The study on the difference of the start-up and heat-transfer performance of the pulsating heat pipe with water−acetone mixtures

An experimental study was conducted to investigate the start-up and heat-transfer performance of a closed-loop pulsating heat pipe with water−acetone mixtures (at mixing ratios of 13:1, 4:1, 1:1, 1:4 and 1:13) and pure water and acetone under various filing ratios (35−70%) and heat inputs (10−100 W). The closed-loop pulsating heat pipe was vertically placed and bottom-heated (i.e., heating wires were wrapped on the evaporation section) with inner and outer diameters of 2.0 and 4.0 mm, respectively. It was observed that (1) compared with pure water, the pulsating heat pipe with water−acetone mixtures of mixing ratios of 13:1, 1:1, 1:4 and 1:13 possessed improved start-up performances, which could be initiated under a heat input of 10 W and filling ratios of 35% and 45%. (2) Under low filling ratios (i.e., 35% and 45%), the pulsating heat pipe with water−acetone mixtures (i.e., at mixing ratios of 4:1, 1:1, 1:4 and 1:13) presented improved performance against the onset of dry-out conditions compared with PHPs using pure water and acetone. Under a heat input of 50 W, the thermal resistances of the PHP with water–acetone mixtures (i.e., at mixing ratios of 4:1, 1:1, 1:4 and 1:13) decreased from 33.6% to 68.9% compared with pure working fluids. The addition of a fraction of pure water into pure acetone (e.g., the 13:1 water−acetone mixture) was found to be effective against dry-out. Conversely, adding a fraction of pure acetone into pure water (e.g., the 1:13 water−acetone mixture) did not prevent the onset of dry-out. (3) For high filling ratios (i.e., 62% and 70%) for which dry-out conditions are rarely encountered, the heat-transfer performances of the pulsating heat pipe with water−acetone mixtures (at mixing ratios of 13:1, 4:1, 1:1, 1:4 and 1:13) were not as efficient as that of the pulsating heat pipe with pure fluids. In contrast with the minima of mixtures under certain heat inputs, the maximum thermal resistances of pure water and acetone decreased by 45.8% and 38.7%, respectively.