Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
2002-09-13
2004-12-28
Doerrler, William C. (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S903000, C165S133000
Reexamination Certificate
active
06834515
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to plate-fin exchangers having textured surfaces and to methods for assembling such plate-fin exchangers. The plate-fin exchangers having fins with textured surfaces according to the present invention have particular application in cryogenic processes such as air separation, although these plate-fin exchangers also may be used in other heat and/or mass transfer processes.
Plate-fin exchangers are generally used for exchanging heat between process streams for the purpose of heating, cooling, boiling, evaporating, or condensing the streams. In this case they may be referred to more particularly as plate-fin heat exchangers. The process conditions in these heat exchangers may involve single phase or two phase heat transfer, wherein the fluid streams flow in a generally upward direction or in a generally downward direction (although the flows may also be in other directions). But in some cases the process streams include mixtures of components so that mass transfer separation also is carried out in addition to heat transfer. In the latter case, vapor and liquid flow in countercurrent directions within a stream passage and the heat/mass exchanger may be referred to as a dephlegmator.
It is known from the prior art that there are several ways to enhance the performance of heat exchangers. See, for example, D. A. Reay, “Heat transfer enhancement—review of techniques and their possible impact on energy efficiency in the UK,” Heat Recovery System & CHP vol. 11, No. 1, p. 1-40, 1991; Some of the techniques known in the prior art include:
the surfaces of some heat exchangers can be roughened to improve the heat transfer performance in single phase flow by promoting turbulence in the boundary layer;
the surfaces of some heat exchangers can be treated with special coatings or modified geometrically to create reentrant cavities which can improve the performance in nucleate boiling;
the surfaces of some heat exchangers can be treated or modified geometrically in order to alter wetting by liquids which can improve the performance by promoting drop-wise condensation or facilitating drainage of the condensate; and
while all of the above techniques are applicable to plate-fin heat exchangers, their performance is most readily improved by the use of perforated, serrated or wavy fins which increase the turbulence relative to plain fins.
However, as persons skilled in the art will recognize, each of the prior art techniques are limited in one or more ways. For example, the improvements obtainable may be limited to single flow applications, to a narrow range of flow and operating conditions, or to a single mode, such as condensation.
An example of the surfaces of a plate-fin heat exchanger being modified is disclosed in U.S. Pat. No. 4,434,842 (Gregory). In this heat exchanger, fins in the boiling regions are made of at least two layers, with at least one of the outer layers having a plurality of holes therein. The corrugated sheets of the fins are in close proximity one to the other such that nucleation of bubbles occurs between the sheets and the bubbles are released by the holes in the sheets.
Although Applicants are not aware of any prior art plate-fin heat exchangers in which the fins have a surface texture in the form of grooves or fluting (such as that used in the present invention), such surface texture has been used on other types of heat exchangers (e.g., shell and tube exchangers) to create or enhance turbulence and improve heat transfer. For example, see U.S. Pat. Nos. 4,434,842; 6,012,514; and 5,966,809. However, in addition to the fact that those patents do not pertain to plate-fin heat exchangers, the teachings of those patents are not pertinent to the teachings of the present invention.
In the field of contact processes which use structured packing, it is well known that surface texture in the form of fluting or grooves can improve mass transfer efficiency, as taught in U.S. Pat. No. 4,296,050. See also U.S. Pat. Nos. 5,730,000 and 5,876,638. These patents teach the use of a bidirectional surface texture in the form of fine grooves applied in patches on the surface of corrugated plates of a packing element such that the texture is substantially horizontal in some regions and substantially vertical in other regions. But this improvement is based on the experience in a specific operating mode, namely downwardly flowing liquid film undergoing mass transfer against vapor which flows upward in a direction countercurrent to the liquid flow. The present invention has a much broader scope and range of applications than that. Also, the overall geometry and flow characteristics within a plate-fin exchanger are very different from those of a structured packing even for generally similar operating modes.
It is desired to increase the efficiency and improve the performance of plate-fin exchangers.
It is further desired to improve the wetting characteristics of a downwardly flowing vapor-liquid stream within the passages of a plate-fin exchanger in order to improve the heat transfer efficiency.
It is still further desired to improve the flow characteristics of an upwardly flowing vapor-liquid stream within the passages of a plate-fin exchanger in order to improve the heat transfer efficiency.
It is still further desired to improve the turbulence characteristics of a single phase stream within the passages of a plate-fin exchanger in order to improve the heat transfer efficiency.
It is still further desired to improve the turbulence characteristics within the flow passages of a counter-current dephlegmator in order to improve the mass transfer efficiency relative to a conventional plate-fin exchanger employed under similar operating conditions.
It is still further desired to improve the wetting characteristics of a downwardly flowing vapor-liquid stream within the passages of a plate-fin exchanger such that the tendency to precipitate out any dissolved components is minimized.
It is still further desired to have a plate-fin exchanger or dephlegmator that shows high performance characteristics for cryogenic applications, such as those used in air separation, and for other heat and/or mass transfer applications.
It is still further desired to have a plate-fin exchanger which overcomes many of the difficulties and disadvantages of the prior art to provide better and more advantageous results.
It is still further desired to have a more efficient air separation process utilizing a plate-fin exchanger or downflow reboiler which is more compact and/or more efficient than the prior art.
It is still further desired to have a plate-fin exchanger design which minimizes the size, weight and/or cost of downflow reboilers, which would result in an air separation process more efficient and/or less expensive per unit quantity of product produced.
It also is further desired to have a method for assembling a plate-fin exchanger or a downflow reboiler which uses fins having a surface texture thereon which affords better performance than the prior art, and which also overcomes many of the difficulties and disadvantages of the prior art to provide better and more advantageous results.
BRIEF SUMMARY OF THE INVENTION
The present invention is a plate-fin exchanger having textured surfaces. The invention also provides a method for assembling such a plate-fin exchanger, and a method for improving the performance of a plate-fin exchanger. The “textured surface” used in the present invention to obtain a “surface texture” is in the form of grooves or fluting formed on or applied to the surface of the fin material used in the plate-fin exchanger.
A first embodiment of the invention is a plate-fin exchanger having a plurality of fins disposed between neighboring parting sheets, at least a portion of at least one of the fins having a textured surface.
A second embodiment is a plate-fin exchanger comprising an assembly of a plurality of substantially parallel parting sheets and a plurality of corrugated fins disposed between adjacent parting sheets, each of the fins having
Houghton Patrick Alan
Kuznetsov Vladimir Vasilievich
Sunder Swaminathan
Air Products and Chemicals Inc.
Doerrler William C.
Jones II Willard
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