Heat transport characteristics of a sodium oscillating heat pipe: thermal performance

For application to thermal protection systems for hypersonic vehicles, an oscillating heat pipe (OHP) with sodium as the working fluid was developed, and its thermal performance was investigated experimen-tally. The OHP was a two-turn closed-type heat pipe made of Incoloy 800HT and had a length of 350 mm, a width of 95 mm, an outer diameter of 5 mm, and an inner diameter of 3 mm. The OHP was filled with about 5.0 g of sodium to achieve a filling ratio of about 50 vol.%, and installed in a furnace with two chambers; the heating chamber and the cooling chamber. The length of the heating, adiabatic, and cool-ing sections were 150, 50, and 150 mm, respectively. The heat transport rate of the OHP was measured from the difference in the heat input with and without the OHP in the experimental apparatus to main-tain the defined temperature in each chamber. The OHP in the bottom-heating mode worked well in the combination of 80 0-90 0 degrees C for the pipe temperature in the heating chamber and 60 0-70 0 degrees C for that in the cooling chamber. Under the condition, the heat transport rate was 298-477 W. The maximum heat transport rate of 477 W was obtained at a combination of the pipe temperatures of 820 degrees C and 609 degrees C. The thermal resistance of the OHP became from 0.3 to 2.8 K/W. When the cooling chamber temperature fell below a certain temperature, the heat transport rate decreased rapidly, indicating that this OHP had two modes of heat transport related to the flow characteristic.(c) 2022 Elsevier Ltd. All rights reserved.