NUMERICAL HEAT TRANSFER MODEL FOR FROST PROTECTION OF CITRUS FRUITS BY WATER FROM A SPRAYING SYSTEM

摘要

A simplified model is developed to simulate the conditions associated with the protection of fruits from frost damage using water from a spraying system. The model simulates the movement of the solidifying waterfront on a single fruit, and based on that determines the spray frequency needed for a water film to continuously surround the ice-coated fruit to prevent the fruit temperature from dropping below 0 ℃. Simulations are presented for the frost protection of sweet oranges (citrus sinensis). The effect of environmental conditions such as air temperature, air velocity, surface radiation, and water film evaporation on the development of the ice layer encasing is considered. Simulations show the effect the encasing ice sheet thickness has on the fruit temperature if water from a spraying system is turned off permanently. Experimental tests are also conducted to determine the change in the thermal properties of citrus sinensis for operating temperatures that range from above freezing to sub-freezing. The results of the experimental tests and the numerical simulations shall lead to a better understanding of fruit protection from frost damage by the application of water from a spraying system.