Vortex characteristics downstream a fan and its effect on the heat transfer of the temperature inversion under late spring coldness

Abstract

Tea plant in East China usually suffers from frost damage due to sudden low temperature under late spring coldness. A fan is a frost protection device that can blow the warmer air aloft to the tea canopy level under radiative frost meteorological event with temperature inversions. In this study, the flow fields and the temperature distribution downstream a fan were numerically simulated. It is found that the flow structure downstream the fan is divided into two flow regimes: one is the jet flow that blows the warmer air aloft downward and the other one is vortex ring that enhances turbulence at the tea canopy level. The jet and the vortex characteristics are nearly independent on the shaft rotation speed. However, the heat transfer process is obviously related to the flow structures, and the temperature distribution on the tea canopy plane coincides with the vortex characteristics. The temperature peak is near the core of the flow vortex, and the high-temperature zone coincides with the vortex ring regime.