An Experimental Investigation of the Boiling Performance of Water-Based Nanofluids

The addition of nanoparticles modifies various thermophysical properties of water such as the thermal conductivity, viscosity and the surface tension. The present work experimentally investigates the influence of the addition of nanoparticles on the boiling performance of water. The effects of the volume fraction of the nanoparticles, the sonication time used in nanofluid preparation by ultrasonic shaking, and the time allowed for sedimentation after preparation, on the boiling performance, have been investigated. The nanofluids used in the present study are stabilized suspensions of aluminum oxide and copper oxide of size ranging from 30 to 40 nm in water. The boiling curve was plotted for the base fluid and the nanofluids using a suitable experimental set up by means of a power-controlled experimentation. Comparison of experimental results with pure water indicated a considerable increase in the burn out heat flux in the nanofluids, and also gave the variation of the burn out heat flux with respect to the volume fraction of nanoparticles in the suspension. For all volume fractions of nanoparticles, the heat transfer coefficients in the natural convection and the nucleate boiling regimes were observed to be lower than in pure water, which implies a reduction in the boiling performance. A slight increase in the boiling point of water was observed with the addition of nanoparticles. The burn out heat flux was found to increase with the agitation time in preparing the nanofluids, but this enhancement decreased on sedimentation of nanoparticles. Experiments were conducted using heating elements of different thicknesses, and the effect of the heater size on the burn out heat flux was found to be diminishing in the nanofluids, with an increasing particle concentration.