A Heat Transfer Model for an Apple Orchard Equipped with Mobile Heaters During Frost

Frost is one of the severe weather events causing economic losses in agriculture, and much effort has been made to reduce frost damage to crops. Traditional heating strategies can be insufficient or wasteful due to a lack of spatial temperature information thus failing frost protection or causing uneven heating problems. A three-dimensional computational fluid dynamics (CFD) model for simulation of airflow and heat transfer in an apple orchard was developed, calibrated, and validated. The validated model accurately predicted the spatial temperature inside canopies for three heating schemes (heater angled 0°, 45°, and 90° toward a tree row) with the average root mean square errors (RMSEs) of 1.2 °C, 2.9 °C, and 3.8 °C, respectively. In this model, the effects of heater output, heating duration, and heating angle were analyzed. The model showed that increasing heater outputs and optimizing heating angles could enhance the protected canopy volume percentage from 20.0 % to 91.9 %. In addition, a case comparison between a fixed and a mobile heating method was analyzed, and the results indicated that the mobile heating method had more capability than the fixed heating method for preventing frost damage, protecting more than 7 % of the volume of canopies for one movement, while the mobile heating method required precise planning. Overall, the outcome of the heat transfer study by incorporating the CFD model will be beneficial for making frost protection decisions in apple orchards.