Calculating model for critical heat flux and dynamical characteristics of film boiling regime development at transient heat generation on nonisothermal surfaces in cryogenic liquids

Development of Methods for Heat Transfer Enhancement During Nitrogen Boiling to Ensure Stabilization of HTS Devices

“…With highspeed video recording of boiling, experimental data on the departure bubble diameters were obtained and qualitative assessment of the density of active nucleation sites was done for both types of heaters. Studies [71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89] concern the main characteristics of boiling processes [71][72][73][74][75][76] and development of heat transfer and CHF [77][78][79][80][81][82][83][84][85][86][87][88][89] under various nonstationary laws of heat release in nitrogen. In [71,[74][75][76], it was shown that at overheating above a certain threshold value, there occurred nitrogen boiling modes in the form of so-called self-sustained evaporation fronts, propagating along the heatrelease surface (see Fig.…”

“…An extensive series of studies [77][78][79][80][81][82][83][84][85][86][87][88][89] presents results on the dynamics of transient processes, unsteady heat transfer, and CHF under various laws of heat release in nitrogen (stepwise, periodic pulsed, and power laws of heat load increase). It is shown in [80,82,86,87] that the character of crisis development and CHF for nonstationary heat release significantly depend on the characteristics determining the temperature head of liquid boiling-up.…”

“…It has been found that a change in nonstationary CHF at large times between pulses of periodic heat release is connected with deactivation of ready nucleation sites on the heat-release surface. Results of experiments on development of crisis phenomena for different laws of heat release and model description of nonstationary heat transfer crisis with consideration of two stages of process development (nonstationary thermal conductivity up to liquid boiling-up and vapor bubble growth before the transition to film boiling) are presented in [82,83]. The derived model enabled calculation of the dependences for the minimum nonstationary CHF with consideration of parameters of liquid boiling-up, the boiling prehistory (process of nucleation site deactivation on the heat-release surface), curvature, and thermal inertia of the heater.…”

“…It is shown that with increase or decrease in the earlier constant heat release on a heater with gradual temperature growth, there is an expressed hysteresis of the nonstationary CHF. The model and calculation method developed in [82,83] for the maximum admissible heat flux at nonstationary boiling crisis in a large volume with consideration of all the main factors affecting its value offer an answer to the main questions arising during analysis of admissible heat fluxes at nonstationary heat release on heating surfaces cooled by boiling nitrogen.…”

“…On one side of these plates, Nichrome film was deposited, which served as a heat source, and the other side of these plates accommodated a pulsed heater and temperature probes, which picked up instantaneous spatial distribution of the temperature and temperature alteration with time at 14 points of the heat-release surface. In [83,86,91,92], the existing concepts on the dynamics and thermal stability of film boiling sites are also presented. Results of numerical simulation of development of one-and two-dimensional sites of film boiling were analyzed.…”