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Advanced Course in Heat Exchangers: Theory and Practice. ICHMT Symposium.
1981, Dubrovnik, Croatia

DOI: 10.1615/ICHMT.1981.AdvCourseHeatExch


ISBN Print: 978-0-07062-806-9

Heat Exchange Equipment for the Cryogenic Process Industry

pages 469-493
DOI: 10.1615/ICHMT.1981.AdvCourseHeatExch.310
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要約

Chemical processes carried out at low temperature include the separation and liquefaction of oxygen and nitrogen and the separation of olefin products from the cracking of heavy hydrocarbons in ethylene plants. Recovery and upgrading of gases such as carbon monoxide and hydrogen from waste-product streams is also undertaken at low temperature. Recently the liquefaction of natural gas for storage and for the separation of constituents, and also its vaporisation, has become of importance.
The economics of these processes are dominated to a certain extent by the energy requirements of compressors and thermodynamic considerations have emphasised the requirements for very small temperature differences between streams exchanging heat. This had lead to the development of heat exchangers which contain an enormous heat transfer surface area per unit volume, and this is associated with large numbers of flow passages for streams flowing at very low mass-fluxes.
To undertake these special duties, two main types of heat exchanger have evolved and are now widely used: the plate-fin or brazed-aluminium heat exchanger and the wound-coil or Hampson heat exchanger. These are constructed from materials such as aluminium, copper or stainless steel which are mechanically satisfactory at very low temperature. Both exchangers are frequently designed to contain several streams within the one unit. Inside a plate-fin heat exchanger, for example, heat may be exchanged among five or six streams.
There are, therefore, many features in these exchangers which are not normally encountered in industrial practice and these also influence the characteristics of boiling and condensing: the addition of secondary, or finned, heat transfer surfaces in the plate-fin heat exchanger; in the wound-coil exchanger, condensing may take place in upflow in the helically-wound tubes. The considerable number of passages or channels required in these heat exchangers is a result of the large surface area and highlights the importance of uniform distribution, particularly of two phases, of each stream so that thermal performance is not impaired.
In the paper, the heat transfer and flow characteristics of these exchangers, their thermal design and their structural details are described and the published information is reviewed.

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