Research On Heat Transfer Of Supercritical Carbon-dioxide In Tubes

The process of supercritical carbondioxide's mixed convection and heat transfer in cube has been investigated through numerical simulation and experiment.We have researched on a variety of independent variables,tried to figure out their functions on heat transfer.All of these outcomes will contribute to better modification of numerical models and more specific prediction of heat transfer,which may help to explain the mechanism of heat transfer deterioration.They can be used as database or reference for the coming design and prediction of experiment cases.A quatity of models' identification and sensative analyses have been taken to decrease the comsumptioon of computing resources and improve simulation's exactness,SST k-w turbulence model was chosen to predict the process of fluid's heat transfer and quatity transfer.The variation of physical properties in heat transfer deterioration and normal heat transfer are investigated and explained through the comparison and analysis of experimental datas and numerical outcomes.There are a series of cases designed to investigate the affections of flow rate?inlet's pressure and heat flux on heat transfer.The connection between buoyancy force?thermal acceleration?thermal load and heat transfer are also analysed through some dimensionless numbers,such as Bo and Ac.It has been proved by the simulation's outcome,in the cases of normal heat transfer,while the temperature of wall has exceed pseudocritical temperature and bulk temperature of fluid is still lower than pseudocritical temperature,a specific zone of fluid's temperture which is around pseudo temperature mainly appears in the buffer layer(5<y+<60)in the radial direction of tube.Tha gradient of the properties of flow is smooth,the flow develops like a fully developed turbulence while the turbulent kinetic and heat transfer coefficence are stable.Large specific-heat region won't develop into the core flow of turbulence until bulk temperature approach pseudocritical temperature.Heat transfer crisis won't happen because the curve of thermal properties remain smooth.While heat transfer deterioration appears,its wall temperture usually exceeds pseudocritical temperature a lot,but its bulk temperture remains much lower than pseudocritical temperature.In these cases,large specific-heat region develops from buffer layer into core flow fast,which contributes into the formation of low density layer near the wall.The curve of velocity in the core flow is smooth,which indicates the gradient of velocity and tubulent intensity approach zero and the Reynold shear stress continues to decrease.Heat transfer deterioration won't be curved until M-shape flow develops,which means the direction of Reynold shear stress starts to change and the level of Reynold shear stress in buffer layer begins to recover.Although wall temperature is still increasing,its growth rate is diminishing.Heat transfer deterioration won't end until the temperature of wall reach peak point,during this section the coefficience of heat transfer will recover.