Study On Mechanism Of Enhancement Of Heat Transfer Performance For Heat Pipe Using Nanofluid

Nanofluid is a new class of heat transfer fluid which containing suspended metallic or non-metallic nanoparticles in traditional fluid. Compared with pure liquid, nanofluid has the advantage of better thermal conductivity, and more easily to be suspended in base fluid than that of micron or millimeter particles. So we can expect that adding nanofluid in heat pipe instead of conventional heat transfer fluid can significantly improve the heat transfer performance of heat pipe.This paper presents the heat transfer performance of the heat pipe using CuO-water, Al₂O₃-water and SiO₂-water nanofluid. The heat transfer enhancement mechanism of heat pipe has been discussed from thermal conductivity of nanofluid and convection heat transfer properties of heat pipe with nanofluid. This study was designed to explore the using of nanofluid in thermal engineering and broad the approach of enhancing heat transfer performance of heat pipe. The main contents are presented as follows:1. Three types of nanofluid including CuO-water, Al₂O₃-water and SiO₂-water nanofluid were prepared with a two step method. Ultrasonic vibration was used to adjust the dispersion stability of nanofluid. Experimental results showed a good suspension stability of nanofluid.2. The heat pipe was made after nanofluid was added into it. An experimental setup used for testing the heat transfer performance of nanofluid was assembled. The start-up process, wall temperature distribution, heat transfer coefficient and thermal resistance have been investigated experimentally. The results showed that the heat transfer performance of heat pipe is affected by the mass concentration of nanofluid, particle size and input power etc. The use of nanofluid hold a shorter start-up time and lower start-up temperature for the evaporation section of the heat pipe compared to water. The wall temperature distribution of the heat pipe using nanofluid is significantly lower than that of water along the evaporation section, while it's significantly higher than that of water along the condenser section under the same input power. The heat pipe using nanofluid shows a better isothermal performance than that of water. The heat pipe using nanofluid hold a higher heat transfer coefficient and lower thermal resistance compared to water. There is an optimal mass concentration for nanofluid. The heat pipe using nanofluid has a better isothermal performance, higher heat transfer coefficient and lower thermal resistance at this concentration. This concentration is 1.0% and 1.0% for CuO-water and Al₂O₃-water nanofluid, respectively.3. The heat transfer enhancement mechanism of heat pipe was discussed. The use of nanofluid has significantly increased thermal conductivity and enhanced the convection heat transfer properties of heat pipe. This explains the internal reasons of heat transfer enhancement of heat pipe using nanofluid.