Study On Thermal Properties And Phase Change Storage Characteristics Of Nanofluids

Ice storage has a great significance in industrial applications,especially in the air-conditioning industry.However,due to the low thermal conductivity of water and the large undercooling degree during crystallization,the efficiency of the cooling system is reduced and energy consumption is increased.In this paper,the main properties of nanofluids such as thermal conductivity,viscosity,supercooling and cold storage are analyzed.The application prospects of nanofluids in ice storage are analyzed,and the experimental basis for its practical application is provided.Different concentrations of carbon nanotube/water nanometer fluids were prepared by two-step method.The effects of dispersant,ultrasonic vibration and other factors were studied by gravity sedimentation method.The effects of temperature,concentration and particle size on the thermal conductivity were analyzed by using Hot-disk.The influence of dispersant,temperature and concentration on the viscosity were studied by using a viscometer.The influence of fluid viscosity;the subcooling of nanofluids and the cold storage characteristics of the cold storage process were studied by self-built experimental bench.The results shows that the carbon nanotube/water nanofluid has good dispersion stability which prepared by using GA(gum arabic)as surfactants and ultrasonic vibration for 1.5 hours.The addition of nanoparticles can significantly improve the thermal conductivity of the base fluid,and the thermal conductivity increases with the increase of temperature and particle concentration and basically changes linearly.When the shape factor of the carbon nanotubes is 13,the H-C model can predict the thermal conductivity of water-based nanofluids accurately.The viscosity of carbon nanofluids decreased with the increase of temperature,increased with the increase of particle concentration.Compared with the classic model,the K-D model can predict the viscosity accurately.Nanoparticle can significantly reduce the degree supercooling of water,the supercooling of nanofluid is affected by the mass fraction of nanofluids,particle size of nanometer particles,and the temperature of cooling,and the mass fraction of nanoparticle is the most important factor influencing the phase transition,With the increase of the mass fraction,the time of the cold storage phase transition of the nanofluid is advanced,and the phase transition time is shortened.At the same time,the cold release process of the nanofluid is hardly affected by the mass fraction.