Flowing Heat Transfer And Optimization Of S-CO₂ Brayton Cycle Microchannel For Advanced Nuclear Energy

The Brayton cycle is a heat exchange cycle system which usually used in large heat exchange equipment in recent years.The cycle efficiency of the entire closed system is higher than that of the traditional Rankine cycle.Applying it to the nuclear heat transfer system will increase the efficiency of the entire equipment to achieve the purpose of optimal use of resources.Compared with conventional plate heat exchangers,PCHE(printed plate heat exchanger)has the advantages of compact structure and good safety.Based on the PCHE microchannel in the Brayton cycle system of nuclear,a three-dimensional modeling software PROE is used to establish a physical model of the microchannel in this paper.Numerical simulation of heat transfer characteristics and entropy production during the flow of supercritical carbon dioxide working fluid in micro channels by numerical simulation software.According to the calculation results,the influence of each working condition parameter on the heat transfer efficiency is analyzed,and its purpose is to provide a safety reference in practical applications.Theoretical analysis on the change of thermal properties parameters of supercritical carbon dioxide.Supercritical carbon dioxide is a safe and non-toxic working medium with good heat transfer effect and easy access.Applying it to the microchannel of the heat exchanger will improve the working efficiency of the entire heat exchange equipment to a certain extent.The pressure and temperature of supercritical carbon dioxide,that is,carbon dioxide,are both at critical values(7.38 MPa,31.04 ° C),and their physical parameters have relatively obvious changes near the critical values.From the distribution curve of carbon dioxide density and specific volume,it can be seen that pressure and temperature have a greater impact on the thermal physical parameters of carbon dioxide,especially the specific heat capacity,which is specifically expressed as the distribution curve of the specific heat capacity ofcarbon dioxide that first increases and then decreases with the increase of temperature,especially near the critical point,the specific heat capacity changes sharply,rising sharply to a peak value and then decreasing sharply.The specific heat capacity peak value gradually shifts to the right as the temperature increases,and when the pressure parameter is 8 MPa,the specific heat capacity reaches its peak value and supercritical carbon dioxide heat transfer at this time.best effect.Study on the influence of supercritical carbon dioxide heat transfer characteristics in micro channels.This paper uses numerical simulation software to calculate and analyze the heat transfer characteristics of supercritical carbon dioxide in micro channels based on the three-dimensional microchannel physical model.Based on the PCHE single channel model,this paper first conducts a numerical study on the cross sectional shape of the channel,and calculates the influence of the change of the cross sectional shape of the channel on the heat transfer characteristics of supercritical carbon dioxide in the channel.In the process of numerical simulation researching,the dimensionless parameter of the structural factor is introduced.The analysis results show that different channel cross-sectional shapes have a certain degree of influence on the heat transfer characteristics of the flowing working fluid in the tube.When the crosssectional shape structural factor is 1,that is,the channel cross-sectional shape is semicircular,the supercritical carbon dioxide working fluid in the tube has the highest heat transfer efficiency.It can be known that the change of working condition parameters has a certain degree of influence on the heat transfer characteristics of the flowing working fluid in the channel.This time,we mainly studied the effects of system pressure,inlet mass flow rate,and hot fluid inlet temperature on the heat transfer characteristics in the channel.The decrease in system pressure will bring the supercritical carbon dioxide physical properties closer to the critical physical properties,that is,the larger the specific heat capacity,the higher the temperature of the cold fluid outlet,the greater the disturbance in the channel,the Reynolds number,and the heat exchange effect between the cold and hot fluid in the microchannel The better.Similarly,the increase of the inlet mass flow rate and the temperature of the hot fluid inlet will both increase the temperature of the cold fluid outlet and increase the heat exchange effect between the cold and hot working fluids.Study on Entropy Production Law of Supercritical Carbon Dioxide Heat Transfer in Microchannel.Entropy production is a physical quantity describing the irreversible degree of the system.it can be used as a parameter to measure the heat transfer effect in the system.Based on the PCHE microchannel physical model,numerical simulation software was used to calculate the entropy production of cold and hot fluid in the channel under different operating conditions,and the influence of different operating conditions parameters on the entropy production in the channel was analyzed.According to the analysis and calculation results,it can be known that the increase of the system pressure will cause the increase of the entropy production,that is,the decrease of the heat exchange efficiency in the channel.As the system pressure increases,the entropy production will increase,and the irreversibility of the system will increase.At the same time,the increase of the inlet mass flow rate and the increase of the hot fluid inlet temperature will cause the entropy production in the channel to increase,and the heat exchange effect in the channel will be deteriorated.