EXPERIMENTAL MEASUREMENT OF THE INTERFACE HEAT CONDUCTANCE BETWEEN NONCONFORMING BERYLLIUM AND TYPE 316 STAINLESS STEEL SURFACES SUBJECTED TO NONUNIFORM THERMAL DEFORMATIONS

In fusion blanket designs that employ beryllium as a neutron multiplier, the interface conductance h plays a key role in evaluating the blanket’s thermal profile. There-fore, an extensive experimental program was conducted to measure the magnitude of h between nonconforming beryllium and Type 316 stainless steel surfaces sub-jected to nonuniform thermal deformations. The mag-nitude of h was measured as a function of relevant environmental, surface, and geometric parameters, in-cluding surface roughness, contact pressure, gas pres-sure, gas type, and magnitude and direction of heat flow. The results indicate the following: (a) Decreasing the in-terfacial surface roughness from 6.28 to 0.28 mm, in 760 Torr of helium, increased the magnitude of h by up to 100%; however, increasing the surface roughness reduced the dependence of h on the magnitude of the contact pressure. (b) The interface conductance was sig-nificantly higher for measurements made in helium gas as opposed to air. Additionally, the sensitivity of h to the gas pressure was significantly greater for runs con-ducted in helium and/or with smoother surfaces. This sensitivity was reduced in air and/or with roughened surfaces, and it was essentially nonexistent for the 6.25-mm specimen for air pressures exceeding 76 Torr. (c) For runs conducted in vacuum, the interface con-ductance was more sensitive to heat flux than when runs were conducted in 760 Torr of helium. (d) The interface conductance was found to be dependent on the direc-tion of heat flux. When the specimens were arranged so that heat flowed from the steel to the beryllium disk, the magnitude of h was generally greater than in the oppo-site direction. I