HEAT-TRANSFER PROPERTIES OF A SCRAPED-SURFACE HEAT-EXCHANGER IN THE TURBULENT-FLOW REGIME

Heat transfer in scraped-surface heat exchangers processing turbulent flowing media has been modelled by combining a regular model for turbulent pipe flow with penetration theory to account for the disturbance of the thermal boundary layer by the scraper action. Comparison of the model with experimental data obtained with a bench scale unit revealed that the heat transfer coefficient depends more strongly on the rotational frequency of the scrapers than the model predicts. This phenomenon could be ascribed to the generation of vortices due to the scraper action, as has been confirmed by computer simulation as well as experimental flow visualization. Correction of the model for the occurrence of these vortices yielded a satisfying agreement between predicted and experimentally determined heat transfer coefficients.