Study On The Drying Characteristics Of Continuous And Intermittent Ultrasonic Combined Heat Pump Drying Of Mung Bean Seeds

The foundation of modern agriculture is planting,which relies on seeds to continue and develop.Reasonable drying technology can prolong the storage time of seeds and ensure the sowing quality of seeds,thus promoting the sustainable development of modern agriculture.In order to improve the drying rate and ensure the drying quality,the continuous ultrasound combined heat pump drying kinetics experiments of mung bean seeds were conducted to provide the experimental and theoretical basis for the development of new drying technology.And on the basis of continuous drying,the intermittent ultrasound assisted heat pump drying characteristics of mung bean seeds were further studied to optimize the drying process.The main contents of this paper are summarized as follows:The ultrasound assisted heat pump drying system was constructed based on the closed air-borne heat pump drying system and ultrasonic generating device.In this combined drying system,the mung bean seeds were dried by controlled variable method.The results showed that increasing the ultrasonic power,frequency and drying temperature significantly increased the drying rate and the effective moisture diffusion coefficient.Moreover,the Midilli model was the best mathematical model to describe and predict the drying process of mung bean seeds.However,the effect of ultrasound on the activation energy of the drying process is not obvious.In order to evaluate the sowing quality of the dried mung bean seeds,the vitality characteristics and germination characteristics under different drying conditions were determined.It was found that increasing the drying temperature significantly decreased the activities of enzymes such as SOD,POD and CAT,and increased the content of toxic substance MDA significantly,meanwhile reducing the germination ability of the seeds.The application of ultrasound can significantly increase the activity of enzymes such as SOD,POD and CAT,and significantly reduce the content of toxic substance MDA,meanwhile improving the germination ability of seeds.However,there is no obvious rule for the influence on the sowing quality of mung bean seeds when improving the power and frequency of ultrasonic waves.On the basis of continuous drying,the intermittent ultrasonic assisted heat pump drying kinetics experiments were carried out to study the drying kinetics of mung bean seeds under different drying temperatures(28?,33? and 38?),the same ultrasonic conditions(ultrasonic power 100 W,ultrasonic frequency 28kHz)and different intermittent ration(0,1/3 and 1/2).The results showed that intermittent drying can reduce the effective drying time and improve energy efficiency.Different drying temperatures were required to choose a suitable intermittent ratio to improve the drying result more effectively.When the drying was lower,a high intermittent ration should be chosen,and a low intermittent ratio should be chosen when the drying temperature was higher.The tempering period can increase the drying rate in the subsequent drying stage,especially in the late drying stage.At the same time,combined with the experimental results and related literature,it was found that intermittent drying is suitable for drying heat-sensitive materials.