Abstract

The understanding of transient heat transfer into a confined compressible fluid is of considerable value in engine design, nuclear power plant development, and chemical engineering. Interest centers on the thermal profile, particularly as fluid expansivity and compressibility increase while approaching the critical point. Computer models which simulate this phenomena have been developed by NBS and need experimental testing. However, traditional measurement methods are indirect, while optical methods are direct, nonintru- sive, and rapid. Unfortunately, the extreme conditions of transient heat transfer and near critical conditions in the fluid boundary layer induce substantial changes in refractive indices, causing optical beam disturbances large enough to render standard phase measurements nearly useless. Even refractive techniques are difficult to apply. However, the application of holographic microscopy makes it feasible to introduce a diffusive sample beam, minimizing refractive errors. It thereby proved possible to thermally map the upper three- quarters of a boundary layer which was only a few tenths of a millimeter thick with 1-ms time resolution. In the remaining lower layer fringe packing was so extreme as to make resolution at visible wavelengths impossible.

© 1986 Optical Society of America