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ISSN Online: 2377-424X

International Heat Transfer Conference 12
August, 18-23, 2002, Grenoble, France

Thermodynamic optimization of insulation systems with a finite number of heat intercepts in cryogenic applications

Get access (open in a dialog) DOI: 10.1615/IHTC12.2840
6 pages

Resumo

Some authors assumed that the second-law efficiency of reversed cryogenic cycles was independent of the minimum temperature of the working fluid. On the contrary Bejan showed, by means of empirical and theoretical arguments, that exergy efficiency values decrease with the minimum working temperature. A way to reduce energy consumption in cryogenic applications is the use of heat intercepts, to change the heat fluxes inside the thermal insulation. The aim of this paper is to study the thermodynamic (second law) optimization of the location and temperature level of multiple heat intercepts, in order to achieve proper variations of the heat transfer rate in a finite number of points across the thermal insulation. The general case of one-dimensional heat transfer in systems consisting of different materials in series is presented and thermodynamic optimization is numerically performed to the specific, technologically relevant, case of the insulation of liquid helium. Results of the numerical calculations are reported for the specific case of liquid helium in plane geometry with one single (nitrogen) heat intercept or a double thermal shield (nitrogen and neon). Suggestion are given on the best locations to be adopted for given working temperatures of the shields, and considerations are made on the extent of performance enhancement achievable in terms of global entropy generation reduction.