A Theoretical Model to Predict Pool Boiling Critical Heat Flux for Micro/Nano-Structured Surfaces

Abstract

Accurate estimation of critical heat flux (CHF) is essential in determining the maximum heat a boiling system is capable of extracting. This study presents a theoretical model for predicting CHF over microchannel, unidirectionally roughened, and coated surfaces. The researchers started developing theoretical models on this phenomenon considering the hydrodynamic instability. However, effects of parameters like capillarity, wettability, wicking ability, and surface geometry have been considered in the theoretical models developed in recent years. In the present work, a theoretical model has been developed to predict the CHF for pool boiling applications by combining these factors. The capillary effect causes the liquid microlayer beneath the evaporating bubble to occupy the dry spot and thus delay CHF. Hence, in this model, the capillary force has been added along with the momentum, hydrostatic, and surface tension forces acting at the liquid–vapor interface on the evaporating vapor bubble. The roughness factor has also been factored in with the contact angle to incorporate the effect of change in contact area of the solid–liquid interface in rough surfaces. The results from the model agree with the results of previously conducted experimental studies with 20% accuracy. The correlation is primarily derived for microchannels and has also been extended to randomly roughened surfaces with micro/nanostructures.