Effect of phase changes on the effectiveness of cooling by emulsions

Abstract

The paper considers the effect of the low-boiling dispersed phase on the nature of heat transfer in systems of immiscible liquids. In particular, the behavior of droplets of the dispersed phase during bubble boiling in the volume of an underheated continuous emulsion medium has been studied. Phase transformations predetermine the complex nature of the joint behavior of hydrodynamic and thermal processes. During cooling, the thermal energy is converted into mechanical energy of the vaporized motion of the evaporating liquid disturbed by vapor bubbles. This leads to a change in the volume and size of the droplets of the dispersed phase. It is known that controlled dispersion conditions with a minimum amount of cooling lubricant (emulsion concentration) can improve the quality of metal processing by 10-18%. The dependence obtained by Labuntsov for boiling a homogeneous liquid was used as a characteristic for the rate of thermal motion. The modification of the Labuntsov model is made on the basis of the nature of the physical processes occurring during boiling inside the emulsion droplets at the interface. Based on the analysis of the experimental data of Bulanov, features of heat transfer in the emulsion during bubble boiling of dispersed drops of a low boiling liquid were revealed. The heterogeneity of heat transfer is noted; it is associated with the formation of a kind of steam shroud of boiled droplets near a heated surface, which blocks the heat flow. A good agreement with experimental data confirms the adequacy of the model concepts of boiling drops in liquid emulsions.