Numerical simulation of heat transfer and determination of critical heat fluxes at nonsteady heat generation in falling wavy liquid films

In the current work, we present the mathematical model, which allows the calculation of the wave surface profile, velocity and temperature fields as well as the study of their evolution at a drastic change in heat loads with time. This model allows calculations of the wave characteristics and parameters of liquid film decay at different regime parameters. Using the presented model, we have simulated the wave formation process in falling film of liquid nitrogen and retrieved the resulting average wave characteristics for different inlet Reynolds numbers. We have also calculated the dependencies of boiling expectation time and total local evaporation time in falling wavy films of liquid nitrogen on heat flux density for different inlet Reynolds numbers. It was found out that all calculated dependencies are approximately similar in the area of high heat flux rates for all examined inlet Reynolds numbers indicating the weak influence of irrigation rate on boiling expectation time in this range of heat loads. Discrepancy of calculated dependencies was found in the area of low heat flux rates, what could be explained by significant influence of evaporation on heat transfer under such conditions. The dependencies of characteristic heat flux density of boiling suppression and total local evaporation suppression on the inlet Reynolds number were also presented. The regime map, which defines the different mechanisms of decay of falling wavy film of liquid nitrogen, was obtained by summing up the results of numerical simulation. The results of numerical simulations are in satisfactory agreement with experimental data. (C) 2016 Elsevier Ltd. All rights reserved.