Frost formation mechanisms in packaged frozen fruits considering porous structure under temperature fluctuations: Experimental and CFD analysis

Abstract

This study aims to investigate the influence of temperature fluctuations on frost formation in packaged frozen food by experiments and Computational Fluid Dynamics (CFD) simulations. A cylindrically-cut apple was placed in a polypropylene container with a lid and stored in an environmental chamber set at an average temperature of −22 °C with imposed temperature amplitudes of ±3 °C to ±7 °C, and fluctuation cycles ranging from 1 to 3 h. Temperature fluctuations within the air layer were recorded, and frost mass was quantified via a repeated weighing protocol. Unlike existing studies, we numerically considered the sublimation and deposition phenomena occurring at the air–frost and porous food interfaces by adopting a diffusion-based phase change model to treat both layers as distinct porous media. Subsequent CFD simulations employing the finite volume method and dynamic mesh algorithms yielded comprehensive insights into the transient heat and mass transfer processes. A comparison of the simulated and measured air layer temperatures and frost mass revealed maximum errors of approximately 9% and 23%, respectively. Numerical analyses have shown that an increase in temperature amplitude and a decrease in fluctuation cycle promote vigorous natural convection and enhanced frost accumulation. Specifically, an increase in fluctuation cycle from 1 to 3 h at a fixed amplitude of ±5 °C results in a reduction of the frost formation rate by approximately 46%, whereas an increase in temperature fluctuation amplitude from ±3 °C to ±7 °C at a fixed cycle of 2 h leads to an increase in the frost formation rate by approximately 178%. The observed trends and correlations indicate that both the amplitude and the cycle period of temperature fluctuations are critical parameters influencing frost development.