POOL BOILING & OPTIMIZATION ANALYSIS OF CRITICAL HEAT FLUX BY USING NANOFLUID (A REVIEW)

Nucleate boiling is efficient heat transfer mode using the vaporization of a liquid. However, it is well known that there exists a critical value of the heat flux at which the heat transfer mechanism changes from the highly efficient nucleate boiling to extremely inefficient film boiling. This limiting heat flux is called Critical Heat Flux (CHF). CHF is the condition where the vapor generated by nucleate boiling becomes so large that it prevents the liquid from reaching and rewetting the surface, therefore it is an undesirable phenomenon causing an excessive increase of the temperature in the boiling phenomenon. It is important to enhance the CHF in order to improve the safety margin and economic performance in a thermal system. With the surge of nanofluids as potential candidates for cooling fluids, many studies have been reported on CHF enhancement using nanofluids. Nanofluids are colloidal dispersions of nanoparticle in a base fluid which is water, oil, bio-fluid and ethylene. Such nanofluids have the capability to enhance the CHF significantly about three times. Over the past decade lots of experiments were performed on the nucleate boiling CHF of nanofluids. The objective of this paper is to provide an exhaustive review of these experiments. The effects of six parameters (i.e. Nanoparticle material, size, concentration, heater size and geometry, heater surface orientation) on CHF enhancement in nanofluids are systemically presented. Nanoparticle material which has shorter Rayleigh-Taylor wavelengths when coated on heater surface shows higher CHF enhancement. For nanoparticle size within nano range there is no significant variation in CHF. But comparing particle size within nano and micro range there is enhancement in CHF for particle size in nano range than particle size in micro range. With increasing concentrations CHF enhancement occurs up to certain concentration then CHF enhancement decreases with increase in nanoparticle concentration. There is lack of work which can give the effect of stabilizer on CHF. More work is required in this area. Higher value of CHF found on smaller heater size, also CHF on cylindrical wires is higher than that of the ribbons heaters. CHF values are higher for horizontal heater.CHF decreases as angle of inclination of heater surface increases. Finally, future research needs are identified.