A novel analytical model to determine the heat flux of subcooled pool boiling in fractal nanofluids is developed.The model considers the fractal character of nanofluids in terms of the fractal dimension of nanoparticles and the fractal dimension of active cavities on the heated surfaces;it also takes into account the effect of the Brownian motion of nanoparticles,which has no empirical constant but has parameters with physical meanings.The proposed model is expressed as a function of the subcooling of fluids and the wall superheat.The fractal analytical model is verified by a reasonable agreement with the experimental data and the results obtained from existing models.
Analytical expressions for nucleate pool boiling heat transfer of nanofluid in the critical heat flux (CHF) region are derived taking into account the effect of nanoparticles moving in liquid based on the fractal geometry theory. The proposed fractal model for the CHF of nanofluid is explicitly related to the average diameter of the nanoparticles, the volumetric nanoparticle concentration, the thermal conductivity of nanoparticles, the fractal dimension of nanoparticles, the fractal dimension of active cavities on the heated surfaces, the temperature, and the properties of the fluid. It is found that the CHF of nanofluid decreases with the increase of the average diameter of nanoparticles. Each parameter of the proposed formulas on CHF has a clear physical meaning. The model predictions are compared with the existing experimental data, and a good agreement between the model predictions and experimental data is found. The validity of the present model is thus verified. The proposed fractal model can reveal the mechanism of heat transfer in nanofluid.
