Experimental Study On The Flow And Heat Transfer Characteristics Of Supercritical Carbon Dioxide In Vertical Tubes

Supercritical CO2(S-CO2)is a kind of coal-fired thermal power generation in recent years,which has aroused great concern.The use of CO2 to replace water,the use of CO2 inactive and high density of materials to reduce the harsh requirements of the material,effectively improve the steam temperature and pressure parameters and power generation efficiency,significantly reducing the unit size.Refrigerating,heating and low grade energy utilization using carbon dioxide as the working fluid have turned out to be a promising research area.Experimental setup construction and proper operation are important for the development of trans-critical cycles and heat transfer facilities.In this experiment,the heat transfer characteristics of supercritical carbon dioxide at high temperature and high pressure are obtained through the construction of the experimental setup.It is hoped that the data collected by the experimental platform and the construction of the experimental setup can be widely used in the single phase of CO2,Two-phase and supercritical fluid heat transfer research,the construction of other heat transfer experimental setup also play a important reference role.When the pressure P=8.2-20.2 MPa,the mass flow rate G=512.7-1524.4 kg/(m2s),and the heat flux density qw=49.7-200 kW/m2,the CO2 was carried out in a stainless steel tube with an inner diameter of 10 mm and a length of 2000 mm.Experimental study of heat transfer characteristics.The effects of pressure,mass flow rate,mainstream enthalpy and heat flux on heat transfer characteristics were analyzed.The results show that the wall temperature increases with the increase of mainstream enthalpy,heat flux and pressure.With the increase of mass flow rate,the wall temperature decreases,and the change of heat transfer coefficient is opposite to the change trend of wall temperature.The Dittus-Boelter,Jackson and Bishop heat transfer correlations were used to predict and compare with the experimental data.It is found that the predicted values are generally small relative to the experimental values when the Nu number is large,and the Bishop correlation is used in the three correlations,which predicted error is minimal.Meanwhile this paper presents an experimental investigation of the pressure drop and friction factor of supercritical CO2 in circular tube.Experimental length and inner diameter of the circular tube are 2000 mm and 10 mm.The experimental pressure P=8.2-20.2 MPa,mass flow rate G=512.7-1524.4 kg/(m2s),and heat flux on the inner wall qw=49.7-200 kW/m2.The variation of flow resistance was obtained and the effects of pressure,mass flux,heat flux and bulk fluid enthalpy on the frictional flow resistance coefficient of the circular tube were analyzed.Results showed that the frictional pressure drop increases significantly with increasing mass flux and pressure,particularly when the bulk enthalpy surpasses the pseudo-critical enthalpy,Increased speed has become more intense,meanwhile,it is found that the influence of heat flux on the friction pressure drop is not too great.The assessment of correlations demonstrated that constant property based correlations fail to predict the friction factor of supercritical CO2.Hence,a new correlation was proposed which captures 83.31%of the experimental data within ±20%error band.