Transient boiling crisis in liquid nitrogen. Influence of heater size and heating rate

It is known that the nucleate boiling of different refrigerants (liquid nitrogen, freons etc.) may drop to the film boiling regime at a heat flux, which is significantly lower than the value from the standard boiling curve. This happens during unsteady heating at a minimum critical heat flux, whose value depends on different parameters of the process: heater geometry, pressure, subcooling relative to saturation, fluid type, initial conditions etc. In this article, we present new experimental results on the influence of the size of the heater and the heating rate on the minimum critical heat flux. The experiments are accompanied by numerical simulations and a theoretical analysis, where we demonstrate how the minimum critical heat flux is computed for a given case. In addition, we demonstrate that the minimum critical heat flux does not depend on the size of the heater at atmospheric pressure when the size of the heater is larger than 1 mm. This parameter is also independent of the temporal history of heat supply. The derived theoretical approach finds applications in the design of the systems based on hightemperature superconductors. (C) 2020 Elsevier Ltd. All rights reserved.