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, th e interface conductance h plays a key role in evaluating the blanket's ther mal profile. Therefore, an extensive experimental program was conducted to measure the magnitude of h between nonconforming beryllium and Type 316 sta inless steel surfaces subjected to nonuniform thermal deformations. The mag nitude of h was measured as a function of relevant environmental, surface, and geometric parameters, including surface roughness, contact pressure, ga s pressure, gas type, and magnitude and direction of heat flow. The results indicate the following: (a) Decreasing the interfacial surface roughness f rom 6.28 to 0.28 mum, in 760 Torr of helium, increased the magnitude of h b y up to 100%; however, increasing the surface roughness reduced the depende nce of h on the magnitude of the contact pressure. (b) The interface conduc tance was significantly higher for measurements made in helium gas as oppos ed to air Additionally, the sensitivity of h to the gas pressure was signif icantly greater for runs conducted 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-mum specimen for air pressures ex ceeding 76 Torr. (c) For runs conducted in vacuum, the interface conductanc e 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 direction of heat flux. When the specimens were arranged so that heat flowe d from the steel to the beryllium disk, the magnitude of h was generally gr eater than in the opposite direction.