Designing and construction, testing and evaluation of a forced air pre-cooling system of horticultural products

Background and objectives: Fruits and vegetables are important crops that have an important role in the human diet in which a considerable part of them losses during the post-harvest stages. One of the most important processes that reduce fruit loss and extends their shelf life is pre-cooling. In this process, the fruits biological activities are decreased rapidly. The aim of this study was designing and constructing the forced air pre-cooling system of horticultural products.
Material Martials and methods: In this study, the forced air pre-cooling system of horticultural products was designed and constructed according to the industrial pattern. To evaluate the performance and uniformity of cooling process in the system, the precooling of Peach was performed using fruit pallets with the three kinds of packages namely one-row package, two and three-row packages. In addition, the airflow rate was evaluated in three levels consists of 0.5, 1 and 1.5 liters per second per kilogram of product.
Results: The evaluation of results indicated that the air velocity field was uniform around the constructed precooling system with cross section dimension of 550×1200 mm and the height of 2050 mm. The suction fan power was 0.5 hp and the cooling capacity of the system about zero ºC. Therefore, all fruits located in the different location of pallet were cooled with an acceptable uniformity viewpoint of the cooling time and temperature. Also, the standard error of cooling time was not significant. Among the studied factors, the effect of airflow rate on the average 3/4 th cooling time of fruits in different boxes in the pallet and their standard deviation were significant. Increasing the airflow rate decreases the cooling time and improves the uniformity of cooling between the various packages, so that with three times increasing the airflow rate, the standard deviation decreases 59%. According to the results, the kind of package had a significant effect on the average 3/4 the cooling time of fruits and the minimum and maximum cooling time were related to the three rows and two rows boxes, respectively; but its effect on the standard deviation was not significant.
Conclusion: The developed precooling system could create and distribute of cold air uniformity between the fruits boxes in different locations of the pallet. There were no significant differences between the cooling time of fruit in both airflow rate of 1 and 1.5 lit s-1 kg p-1. Also, the rate of energy consumption is considerable in the high airflow rates. Therefore, it is recommended usage of cold airflow rate of 1 lit s-1 kg p-1. Although the three rows box had the lowest cooling time, due to the mechanical damage probability, it's using had no advantage as compared to one-row box.