Residence time distribution of food and simulated particles in a model horizontal swept surface heat exchanger

The residence time distribution (RTD) of food and inert particles flowing in a swept surface heat exchanger at room temperature was investigated. The effects of selected experimental conditions on RTD include particle shape (cube, cylinder, and sphere), particle concentration (10, 20, and 30% w/v), particle type (potato, carrot, turkey, green peas, and polystyrene), fluid viscosity (water, 0.5% CMC, and 1.0% CMC), bulk flow rate (5.8 x 10(-4), 7.28 x 10(-4), and 8.71 x 10(-4) m(3)/s) and shaft rotational speed (30, 60, and 90 rpm). Although turkey cubes were denser than other food particles, they moved faster than potato and carrot particles. Mean particle normalized residence time (MNPRT) of food particles (green peas) were found to be significantly higher than that of simulated particles (polystyrene). Cylindrical particles stayed longer than cubic particles in water, but not significantly in CMC solution. MNPRT values were found to be dependent on viscosity. Increasing particle concentration (up to 30 %) tended to decrease MNPRT. Both bulk flow rate and shaft rotational speed tend to decrease MNPRT, thus reducing the lethality achieved. The distribution of residence time curves were narrowed by decreasing particle concentration, bulk flow rate, and shaft rotational speed, and by using fluids with high viscosity. In general, particle velocity was found to be higher than the average bulk velocity. The fastest particle velocity was found to be 3.23 times the average bulk velocity while the ratio was 0.382 for the slowest.