Numerical Analysis Of Heat Transfer In Supercritical Water Upward Flow In Vertical Circular Tube

With the development of research on supercritical heat transfer,thermal power generation working,fluid has been gradually designed to supercritical condition,and its thermal efficiency has been greatly improved,up to 40%,which greatly improves the power plant's economy.As one of the six types of fourth generation advanced reactors,the supercritical water cooled reactor concept design is based on the excellent heat transfer behaviors.The highest utilization energy is about 45%,which is much higher than that of pressurized water reactor(32%).Under the design condition of supercritical water reactor,the system pressure is up to 25 MPa,and the core outlet temperature is higher than 500 ?.As a result,much effect have to be devoted to improve the thermos-hydraulic safety of SCWR.Therefore,the heat transfer of supercritical water flow under supercritical water reactor condition must be studied extensively.At present,the research on supercritical flow heat transfer can be divided into two categories: experimental study and numerical analysis.The experimental study on heat transfer characteristics of supercritical water is very expensive,and it is difficult to obtain flow field analysis at micro level.Therefore,the numerical analysis of supercritical flow heat transfer basing on finite experimental study is not only beneficial to reduce the research cost,but also to study the basic flow heat transfer phenomenon and mechanism in a wider range of parameters.Based on the experimental study of supercritical water heat transfer in10mm-diameter round tube of Shanghai Jiao tong University,the CFD numerical analysis method is used to analyze the heat transfer deterioration,heat transfer enhancement and sensitivity analysis of the main parameters in the vertical circular tube upwelling supercritical heat transfer.At the same time,the influence of turbulence model on numerical analysis results is studied,and the turbulence model is optimized by comparing with experimental data.The main ideas of this paper are as follows: firstly,the pipe model of supercritical water rising flow in vertical circular pipe is established by using CFD software,and the physical model is finite element and meshed.Then the boundary conditions and parameters are determined by reference to the experimental conditions,and the flow heat transfer phenomena under different working conditions are numerically simulated by selecting suitable low Reynolds turbulence calculation model.Finally,the parameters of the flow field at the micro level are obtained,and the normal heat transfer is analyzed.The occurrence mechanism of heat transfer phenomena such as heat transfer enhancement,heat transfer deterioration and so on.In this paper,three kinds of turbulence calculation models are selected,including a high Reynolds number turbulence model and two low Reynolds number turbulence models.The heat transfer characteristics of supercritical water rising flow in a vertical circular tube are numerically simulated by using the control variable method.In the meantime,by analyzing the sensitivity of the three turbulence calculation models,the error caused by the different grid magnitude is eliminated,and the grid structure andquantity are unified.The calculated results of the standard k-? turbulence model,thelow Reynolds k-? turbulence model and the low Reynolds k-? turbulence modelare compared with the experimental measurements under the same condition,and the results show that the standard k-? turbulence model suitable for high Reynoldsnumber can accurately calculate the normal heat transfer.The turbulence model with low Reynolds number is suitable for the calculation of heat transfer deterioration and heat transfer enhancement.Finally,the comparison between the two low Reynolds number models and the experimental results is made,and the better one is selected for the numerical analysis of heat transfer.Through the control variable method,the numerical simulation is carried out under different conditions of different pressure,different wall heat flux and different inlet mass flow rates by using the low Reynolds k-? turbulence model,and thetemperature distribution of the wall is obtained.The parameters of cross section flow field of pipeline under heat transfer deterioration and enhancement are extracted,and the factors affecting heat transfer deterioration and heat transfer enhancement of supercritical water flow in circular pipe are studied,including velocity gradient of flow field,density distribution,heat conductivity coefficient,specific heat of fixed pressure,etc.The heat transfer phenomenon and the corresponding heat transfer mechanism are analyzed in this paper.