CFD Simulation of Porous Canopy Heat Transfer in Apple Orchard-Based Frost Protection

Abstract

Highlights Convective heat transfer in an apple orchard was simulated by Ansys Fluent. The various heating patterns and convective heat transfer coefficients under different heating schemes were obtained. The heating effects of heater output intensity, output velocity, and heating angle were simulated. The heating duration and heat dissipation time were critical for mobile heating. Abstract. Frost events cause high economic losses in agriculture. Frost protection methods, particularly heating, have been implemented in cold-sensitive crops for millennia. Although often effective, traditional heating strategies can be insufficient or wasteful due to a lack of spatial temperature information, resulting in inadequate protection or uneven heating problems. Computational fluid dynamics (CFD) modeling has been widely used to simulate fluid flow, heat, and mass transfer by predicting various processes such as spatial flow velocity, pressure, and temperature distribution within a simulated environment. A three-dimensional CFD model for simulating airflow and heat transfer in an apple orchard was developed and validated, with the effects of heater output intensity and output velocity, heating angle, and heating duration analyzed. The validated model effectively predicted the spatial temperature changes over time inside the canopy for three representative heating schemes (heaters angled 0°, 45°, and 90° toward a tree row) with an average root mean square error (RMSE) of 2.6 °C. The simulated results show that the heating scheme of heaters angled 45° was the most effective, resulting in the largest average percentage of the protected canopy (72.3%), compared with heaters angled 0° (33.1%) and 90° (56.5%). The average percentage of the protected canopy increased by 108.2% when the heater output intensity increased to 477,000 KJ·h-1 and 46.0% when the heater output velocity increased to 15 m·s-1. However, the percentage of the protected canopy showed diminishing returns as the heater output intensity and velocity increased. The simulated heat dissipation time was linearly related to the heating duration, which can be utilized to determine the reheating time for mobile heating. The outcome of the study can be beneficial for making effective frost protection decisions in apple orchards. Keywords: Canopy, Computational fluid dynamics, Frost protection, Heat transfer, Porous media modeling.