A Fractal Analysis Of Boiling Heat Transfer

In this paper, a fractal model for the critical heat flux (CHF) is proposed. The proposed model for the critical heat flux (CHF) is derived based on the fractal distribution of nucleation sites on boiling surfaces. The proposed fractal model for CHF is found to be a function of wall superheat, the contact angle, fractal dimension and physical properties of fluid. No additional/new empirical constant is introduced. The relation between CHF and the number of active nucleation sites is obtained from the fractal distribution of active nucleation sites on boiling surfaces. It is found that the contact angle and the physical properties of fluid have the important effects on CHF. The predicted CHF from a boiling surface based on the proposed fractal model is compared with the existing experimental data. An excellent agreement between the proposed model predictions and experimental data is found.Moreover, a fractal model for subcooled flow boiling heat transfer is also proposed. The analytical expressions for subcooled flow boiling heat transfer are derived based on the fractal distribution of nucleation sites on boiling surfaces. The proposed fractal model for subcooled flow boiling heat transfer is found to be a function of wall superheat, liquid subcooling, bulk velocity of fluid (or Reynolds number), fractal dimension, the minimum and maximum active cavity size, the contact angle and physical properties of fluid. No additional/new empirical constant is introduced, and the proposed model contains less empirical constants than the conventional models. The proposed model takes into account all the possible mechanisms for subcooled flow boiling heat transfer. The model predictions are compared with the existing experimental data, and fair agreement between the model predictions and experimental data is found for different bulk flow rates.