Study On The Characteristics Of Coupled Hot Air And Microwave Drying

This subject mainly studied on the characteristics of coupled hot air and microwave drying technology, discussed the feasibility of this current technology. Effects of some factors on the drying process were studied, the process was optimized, and the mathematic model of coupled drying process was simulated.Carrot slices drying were conducted using a novel lab-scale coupled hot air and microwave dryer which was designed and manufactured by author. Some factors such as microwave power density and hot air temperature were examined. Drying velocity, rehydration characteristic and retention of carotene were investigated and overall quality evaluation was done.Experimental results showed that: 1) Coupled microwave and hot air drying could greatly enhanced the drying rate. The drying rate of microwave drying was higher than hot air drying, and that of current coupled one was the fastest. 2) Products prepared by coupled drying was with more satisfied sensory quality, higher reserved content of carotene, higher rehydration, and better comprehensive evaluation scores. 3) The optimal drying process was done through orthogonal experiments and multiple linear or nonlinear regression, and drying kinetics and its mathematical model was also studied and proposed. Both mathematical model and experimental data showed that drying rate was mainly affected by microwave power density, while the influence of hot air temperature was little during coupled hot air and microwave drying process. Drying rate generally increased with the increase of microwave power density and hot air temperature.The drying characteristics of coupled hot air and microwave was also investigated using jujube as tested material. The drying rate and and sensory quality of it were studied. Experimental results showed that the coupled dried jujube had more satisfied sensory acceptance evaluation, higher reserved content of Vc and higher rehydration. Microwave power, hot air temperature and quantity of sample were chosen as three factors for response surface analysis. The effects of these three factors on the coupled drying were investigated. The experimental results showed that simple linear relationship was among them during coupled drying, the microwave power had the most important effect, quantity of sample followed and the hot air temperature had the least effect on them.The temperature distribution and change during coupled hot air and microwave drying were also investigated using jujube as test material, and related mathematical models were developed. The research showed that the distribution and changes of the temperature in samples were strongly related to the diameter of sphere material dried in coupled dryer. The whole drying process of the coupled hot air and microwave drying can be divided into 2 periods; they were warming-up period and speed-change period. In the warming-up period, the samples temperature depended on microwave power and drying time. While in the speed-change period, the samples temperature depended on microwave power, drying time and hot air temperature.The research showed that the coupled hot air and microwave drring can produce high quality dehydrated fruits and vegetables with higher drying rate. The energy consumption compared with traditional methods was greatly reduced. It hold signification potential for application in agricultural and food products drying.