THE INFLUENCE OF RAPID TRANSIENT HEATING IN CRITICAL HEAT FLUX OF BOILING HEAT TRANSFER

The critical heat flux of fast transient boiling impacts the safety assessment of nuclear reactor designs. This paper conducted a series of experiments to explore the critical heat flux of saturated water boiling at different heating rates on a platinum wire. The wire is placed in a glass box surrounded by deionized water at saturation temperature. The diameter of wire is 126 mu m, and a constant voltage power supply is used. Data is collected at 250k sample/s. A high-speed camera with 50,000 fps is used to record boiling video. Eight tests are presented with 2 steady boiling experiments and 6 transient boiling experiments. In steady boiling experiments, both the wire temperature and heat flux to the water increase until they reach a steady point. In the transient boiling experiments, the wire temperature keeps increasing. But the heat flux reaches a peak first, a critical heat flux; then it goes down to a certain value before the power is shut off. The higher the wire heating rate, the larger the critical heat flux peak will be. The mechanism of the critical heat flux peak relates to bubble formation, propagation, and coalescence, and is discussed based on the high-speed camera images. This initial research in transient boiling paved the way for further experiments with subcooling at prototypical temperature and pressure conditions in a nuclear pressured water reactor.