CFD Simulation of Airflow and Heat Transfer During Forced‐Air Precooling of Apples

Abstract

In this work, we study how different air-inflow velocities affect the appletemperature distribution during forced-convection cooling of individual apples by simultaneously modeling airflow and heat transfer. In general, an increase in airflow velocity increases the cooling rate and heat transfer fluxes across the apple surface and decreases cooling time. The results show that a reasonable increase in cooling rate is obtained with an increase in airflow velocity to 2.5 m/s; any further increase in airflow velocity simply wastes energy because it leads to a relatively low increase in cooling and heat transfer fluxes across the apple surface. By comparing the temperature simulated with and without accounting for respiratory heat, the maximum temperature difference is $0.033 K during cooling. Therefore, respiratory heat has a negligible effect on the temperature variations of fruit. The model was verified by comparing its results with those of experiments. The predicted results are consistent with the measured results. PRACTICAL APPLICATIONSTo ensure the quality and safety of horticultural products and extend their storage and shelf life across the entire cold chain, a critical step in the postharvest cold chain is the rapid precooling after harvest to remove field heat. In this work, we investigate how to improve the cooling rate and minimize the cooling time during forced-convection cooling of apples. In addition, the effect of respiratory heat on temperature variations of fruit is also studied. This research provides not only a more detailed understanding of flow distribution and temperature variations of fruit during cooling, but also a reliable theoretical basis for minimizing unnecessary energy consumption during forced-convection cooling of produce.

Thermal convection coefficient in cooling process of lime fruit: Study through the Galerkin finite element method

“…Among regression constants, the cooling coefficient ( k 2 ) is related to the rate at which a product is cooled and expresses the change of fruit temperature divided by cooling time and by difference of temperature between the product and the surrounding air (Brosnan & Sun, ). Data showed that there was a correlation between air velocity and k 2 , which confirmed that as air flowed faster the cooling time was smaller (Table ), which has also been reported for other cooling processes (Han et al, ). The position of fruit inside the system affected cooling parameters, and k 2 was higher at the input and smaller at the output, which coincided with the smaller value of t 7/8 at the input than that of the output.…”

“…The coefficient h varied between 3.7 and 100.6 W/m 2 °C and was affected by air velocity ( v air ) during cooling, in a way that as v air was higher the coefficient h increased significantly (Table ). This was also an expected result, since it is well documented that a thermal convection coefficient is highly dependent on medium velocity (Han et al, ). On the other hand, the input of the system operated with the highest value of h , followed by the intermediate zone, and finally by the output one, with significant difference between all of them (Table ).…”

“…Estimated values correspond to a model working with 0.0001 m and 1 s in distance between nodes and step size, respectively. that a thermal convection coefficient is highly dependent on medium velocity (Han et al, 2017). On the other hand, the input of the system operated with the highest value of h, followed by the intermediate zone, and finally by the output one, with significant difference between all of them (Table 3).…”

Numerical Analysis of a Convective Drying Chamber from Drying Air Velocity and Temperature Perspective

“…Therefore, it is of great interest to perform an analysis of the process of turbulent flow and air distribution in a fully three-dimensional way, which implies a load not negligible on both computational and in the features and scope of the model [5]. A complete model of the drying process must take into consideration the interaction between heat-and-mass transfer within the material to be dried and the transfer to the drying air flow [9], several studies have been carried out in these aspects and their combinations, both at the simulation of models and at experimental levels performed by Cârlescu et al [10], Villegas et al [11], Lemus-Mondaca et al [5] ( [12]), Han et al [13], Gómez & Ochoa [14], Ozgen [15], Mohan [6], Lamnatou [9] among many others.…”

Sensitivity analysis of heat and mass transfer characteristics during forced‐air cooling process of peaches on different air‐inflow velocities

“…Thus, the reliability of aerodynamic simulation results is reduced and the effect of evaporative cooling is not modeled explicitly. Han et al (2017) found that the maximum temperature difference of a single apple was up to 0.033°C during cooling by comparing the temperature simulated with or without considering respiratory heat. Regarding strawberries, Nalbandi and Seiiedlou (2020) reported that transpiration heat could not be neglected during the cooling process, as the 7/8ths cooling time (SECT) decreased by 31% when this heat was added into the numerical model.…”