provided capable of releasably sealing the matrix so that said passageways are interconnected with one of said hot or said cold fluid stream. Means are provided for causing discontinuous movement of the matrix relative to said hot or cold fluid streams and relative to the seal means, and the seal means seals only when said matrix is stationary with respect to said seal means.
Preferably the matrix is a rotary disc. In some cases the means can be formed of two portions comprising modules which are each exposed to hot and cold fluid flows and then exchanged to transfer heat from one flow to the other.
According to a method of this invention heat is transferred between a hot fluid and a cold fluid by establishing a hot fluid stream and a cold fluid stream. A matrix having portions thereof carrying means for exchanging heat with the hot and cold fluid streams is positioned so as to have at least one of said streams exchange heat therewith. The matrix is discontinuously moved in preselected increments such that matrix portions alternately contact the hot fluid and cold fluid streams and carry heat between the hot fluid stream and the cold fluid stream. The matrix is contacted with a seal for at least one of said hot or cold fluid streams when the matrix is stationary with respect to the one stream thereby creating a substantially leakproof area. The seal is released from the matrix when the matrix is moved with respect to the one stream.
Generally, the invention provides an improvement in a method of exchanging heat between a hot fluid stream and a cold fluid stream in a regenerative heat exchanger having a matrix with first and second passageways for said hot and cold fluid streams respectively and said heat exchanger having sealing means to seal said hot and cold streams from each other. The improvement comprises sealing the hot and cold fluid streams from each other to prevent mixing of said fluids when the matrix is stationary with respect to the position of the fluid streams and releasing the seal and moving the matrix with respect to the position of said fluid streams to exchange heat through said matrix.
It is a feature of this invention that the sealing of the matrix during the stationary phase reduces the amount of fluid leaking from one side of the seal to the other which significantly reduces the seal leakage rate.
It is an object of this invention to provide a regenerative heat exchanger that shares the benefits of conventional rotary heat exchangers while significantly reducing the leakage rate of such conventional rotary heat exchangers.
It is another object of this invention to provide a rotary heat exchanger having a matrix capable of discontinuous movement.
It is another object of this invention to provide a modular heat exchanger having matrix modules capable of discontinuous movement.
It is another object of this invention to provide a rotary heat exchanger that shares the benefits of conventional rotary heat exchangers while significantly reducing the leakage rate thereby.
It is another object to provide heat exchangers useful in gas-turbine engines.
It is yet another object to provide heat exchangers that can be integrated within the ducting of systems presently using conventional-type rotary exchangers.
It is still another object of this invention to provide a method of exchanging heat between hot and cold fluid streams by sealing said streams when a heat exchange matrix is stationary with respect
Atkinson Christopher
Cantor & Colburn LLP
Massachusetts Institute of Technology
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