旋转托盘式微波真空干燥机设计与试验

Design and Experiments of Rotating Tray Microwave Vacuum Dryer

针对传统微波干燥装置存在的物料受热不均、热点难以控制及干燥品质劣变严重等问题,设计了一种旋转托盘式微波真空干燥机。该机由干燥箱、控制系统、真空系统、传动系统、制冷循环系统和微波加热系统等组成。干燥过程中,在驱动装置的作用下物料随旋转托架绕主轴匀速转动,使物料受热均匀;真空系统在抽真空的过程中能及时将物料蒸发出的水分抽离;采用制冷循环系统,可保证真空泵精准维持干燥腔室内所需真空度;控制系统通过控制真空微调阀可使干燥室内的干燥压力在真空与常压之间有规律地变化。以番木瓜为试验原料进行了干燥机性能试验,结果表明,旋转托盘式微波真空干燥机性能较好,与传统微波干燥方式相比,满装载量提高了80%,干燥时间缩短了43.8%,单位能耗降低了29.8%,且脱水量均匀度达到97%,内外色泽一致,具有良好的干燥均匀性。所设计的干燥机可确保物料受热均匀,提高了干燥效率和物料干燥品质。

A rotating tray microwave vacuum(RTMV)dryer was designed to solve the problems of uneven heating of materials,difficult control of hot spots and poor dried quality.The machine was composed of drying box,control system,vacuum system,transmission system,water circulation system and heating system.In order to make the material heating uniformly,the main axis with five evenly distributed rotating bracket was placed into the microwave vacuum drying chamber and driven by a stepper motor.During the drying process,the material was rotated constantly around the main axis with a horizontal level.The vacuum system can remove the moisture evaporated from the material in time during the vacuuming process.The combination of dryer and water circulation system ensured the normal operation of vacuum pump,so as to maintain the vacuum pressure of drying chamber consistently.The control system can be divided into five modules:the main control,A/D conversion,expansion,output control and display screen.The system took the P89V51RD2FN chip as the core to control the coordination of each module,which can adjust the drying pressure in the drying room between vacuum and normal pressure precisely.The papaya was used as the material for the performance test and compared with the traditional microwave drying method.The results showed that the carrying capacity of the dryer was increased by 80%compared with the latter.And the drying time was shortened by 43.8%at the same time.The unit energy consumption of papaya slices treated by RTMV dryer was about 29.8%lower than that by the conventional way.And the dehydration uniformity reached up to 97%with consistent color distribution between inner and outer of the dried sample,showing good drying uniformity of RTMV drying technology.The designed dryer ensured the uniform heating of materials,improved the drying efficiency and guaranteed the drying quality of materials,which provided a reference for the subsequent application.