Study on liquid–vapor interface oscillation characteristics and heat transfer of film boiling during quenching of fuel cladding surfaces

Abstract

It is very important to understand the heat transfer and flow characteristics of the film boiling during the quenching of fuel cladding under severe accident conditions. In order to investigate the liquid–vapor interface oscillation behavior and heat transfer characteristic of the film boiling, an experimental apparatus was established to simulate the quenching process with different liquid subcooling degrees and test sample materials. The image processing technique and the Fast Fourier Transform (FFT) method were combined to capture the characteristics of vapor film, and the inverse heat conduction problem method was employed to calculate the surface temperature and heat flux of the test sample. The results show that the vapor film thickness becomes thinner and the oscillation of the liquid–vapor interface gradually weakens with increasing liquid subcooling degree and decreasing wall temperature. The change in the vapor film characteristics can be attributed to the combined effects of Kelvin-Helmholtz instability of interface and condensation of vapor film, which respectively correspond to the low dominant frequency oscillation (0–35 HZ) and high dominant frequency oscillation (90 HZ) of the liquid–vapor interface observed during the experiment. Besides, it can be concluded that the heat transfer of film boiling is increased with liquid subcooling degree, but not sensitive to the test sample material and axial elevation. Based on the heat transfer results, a new Nusselt correlation of the film boiling that couples the effects of thermophysical properties of the vapor film, thermophysical properties of the coolant, liquid subcooling degree and wall superheat degree is developed with the average error of 10.41 %. The universality of the improved correlation is verified by the experimental data in literatures.