Experimental Study On Convective Heat Transfer Characteristics Of Nanofluids At Low Reynolds Number In Horizontal Circular Tube

Nanofluids are dilute solutions of metal, nonmetal nanoparticles or nanofibers with sizes typically of 1-100nm, 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 economics, reliability and miniaturization of the heat transfer system.This paper focusd most interest on the convective heat transfer characteristics of nanofluids in circular tube at low Reynolds number. 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 low Reynolds number was studied thoroughly. Furthermore, the appropriate correlations of laminar mixed convective heat transfer for nanofluids have been formulated and presented. The main works are as following.1. Properties of nanofluids related to convective heat transferThe two-step method without dispersant or surfactant was used to prepare the nanofluids using a stirrer and a sonicator. The results indicate that nanoparticles suspended in highly viscous base liquid like Ethylene Glycol (EG) will have more favorable stability than that in less viscous liquids like water. The advantages of nanofluids compared to base fluid for heat transfer largely depends on the thermal conductivity and rheological behavior. The mechanisms and models of enhanced thermal conductivity of nanofluids were reviewed and discussed. Experiments research and theoretical analyses about how the particle diameter, concentration, temperature, base fluid and aggregated structure influenced the viscosity of nanofluids were carried out.2. Experimental work on convective heat transfer of nanofluidsThe system for measuring convective heat transfer coefficient of nanofluids at low Reynolds number was set up. The convective heat transfer performance of SiO2-EG and SiO2-EG/water nanofluids (particle sizes of 15nm and 50nm) flow through a circular tube at low Reynolds number (10