Visual Experiment Study On Start-up And Operating Characteristics Of Pulsating Heat Pipe

As a new-style heat pipe, the structure and operational mechanism of pulsating heat pipe (PHP) are quite different from the classical heat pipes. The pulsating heat pipe has no wick structure,the inner size of it is so small that vapor and liquid slugs can naturally formed in capillary tubes. Heat is transported form the evaporation to the condensation zones by means of local axial oscillations and phase change heat transfer in the working fluid. Compared with conventional heat pipes it has many advantages such as simple structure, lower fabrication cost and perfect performance. So it has great potentiality in the application and development of electronic components, aviation and aerospace thermal control technology.Since visualization experiment can not only deepen understanding of the operation and mechanism but also benefit to establish mathematical model, an visualization experiment about PHP was conducted firstly .Additonaly, the pulsating heat pipe start-up and running characteristic not only deciding its practical application but also affecting the stability of electronic devices, so another experiment was also conducted.There are several conclusions as follows .â‘ Visualization experimentTube's flow pattern and direction change are recorded with digital camera, The physical phenomenon which appear in the procedure of start up are analyzed .The observed results indicated that the flow pattern of working fluid in the PHP is long columnar vapors and liquid slugs and mixed with few beads. Through the continual readjustment of inner pressure the flow change form initial non-direction to the final anti-clockwise flowing.â‘¡tart-up and running characteristic of PHPThe results indicate that methyl alcohol compared with water and ethyl alcohol not only have shortest start up time but also have the biggest oscillation amplitude and quickest oscillation frequency. When maintains the working substance type and the inclination angle are invariable, the PHP has the shortest time under condition of 60% filling rate, 45% is shorter and 90% is longest. The PHP can not start-up normally in the anti-gravity mode.â‘¢Calculation of thermal resistance and affecting factors anaysisedHeat transfer performance of PHP is evaluated with thermal resistance.the results showed that When the PHP with methanol as working fluid in the condition of 45% filled rate and vertical placed the PHP have the shortest start-up time, the thermal resistance is 0.181 k/w.â‘£Analysis of the basic theoryThe pulsating heat pipe is theoretically analyzed.The thin film is divided three regions:The governing equations of mass,energy and momentum conservations were established based on the simplification and reasonable assumptions on the PHP system.