Physical dealloying towards pulsating heat pipes performance enhancement

In this work, the physical dealloying (PD) method is explored as a way of creating a porous layer on metallic surfaces to be used for the enhancement of Pulsating Heat Pipe (PHP) thermal performances. This method considerably reduces the environmental impact, as it does not employ the strong acids and bases required in chemical and physico-chemical dealloying methods, while being a simple and universal approach. PD can be applied to metal alloys consisting of components with a high difference between their partial vapor pressure, such as copper and zinc. Commercially available brass (Cu/Zn alloy) capillary tubes with OD = 2mm and ID = 1.3mm were shaped to create a four-turn PHP, with a total length of 949 mm. One standard PHP with the same tube diameter, number of turns and total length was tested as benchmark, while the other two PHPs were subjected to PD for 0.5 and 2 hours at 650 ℃ and 2.5·10-2 mbar. All PHPs were tested in the range of heat load between 3 and 40W at a filling ratio 50% with ethanol. The performed tests show that PHPs after PD display up to 30 °C lower average temperature at the evaporator and up to 7 °C lower average temperature of the condenser compared to the benchmark.The PD treatment drops the PHP thermal resistance by a factor of 4.6 times at low heat power. Moreover, for the PD-treated PHP operational start-up happens faster and at lower temperatures compared to the untreated PHP, which is important for the reliability, safety, and longer lifetime of the equipment thermally managed by PHPs. Besides PHPs, this simple method can be customized for various thermal management equipment, such as conventional, plate, and micro heat exchangers, HVAC equipment, etc., where the heat transfer occurs with phase change.