CFD simulation of heat and mass transfer through cylindrical Zizania latifolia during vacuum cooling

Abstract

As the Zizania latifolia has a delicious taste, high nutritional value and rich moisture, it is easy to rot and deteriorate due to the high moisture content, resulting in short shelf life. In order to maintain quality of Zizania latifolia, the vacuum cooling process of cylindrical vegetables is experimentally studied. Considering the transient heat transfer and mass conservation, a mathematical model of heat and mass transfer in the vacuum cooling process of cylindrical vegetables is established. Meanwhile, the temporal trends of total system pressure, temperature distribution, evaporation rate of water, weight loss and moisture content of Zizania latifolia are simulated by CFD software. The experimental data are compared with the CFD simulation results. It is found that the differences of the temperature between the simulation and the experiments are 4.7%. The amount of water evaporated from the Zizania latifolia by simulation is 5.5% during the whole vacuum cooling, while the tested water loss rate is 9.8%, the maximal deviation of weight loss is within 4%. The simulated result of 83.5% after a cooling time of 850 s, gives a reasonable agreement with the experimential moisture content of 86.7% in the same cooling period. The results show that the CFD simulation values agreed well with the experimental data. It is significant for the study of the water transfer characteristics of cylindrical vegetables tissue and the optimization of the vacuum cooling process of the food industry.