Optimal Thermal Design of Helium Dewar with Liquid Nitrogen and Vaporized Helium Cooled Intercepts

Abstract

An optimal thermal design method for helium dewars with liquid nitrogen and vaporized helium cooled heat intercepts is presented. The method minimizes total refrigeration power required for the nitrogen and helium liquefiers by optimizing the liquid nitrogen and vaporized helium cooled intercepts both in superinsulation and on supports. The optimization method is based on the Lagrange multipliers method and the simultaneous equations are solved numerically. Results are calculated for superinsulated helium dewars with stainless steel 304 and epoxy-fiberglass G-10CR supports, respectively. The optimized intercept locations in superinsulation and on supports as well as required refrigeration power are graphed and normalized for different η _N /η _He and α= (A _I L _S )/(A _S L _I ). The technique described provides a convenient way to optimize design of helium dewars.