A study of the heat transfer performance of a pulsating heat pipe with ethanol-based mixtures

The heat transfer performances of a pulsating heat pipe (PHP) with ethanol-water, ethanol-methanol and ethanol-acetone are investigated experimentally. The mixing ratios (MRs) of the ethanol-based mixed working fluids are 2:1 and 4:1, the volume filling ratios (FRs) range from 45% to 90% and the heat input ranges from 10 W to 100 W. The experimental results are as follows: When the mixing ratio is 2:1, the heat transfer performance of PHP with ethanol-water is better than other working fluids at a filling ratio of 45% because of the phase-change inhibition in ethanol-water; at a filling ratio of 55%, PHP with ethanol-acetone shows better performance among those with mixed working fluids. Acetone with a relatively high value of (dpiciT)(sat) (saturation pressure gradient versus temperature) and relatively lower dynamic viscosity can lead to relatively high velocity in the PHP, which can decrease the temperature difference between the evaporation section and condensation section. When the mixing ratio is 4:1, the thermal resistance of PHP with ethanol-water that is close to being dried out under a filling ratio of 45% rises faster than that at a mixing ratio of 2:1 due to the presence of less deionized water (DI water); the heat transfer performance of PHP with ethanol-acetone is excellent at a filling ratio of 55% among the ethanol-based mixed working fluids because the thermal resistance is relatively small and the maximum heat input that PHP can endure is highest. When the volume filling ratio reaches 62%, 70% and 90%, the heat transfer performance of PHP with pure working fluids is better than that with ethanol-based mixed working fluids. This may be partially attributed to the offset of flow driving force caused by the mass transfer due to the concentration difference between the liquid and the vapour phase of mixtures. The filling ratio of 62% shows a marginal leading in terms of lower thermal resistance. (C) 2016 Elsevier Ltd. All rights reserved.