An Experimental Study of Heat Transfer in Multilayer Insulation Systems from Room Temperature to 77 K

Abstract

The total heat transfer from approximately to 77 K was experimentally studied for a series of different arrangements of multilayer insulation (MLI) on black painted and aluminum taped copper surfaces. The heat flux as a function of the number of MLI layers and of the overall vacuum level was measured. The flux to a painted surface was 24.7 W/m² with no MLI and 0.64 W/m² with 30 layers, both at a vacuum of 1.5 × 10⁻⁵ torr. The corresponding values to a taped surface were 4.8 W/m² and 0.52 W/m². At 1.5 × 10⁻⁵ torr, the use of aluminum tape permits one to use approximately one-half as many layers for the same heat flux. The heat flux was measured for six insulation systems from 1.5 x 10⁻⁵ torr to ∿ 1 × 10⁻³ torr. The temperature distribution through the MLI was measured as a function of vacuum level. It was deduced that the apparent thermal conductivity increases with the distance from the cold surface. The effect of cracks in a paint-MLI system was studied by cutting 6-mm wide cracks through a 90-layer blanket. The heat load increased by more than three times the value calculated from the exposed area only.

Work sponsored by Universities Research Association under contract with U.S. Department of Energy