The Mechanism Of Start-up And Operating Performance Of The Close Loop Pulsating Heat Pipe And Its Empirical Correlation Research

In this paper, the start-up and operation stages of the pulsating heat pipe (PHP) were studied by visualization method. The mechanism of the start-up and operation process of the PHP was discussed. The heat transfer experiments of the start-up and operation process of the PHP were carried out. The experiment data were received. On the analysis of the influence on the dimensionless heat flex Ku, the empirical correlations of the start-up and operation conditions of the PHP were fitted respectively.Nucleate boiling, gas slugs’ merging and abruption, liquid slugs’ abruption and back flow were observed in the stage of the start-up. The dynamics of the pulsating were supplied by them both in the start-up and operation process. Three flow patterns were found in the stage of start-up:bubble flow, bubble-slug flow and slug flow.In the early stage of the start-up, the liquid and gas slugs distributed randomly, at the end of the stage the distribution of them were benefit to the pulsating. This distribution was built by the force of the pressure difference in the PHP which was generated by the phenomenon mentioned above. The stage of the start-up is the stage for redistribution of gas slugs and liquid slugs. Three flow patterns were found in the stage of the operation process:slug flow, mix flow, annular flow. In the visualization experiment the stable one-way circulation flow was not observed at low heating load. And the pulsating always changed direction and stagnated. The stable one-way circulation flow was observed at high heating load. The changing direction of pulsating and stagnation of pulsating was also observed.In the process of fitting empirical correlations, in order to ensure good heat insulation measures, the thermal balance experiment was taken. By analysis of the influence of the dimensionless parameters Ja, Bo, Pr, filling rate, heating angle on the dimensionless heat flux Ku, the independent variables of the empirical correlations were determined. By analysis of the existing empirical correlation, it was limited of the application because of the defects such as the filling rate fact wasn’t considered, the index of the independent variables was too large, and the correlation was fitted by data of single working medium. So the empirical correlations of the start-up and operation conditions were fitted respectively by the data of multiple working mediums. And compared with the existing correlation, in the new correlations the filling rate fact was taken into consideration, the absolute value and plus-minus of the index of the independent variables was reasonable. The results showed that the Ku calculated by the empirical correlations were well fitted with the experimental Ku.