Numerical Simulation of Salmon Freezing Using Pulsating Airflow in a Model Tunnel

Abstract

Highlights: What are the main findings? CFD conjugate model for improved salmon freezing in a tunnel with a pulsed airflow Pulsating airflow freezing allowed important energy savings compared to steady flow Higher Nusselt number in food and faster freezing achieved by pulsed inlet airflow Fast numerical predictions and third-order accuracy calculation of transient terms High-quality freezing of solid food in mixed convective heat refrigeration tunnel Food freezing is an energy-intensive thermal process that has required exploring new technologies to enhance productivity and efficiency. This work provides a detailed insight into the energy analysis for the improved cooling of solid food during the freezing process, which originated by imposing a pulsating airflow at the entrance of a convective freezer tunnel. Continuity, linear momentum, and energy equations described simultaneously the conjugate transient heat conduction with liquid-to-solid phase change of the water content of a square salmon piece and the unsteady heat transfer by mixed convection in the surrounding airflow. The Finite Volume Method and a recently developed fast-accurate pressure-correction algorithm allowed an accurate prediction for the effects of imposing an inlet pulsating cooling airflow on the evolution of vortex-shedding, food freezing, cooling rate, heat flow, and energy savings. The variation in the values of the local heat fluxes at the food surface was reported, analyzed, and discussed by the evolution of the local Nusselt number around the square salmon piece. The study found that using an inlet pulsed airflow during salmon freezing improved temperature distribution and reduced energy consumption by 21% compared to using an inlet constant velocity airflow. The findings conclude that using pulsed airflow can improve temperature distribution in the food and significantly reduce energy consumption. Future investigations should consider a three-dimensional analysis, real salmon shape, turbulent conjugate convective freezing, an ensemble of salmon pieces, and exergy analysis to improve freezing tunnel design.