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/m**2 with no MLI and 0. 64 W/m**2 with 30 layers, both at a vacuum of 1. 5 multiplied by 10** minus **5 torr. The corresponding values to a taped surface were 4. 8 W/m**2 and 0. 52 W/m**2. At 1. 5 multiplied by 10** minus **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 multiplied by 10** minus **5 torr to approximately 1 multiplied by 10** minus **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.