Study On The Enhancement Of Heat Transfer For Isothermal Chamber During Discharging

Isothermal chamber,which is fabricated by empty chamber stuffed with a certain mount thin copper wire in filled uniformly generally.Because the air temperature in the isothermal chamber is almost constant during charging or discharging,so it is applied widely in the testing and control of pneumatic system.However,the tiny temperature change still exists in isothermal chamber during actual charging or discharging.The scale of deviation to isothermal process can be regard as an index to measure the performance of isothermal chamber,also that can be called isothermal characteristic.In order to improve the isothermal characteristic of isothermal chamber and enhance the testing and control precision during application process,this paper regards the thin copper wire as porous media with large porosity,and study on effects of its distribution on the heat transfer enhancement during discharging for isothermal chamber.During discharging,the chamber wall and the copper wire are the main heat source,and the main forms of heat transfer are heat conduction and heat convection.Firstly,enhance the heat conduction from the chamber wall to internal in order to narrow down the temperature difference between the chamber wall and the center of chamber.Therefore,the distribution of thin copper wire on chamber cross section was studied and the heat conduction model was established.The linear variable density filling method and the adaptive growth method were used respectively to optimize the distribution of copper wire.Compared with the uniformly filled case,the results of the center temperature were increased 4.94% and 16.50% respectively.Then the heat conduction experiment and simulation were carried out to verify it.It turned out that the distribution of thin copper wires can enhance the heat conduction from the wall to internal,and the two methods could be used to optimize the structure of thermal conductivity material,moreover the result of adaptive growth method is better than the linear variable density method.Secondly,the convection heat transfer model of isothermal chamber during discharging was studied.Four kinds of isothermal chambers were discharged by four solenoid valves with known flow rate characteristics respectively,the pressure curves were collected by experiment and the temperature curves were obtained by “stop method”.Based on the thermodynamic model and combined with pressure curves and temperature curves,the convection heat transfer empirical formulae were achievedaccording to the similarity principle.And then the discharging experiments by two different solenoid valves were carried to verify the correctness of the empirical formulae.These empirical formulae not only reflect the quantitative relation between the discharging speed,the copper wire filling density and the heat transfer intensity but also the influence of the air compression ratio to heat convection.Furthermore this convection heat transfer model including the convection heat transfer empirical formulae can be used to predict the isothermal characteristic of isothermal chamber during discharging.Finally,in order to improve the isothermal characteristic of isothermal chamber,the distribution of thin copper wire in isothermal chamber was studied which was aim to enhance the heat transfer during discharging.Based on the velocity field and the temperature field of isothermal chamber in the longitudinal section during discharging by simulation,combined with the distribution rule of copper wire in cross section,the optimized distribution scheme was determined according to the field synergy theory.Based on the distribution scheme,several comparison experimental scheme were designed.According to the analysis of experimental results,it can be shown that the optimized distribution scheme can improve the isothermal characteristic of isothermal chamber effectively.