Semi-Analytical Modeling of Critical Heat Flux in Convective Boiling of Nanofluids

Abstract

Using two-phase flows because of their high thermal conductivity coefficients is favorable in various industries such as oil, petro chemistry, and power plants that require significant thermal conductivity coefficients in heat exchangers. On the other hand, the limiting factor in benefiting from these flows is the critical heat flux phenomenon, the onset of which must be delayed by various means. One of the methods to achieve this goal is using nanofluids. Nanofluids, due to their higher thermal conductivity in comparison with base fluids, have demonstrated the capability to delay the onset of critical heat flux phenomenon. In the present Paper, silver, copper, alumina and nickel water-based nanofluidic flows in heat exchangers are analytically studied, and the critical heat flux is assessed under different mass flux and volume fraction conditions. Reports of Look Up Table are employed for calculation of critical heat flux in the present Paper. All four mechanisms of mass transfer are simulated, and pressure variations in both dimensions are considered. Effects of mass transfer on vapor core pressure are comprehensively assessed. The results obtained indicate a directly proportional relation between mass velocity and critical heat flux. In addition, increasing the concentration of nanoparticles also increases the critical heat flux. Of the studied nanofluids, the highest critical heat flux increase was observed for a 5 vol % water–silver nanofluid with a 81.6% increase in the critical heat flux relative to pure water.