Experimental Study And Equipment Design Of Hot-air Vacuum Combination Drying For Fruits And Vegetables

Traditional drying technology is unable to meet the needs of modern social production due to its simple way,low efficiency and high energy consumption.In recent years,the emerging combination drying technology has been widely concerned by scholars and business staff in the drying field,its drying process is more scientific,efficient and more energy saving.As one of them,hot-air vacuum combination drying not only accelerates the drying efficiency,saves energy,but also improves the quality of the products.It uses hot air drying to remove free water and vacuum drying to remove the bound water in fruits and vegetables.Although some domestic research institutions have developed equipment for hot-air vacuum combination drying,it's just a simple realization of hot air drying and vacuum drying in the same equipment.The energy consumption of the equipment itself,the controllability of operating condition,the problems of on-line monitoring and automation are urgent to be solved.So to design a sophisticated and advanced test equipment is very significant for theory research and industry promotion of this technology.This thesis does experimental study,summarizes deficiency of the equipment and optimizes the equipment by using the test data.The thesis is with support of industrial project which is named "design and study of equipment for hot-air vacuum combination drying(2014K07-19)",and which is approved by Shaanxi province science and technology department.The specific contents are as follows:(1)Experimental studyThe optimum parameters of hot-air vacuum combination drying process for lemon and cabbage etc are optimized by single factor test and orthogonal test,it provids theoretical and technical support for the subsequent design of equipment.Meanwhile,problems existed in the pilot-pant are analyzed and summarized.(2)Drying equipment designDesign a new drying box respect to problems found in the process and establish its three-dimensional model by Solid Works,then use ANSYS Workbench CFD numerical simulation to verify the feasibility of the box.In order to improve the utilization rate of solar energy,the energy calculation is used to calculate the water tank and collector of solar energy system.(3)Design of control systemAdd the corresponding automatic detection instruments according to the test process and design control system using the SIEMENS S7-200 PLC controller as the main hardware,MicroWIN as software development tool.To solve the visual operation problem during drying process,make the new equipment can monitoring test data on-line,reduce the operation errors in the process,provid a more sophisticated hardware platform for the hot-air vacuum combination drying.In this master's thesis,the best combination drying process parameters of lemon,cabbage etc are optimized and embedded in the designed automatic control system.The structure of the rotating material tray,conical air duct and spiral hot water coil are designed according to the problems reflected in the test and establish the three-dimensional model with SolidWorks.The result of CFD numerical simulation shows that the design scheme is feasible.The flat plate heat collector of solar system is replaced by 35 Phi 58×1800 mm all glass vacuum tube collector and water ank capacity is changed to 1m3 by calculation.The infrared moisture sensor,PC,SIEMENS S7-200 PLC and other hardware are added to the original system,and the control system is designed by using MicroWIN as the software development tool.