NUMERICAL SIMULATION AND EXPERIMENT ON THE RELATIONSHIP BETWEEN LETTUCE FORCED-AIR PRECOOLING UNIFORMITY AND AIR SUPPLY SPEED

摘要

Forced-air precooling simulation model of lettuces was established. It was carried out by FLUENT softwareand the differences in forced air pre-cooling effects of lettuces at air inlet and outlet in the same basket underdifferent air supply conditions were verified experimentally and compared. Experimental results showed that,lettuces precooled from 20°C to an average of 3°C, when the feed air velocity increased to 1.5m/s, the axialfan frequency was 50Hz, the lettuce precooling to the termination temperature, the difference between thehighest temperature and the lowest temperature of the simulated value and the experimental value was 1°Cand 1.5°C, respectively. When it down to 1.0m/s, the frequency was 40Hz, the temperature difference was1.5°C and 2°C, respectively. When it down to 0.76m/s, the frequency was 30Hz, the temperature differencewas 1.8°C and 2.5°C, respectively. When the wind speed was 1.5m/s, the precooling time was shortened by30min. The simulation results were consistent with the experimental results. The decrease of the axial fanfrequency leaded to the prolongation of the precooling time, which made the precooling non-uniform andcould not achieve the purpose of energy saving. If pre-cooled lettuce in large-scale, the problem of poorprecooling uniformity would be even more pronounced.