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Research On The Control Of Temperature Field For The Spacecraft Thermal Cycling Test System Based On Mixed Convection Heat Transfer

Posted on:2017-05-12Degree:DoctorType:Dissertation
Country:ChinaCandidate:G YangFull Text:PDF
GTID:1362330590490787Subject:Refrigeration and Cryogenic Engineering
Abstract/Summary:PDF Full Text Request
All space vehicles are subjected to extensive ground test to ensure their successful operational use.In the aspect of thermal performance test,the Thermal-Cycling-Test(TCT)has received much attention in recent years due to its advantages in efficiency and cost over traditional Thermal-Vacuum-Test(TVT).With the rapid development of aerospace engineering,the size of the space vehicle and the extreme temperature it will experience are ever increasing.It leads to an urgent demand for large scale TCT system with higher temperature field control technology.Aiming at these problems,this article presents a continually in-depth investigation to obtain a temperature field control theory for large scale TCT systems based on mixed convection heat transfer.The research is performed in the levels from mechanisms,methods,components,to system,which is presented as follows:Firstly,numerical simulation is carried out to study the flow structure,temperature distribution,heat transfer and entropy generation in a three dimensional vertical duct of laminar mixed convection heat transfer.The critical buoyancy parameter,above which the flow reversal occurs has been revealed for both assisted and opposed mixed convection.By this,the present flow reversal mechanism has been extended from two dimensional to three dimensional.Furthermore,the effects of such flow reversal phenomenon on temperature field,heat transfer and entropy generation are obtained and useful correlations are summarized.Secondly,as the accuracies of turbulent models for mixed convection or natural convection heat transfer with high Rayleigh number of Ra>1012 are unknown,an experimental system is designed to obtain applicative experimental data for the evaluation of the models.Hot wire anemometer and Platinum resistance thermometer are used to measure the velocity and temperature distributions point by point.Three turbulent models,which are RNG k-εmodel,L-B low Re k-εmodel and SST k-ωmodel,are used to simulate the experimental condition.By comparison with experimental time-averaged velocity,time-averaged temperature and turbulent turbulence,the L-B low Re k-εmodel is found to get the best result.Thirdly,turbulent mixed convection heat transfer in a large scale vertical duct with the size scale of 10 m is numerically investigated using the L-B low Re k-εmodel.The flow structure and temperature distribution under opposed and assisted buoyancy are analyzed,which extend the flow reversal characteristics from laminar flow to turbulent flow.The assisted buoyancy is found can lead to thermal stratification in the vertical direction,which makes the temperature uniformity much worse than that of opposed buoyancy.Furthermore,the correlations of the standard deviation of temperatures and entropy generation in the duct are obtained.Besides,the entropy generation by fluid friction is found negligible compared to that by heat transfer.Fourthly,the system circulation process based on opposed mixed convection heat transfer is designed for the large scale TCT system.An iterative method based on zero-dimension wall conduction model and the obtained mixed convection heat transfer correlation is provided to solve the heat transfer with complex wall structures.An optimization method based on entropy generation minimization(EGM)and temperature deviation minimization(TDM)is proposed for the real TCT system.On the other hand,experiments are carried out in the practical TCT system.The steady state temperature distributions for both heating and cooling cases prove the system can meet the demands for spacecraft thermal cycling test.By comparing numerical results with experimental data,the accuracy of the numerical method used in the foregoing chapters is found acceptable.At last,the thermodynamic model for the TCT system is built,and a dynamic simulation of the system is preformed to obtain the control characteristics.
Keywords/Search Tags:Thermal Cycling Test, Mixed Convection, Buoyancy Force, Spacecraft, Entropy Generation
PDF Full Text Request
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