Heat transfer modeling with fixed and mobile heaters for frost protection in apple orchards

Effective heating is important for protection of commercial crops from frost. In this study, a three-dimensional computational fluid dynamics (CFD) orchard model was developed to predict temperature distributions in an apple orchard from two forced air heaters under different wind conditions and fixed heating layouts. The simulated results show that placing heaters angled upwind had a larger average volume percentage of protected canopy (VPPC) than angled downwind. Reducing the interaction of heat flows between heaters improved the average canopy temperature (ACT) and VPPC in the fixed heating layouts. However, the proposed fixed heating layouts provided insufficient protection performance of the canopy with only a maximum VPPC of 32.2%. A mobile heating case i.e., moving the heaters from one end of the tree row to the other, was modeled based on a moving mesh simulation. Quantitative comparisons between the mobile heating case and three fixed heating cases, i.e., placing the heaters angled 45° at one end of the tree row, the middle of the tree row, and the other end of the tree row were conducted. The results show that the simulated VPPC for the mobile heating case increased by 1,180.0% compared to the first fixed heating cases, and 141.5% compared to the second and third fixed heating cases.