Research On The Heat Transfer Characteristics And Application Of In-tube Supercritical Flow

Supercritical fluid is a substance of especial status between gas and liquid.It has both the characteristics and advantages of gases and liquids,and has been widely used in the areas of power engineering,nuclear power,cryogenic superconductor,HVAC,aerospace,and so on.One of the most important characteristics of supercritical fluid is that its thermal properties vary dramatically with temperature,especially in the vicinity of the critical and pseudo-critical points,which makes the heat transfer characteristics differ from that of conventional forced convection.This paper takes supercritical carbon dioxide as the research subject first for numerical studies to find out the flow and heat transfer characteristics of laminar and turbulent flow under supercritical pressure.Then,on the basis of the numerical calculation results,the existing heat transfer calculation methods of supercritical fluid are summarized,analyzed,and assessed.According to the supercritical heat transfer correction criteria and the least square method,new heat transfer correlations are proposed,based on which,the application of supercritical hydrocarbon fuel in the design process of hypersonic vehicle integrated thermal management system is implemented.The main work and achievements are listed as follow:(1)The two-dimensional governing equations of supercritical heat transfer of laminar flow under cylindric coordinate system are established.The calculation method to the equations is programmed and the results are verified by experimental data.According to the calculation method,the distributions of velocity,temperature,and heat transfer of in-tube laminar flow under supercritical pressure are obtained.Finally,the influences of the inlet pressure,tube diameter,mass flux,heat flux,inlet temperature,and flow direction to the supercritical heat transfer of laminar flow are discussed.(2)The three-dimensional governing equations of supercritical heat transfer of turbulent flow under cartesian coordinate system are established.The SST k-? turbulence model and the CFD software are adopted to calculate the equations and the results are verified by experimental data.According to the calculation method,the distributions of velocity,turbulent kinetic energy,temperature,and heat transfer of in-tube turbulent flow under supercritical pressure are obtained.Finally,the influences of the inlet pressure,tube diameter,mass flux,heat flux,and flow direction to the supercritical heat transfer of turbulent flow are discussed.(3)Based on the comprehensive compiling and processing of the existing supercritical heat transfer correlations,the features of the existing correlations are summarized.Wide-ranging experimental databases of supercritical heat transfer,which have been classified into different categories according to a partition criterion,are set up for the assessment of correlations.After comparing the existing correlations to the databases,the conclusions of the adaptability analysis for the correlations can be made,which is the basis for the selection of the existing correlations and the development of new correlations.(4)The general form of a new supercritical heat transfer correlation to be determined can be given by the supercritical heat transfer correction criteria and the adaptability analysis results summarized in this paper.By using the least square method and MATLAB programming,the implementation of solving the fitness between various combinations of dimensionless numbers and the databases of supercritical water and supercritical hydrocarbon fuel,can be optimized through iteration.Two new correlations of supercritical water and supercritical hydrocarbon fuel are proposed with a simple form,wide-ranging applicability,and high prediction accuracy.(5)Plans for hypersonic vehicle integrated thermal management system are discussed.According to the supercritical heat transfer calculation method proposed in this paper and the graphical interactive interface of MATLAB / SIMULINK platform,the main functional modules of integrated thermal management system are packaged and used to accomplish the design process of the supercritical hydrocarbon fuel integrated thermal management system.Finally,the influences of the design parameters to the results of the system design are analyzed.