基于传热传质的荔枝预冷果温和质量损失率预测

Prediction on Fruit Temperature and Weight Loss Rate for Litchi Pre-cooling Based on Heat and Mass Transfer

为掌握荔枝预冷过程传热传质规律,以果蔬气调保鲜试验平台为研究对象,依据热力学和水分迁移理论,建立了荔枝果实预冷过程传热传质数学模型,获得了果实在预冷过程中温度、质量损失率等参数的变化情况,分析了果实质量、初始温度对预冷时间、质量损失率变化的影响。经计算发现,同一堆放方式下,荔枝果实质量越大,果实失水速率越小;当荔枝果实质量为10 kg时,果实平均温度从25℃降至5℃约需350 min,平均质量损失率为2. 16%;果实初始温度低,可以减缓果实质量损失率上升。经试验验证,计算结果与模拟结果吻合较好,对应时刻果实温度最大偏差为2. 8 K,平均相对误差为13. 1%;质量损失率计算值与试验值最大偏差小于0. 3%,平均相对误差为10. 7%。

Pre-cooling is one of the key measurements for litchi fruit preservation after being harvested,and the performance of pre-cooling has a great influence on the quality change of litchi fruit.In order to investigate the heat and mass transfer during the pre-cooling process,a mathematical model was built to describe the heat and mass transfer phenomenon in the test bed with controlled atmosphere for fruits and vegetables.The mathematical model was built based on the theory in heat dynamic mass transfer,and the temperature and moisture loss of the litchi fruit during pre-cooling process was calculated.The effects of fruit weight and initial temperature on the process were investigated.After that,some results can be made.The time of pre-cooling became longer as the weight of fruit was increased,however,the speed of moisture loss would be decreased.When there were 10 kg litchi fruits,it took about 350 min for the temperature of fruit decrease from 25℃to 5℃by the same stack method,and the weight loss rate was roughly 2.16%after pre-cooling.It can also be drawn that the speed of weight loss can be reduced by decreasing the initial temperature of litchi fruit.A test was done to verify the accuracy of the model,and the test results were matched well with the results from calculation,the maximum difference between them in fruit temperature and weight loss rate was 2.8 K and 0.3%,and the mean difference rate was 13.1%and 10.7%,respectively.The research results can be useful for the investigation of the heat and mass transfer mechanism in a cool room and can be used to predict the temperature and weight loss of fruits during pre-cooling process.