Study On Drying Kinetic Of Lotus Seed By Hot-air And Microwave Temperature Control And Optimization Of Combined Drying Process Parameters

Lotus seeds have high nutritional value,medicinal value and economic value.In order to reduce the huge losses caused by rotten and spoilage of fresh lotus seeds,It is necessary that apply model drying technology to lotus seed drying.Hot-air drying,in particular,is a widely used method which has the advantages of low cost and simple operation.Microwave drying is a excellent model drying method which has the advantages of high drying efficiency.Combined drying technology could combine the advantages of single drying method which was considered to be one of the development trends of future drying technology.In order to study kineric and drying charcateristics of Lotus seeds with hot air drying process,the hot-air drying characteristics of different temperatures were studied.The main results as following:the hot-air temperature has a great influence on drying time.The whole drying process was in the falling rate period.The effective diffusion coefficients of hot-air drying temperature were 6.32691×10^-101.62072×10^-9m²/s.The activation energy values of hot-air drying lotus seeds were30.17 kJ/mol.In order to solve the problem that the material quality declined caused by the drying temperature rapid raised in the later stage of drying,Expertiment lotus seeds with microwave drying with temperature control,Effect of different microwave power and material surface temperature range on microwave drying characteristics and kinetic with temperature control.Results showed that the material surface temperature range has a great influence on microwave drying of lotus seeds,the microwave power has little effect on microwave drying of lotus seeds during microwave drying with temperature control.The Midilli model could describe the microwave drying lotus seeds with best accurate among 7 models.The effective diffusion coefficients were8.73646×10^-10m²/s².22431×10^-9 m²/s under different microwave drying condition.The activation energy values of microwave drying lotus seeds under different material surface temperature range was 79.85 kJ/mol.The material surface temperature range had a significant effect on scale parameterαand shape parameterβ.There was little different in rehydration ratio of the dried lotus seed（p>0.05）,the hardness of dried lotus seed which microwave under temperature control dried was higher than the hardness of dried lotus seed which hot-air dried,the microwave drying under temperature control involved higher drying energy consumption and shorter drying time than hot-air drying.In order to study combined the temperature controlled microwave drying with hot-air drying and determine the optimum drying process of conbined drying technology,according to response surface method,carried out the three-factor and three-level response surface test on lotus seeds.The result showed that the comprehensive optimization process condition was determined with（51.27-56.27℃）of the material surface temperature range,27%of conversion point moisture content,800W of microwave power,the response value of the relative energy consumption was 19.7137 kJ/g,the average intensity of drying was 0.0049523 g/g·min,and hardness of lotus seed was 9618.2 under this drying process conditions.Compared with the temperature controlled microwave single factor drying of microwave power800W,the relative unit energy consumption of combined drying is reduced by at least33.1%.The results of this study provide a reference for the temperature controlled microwave drying and combined microwave with hot-air drying.