Revisit On The Scaling Of The Critical Heat Flux On Cylinders

Critical heat flux (CHF) is an important topic in the field of boiling. The hydrodynamic theory of CHF proposed by Professor S. S. Kutateladze is one of the great scientific heritages. Progress on this topic has been made for more than a half-century. Recently, however, the commonly accepted figure on CHF scaling, which is built on experimental data obtained in normal gravity, has received strong challenges from microgravity research. It has been found that CHF on cylinders in microgravity shows the same trend as that predicted by the commonly accepted Lienhard-Dhir-Zuber correlation, although the dimensionless radius is extended to over two orders of magnitude of the correlation's original lower value. The present paper revisits CHF scaling on cylinders, particularly on small cylinders with very small Bond numbers. A new series of experimental data on CHF on small cylinders in normal gravity is presented and discussed. Platinum wires of 30 mm in length are simultaneously used as heaters and thermometers. Their diameters are 100, 60, and 25 mu m, respectively. Degassed FC-72 and acetone are used as the working fluids, and the range of subcooling is 0 K to approximately 50 K. Different CHF scaling behaviors at saturated pool boiling are observed for the two fluids. It is very evident that cylinder diameter, as well as material parameters, has an influence on the dependence of CHF on subcooling in the case of small cylinder diameters. Thus, taking into consideration the observation of CHF on cylinders in microgravity, it is conjectured that some other parameters in addition to the Bond number, play important roles in CHF with small Bond numbers.