Parametric analysis of spherical foods during vacuum cooling

A mathematical model is developed for the heat and mass transfer of spherical foods during vacuum cooling. Variation histories of total pressure of the vacuum system, product mass as well as product temperature(including surface temperature,center temperature and mass-average temperature) are achieved by numerical calculation. Data collecting system with high accuracy can test and record the vacuum pressure, product mass, and product temperatures at different positions. The experiment was carried out on the vacuum cooling of spring-harvested head lettuce. The maxium difference between the simulated pressure and tested pressure is less than 100 Pa when the pressure ranges from 10000 Pa to 600 Pa. The maxium difference between the simulated temperature and tested temperature is 1℃. The simulated water loss ratio of head lettuce is 3.32%, while the tested water loss ratio is 2.97%, the difference is 0.35%. The research results provide some basic rules for flow and heat transfer about the characteriatics of evaporation heat transfer of product during vacuum cooling.