Experimental studies of forced, natural and combined convective heat transfer at cryogenic temperatures

A novel heat transfer technique, the use of cryogenic temperatures for convective modeling, is used in this study to obtain significant increases in the ratios of the square of the density, times the expansion coefficient, to the square of the dynamic viscosity and of the density to the dynamic viscosity in order to obtain simultaneously large Grashof and Reynolds numbers on a vertical cylinder. The research is motivated by the need to predict combined convective losses from large, high-temperature objects such as solar 'power tower' receivers where the magnitudes of both the Grashof and Reynolds numbers are large. The cryogenic heat transfer tunnel provides an economical method of obtaining these large Grashof and Reynolds numbers with an appropriate and near-constant Prandtl number; thus it is an excellent tool for study of convective heat transfer. Low-temperature modeling, a cryogenic testing facility, and a transient measurement technique are discussed.