Effective thermal conductivity parallel to the laminations, and total conductance of multilayer insulation.

Abstract

Multilayer, aluminized-plastic-foil insulation systems are highly anisotropic, and there has been a lack of data on heat-transfer characteristics parallel to the laminations. This paper describes experimental techniques and presents data for parallel heat flux and for combined parallel and normal heat flux. Except for one sample with fiberglass spacer material between foil layers, the samples were without spacer material and, being uncrinkled, had very high layer densities compared with normal usage. Results show that calculations (based on the energy transport characteristics of the bulk materials) that do not consider radiation leakage between layers could lead to underestimati ons by a factor greater than 3 in many cases. Measurements were made using steady-state calorimetric techniques and small samples. The effective thermal conductivity parallel to the laminations, based on aluminum-film crosssectional area, increased with gap width and sample length. Exposure of the sample's external surface to blackbody radiation at hot-end temperatures increased the total heat transfer very little.