Study On The Solidification And Supercooling Characteristics Of Nanofluids And The Flow And Heat Transfer Of Ice Slurry

Ice slurry is an excellent cold storage and cooling medium.Compared with other cooling media,it has the advantages of low production cost,safe production,high heat exchange efficiency,energy saving and environmental protection.It is widely used in energy storage,building energy saving,etc.Many areas.Adding nanoparticles to the slurry liquid can not only greatly reduce the degree of subcooling,promote the nucleation phase transition,but also increase the thermal conductivity and enhance the heat transfer.In this paper,the solidification and supercooling characteristics of the graphene oxide-Al2O3 hybrid nanofluid solution and the flow and heat transfer of the ice slurry are systematically studied.Firstly,a stable graphene oxide-Al2O3 hybrid nanofluid solution was prepared by a "two-step method".Secondly,in order to reduce the influence of external vibration and other factors on the subcooling measurement,a phase change material-assisted circular tube inner subcooling test experimental system was built.The supercooling degree of deionized water and hybrid nanofluid solution was measured.Experimental results show that adding nanoparticles to deionized water can reduce the degree of supercooling of deionized water.The supercooling degree of nanofluid solution gradually decreases with the increase of concentration.When the mass fraction of hybrid nanofluid is 0.05-0.2wt%,compared with deionized water,it is reduced by 12.5%,23.9%,23.8%,and 37.5%,respectively.Although the SDS dispersant also reduces the subcooling degree of deionized water,the supercooling degree of the hybrid nanofluid is reduced the most.The initial temperature has little effect on the degree of subcooling of deionized water.The external cooling temperature has a great influence on the supercooling degree of the nanofluid.The lower the cooling temperature,the greater the supercooling degree.When the cooling temperature is-17?,the maximum drop rate can reach 26.9%.The contact angle of hybrid nanofluid droplets on the surface of stainless steel was measured.It is found that as the mass fraction of the hybrid nanofluid increases,the contact angle continues to decrease.Under 0.05wt%-0.2wt%,the minimum contact angle of the hybrid nanofluid is 45.8°.The empirical model and heat transfer model are used to study the convective heat transfer coefficient outside the subcooling test tube.The empirical parameters in the empirical model are mainly used in the natural convection of pure fluids.The fluid in this study is a solid-liquid two-phase coexistence,and its physical phenomena and physical properties are inconsistent with the empirical parameters in the empirical model.There are no empirical parameters in the heat transfer model,but the convective heat transfer coefficient is calculated by calculating the heat transfer in the heat transfer process,so it is more accurate to use the heat transfer model.The influence of whether the heat transfer of the cylinder is added or not in the heat transfer model is studied.The results show that in the phase change phase,the heat exchange of the cylinder is much smaller than the heat release of the solution,so the addition of heat exchange of the cylinder has little effect on the results,and the deviations at this stage are all within 2%.In the remaining stages,the heat exchange value of the cylinder is not much different from that of the solution.Therefore,the calculation of the heat exchange when the cylinder is removed is relatively large,and the maximum deviation can reach 77.88%.Based on the particle fluid dynamics and considering the solid-liquid two-phase flow characteristics of hybrid nanofluid ice slurry,a numerical model of Euler-Euler two-phase flow is established.The interphase mass transfer model is embedded in the Euler model to study the flow and heat transfer characteristics of the hybrid nanofluid ice slurry in the pipeline.The friction loss of ice crystals during the flow mainly includes viscous friction and mechanical friction.Therefore,as the inlet ice content and flow rate increase,the pressure drop of the hybrid nanofluid ice slurry in the pipeline also increases.During the flow of ice slurry,the lift generated by the density difference between the solid phase and the liquid phase,as well as the buoyancy of the ice particles themselves,strengthen the upward trend of ice crystals,causing ice crystals to accumulate on the top of the pipeline.In the range of inlet IPF=10?40% and flow velocity 0.64?0.83m/s,the volume distribution of ice crystals along the pipe section is more obvious,and the flow and stratification of hybrid nanofluid ice slurry in the pipe is more significant.When the inlet flow rate increases,the turbulent intensity of the liquid phase increases and the phase transition process of ice crystals is also enhanced,which promotes the melting of ice crystals,and the deviation of the maximum velocity gradually decreases.The thickness of the laminar boundary layer at the wall continues to decrease.The temperature distribution of the ice slurry fluid in the pipeline is affected by the volume distribution of ice crystals.The collision between the ice crystal particles and the intermittent or continuous collision between the ice crystal particles and the wall surface promotes the heat transfer between the ice crystal particles.While ice crystal particles accumulate on the top of the pipe,the contribution of the ice crystal phase change to heat transfer in this area increases,resulting in a significantly lower temperature at the top of the pipe than at the bottom.