Experimental and numerical studies of the pulsating heat pipe stopover regime

The experimental data previously obtained with a “Smart loop” (Abela et al. 2024) configured as an eleven-turn pulsating heat pipe (PHP) are compared here to simulation results obtained with the in house 1D transient code CASCO (French acronym for Code Avancé de Simulation du Caloduc Oscillant: Advanced PHP Simulation Code in English) version 4. CASCO has been set-up in terms of geometry, topology, material properties and thermal boundary conditions to mimic the experimental device. A comparison between numerical and experimental results is performed simultaneously on multiple parameters. First, we compare the overall heat transfer performance with a good agreement. Then we discuss the temporal evolution of fluid temperature and pressure at fixed locations. The stopover regime is deeply investigated. It is found that it is characterized by a repeating sequence of fast pressure growth (corresponding to oscillations) followed by a slower pressure decay (corresponding to PHP stopover). The dominant frequency was computed both for experimental and simulation data; an agreement was found. Similarly, the experimental and simulation data on the pressure decay rate agree. The decrease of the PHP thermal resistance with heating load is explained by a decrease of the stopover time caused by a larger pressure decay rate appearing because of a faster liquid film drying.