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 po ol boiling experiments with controlled steady-state and transient wall temp erature up to 50 K/s is presented. Throughout all phases of the described a pproach, the requirements on the experimental infrastructure for reproducib le 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 fluori nert FC-72. The liquid boiled on top of a horizontally positioned copper he ater with a diameter of 18.2 and 5 mm thickness. Temperature measurements b y sheathed thermocouples, implanted inside the heater, are used to obtain t ransient boiling curves by solving a one-dimensional inverse heat conductio n problem (IHCP). At the same wall superheat boiling heat flux increases wh en transient heating rates are increased. This is the case in all boiling r egimes. Transient cooling leads to lower transferred heat fluxes. Very clos e to the boiling surface, temperature fluctuations as a result of evaporati on are measured by six microthermocouples. Analysis of the data shows that there seems to be no distinct difference in the fluctuations with respect t o steady-state and transient runs. (C) 2001 Elsevier Science Ltd. All right s reserved.