干切牛肉冷冻干燥中解析干燥过程的动态模拟及优化

Dynamic simulation and optimization for desorption drying process during freeze drying of cooked beef slice

该文通过对干切牛肉冷冻干燥中解析阶段含水率、物料温度的动态模拟及干燥速率与耗能分析,确立干切牛肉冷冻干燥中解析干燥的优化操作条件。通过建立解析阶段中脱除水分所需干燥时间以及相应的物料表面温度、物料中心温度的数学模型,并假设解析干燥过程中物料含水率由升华结束时的10.0%下降到干燥结束的0,以含水率变化为自变量,模拟了物料厚度为6、8、12、15mm的干切牛肉在干燥室压强10Pa,加热板温度80℃的操作条件下含水率、物料温度随时间的动态变化。以所建模型预测厚度7、9、10、11、12、13、14mm的干切牛肉在该操作条件下含水率、物料温度的动态值及解析干燥周期。验证试验表明:预测与实测含水率相对误差小于10%,物料中心温度计算值与实测值的绝对误差小于5℃,说明所建模型可用于模拟、预测6～15mm干切牛肉冷冻干燥中解析干燥阶段的参数变化。比较不同厚度干切牛肉冷冻干燥中解析干燥阶段的干燥比耗时、干燥效率,结果是采用6mm厚度切片进行干燥,生产单位产品耗能最低,且生产率最大。

The dynamic change of moisture ratio and sample temperature during desorption drying in freeze drying of cooked beef slice were simulated,and the optimal operation conditions were determined through the analysis of the drying rate and energy consumption.Mathematical models were established for desorption time,sample center temperature and sample surface temperature while the moisture of sample was dehydrated during the desorption drying.Moisture ratio was taken as independent variable.On the assumption that the moisture ratio descended from the terminal moisture ratio of sublimation drying（10.0%）to terminal moisture ratio of desorption drying（0）,dynamic changes of the moisture ratio,surface and center temperatures of the samples with time during desorption drying in freeze drying experiments were simulated successfully.The experimental conditions were as follows：chamber pressure was 10 Pa,heating board temperature was 80℃,the sample thickness were 6,8,12 and 15 mm,respectively,Moreover,the moisture ratio,center and surface temperature changing and desorption periods of cooked beef slice in thickness of 7,9,10,11,12,13,14 mm during desorption drying were forecasted.The validation experiments were conducted and the results showed that the comparative errors between forecasted and measured moisture ratio were lower than 10%,and absolute errors between forecasted and measured centre temperature of drying sample were lower than 5℃.It can be concluded that the predictive model can be applied to simulate and forecast the changes of operational parameters during desorption drying of cooked beef slice in thickness of 6-15 mm in freeze drying.Compared comparative time-consuming and efficiency of desorption drying,the highest productivity and the lowest energy consumption to produce a certain quantity of products are obtained when sample thickness is 6 mm.