Assessment of nanofluids pool boiling critical heat flux

Abstract

Despite contradiction in nucleate pool boiling heat transfer coefficient of nanofluids, the enhancement in critical heat flux (CHF) has been widely approved. This study is dedicated to the assessment of pool boiling CHF of the nanofluids. The assessment is based on a new consolidated CHF database consisting of 431 data points amassed from 62 sources, and includes 14 nanoparticle materials and 4 base fluids, pressures from 3 to 1100 kPa, orientation angles from 0 to 150°, and covering a variety of particle concentrations. It is shown that the maximum CHF ratio of nanofluid to base fluid can achieve 4 and 4.6 for upward-facing heater and inclined heater, respectively. The heater type (wire or block) has an important effect on CHF, as the direct electric-heating wire heater causes electrophoresis, accelerating nanoparticle deposition. The CHF ratio is reduced with increasing pressure in the present range, but nanoparticle size has a minor effect on it, which is more determined by the dispersion level of particles in base fluid. Two major mechanisms, including improved wettability and enhanced capillary wicking caused by nanoparticle deposition, are responsible for the enhancement of CHF, latter of which warrants more theoretical studies in the future.