Investigation On Heat Transfer Performance And Design Method Of Supercritical CO₂ Brayton Cycle Printed Circuit Heat Exchanger

At present,China,as a resource-consuming country,is facing the problem of energy exhaustion.As a renewable and clean energy,the rational utilization of solar energy can effectively alleviate the problem of energy shortage.The Brayton cycle using supercritical CO₂as working medium instead of the traditional steam power cycle can significantly improve the efficiency of photothermal power generation.The heat transfer performance of the regenerator in the cycle determines whether the heat can be fully recovered and utilized,thus affecting the thermal efficiency of the whole cycle system.Therefore,in this paper,sensitivity research,heat transfer flow analysis and design of key equipment（regenerator）in the Bretton cycle are carried out with supercritical CO₂ as circulating working medium in the background of Bretton cycle.In this paper,the recompression Brayton cycle is simulated based on Sandia experimental database.Two working conditions（537℃and 650℃）in the database were used for process simulation,and the database was checked and verified to obtain the key working parameters of the high temperature regenerator,which provided a numerical basis for the establishment of the design model and subsequent flow heat transfer research.At the same time,the sensitivity of the high and low temperature regenerator is analyzed by changing the shunt coefficient,the outlet temperature of the precooler,the total flow rate and other variables.The results show that the low temperature regenerator has a higher sensitivity to the outlet temperature of the precooler,while the split coefficient and the total flow rate have a great influence on the thermal load of the high and low temperature regenerator.The higher the split coefficient is,the higher the thermal load is,and the maximum difference of the corresponding thermal load is nearly 2times.（2）Based on the working parameters of the regenerator in the circulating system,the S type channel of the regenerator was numerically simulated by CFD.The amplitude A of the S-type channel is 0.4mm,0.6mm,0.8mm and 1mm,respectively.The period LPs were 4mm,8mm and 16mm respectively.CFD simulation was carried out for 96 groups of models based on 2 working conditions and 4 groups of inlet and outlet velocities of hot and cold fluids.The results show that with the increase of velocity or the decrease of operating temperature,the pressure drop△P and friction coefficient f at the corresponding position increase,and the heat transfer coefficient H and Nussel number Nu increase.The larger the amplitude or the smaller the period,the larger the fluctuation degree of the corresponding model,and the larger the pressure drop△P and the friction coefficient f at the corresponding position.At the same time,the influence of semicircular and rectangular cross-sections on flow heat transfer was investigated by changing the cross-section shape of S-shaped channel.The results show that the heat transfer intensity of rectangular cross-section is higher than that of semi-circular cross-section model,but the pressure loss is relatively higher.（3）According to the empirical formula,the above flow heat transfer data were respectively fitted with multiple linear equations,and the flow heat transfer correlations of different structures were obtained,which can be used to guide the design of PCHE.The error analysis between the calculated value of the correlation formula and the CFD simulation value shows that the error is between 0%and 30%,which meets the error requirements of fitting.At the same time,the PCHE thermal design and development of the fitting correlation formula were carried out.The distributed principle was used to calculate the heat transfer area of channels with the same heat load and different sections.