Model of steady motion of the interface in a layer of a strongly superheated liquid

Abstract

UDC 536.423 S. P. Aktershev and V. V. Ovchinnikov Steady propagation of the boundary of a vapor cavity in a layer of a metastable liquid along the heater surface is considered. The temperature and velocity of interface propagation are determined from the equations of conservation of mass, momentum, and energy in the neighborhood of the stagnation point of the vapor cavity and the condition of stability of steady motion of the interface. It is shown that a solution of these equations exists only if the liquid is heated above a threshold value. The calculated velocity of interface motion and the threshold value of temperature are in reasonable agreement with available experimental data for various liquids within wide ranges of saturation pressures and temperatures of the superheated liquid.Introduction. The problem of growth of the vapor phase in a superheated liquid is important for understanding the fundamental features of the boiling process. In the general statement, this problem is extremely complicated, because the growth of the vapor phase depends on many interrelated factors: heat-transfer intensity, evaporation kinetics, liquid dynamics, etc. The experiments [1-4] revealed degeneration of the bubble boiling mode, when already the first emergence of the vapor phase led to formation of a stable vapor film, skipping the bubble boiling mode (third crisis of heat transfer). It was demonstrated [4] that there exists a lower boundary of superheating prior to incipience for the third crisis, and the values of heat fluxes in such a situation are lower than the values of the first critical flux. In this case, instability starts to develop in the contact zone between the vapor bubble surface and the heater, and conical vapor cavities propagating along the heater are formed (Fig. 1).It was shown [5, 6] that the stagnation point of a conical vapor cavity (evaporation front) moves with a constant velocity. The velocity of the evaporation front substantially depends on liquid superheating and can reach tens of meters per second. The data on the evaporation front velocity for various organic liquids, water, and liquid nitrogen, were obtained in [5][6][7][8][9][10][11]. The experiments were performed at pressures both below and above the atmospheric value, with the use of a cylindrical heater and a plane heater under conditions of quasi-steady heating and a stepwise increase in power. It should be noted that the character of motion of the evaporation front is considerably different from the character of motion of the incipience wave, when the incipience zone consisting of isolated growing vapor bubbles propagates along the heated surface with an approximately constant velocity [6,8]. In contrast to the incipience wave, the evaporation front is a moving interface. If the superheating is close to the threshold value, either the evaporation front or the incipience front can be observed; a transition from the incipience front to the evaporation front is also possible [8].The evaporation front has some specific features and is ...

Investigation of transient processes at liquid boiling under nonstationary heat generation conditions

“…As a result of the lost hydrodynamic stability and the existence of feedback between the local velocity and the local pressure, during liquid flowing around, there establish conditions in which the motion of different points of the front is essentially nonstationary. At the same time, the model [76] validated the conclusion formulated by authors of [72,74] on the threshold character of initiating the self-sustained evaporation fronts upon reaching the critical values of the Jacob number.…”

“…Works [46,[72][73][74][75][76] represent different approaches to the model description of a self-sustained evaporation front. In [72], from the conditions of conservation of energy, pulse, and mass fluxes at the head critical point on the interphase surface, the author obtained a calculation expression for the propagation velocity of evaporation front.…”

“…Authors of [76] proposed a model of stationary motion of a multiphase surface in metastable liquid under assumption that the front propagation velocity does not depend on surface curvature at a supposed head point of the vapor cavity. However, the authors' assumption on the immunity of the evaporation front velocity to small fluctuations of the interface near the head point of the cavity contradicts the abovedescribed experimental data on the dynamics of front development at high Jacob numbers.…”

On the shape of self-sustained evaporation front in a metastable liquid

“…Models proposed previously [1,[5][6][7][8][9] aimed at approximate description of the dependence of evaporation front propagation velocity on some set of physical parameters. Some of these models [5,7,9] suggest that a "frontal stagnation point" exists at the interface. However, some recent experimental data did not confirm the existence of the frontal stagnation point [2], which implies the need for developing a new approach to the description of these phenomena.…”

Studying the development of evaporation front interface in Freon R21 at non-stationary heat release

“…This effect can be shown both in the systems of film and droplet irrigation [1][2][3], and under the conditions of a large volume [4]. There are a number of models describing distribution of the self-sustained undisturbed evaporation front [5,6], as well as the single attempts to model the dynamics of front propagation with consideration of small-scale interface perturbations the under conditions of intense evaporation [7].…”