Experimental investigation of critical heat flux of nucleate pool boiling of water and nanofluid on platinum wire under hypergravity and Earth gravity

Abstract

The experimental investigation of the critical heat flux (CHF) of saturated nucleate pool boiling of pure water and water-based Al2O3 nanofluids on the platinum wire with a diameter of 50 µm was conducted under earth gravity and hypergravity. The gravity level ranges from 1 to 3 g, the saturation pressures range from 0.1 to 0.6 MPa, and the Al2O3 concentrations in the nanofluids ranges from 0.001wt% to 0.015wt%. The experimental results show that both pressure and gravity are vital factors enhancing the CHF, with the effect of pressure more pronounced. The mechanisms of CHF enhancement due to pressure increasing is that increasing pressure changes the fluid properties, yielding the synthetical results of activating more nucleate sites and increasing the bubble departure frequency. The reasons for the CHF enhancement by hypergravity may mainly be that the buoyancy force increases with increasing gravity levels, which makes the bubbles more likely to be removed from the surface, and that the formation of large vapor patches covering the heating wire gets harder. Besides, a nanofluid has a stronger enhancement to the pool boiling CHF than the combination of the heating surface coated with the same kind of nanoparticles and the base fluid. The reason may be that the latter mainly relies on the heater surface modification, while the former relies on the nanoparticle suspension in the nanofluid and the interaction between the nanoparticle deposition and the nanoparticle suspension, plus the heater surface modification.