CALCULATION OF STEAM AND CRYSTAL FORMATION PROCESSES FOR HEAT EXCHANGE IN FILM EVAPORATORS

The processes of boiling solutions with soluble salts release are widely used in various industries. The technological features of the evaporation process and the requirements for the product being processed determine the choice of a specific type of evaporation unit. Film evaporators, in which heat exchange processes take place in a turbulent flowing film, are the most effective both from an economic reason and finished product quality. The use of film evaporators is usually limited by the purity of the solution being processed. However, expanding the scope of application of this type of apparatus is possible if the initial solution contains a small number of particles of salts (liquid suspension). Thus, the study of heat and mass transfer processes in a turbulent film of a multiphase flowing liquid suspension and the development of their mathematical description is of theoretical and practical interest. A mathematical model of film flow of a three-phase suspension is presented in this work. The initial assumptions were as follows. A liquid suspension consists of liquid and solid phases. The liquid phase is a multicomponent system that contains a solvent and components that crystallize and do not crystallize. The flow of a film of a flowing liquid suspension occurs under the influence of gravitational forces and surface tension forces at the suspension-vapor boundary (the movement of the vapor coincides with the movement of the film). The relative speed of movement of solid particles in a film of a continuous flowing medium can be neglected due to their chaotic movement, while the flow rate of the film can be considered constant. The flowing film is turbulent along its entire length, which is caused by the chaotic movement of the dispersed phase. Thus, the temperatures of the liquid and solid phases, as well as the thermophysical parameters in the cross section of the film, are the same. When a liquid suspension flows along a heated surface, a change in the concentrations of the liquid phase and the amount of the solid phase occurs on the surface of the film due to the removal of the solvent during boiling. The amount of the newly formed solid phase is significantly less than the total mass of crystals in suspension. The model presented in the work reflects the physical essence of the evaporation process in a flowing film of a multiphase suspension and contains equations of motion, continuity, energy, equations for changes in phase concentrations and heat transfer.