EXPERIMENTAL AND CFD ANALYSIS OF SCRAPED SURFACE HEAT EXCHANGERS FOR HAZELNUT PASTE STERILIZATION

This paper describes the experimental and numerical results on the heat transfer in a scraped surface heat exchanger, SSHE, for the sterilization of hazelnut paste. Experimental analyses include the rheological characterization of the hazelnut paste and the evaluation of the average heat transfer coefficient in different working conditions in an alternate blades SSHE. Three-dimensional axial-symmetric CFD simulations of the SSHE have been eventually carried out by using the software Fluent 6.2 under the same conditions of the experimental run matrix. Numerical tests have been carried out on SSHE with both continuous (C-SSHE) and alternate (A-SSHE) blades. In the first case, heat transfer coefficient estimation by CFD results are well fitted by the classical empirical models for SSHE with continuous blades (C-SSHE). For an A-SSHE CFD results are consistent with the experiments in evaluating a heat transfer coefficient almost double than the one for C-SSHE. The analysis of the fluid dynamic field and of the thermal profiles in the A-SSHE show that the higher heat transfer coefficient are related to the occurrence of turbulent flow fields in the regions around the blade alternation due to backmixing phenomena.