Thermal Resistances of Stacks of Thin Layers under Compression

Abstract

Stacks, each comprising a number of thin, ‘flat’ layers of tin-coated steel, were compressed in a direction normal to the individual layers under loadings of up to 8 times 10⁶Nm^-2. Two distinct modes of deformation occurred: a layer-flattening region at low loads (P/M < 10^-3), and a surface-waviness deformation region under higher loading pressures. The thermal resistance per unit area per unit length of each stack (in a vacuum of better than 7 times 10^-2Nm^-2) was inversely proportional to the compression per layer for freshly-assembled stacks throughout the loading region corresponding to macroscopic conformity. Hystereses in the thermal resistance and compression characteristics were observed during the initial loading/unloading cycles. A dimensionless correlation relating conductance to applied loading is proposed for stacks of bedded-down thin layers.