The Simulation Study Of Thermal Conductivity Properties For H₂O/CO₂/H₂ Mixtures In Supercritical Regions Of Water

Coal is still the domain source of power generation for China in the next decades.The comprehensive utilization efficiency of coal-fired power plant is relatively low and it causes serious environmental pollution.That is an urgent problem need to be solved.Supercritical water coal gasification technology is a new kind of coal clean utilization and conversion technology.The organic matter of coal are gasified in supercritical water environment and mainly converted into H₂,CO₂ and inorganic precipitation.It prevents the formation of SOx and NOx.At present,the supercritical water coal gasification technology is not widely used in industry,so further research is needed.The thermophysical properties study of supercritical H₂O/CO₂/H₂ or H₂O/CO₂ mixtures is the key point for supercritical water coal gasification technology.Thermal conductivity is a very important thermal transport parameter for working fluids.However,there is not report for the thermal conductivity of H₂O/CO₂,H₂O/H₂ and H₂O/CO₂/H₂ mixtures in supercritical regions at present.In this paper,we used the equilibrium molecular dynamics simulation method（EMD）to investigate the thermal conductivity of H₂O/CO₂,H₂O/H₂ and H₂O/CO₂/H₂ mixtures,and compared the simulation results with theoretical calculation results.The main work of this paper as follows:（1）The thermal conductivities of multiple pure working fluid force field models are calculated by the molecular dynamics simulation.The simulation results are compared with the experimental values or NIST data,then the appropriate force field models are selected to be used in the simulation calculation of mixtures.（2）The system model of binary mixtures are established.Firstly,the thermal conductivities of CO₂/H₂ mixtures are calculated by EMD.we can found that the simulation results are closer to the NIST data than theoretical model calculation results,by comparing the simulation results with NIST data and KM and MS theoretical model calculation results.Then we calculated the thermal conductivities of H₂O/CO₂ and H₂O/H₂ binary mixtures by EMD.The results show that at the temperature of 850K and the pressure of 24-32 MPa,the thermal conductivities of H₂O/CO₂ and H₂O/H₂increase with the increase of pressure.（3）The system model of ternary mixtures are established.And the thermal conductivities of H₂O/CO₂/H₂ mixtures are calculated by EMD,then the simulation results are compared with KM and MS theoretical model calculation results.We found that at the pressure of 25MPa and the temperature of 673-973K,the thermal conductivities of H₂O/CO₂/H₂ declines firstly and then increases with the increasing temperature.When the X_H2 is relatively large,the average absolute relative deviation between the MD simulation results and calculation results is also relatively large.We investigated whether the system size have the effect on the thermal conductivities simulation results.Finally,the radial distribution function of H₂O/CO₂/H₂ mixtures are analyzed.