Study On Flow And Heat Transfer Characteristics And System Optimization Of Heat Conducting Oil Electric Heaters

The thermal oil electric heating system uses the thermal oil as the heat carrier and realizes the heat transfer between the electric heater and the thermal equipment by convection heat transfer.It has the advantages of uniform heating and high temperature control precision,which can ensure the quality of polyethylene products.It is widely used in the heating device of polyethylene extruder.However,existing electric heaters usually use a bow baffle.There is a flow dead zone on the lee side of the baffle,which is easy to cause the temperature of local oil film to be too high,resulting in coking of heat conduction oil.When the oil film temperature reaches 700 ℃,it is easy to burn the electric heating tube.In this paper,the influence of baffle structure is studied to optimize the oil film temperature distribution uniformity of thermal oil electric heater and guide the design theory and practice of thermal oil electric heating system.The main research results and conclusions are as follows:In this paper,the spiral baffle electric heater is studied by numerical simulation.The results show that the spiral baffle can effectively improve the flow dead zone on the lee side of the curved baffle and greatly reduce the maximum oil film temperature.Compared with the curved baffle scheme,the oil film temperature is reduced by 39 K.However,due to the uneven velocity distribution in the inlet section of the spiral baffle,there exists a low velocity zone,which leads to the increase of the oil film temperature.Based on the four-part spiral baffle,electric heater models with different inclination angles are established.The PEC index was used to characterize the comprehensive performance of the heat-conducting oil-electric heater.And considering the influence of Nusselt number and friction factor on the comprehensive performance.It is concluded that 38 ° inclination Angle has the best comprehensive performance.In order to solve the problem of uneven velocity distribution in the inlet section of spiral baffle,the design of compound baffle electric heater is proposed.The influence of the structure of different inlet baffle and the lap mode of baffle on the performance of electric heater is studied.The results show that the uniformity of velocity distribution in the inlet section is the best when the inlet baffle is located at the upper part of the shell,the radius of the through hole is 8 mm and the central Angle is 45 °.Compared with the original scheme,the maximum oil film temperature is reduced by 70.34 K.When the difference between the equivalent incline angle and the incline angle is less than 4 °,the axial separation and lap bonding can enhance the comprehensive performance of the electric heater.An optimal expression DU for the uniformity of velocity distribution of a heat conducting oil electric heater is presented.Compared with CV,it can effectively reflect the influence of low flow velocity zone on the maximum oil film temperature.A 480 kW electric heater and a supporting process system are designed,and a test system is set up for heating the barrel of the extruder.Through the experimental test in a company in Dalian,the results show that the difference between the simulated value and the experimental value of the electric heater pressure drop is 6.232%.The reliability of numerical simulation method and system optimization is proved.