HEAT AND MASS TRANSFER IN SOLID – LIQUID SYSTEM WITH SUPERFICIAL HEAT SOURCE

Abstract

The interaction between a solid (zinc) and a liquid reagent (a solution of hydrochloric acid) was studied theoretically and experi-mentally. These processes are used in the dimensional processing of metals in order to give those appropriate shapes. A cylindrical zinc billet was used as the object of the study. The billet lateral surface is protected by an acid-resistant coating and the dissolution process occurred only along the plane of the work piece section. The experimental installation scheme with the description of ex-perimental researches technique is resulted too. The zinc billet dissolution proceeds with the release of the gaseous phase during the nucleation of the bubbles, growth and separation from the solid surface where they nucleate. It promotes intensive mixing of the liq-uid and turbulizes the boundary diffuse layer. As a result, the process of maso-visualization is intensified. This process is controlled by diffusion and its intensity is determined by the mass-transfer coefficient. The value of the mass-transfer coefficient is presented in this work. The interaction is accompanied by significant thermal effects. This enhances the process of dissolving zinc with hydro-chloric acid. The heat source is located on the interaction surface and spreads by convection in a liquid reagent and thermal conduc-tivity in a solid, respectively. The temperature at the interaction surface is important to know, since it determines the values of the physical quantities that are used to mass-exchange processes calculation. The process of thermal conductivity in a semibounded body with a continuously operating surface heat source is considered in the condition of constant convective heat flow into liquid medium. A differential heat equation with a constantly acting heat source on the solid surface with the corresponding initial and boundary conditions is used to describe the dissolution process. The results of experiments are shown in the graphs form. The temperature of the interaction surface is determined as a function of time. It is also found that the largest surface temperature gradients are observed at the initial periods. The temperature field in a bar-shaped metal blank was determined theoretically and experimentally and it ade-quacy has been confirmed.