Study On The Convective Heat Transfer Characteristics Of Nanofluid With Laminar Flow In Tube

Nanofluids are dilute solutions of metal,nonmetal nanoparticles or nanofibers with sizes typically of1-100nm,and have become a new type of heat transfer fluid. Recent experiments indicated that nanoparticles suspended in liquids could significantly increase the thermal conductivity of the liquid, therefore the heat transfer efficiency is enhanced.That is significant for improving economiy, reliability and miniaturization of the heat transfer system.This paper focuses most interest on the convective heat transfer characteristics of nanofluids in circular tube at laminar flow. Firstly, experimental and theoretical research was conducted to investigate the Basic properties of nanofluids (such as the preparation, stability, thermal conductivity and viscosity). Then, the convective heat transfer performance of nanofluids flowing through a circular tube at laminar flow was studied thoroughly. The main contents are as following.ZrO2-water nanofluids, Al2O3-water nanofluids, Fe3O4-water nanofluids,and CuO-water nanofluids are prepared by two-step method. Fisrtly, nanoparticles are weighed by Electronic balance, and then let nanoparticles and liquid be mixed firsthand. the even distributed and stabilized suspensions are prepared by means of appending the different dosage of dispersant and using ultrasonic vibration.The transient hot-wire instrument for measuring the thermal conductivity of nanofluids is developed.The nanofluids prepared are measured. Experimental results show that thermal conductivities of the four kinds of nanofluids increase with the increase of mass fraction.Using an Ubbelohde viscometer to measure the viscosity of the four types of nanofluid and analyze the factors affecting viscosity.An experimental system is set up to investigate the convective heat transfer in a tube. For the R eynolds number200～2500, the convective heat transfer coefficient of nanofluids are measured.The experimental results show that compared with the convective heat transfer coefficient of the base fluid, that of nanofluid increases remarkably.In order to investigate the nanofluid enhanced heat transfer, mechanism,both quality fraction and types are analyzed.