We are measuring the viscosity and nonlinear viscosity of simple fluids near their critical points. One usually applies these rheological concepts only to complex fluids such as polymer melts. However, as demonstrated in our 1997 Space Shuttle experiment, viscoelasticity appears near the critical point of a fluid as simple as xenon. A possible project is collaboration on a second microgravity experiment being prepared to measure shear thinning near xenon's critical point. Other projects include measuring the effects of frequency, shear-rate, or finite size on the viscosity near the critical consolute point of a binary liquid mixture.
Additional opportunities are available in the following areas.
We are studying fundamental aspects nucleate boiling, using a versatile, automated apparatus to measure the heat transfer from surfaces with single, well-characterized nucleation sites, and from surfaces with arrays of such sites. In addition to probes measuring pressure and substrate, liquid, and vapor temperatures, this apparatus has windows which enable us to observe bubble growth and interaction, and to perform optical measurements of composition changes. When modeling these results, we examine the interaction of the heat of evaporation, wetting, and heat transport with flows driven by surface tension and buoyancy. A valuable resource is the Division's expertise in determining the thermophysical properties of the test fluids. We expect that the results will advance the understanding of the ultimate performance limits of enhanced heat transfer surfaces.