Thermal Performance And Visualization Experimental Study On The Heat Transfer Limit Of Pulsating Heat Pipe

In recent years, electronic products develop rapidly, but the integration and miniaturization lead to high flux within small space which constraining the further development of the product. Pulsating heat pipe (PHP) is widely used in the cooling of electronic components for its excellent heat transfer characteristics except of its own problem of heat transfer. On the basis of the related literature, this paper research and analyze the heat transfer limit of PHP based on the experimental dates and existing research results.It was found that heat transfer limit of PHP is proportional to the inclination angle which has less influence in low filling rate and significant influence in high filling rate. Under the circumstance of same inclination angle, the heat transfer limit of PHP first increase and then decrease with the increasing of filling rate and reach the maximum at around 60%. The thermal resistance first decrease and then increase with the increasing of filling rate and reach the minimum point around 60%. Under the same working condition, the heat transfer limit and thermal resistance of water are both higher than that of acetone, so the temperature differences of water is much larger than that of acetone when reaching the heat transfer limit. The overall thermal resistance of PHP has a downward trend with the increasing of heating power. The results of orthogonal analysis which was carried out in this paper indicate that the order of factors affect the ultimate power of PHP is: filling rate>refrigerant>angle.Various types of flow such as slug flow,mixed flow and annular flow were observed by visualization experiments. The experimental results show that flow changes in pipe greatly affect the heat transfer performance of PHP. Under certain working condition, a wide range of annular flow emerge in pipe when reach a certain heat flux density , and will induce to the phenomenon of dry up if continue being heated. There will be two types of dry out: 1,U-bend of heating section dry out in the same time; 2,U-bend of heating section dry out partially. Research found that dry out leads to the heat transfer limit, and the rewetting induces different manifestation of heat transfer limit. The heat transfer limit of PHP was mainly studied in this paper which will benefit to the selection and application of PHP, and also lay a foundation to the further research of PHP's heat transfer limit mechanism.