Research On Heat Transfer Mechanism Of Supercritical Carbon Dioxide In Solar Receiver Tubes

In recent years,with the massive using of fossil energy,on the one hand,the non-renewability of fossil energy has caused public concern about energy depletion;on the one hand,greenhouse gas emissions have intensified environmental damage.Solar energy has become a clean and renewable alternative to future energy.Research on solar power technology has gradually gained more and more attention from various countries.As the most important technology for solar power generation,an efficient energy carrier is used to realize the conversion of solar energy.The power generation technology can be greatly improved,and supercritical CO₂ has attracted the attention of researchers due to its excellent heat exchange capacity and high Brayton cycle efficiency.Based on this background,the heat transfer mechanism of supercritical CO₂ in the heat absorbing tube of solar solar receiver is simulated.Through the NIST physical property database and Fluent interface instructions,we can set the physical properties of supercritical CO₂ in Fluent,then design the single tube physical model and tube row heat sink physical model,and perform grid independence verification.The Reynolds number was used to determine the turbulent state at the convective heat transfer of a single tube.Standard k-?,RNG k-?,SST k-?,and three Low-Re k-? turbulence models were used to simulate.Obtain a turbulence model applicable to the project conditions.The single pipe simulation is used to analyze the influence of the inlet effect in the single pipe simulation to determine the inlet length.To analyze the causes of buoyancy effect and flow acceleration effect,the buoyancy factor number and Richardson Ri number is introduced to determine the degree of buoyancy effect on convective heat transfer,and dimensionless K_vt and K_vp is introduced to determine the effect of flow acceleration effect on convective heat transfer.Selecting appropriate working conditions for simulation is to analyze inlet temperature,system pressure,inlet flow,heat flux density,and tube diameter on supercritical CO₂ convection heat transfer.Count the current commonly used Nussel correlations,and determine whether there is a buoyancy correction term and a flow acceleration factor correction term based on the analysis of buoyancy and flow acceleration effects.Select several types of correlated Nusselt numbers and simulate convection.The Nusselt numbers obtained by back-calculating the thermal coefficients are compared,and the appropriate correlations with the smallest errors are obtained for improvement,and the Nusselt numbers with the highest reliability and accuracy are obtained.A tube-row type heat sink was designed to simulate the heat transfer of the heatsink in the project.Under the uniform heat flux density of the half wall,the simulation was carried out under different inlet flow rates to analyze the uniformity variation of the flow distribution of each heat absorbing tube of the solar receiver.In practical applications,the heat flux density of the wall of the heat sink should be uneven,and there is heat loss problem on the outer wall surface and the outside.In this chapter,the UDF is used to simulate the convective heat transfer under the wall heat flux density of three kinds of unevenness.The influence of wall heat flow non-uniformity on the wall temperature of the solar receiver,the temperature distribution of the fluid,and the working efficiency.A tube-row type heat sink with inlet side of the header is designed to analyze the influence of different inlets on the flow and heat transfer of the solar receiver,and the advantages and disadvantages of the two inlet methods are determined to provide theoretical research of the designing the inlet structure of the solar receiver.