AN INVESTIGATION OF POOL BOILING CHF FOR CYLINDRICAL HEATERS: HYDRODYNAMIC INSTABILITIES AND MODES OF HEAT DISSIPATION

摘要

An experimental study is performed to investigate the critical heat flux (CHF) of wires in various thermodynamic states of FC-72. It is well known that the system temperature greatly affects nucleate boiling performance as well as CHF. When the system temperature is below saturation for a given system pressure, the thermodynamic state is either pure-subcooled or gas-saturated depending on the dissolved gas concentration within the liquid. The effects on CHF are investigated parametrically as a function of length scale, subcooling, and dissolved gas content. Taylor and Helmholtz instabilities, which contribute to the occurrence of the hydrodynamic CHF mechanism, are investigated using photographic observations and experimental CHF data. A correlation is proposed which predicts Taylor wavelength at CHF for cylindrical heaters. In addition, to provide insight into the differences between pure-subcooling and gas-saturation, three modes of heat dissipation at CHF are identified and compared versus length scale and level of subcooling.