Pre-cooling and humidification conditioning for fresh storage and preservation of perishable foods: an experimental study

The high demand for perishable food products outside their growing and harvesting seasons, as well as in areas where cultivation is difficult, and the need to preserve perishable food products after harvesting, picking, or slaughtering, has increased the need for storage and preservation techniques, including precooling technology. Precooling is the firststep in the cooling process after harvesting, picking, or slaughtering, and before storage and transportation to markets. which invloves cooling food products to low temperatures to remove field or slaughter heat. In this study, we experimentally analyze heat transfer during the precooling process, which takes place in a rectangular channel made of polyurethane material coated with a layer of aluminum with a thickness of (25-200) micrometers, connected to a second channel used for recycling air into the main channel, with the possibility of air entry and exit. The results showed that air recycling with closed air entry and exit doors, increasing air velocity, and using humidification in high-speed of air flow (4.8) reduced the dimensionless temperature of yellow watermelon, while increasing the refrigeration coefficient and heat transfer coefficient. For red cabbage, air velocity, air recycling, and humidification had a similar effect on dimensionless temperature change, resulting in a decrease in dimensionless temperature and an increase in refrigeration coefficient and heat transfer coefficient, but to a lesser extent than in yellow watermelon. For eggplant, high air velocity had an inverse effect, increasing dimensionless temperature rate, while decreasing the refrigeration and heat transfer coefficients. Opening the exit door and notrely on air recycling resulted in a very slow decrease in dimensionless temprature, whileusing the humidification at highest speed air with closed air entry and exit doors resultedin a significantly balanced decrease in temperature while preserving the freshness of foodproducts. Keywords: Process, precooling, vegetables, fruits, preservation, refrigeration.