Speaker
Description
Cryogenic Systems require a highly efficient insulation so as to limit the heat ingress and boil-off, which is generally achieved through the use of vacuum combined with an insulated media. The performance of two families of vacuum insulated technologies, Multi layer Insulation (MLI) and Microspheres (MS), will be investigated with detailed thermal models developed to account for all the heat transfer contributions, solid conduction, gaseous conduction and radiation. Results are presented for an usual cold vacuum pressure (CVP) corresponding to high vacuum (<10-6 mbar) and compared with available experimental measurements for state of the art technologies. The nominal thermal performances are then evaluated for a cold temperature of 20K (representative of liquid hydrogen storage temperature), for a degraded CVP with hydrogen and air as residual gases and for increased hot boundary temperatures. A sensitivity of the thermal performance is also presented with a pressure gradient through the insulation thickness, induced by cryopumping and materials outgassing. Finally, other parameters are also discussed such as, for MLI family, the number of layers, material, layers density, venting options, assembly process and material optical properties; and for MS family, the density, the mean particle size, their properties and distribution.
