Impact of Mixed Convection on the Cooling Kinetics of Heat-Generating Products Within a Ventilated Pallet: Application to Cheese

Abstract

Cheese temperature control in the cold chain is essential for quality preservation and waste reduction, especially for soft cheeses, which generate heat due to their microbiological activity. This study first analyses, at steady state, the natural convection effect on the temperature distribution along three pallet rows (from upstream to downstream). Second, it investigates, under unsteady state, the effect of upwind air velocity (0.25 m/s and 0.64 m/s), product heat generation (0 W, 0.05 W, and 0.3 W per product item), and initial product temperature heterogeneity on the cooling rate within a ventilated pallet in a cold room. The cheeses were replaced with plaster cylinders equipped with controllable resistance heaters to simulate heat generation by cheeses. At steady state, the temperature measurements confirmed the presence of a thermal plume on the pallet downstream row when natural convection was predominant (Richardson number = 6.53). Under unsteady state conditions, increasing the air velocity from 0.25 to 0.64 m/s reduced the half cooling time (HCT) and seven-eighths cooling time (SECT) by at least 26% and 37%, respectively. Greater heat generation increased the product temperature but, interestingly, reduced the product cooling time.