Transient heat transfer from smooth surfaces into liquid nitrogen

A hot-strip technique was used to examine transient heat transfer from different smooth surfaces into liquid nitrogen. In this way the temperature of a surface subjected to a heat pulse was measured. In addition, optical methods were used to observe bubble formation and growth. The onset of nucleate boiling, temperature development and critical heat flux were investigated under transient conditions. It was observed that the temperature development and critical heat flux are significantly influenced by the type of surface material. The critical heat flux, which characterizes the transition to film boiling, varied between 10 W cm(-2) for nickel surfaces and 18 W cm(-2) for varnish surfaces. Furthermore, the impact of surface orientation and preheating flux on the transient heat transfer into liquid nitrogen was investigated experimentally. Whereas the former is distinct, the latter turned out to be smaller than expected.