Experiment Investigation On Operating Limitation Of Oscillating Heat Pipe And Modeling Analysis

The oscillating heat pipe (OHP) as a new and efficient heat transfer component has been widely studied by the researchers. Utilizing the thermally-excited oscillating motion and phase change heat transfer, an oscillating heat pipe transports heat from evaporator to condenser, which is regarded as one of the most effective way to solve the problem of high heat flux cooling. Nowadays, the requirement of efficient heat transfer on the modern ship increases sharply. Using the OHP to solve the problem of heat transfer on the modern ship has been one of the most important issues. Since the oscillating heat pipe was invented in the 1990s, a lot of researches on the relevant factors affecting OHP performance have been done.However, the research on the operating limitation of the OHP is rare. So this paper investigated the operating limitation of the OHP by experiments and establishing the model to analysis the phenomena.In the experiments, the OHP was charged with water, alcohol, HFE-7100 and Al2O3/water, Al2O3/alcohol, which were defined as the working fluid.The filling ratio varied from 30% to 70%, the tilt angle varied from 0°o 90°, and the operating temperature at 20℃ or 60℃. Through the analysis of experimental data, it shows that the filling ratio, the tilt angle, the working fluid and the operating temperature affect the operating limitation and heat transfer performance of the OHP. In addition, the experimental result of the nanofluid working fluid was compared with the pure working fluid, to get the reason that the nanofluid could enhance the performance of the OHP. In modeling analysis, with based on the π theorem and analyzing the experiment result, it was easy to fit the semi-empirical formula to predict the limitation of the OHP, and got a semi-empirical model. By studying the motion state of the plugs and slugs in the OHP, the motion model on the limitation of the OHP was established, and the theoretical input power when the limitation of the OHP occurred was calculated. Moreover, compared the calculation result and experiment results, the credibility of the limitation model was determined.Through the experiments and modeling analysis, the following conclusion can be got:(1)The limitation of the OHP increases as the filling ratio and the tilt angle increasing; (2)Working fluid affects the OHP’s operating limitation significantly, and the operating limitation of the OHP charged with water is greater than the OHP charged with HFE-7100; (3)The relationship between the operating temperature and limitation is different with the different kinds of working fluid; (4)Different kinds of working fluid have different best filling ratio; For the OHP charged with water, the best filling ratio is generally between 40% and 50%, and for the OHP charged with alcohol or HFE-7100, it is generally 70%; (5)A semi-empirical correlation was obtained to predict the operating limitation of the OHP by the experiment result. Compared with the test results, the relative error was approximately less than 30%.