ISSN Online: 2377-424X
International Heat Transfer Conference 12
Thermodynamic optimization of insulation systems with a finite number of heat intercepts in cryogenic applications
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.