Conjugate heat transfer model of non-Newtonian fruit pulp freezing by turbulent convective air flow in a refrigeration cabinet.

This study develops a three-dimensional conjugate numerical model to predict the unsteady solidification of blueberry pulp in a container cooled by buoyancy-driven turbulent natural convection within a domestic freezer. The finite volume method, combined with the SIMPLERnP algorithm, simultaneously solves airflow turbulence, heat conduction, natural convection within the pulp, and the liquid-to-solid phase change. Results demonstrate that reducing food thickness and optimizing placement enhance heat transfer, shorten freezing time, and lower energy consumption. Specifically, thinner samples (aspect ratio 0.125) achieved a 200% increase in heat flux compared to the baseline, while dividing the food into two batches placed at the corners increased heat flux by 223%, reducing freezing time by nearly half. The average drip loss decreased from ~17% in thicker samples to ~15% in thinner ones, and the pectin content increased from 0.90 to 0.99 g/kg, indicating improved texture and quality. The model also captured differences in airflow, predicting counter-rotating vortices and boundary-layer thinning, which reinforced convection and accelerated cooling. It accurately reproduces freezing curves, isotherms, velocity fields, and Nusselt numbers, confirming its reliability. Overall, the model underscores the significant impact of food geometry and placement in the freezer on performance, offering a robust tool to optimize energy efficiency and product quality in frozen fruit pulps.