Molecular Dynamics Study On Heat Transfer Characteristics Of Cu-Water Nanofluids Under Supercritical Conditions

Although the traditional solid suspension can enhance the thermal conductivity of the fluid,there are still many shortcomings such as easy precipitation,excessive viscosity,etc.,and the practical application is limited.The nanofluids formed by adding nanoparticles in the working fluid developed in the new century have broken through many restrictions and become a hot research topic.At present,scholars' research on nanofluids mainly focuses on the normal temperature section,and there are few studies on the situation that the fluid is in a supercritical state.In this paper,the molecular dynamics method was used to simulate the Cu-water nanofluids under supercritical conditions.The variation of thermal conductivity and viscosity of Cu-water nanofluids was studied.In this paper,the three water models SPC/E,TIP3 P and TIP4 P are selected to simulate the water density and thermal conductivity parameters.After comparison,the TIP4 P model is selected as the potential energy model of the water,and the TIP4 P model is verified.Simulate the reliability of viscosity parameters.Firstly,three water models,SPC/E,TIP3 P and TIP4 P,are selected to simulate and calculate the density and thermal conductivity of water.After comparison,the TIP4 P model is selected as the potential energy model of water in this paper.On this basis,the reliability of TIP4 P model to simulate the viscosity parameters is verified.The thermal conductivity and viscosity of the TIP4 P model at different temperatures is calculated.It is found that the thermal conductivity and viscosity of the TIP4 P model obtained in the high temperature region are more accurate than the normal temperature,and the density error is larger than the normal temperature.Using the equilibrium molecular dynamics to study the thermal conductivity and viscosity of nanofluids under supercritical conditions,it is found that the higher the ambient temperature,the greater the thermal conductivity of nanofluids.It is more than 3 times higher than pure water,even under supercritical conditions;the larger the mass fraction of the fluid occupied by the particles,the larger the thermal conductivity of the nanofluid,and the thermal conductivity of the nanofluid increases with the mass fraction of the particles under supercritical conditions compared with normal temperature;At the same time,at the same mass fraction,the thermal conductivity of the nanofluid increases with the radius of the nanoparticle.If the multiparticle system is aggregated,the thermal conductivity will be greater than the thermal conductivity of the single particle system of the same mass fraction.The viscosity of the nanofluid under supercritical conditions is simulated: the viscosity of the nanofluid decreases slightly with increasing temperature,and the viscosity obtained by simulation near the critical point is greater than the actual viscosity of water,and then gradually reduce to less than the actual viscosity of the water.In the case of supercritical conditions keeping the particle mass fraction constant,the viscosity of the fluid first decreases with increasing particle radius and then increases with increasing radius,but its size is always greater than the viscosity of water.