Numerical simulation and experiment on the relationship between lettuce forced-air precooling uniformity and air supply speed.

Forced-air precooling simulation model of lettuces was established. It was carried out by FLUENT software and the differences in forced air pre-cooling effects of lettuces at air inlet and outlet in the same basket under different air supply conditions were verified experimentally and compared. Experimental results showed that, lettuces precooled from 20℃ to an average of 3℃, when the feed air velocity increased to 1.5m/s, the axial fan frequency was 50Hz, the lettuce precooling to the termination temperature, the difference between the highest temperature and the lowest temperature of the simulated value and the experimental value was 1℃
and 1.5℃, respectively. when it down to 1.0m/s, the frequency was 40Hz, the temperature difference was 1.5℃ and 2℃, respectively. When it down to 0.76m/s, the frequency was 30Hz, the temperature difference was 1.8℃ and 2.5℃, respectively. When the wind speed was 1.5m/s, the precooling time was shortened by 30min. The simulation results were consistent with the experimental results. The decrease of the axial fan frequency leaded to the prolongation of the precooling time, which made the precooling non-uniform and could not achieve the purpose of energy saving. If pre-cooled lettuce in large-scale, the problem of poor precooling uniformity would be even more pronounced.