MODELING OF BOILING HEAT TRANSFER

Abstract

This dissertation discusses the development of a model for the boiling of saturated liquids. Basically, it has considered an analysis of various forces acting on vapor-bubble during its various stages. As a result of this analysis, it has been found that bubble growth period in ebullition cycle depends on the value of Jakob number, which characterize the boiling of liquids. Various forces which act in different regimes of Jakob number have been identified and force balance has been carried out for each range of Jakob number to obtain expressions of bubble departure diameter. The computed values of bubble departure diameter for each range have been compared against experimentally obtained values of various investigators and agreement between the two has been found to be very good. Using bubble growth equations due to Cole & Shulman [5] for different ranges of Jakob number, growth period and subsequently waiting period have been determined. These values also resulted in the determination of bubble emission frequency. The computed values of frequencies have been found to match with the experimentally-determined values of Cole H. Analysis has also been extended for the determination of validity of transient heat conduction model due to Mikic & Rohsenow [24 and latent heat transport model due to Rallis & Jawurek [33]. The analysis has yielded that neither of them can determine the heat flux during boiling of liquids. Therefore, the cumulative values have been compared against total heat flux. The cumulative values of transient heat and latent heat can provide total heat flux for low values of heat flux. This is an expected outcome, as this analysis holds true for isolated bubble regime in low heat flux region. Thus, transient heat conduction mechanism and latent heat transport mechanism, occurs simultaneously and therefore can describe the process of boiling of liquid satisfactorily for low values of heat flux.