Studies of PHP with CASCO code and its experimental validation

arXiv:2606.09333v1 Announce Type: new Abstract: We discuss here two major issues related to the steady functioning of the pulsating (oscillating) heat pipe (PHP): the effect of the surface properties and stopovers. They are studied with the CASCO simulation software (Code Avanc{\'e} de Simulation du Caloduc Oscillant: Advanced PHP Simulation Code in French) version 4. Its experimental validation against two different prototypes is presented. The first is used also to study the effect of the nucleation barrier (the wall superheating necessary for the bubble nucleation) that reflects the wall wettability and roughness. An optimal value of the nucleation barrier is found where the thermal resistance achieves a minimum for a given evaporator power. The functioning regime is continuous showing pressure waves propagating along all the PHP channel. The stopover regime is observed both for small and large barriers. The second experimental setup (PHP Smart Loop) is used to study the stopover regime. It is found that it is characterized by a chaotically repeating sequence of fast pressure growth (corresponding to oscillations) followed by a slower pressure decay during a stopover. The decrease of the thermal resistance with heating load is explained by a decrease of the stopover time caused by a faster liquid film shrinking.