Fundamental Research on High Heat Flux Cooling of Future Energy Systems -Heat Removal Limits

Abstract

 The sound development of knowledge for generalized saturated and subcooled pool boiling critical heat flux (CHF) mechanisms and corresponding correlations for various test heater configurations and surface conditions in water and other wetting liquids are becoming increasingly important as the fundamental database not only for the design such as the high heat flux cooling systems using subcooled water pool boiling, but for the super-conducting magnets cooled by liquid helium and liquid nitrogen, the thermal control of microelectronic assemblies cooled FC liquids for future super-computers. Firstly, the subcooled pool boiling CHF data measured using test horizontal cylinders were investigated to clarify the effect of test cylinder diameters in water and ethanol on the CHF. The CHF data for larger diameter cylinders were clearly divided into two groups for low and high subcooling. The CHF correlations representing the CHF resulting from the hydrodynamic instability (HI), and the heterogeneous spontaneous nucleation (HSN), were derived for the wide ranges of subcooling and pressure including the effect of test cylinder diameter respectively. Secondly, it was observed experimentally that there existed the CHF resulting from HI measured for the same size horizontal cylinders with commercial, rough and mirror surfaces (CS, RS and MS) in a pool of water which agreed with one another independently of the surface conditions at lower pressures for lower subcooling. Thirdly, nonlinear trend of subcooled water flow boiling CHF versus outlet subcooling for flow velocities at outlet pressures in horizontal or vertical tubes with twisted tapes of twist ratios having flowing subcooled water was studied using existing database based on the corresponding correlations extending the new correlations with different mechanisms recently developed for the nonlinear trend of CHF in through tubes with wide ranges of inside diameter, and length-to-diameter ratio for wide ranges of flow velocities, outlet pressure and outlet subcooling.