Heat transfer to a stationary cubic particle in a laminar tube flow: Computational fluid dynamics simulations and experiments

In continuous aseptic processing involving liquid food suspensions, the suspended particles must receive sufficient heat treatment without affecting their nutritional or sensory qualities. Optimal process design for the sterilization of particulates in liquid food therefore requires good estimates of convective heat transfer coefficient at the fluid to particle interface. Relatively few studies have been reported involving coarse non-spherical particles in a confined flow. In this work, we have used a combination of computational fluid dynamics (CFD) simulations and experiments to investigate the heat transfer rate to a coarse cubic particle suspended in a laminar fluid flow within a circular tube. We carried out the simulations using ANSYS Fluent software, whereas for the experimental investigations, we used the stationary particle method, employing a thermocouple to measure the particle temperature at the centre. We conducted all tests using a sugar solution as the heat-carrying fluid, and we employed two types of cubic particles, one fabricated from peach fruit and one from polycarbonate plastic. We varied the particle orientation, the fluid flow rate, and the radial position of the particle in the tube. For all the above parameters, we validated the time-temperature profiles of the particle obtained from the simulations against the values measured in the experiments. The temperature data from the simulations for the polycarbonate particle showed fairly good agreement with the experimental data (within 5%) for all flow rates and particle orientations. However, for the peach fruit particle, the agreement between the simulated and experimental data was unacceptable, especially for non-central positions in the tube, with obvious deviations between the simulated and experimental data, where the maximum deviations were between 15% and 25%. The evaluated average fluid-particle heat transfer coefficients for polycarbonate particles were compared with the values obtained from correlations in the literature. The comparison resulted in either overestimation (up to 50%) or underestimation (up to 35%) of the average fluid-particle heat transfer coefficients.