Investigation of the temperature of the film boiling discontinuation

The process of repeated wetting under film boiling and transition from low to high-intensity heat removal is experimentally investigated. The results are presented of experiments on determination of the film boiling discontinuation temperature Tsub(cr) carried out at a pressure varying from 0.5 to 7.0 MPa; vapour content x from 0.4 to 0.7, mass flow rate from 85 to 430 kg/(m2xs). The experimental channel cross section imitates the space between four tubes arranged as a triangular lattice (hydraulic diameter of the channel is 5.7 mm). Processing the experimental data was based on solving the inverse problem of heat conductivity. The temperature on the integnal surface Tsub(in) and heat flux to the coolant q have been determined from the temperature of the external surface of the section Tsub(ex.) known from the experiment. The solution has been performed using the method of expansion of the sought-for functions in seAies by derivatives of Tsub(ex.) with respect to time. The formula for calculation of thermal head (Tsub(in.)-Tsub(ex.)) corresponding to the film boiling discontinuation ΔTsub(cr.)=120-174 x is suggested on the basis of the obtained experimental material, the formula describes the data in the 0.5-7.0 MPa pressure range, 0.4-0.5 range of void fraction and mass flow rates in the 85-430 kg/(m2xs) range with the error of +-20%