Model-based experimental analysis of pool boiling heat transfer with controlled wall temperature transients

A model-based approach for design, control, operation, and evaluation of pool boiling experiments with controlled steady-state and transient wall temperature up to 50 K/s is presented. Throughout all phases of the described approach, the requirements on the experimental infrastructure for reproducible boiling experiments are addressed by the integration of theoretical and experimental investigations. In the early design phase, these are concerned with the heater design as well as the development and the optimization, of a control concept. Systematic experiments were carried out with the fluorinert FC-72. The liquid boiled on top of a horizontally positioned copper heater with a diameter of 18.2 and 5 mm thickness. Temperature measurements by sheathed thermocouples, implanted inside the heater, are used to obtain transient boiling curves by solving a one-dimensional inverse heat conduction problem (IHCP). At the same wall superheat boiling heat flux increases when transient heating rates are increased. This is the case in all boiling regimes. Transient cooling leads to lower transferred heat fluxes. Very close to the boiling surface, temperature fluctuations as a result of evaporation are measured by six microthermocouples. Analysis of the data shows that there seems to be no distinct difference in the fluctuations with respect to steady-state and transient runs. (C) 2001 Elsevier Science Ltd. All rights reserved.