Design And Experiment On Ohmic Heating Temperaturecontrol System Of Food

Heat treatment of food is an important technology in food processing,and heat treatment technology related to the quality of foods and the final heat treatment costs. Ohmic heating provides a new way of thermal food processes,and has more advantages than conventional heating methods such as conduction and convection. However, because the constant voltage is applied in current ohmic heating technology,the heating rate and temperature holding can not be effectively controlled. Therefore, the design of an ohmic heating system heating rate and holding temperature has important value and practical significance.This study designed an ohmic heating temperature-controled system. And the research contents and conclusions are as follows:(1) Determination:system design module with automatic voltage regulator modules,data acquisition modules,input and output modules,heating bath with parallel plate electrodes.Determine the structure of the relationship between the main modules and each module according to the demand.(2) Hardware system:automatic voltage regulator module mainly comprises a silicon controlled automatic pressure regulating system.Data acquisition module mainly consists of current acquisition system, voltage acquisition system and temperature acquisition system.Input and output module mainly contains a display screen,indicating lamps and the function keys.Finally all modules are integrated as ohmic heating temperature control board.(3) Software system:complete the test of functional keys program, control procedures of heating rate and heat preservation.Before the system works,set required heating rate holding temperature and holding time.After completing parameter setting,the system will enter the heated state by pressing the start key. When the temperature reaches holding temperature,the system will enter the insulating state.After reaching the holding time,the system automatically closes,and the heat treatment is finished.(4) System test verification and evaluation:Use the pure milk as heating object Set different heating rate and heat preservation temperature,and carry out ohmic heating test.The results show that the temperature increases linearly with time and the relative error between the actual heating rates and the set values are between 1% to 4%,so the system can effectively control the heating rate. Then,the thermal insulation test was completed by setting different holding temperature. The experimental results show that the temperature in the heat preservation time is less than 20 s,the maximum temperature overshoot is less than 1.5℃,and the maximum temperature difference at the stabilization process is less than 1℃.The temperature stables gradually near the set temperature during heat preservation process,so the system can effectively control the temperature.