Experimental And Numerical Investigation On The Thermodynamic Vent System With R141b As Working Fluid

Deep space exploration and space station operation call for technologies for long term storage of cryogenic propellants such as LH₂,LO₂ and LCH₄.Even for well-insulated cryogenic storage systems,space thermal radiation can still bring in heat leak with rates on a level of0.1¹W/m²,which,althouth low,will result in inevitable pressurization of the closed storage tanks.The vaporation on the tank has to be vented when the pressure reaches the up-limit of operating pressure.Spray-bar thermodynamic vent system（TVS）has emerged as a promising mechanism that enables tank pressure control of cryogenic propellants on orbit with a minimum penalty in mass loss.To investigate the primary principle of TVS in pressure control is of important theoretical and practical significance for the long term storage of cryogenic propellants.In literature,the effects of control strategy,un-uniform heating,etc.on the TVS havn’t been studied experimentally.Most simulations on TVS used homogeneous model,lumped parameter approach and 0-dimention model based on the thermodynamic process,which were not able to reveal the temperature and flow fields,expecially when it works under the injection mode.Regarding these problems,the following contents have been carried out:First of all,a simulator of TVS working at room temperature has been developed.The heat exchanger/spray bar apparatus adoped in this system couples the functions of heat exchange and spray.This system can not only achieve uniform heating but also un-uniform heating.The sealing and repeatability of the system are tested.It shows that the repeatability is more than 98%.It shows that this setup is able to simulate the progress of thermodynamic vent of evaporative fluids in a container under the condition of safety,reliability and low cost.Secondly,the effects of heat load,fill level,pressure control band,control strategy and un-uniform heating on TVS have been carried out.The pressure control characteristics and mass loss were obtained.The ullage pressure was found to increase linearly during self-pressurization.The rate of pressure increases under the spray and vent mode is lower than that of spray mode.Mass loss as a result of tank pressure control is compared between the TVS method and the direct gas vent method.Taking the heat load of 120W as an example,the mass loss can be reduced by79.3%.It is proved that the TVS method can not only control the tank pressure but also significantly reduce the loss of the storage fluid.Thirdly,a three-dimensional model based on VOF method was established to simulate the self-pressurization process.This model was solved by commercial software FLUENT.The heat transfer coefficient at the top and bottom wall of tank is determined by comparing with experimental measurement.The model is verified through experimental results with different fill level（50%,65%）and heat load（120W,160W）.The error between experiment and simulation is less than 1.13%。The flow and temperature contours are analysed.The mass change of vapor and liquid phase is also investigated.Fourthly,a one-dimensional,incompressible model has been developed to predict the flow distribution on spray orifices before simulating the spray process.Then,a three-dimensional model is applied to simulate the spray process.The error between measurement and simulation is less than 0.54%.The flow and temperature contours during spray are analysed.