Controlled transient pool boiling experiments - methodology and results

A new approach to the measurement of transient heat transfer under pool boiling conditions is presented. An experimental apparatus was designed to measure heat transfer under steady-state conditions and with controlled temperature transients. The entire boiling curve was measured for the Fluorinert FC-72 on a horizontal copper heater. Experiments with heating transients of up to 10 K/s were performed while cooling transients were limited by the thermal inertia of the heater. The control system showed good performance in controlling the wall temperature along the entire boiling curve both in steady-state and transient experiments. Two schemes for the solution of the Inverse Heat Conduction Problem arising from the evaluation of transient heat transfer experiments were implemented and compared with respect to estimation quality and computational requirements. Regularization was chosen as the algorithm for data evaluation. First results show that the critical heat flux rises significantly for fast heating transients (#propor to#10 K/s) and drops significantly even for moderate cooling transients (#propor to#2 K/s). In film boiling, the heat flux rises with increasing heating transients while no difference was measured for the slow cooling transients. (orig.)SIGLEAvailable from TIB Hannover: RR 8872(1996,12) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman