Numerical And Experimental Study On Flow And Heat Transfer Characteristics Of Supercritical Carbon Dioxide In Airfoil Pche

The"double carbon"goal puts forward new requirements for clean and efficient utilization of coal.Further reducing the energy consumption of thermal power industry is one of the important means of energy conservation and emission reduction.Compared with the traditional steam Rankine cycle,the supercritical carbon dioxide（S-CO₂）Brayton cycle has the advantages of high cycle efficiency and compact structure,and has great development prospects.Among them,the low-temperature regenerator has large heat load and high heat loss,and its design is related to the compactness and cycle efficiency of the system.In this paper,for the 600 MW primary reheat recompression S-CO₂ coal-fired cycle power generation system designed by Li Pingjiao,the airfoil PCHE is selected to study the flow and heat transfer characteristics in the low-temperature regenerator,and the airfoil PCHE is optimized.Firstly,the three-dimensional mathematical and physical model of the straight channel PCHE is constructed,and the working conditions of the precooler in the 600 MW primary reheat and recompression S-CO₂ coal-fired cycle power generation system are numerically simulated.The PCHE test platform is built to test the straight channel PCHE test pieces to verify the effectiveness of the mathematical model.Based on the working condition of low-temperature regenerator in S-CO₂ Brayton cycle system,the off design numerical simulation of operating conditions was carried out,and the effects of mass flow,inlet temperature and outlet pressure on the flow and heat transfer characteristics of airfoil PCHE were studied.The results show that in the allowable range of pressure drop and fluid outlet temperature,improving the fluid mass flow is beneficial to the comprehensive performance of airfoil PCHE,but the improvement effect decreases with the increase of mass flow;The influence of fluid inlet temperature on fanning friction factor is less than 6%,and the influence on total heat transfer coefficient is less than 1.5%.Using lower fluid inlet temperature can reduce the pressure loss of fluid,improve the Nusselt number of hot fluid,and improve the comprehensive performance of airfoil PCHE;The influence of fluid outlet pressure on fanning friction factor is no more than 1%.Under low cold fluid outlet pressure,the Nusselt number of cold fluid is increased by 6.7%,the total heat transfer coefficient is increased by 0.3%,and the comprehensive performance of airfoil PCHE is improved,while the hot fluid outlet pressure has little effect on the heat transfer performance and comprehensive performance of airfoil PCHE.At the same time,in order to obtain the airfoil PCHE structure suitable for the low-temperature regenerator in the S-CO₂ Brayton cycle system,the airfoil PCHE models with different fin arrangement are constructed to explore the effects of fin interleaving degree,vertical distance and horizontal distance on the flow and heat transfer characteristics of the airfoil PCHE.The results show that the comprehensive performance of the airfoil PCHE with fully interleaved fins is 50%higher than that of the in-line airfoil PCHE;With the increase of the vertical distance of fins,the comprehensive performance of airfoil PCHE continues to improve,but the improvement range gradually decreases;When the horizontal distance of fins increases,the pressure drop will increase and the heat transfer will not be strengthened.The comprehensive performance of airfoil PCHE with smaller horizontal distance of fins is better.Based on the conclusions of the above operating conditions and fin arrangement on the flow and heat transfer characteristics of airfoil PCHE,the shape of airfoil fins is optimized.After optimization,the fluid pressure loss in PCHE is reduced,the value of Nu/Eu is higher,and the synergy between flow field and temperature gradient field is better.The off design performance analysis of the optimized PCHE shows that the comprehensive performance of the optimized PCHE decreases under high cold fluid outlet pressure;At higher cold fluid inlet temperature,the heat transfer performance in PCHE after optimization is reduced,the comprehensive performance of cold fluid is increased by 21.4%,and the comprehensive performance of hot fluid is reduced by 3.2%;Lower inlet temperature of hot fluid can reduce fluid pressure drop and improve comprehensive performance.The optimized flow heat transfer correlation in PCHE is proposed in the range of 8800～223000 Reynolds numbers to provide an efficient low-temperature regenerator design scheme for 600 MW primary reheat recompression S-CO₂ coal-fired circulating power generation system.