Bubble dynamics is the most important sub-phenomenon, which basically affects the nucleate pool boiling heat transfer coefficient. In this research, bubble departure diameter values were experimentally measured for heat fluxes up to 110 kW.m-2. Experiments were carried out for pool boiling of pure liquids, including water, ethanol and methanol on a horizontal smoothed cylinder, at atmospheric pressure. For ethanol and methanol, rigid spherical bubbles with small contact area were observed. The spherical shapes seem to be because of small diameters.For all test fluids, experimental results show that bubble diameter increases with increasing heat flux. Most predictions have a similar trend for increasing bubble diameter versus increasing heat flux. Also, the existing well-known and most common used correlations are comparatively discussedwith the present experimental data. Finally, a new model for the prediction of vapor bubble departure diameter, based on Buckingham theory, in nucleate boiling is proposed, which predicts the experimental data with a satisfactory accuracy.
Prediction of boiling heat transfer for pool boiling systems is crucial from the viewpoint of safe operation as well as in terms of logical use of energy. Here, five pool boiling processes for calculating the bubble detachment diameters are described. The effects of liquid density and vapor density on the bubble detachment diameter of these pool boiling systems, namely, ethanol, methanol, water, Na 2 SO 4 -water, and NaCl-water, are determined by applying response surface methodology. According to P-values and analysis of variance, there is a good agreement between the obtained regression models for the five pool boiling processes and experimental data for estimation of the bubble detachment diameters.
The artificial neural network (ANN) method and response surface methodology (RSM) were used to predict the bubble departure frequency for the pool-boiling heat transfer of pure liquids, by using experimental data. The effects of vaporliquid density difference, vapor-liquid viscosity difference, surface tension, thermal conductivity, and heat flux on the departure frequency of vapor bubbles were investigated by RSM and ANN. The results showed that the outputs of the ANN and RSM had a suitable overlap with the experimental data, but the RSM model was more accurate than the ANN model.
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