Impact of different channel cross sections on the thermal performance of a spiral pulsating heat pipe

Pulsating Heat Pipes (PHP) are two-phase passive heat exchangers which rely on phase change phenomena to induce the self-sustained fluid motion, thus promoting the heat transfer. The geometric configuration of the PHP plays a fundamental role in the exploitation of capillary forces and consequently in the operational stability. In this research a PHP, with inner/outer diameter 2 mm and 2,5 mm respectively, is shaped in a six loops spiral planar configuration. The tube is made of stainless steel SS316L having a variable cross section: triangular in the evaporator section and flattened on one side of the adiabatic section, circular in the rest of the PHP. The filling fluid is HFO R1233zd(E) (filling ratio 50%), making the device operation very close to the capillary limit. The device is monitored with 16 T-Type thermocouples and tested at different heat inputs (5 W, 7.5 W, and 10 W) and different orientations with respect to gravity (horizontal, lateral (with elliptic section at the bottom and at the top, bottom heated). Results show that, despite the small number of heated and cooled section, the PHP is activated in the horizontal orientation with an intermittent operation, and it works stably in all the other positions. Nevertheless, performances are still deeply affected by the gravity field.

Billi, A., Marchi, I., Mazzini, J., Mameli, M., Filippeschi, S., Iwata, N., Dupont, V., and de Ryckel, A.

Journal of Physics: Conference Series, 3258, Proceedings of the 42nd UIT International Heat Transfer Conference, Florence, Italy, 23–25 June 2025, published 2026