This paper deal with the overall heat transfer process and confrontation of experimental measurements and their numerical solutions on simplified model, inside the horizontal scraped surface heat exchanger. The experimental measurements were done on two horizontal scraped surface heat exchangers connected in series. As a product was thermally treated water, heated by vapor in the first stage and cooled by cold water in the second stage. Applied mass flow of the product: m=250, 500, 750, 1000 kgh−1 and rotary velocity of the shaft, scraper blades: rpm=20, 30, (45), 60, 90 min−1. For numerical analyses the simplified model was used, with taking only the area between the heat transfer tube, and the shaft with an aim to compare the result to experimental measurements and validate the obtained overall heat exchange, as justify the simplification. As a results from experimental measurements were obtained the correlations for Nusselt number in a form of Nu=f(Re,Pr,ηf/ηw). Based on the confrontation of results, it can be stated that the level of simplification used at numerical solutions, gives still an acceptable accuracy of overall heat transfer values. From numerical simulations were obtained further results as the velocity, temperature fields, which were used to make certain adaptation on proposed construction and their examination by additional numerical simulations. All these acquired results lead to better understanding the overall process inside the horizontal scraped surface heat exchangers and the proposed construction of mutators can increase the efficiency of heat transfer process for many products in a real processing.

No abstract

Thermal processing (heating, cooling, crystallization) of high viscous or sticky products, usually containing particles or alter state when thermally processed are managed in chemical, food and consumption industry by scraped surface heat exchangers. These products are in most of the time non-Newtonian and sensitive products. Because of intensive presence of fouling and low heat transfer coefficient the rotating shaft (usually speaking of votator type of scraped surface heat exchangers) is equipped with scraper blades to keep clean the heat transfer surface and to mix the product as much as possible from the heat transfer surface into the main axial flow. Often, at the entrance of the product from the inlet cell to the main cylindrical heat exchanger part, a specific static mixers, homogenizers are applied (at outlet as well, but for different purpose -make additional mixing after thermal processing of the product). At inlet side the mixers are applied to flatten the velocity profile which is beneficial for the heat exchange process. The presented paper deal with the type of static mixers at the entrance and outlet from the point of view how the velocity profiles looks like and what is the effect on the pressure drop through them. The results show that the usage of different type of the mixers have no significant effect on the velocity profile when product is already managed by rotating scrapers. On the other hand it has quite significant impact on the pressure drop, what can lead to the higher energy consumption.