Experimental investigation of flat plate closed loop pulsating heat pipe

Pulsating heat pipes (PHPs) have promised to be effective heat spreaders. From the fabrication perspective, the PHPs are less intensive than their conventional counterparts. Despite the advantages, there still exists shortage of data in both experimental and analytical domains towards reliable design and prediction of PHP performance. In this study, a flat plate closed loop PHP has been experimentally investigated for its thermal performance. The PHP with 12 channels, each 2.2 mm deep x 2.0 mm wide, was tested with deionized water for a fill ratio of 70% by volume for various orientations starting from vertical evaporator below condenser (90 degrees) to near horizontal (7.5 degrees) orientation for a single heat load of 50 W to calibrate the test setup against published literature. The PHP was also tested for methanol with various fill ratios (30, 40, 50, 60 and 70%) for 50 W. The best performing fill ratio of methanol was tested for various heat loads (10 to 100 W) for the vertical and the near horizontal orientation. An attempt has been made to resolve the critical angle after which the PHP ceases to perform when tilted towards horizontal orientation. The PHP performance as expected was best at the 90 degrees (vertical) orientation with very little deterioration up to 45 degrees. The thermal resistances were estimated for two fluids, for various orientations, heat loads and fill ratios. The results indicate that at near horizontal orientation methanol performed better than water for 70% fill ratio. The 40% fill ratio of methanol yielded the least thermal resistance for all orientations. Also the thermal resistance of the PHP decreased with increasing heat load for different orientations. The PHP operated successfully up to 7.5-10 degrees below which the PHP was observed to have dry out.