IMPROVING A VACUUM-EVAPORATOR WITH ENLARGED HEAT EXCHANGE SURFACE FOR MAKING FRUIT AND VEGETABLE SEMI-FINISHED PRODUCTS

Most of the designs of vacuum-evaporators for concentration have the problem of heat supply stabilization over the entire heat exchange surface. This is due to the presence of a steam shell, which complicates the uniform heat supply. The shortcomings also include the lack of the possibility of the rational increase in the heat transfer surface, which in turn affects the duration of thermal treatment and product quality. In order to eliminate the main disadvantages of vacuum-evaporators, it is proposed to use the method of heat supply with increased heating surface. To solve the set improvement tasks, it is proposed to use modern flexible film resistive electric heaters of radiation type (FFREhRT). They are characterized by low inertia, metal capacity, ease of automation and maintenance. Such electric heater is capable to ensure the uniformity of heat flow and to take any geometric shape of the heat transfer surface. In accordance with the design and technological solution, it is proposed to perform heating with the heat-insulated FFREhRT, which is also located in the hollow space of the stirrer and blades shaft and blades, instead of steam shell. Thus, the increase in heat transfer surface from 3.7 m3 to 4.15 m3, that is by 12 %, is ensured. We detected a decrease in boundary shear stress at an increase in temperature: if t=10 °C, q0=79 Pа; respectively, t=70 °C, q0=12 Pа. Effective viscosity at t=10 °C is ηef =392 Pа∙s, for t=70 °C ηef =2 Pа∙s. In the course of testing the model sample of the VEHS during concentration (50...65 °C), shear rate was determined: 0.5...2.5 s-1. Effective viscosity is within 2.0...4.5 Pа∙s. The improved VEHS is characterized by the reduced duration of entering the stationary mode decreased by 29 % compared to the prototype (MZS-320). The effectiveness of the design and technical solution is proved by a decrease in the weight of the unit by 35 %, of specific metal capacity by 42 %, of treatment duration by 12