Heating and cooling of hazelnut paste in alternate blades scraped surface heat exchangers

This paper extends a former analysis on the thermal behavior of a new kind of scraped surface heat exchanger operated in laminar regime to treat hazelnut paste, a high viscous non-Newtonian fluid largely adopted in the Italian confectionary industry. This unit, named A-SSHE, presents an alternate arrangement of the scraping blades that allows doubling the exchanger thermal efficiency respect to conventional SSHE with continuous blades, mainly thanks to backmixing phenomena.Three-dimensional CFD simulations of the A-SSHE are used to estimate the overall heat transfer coefficient as a function of the main process parameters: blades rotational speed, flow rate and wall temperature. The heat transfer coefficient results slightly higher during cooling than during heating and increases much more with blades rotational speed than with mass flow rate. Dimensional analysis provides a correlation among heat transfer coefficient, fluid properties and easily measurable flow parameters. This correlation is useful to design and operate an A-SSHE treating high viscous food pastes.

► CFD simulations are used to study heat transfer in a new SSHE with alternate blades.
► Heating and cooling of hazelnut paste, a high viscous non-Newtonian fluid, is studied.
► Thermal efficiency of the SSHE is higher during cooling than during heating.
► The heat transfer coefficient increases more with rotational speed than with flow rate.
► Equation: Nu = 4.91 Rer0.3Reax0.03Pr1/3n0.25 can be used for SSHE preliminary design.