An Experimental Investigation On Heat Transfer Performance Of Nanofluid Pulsating Heat Pipe

Nanofluid pulsating heat pipe (PHP) gains great interests in the field of enhanced heat transfer during recent years. However, due to the complexity of the phase-change heat transfer process of nanofluid, the mechanism of it is still not clear enough. In this study, a PHP experimental system is built to investigate the thermal characteristics of nanofluid PHP based on different working fluids at various conditions. Meanwhile, analytical method is also introduced in the paper to probe the heat transfer theory on nanofluid PHP.Firstly, in order to explore the heat transfer characteristics of PHP with different weight percentage of nanofluids, the experiments that take DI water as working fluid are chosen as the base case. The results from different experiments with various SiO2/H2O concentrations are compared with each other. It shows that high fraction of SiO2/H2O will deteriorate the performance of PHP compared with DI water, i.e. the thermal resistance and the temperature of evaporation section increases. It is contrary for the case of low fraction of SiO2/H2O. Meanwhile, the start-up time is shorter and fluctuation of temperature decreases for all the experiments using nanofluids as working fluids.Furthermore, thermal characteristics of nanofluid PHP running at different heating powers, cooling medium temperatures and different suspension characteristics of nanofluids are examined. The experimental results show that the thermal resistance decreases, the start-up time decreases and the operating temperature rises, as the heating power increases. Additionally, thermal resistance of the test using0.1%wt. SiO2/H2O as working fluid is reduced, with the raise of the temperature of the cooling medium. When the temperature of the cooling medium is43℃, the thermal resistance decreases by18%compared to that of23℃, while it is nearly unchanged as for the test using DI water. It is found that both the thermal resistance of nanofluid PHP and the temperature of evaporation section increase after putting the PHP aside for a period and it is the same trend for the temperature fluctuation at the identical heating power for PHP.Finally, the present paper also investigates the thermal characteristics of nanofluid PHP theoretically. The flow and heat transfer model for vapor-liquid slug is established for a closed loop heat pipe based on the law of Momentum-Quality— Energy conservation. The performance of PHP is compared for the cases of ethanol and water as working fluids. The results are compared to the experimental results and they are in good agreement. Moreover, the model for pure-fluid is modified to make it suitable for simulating the operation on of nanofluid PHP. The calculated results show that the particle concentration of nanofluids has a significant effect on the heat transfer performance of PHP and there is an optimum value.