Research On Key Technologies For The Design Of Air Electric Heating Devices In Complex Channels

The channel type gas electric heating device is an important equipment for conducting aerodynamic field tests in the aerospace field.Unlike ordinary gas electric heating devices,it is characterized by high temperature,high pressure,and high heating power for gas heating.In its design process,theoretical issues such as heat transfer,fluid flow,and electrothermal conversion are involved.There is no relevant design method or suitable heat transfer empirical correlation in China.This article studies the key technologies involved through a combination of theoretical calculation,simulation,and experimental analysis.Four classic convective heat transfer correlations in existing technologies were verified and calculated under 76 operating conditions.According to the needs of practical engineering,the coupling relationship between heat transfer,fluid,and electric heating was analyzed,and a preliminary design method was provided.At the same time,based on relevant enhanced heat transfer theories,Three complex channel structures were proposed to reduce the wall temperature of electric heating elements and meet the constantly evolving needs.Relevant simulation calculations were conducted on them,and the main conclusions are as follows:The relevant heat transfer and fluid theoretical calculation of the channel type gas electric heating device are carried out.The results show that when the air inlet pressure is kept at 4.2MPa and the air inlet and outlet temperature is constant,with the increase of the air inlet flow rate,the air heat transfer coefficient and the maximum temperature of the metal wall increase,and the air outlet pressure decreases;When the mass flow rate is 0.486kg/s and remains unchanged,the inlet flow rate of air gradually decreases with the increase of air inlet pressure,but the air heat transfer coefficient,the maximum temperature of metal wall and the pressure drop loss of air inlet and outlet basically remain unchanged;Based on the principle of enhanced heat transfer,three new complex channel type gas electric heating device structural schemes have been proposed on the basis of the existing channel type structure,which are double-layer casing structure,jet heat transfer form,and shell and tube heat exchanger structure.The simulation of channel gas electric heating device shows that the simulation results are closest to the calculation results of the Grenski’s formula among the four classical convective heat transfer correlation formulas,and the change trend of air outlet pressure is the same as the change trend of the theoretical calculation results.The pressure condition of 0.15MPa～0.4MPa was simulated and calculated,and the simulation data such as channel wall temperature and air heat transfer coefficient were obtained.The three complex channel gas electric heating device structures designed in this thesis are simulated,and the results show that the heat transfer effect of the shell and tube heat exchanger structure is the best,the heat transfer effect of the single-tube heating structure is relatively poor,and the heat transfer effect of the jet heat exchange structure is close to that of the shell and tube heat exchanger structure when the flow rate is greater than 60m/s.The experimental data are compared with the simulation data of 0.15MPa～0.4MPa pressure condition,and the results show that the results obtained by the experiment are greater than the results of the simulation calculation,but the overall error is about 10%,which proves the relative accuracy of the simulation within the acceptable range.The experimental data are processed and the empirical formula of heat transfer law under different pressure conditions is returned,and the results show that for the channel gas electric heating device,in the pressure range of 0.15MPa～0.4MPa,the pressure has little effect on the convective heat transfer coefficient,which is consistent with the theoretical calculation under high pressure conditions.The work in this thesis analyzes and explores the design of channel type gas electric heating device,which provides theoretical support for the expansion and serialization of the product,and has certain reference significance for the design of complex channel type gas electric heating device.