The aim of the article is to numerically model a two-dimensional multiphase flow based on the volume of fluid method (VOF) in a pulsating heat pipe (PHP). The current state of knowledge regarding the modeling of these devices was studied and summarised. The proposed model is developed within open source software, OpenFOAM, based on the predefined solver called interPhaseChangeFoam. The analyses were carried out in terms of the influence of four different mass transfer models between the phases, proposed by Tanasawa, Lee, Kafeel and Turan, and Xu et al. on the shape and dynamics of the internal flow structures. The numerical models were validated against data obtained from a specially designed experimental setup, consisting of three bends of pulsating heat pipes. The numerical calculations were carried out with ethanol being treated as a working medium and the initial and boundary conditions taken directly from the measurement procedures. The variable input parameter for the model was the heat flux implemented in the evaporation section and a fixed temperature applied to the condensation section. The flow structures obtained from the numerical analyses were compared and discussed with the flow structures gained from experimental studies by employing a high speed camera. In addition, to verify the quantitative results obtained from the numerical analyses with the experimental data, a technique called particle image velocimetry (PIV) was used for the velocity vector field. For the analysed velocity ranges, the relative error obtained was reached at the level of 10%.

The Volume 10, published for JFFHMT Journal.

The interaction between surrounding liquids and optical fibers with protective coatings immersed in them is investigated in this paper. The research aims to determine whether, and to what extent, the liquid impacts the properties of the fiber coatings. Using long-term spectral shift monitoring by Rayleigh backscattering optical frequency domain reflectometry (OFDR), the study examines how different coatings behave when exposed to different liquids, including water, acetone, ethanol, and methanol. These findings provide valuable insight into selecting appropriate optical fiber coatings, which could be used as sensors in various fluids. The results led to the determination of the stabilization period, after which the influence of the liquid on the coating - indirectly on the fiber - stabilizes, providing accurate and reliable measurements by Rayleigh-based OFDR. Spectral shifts in used fibers immersed in different liquids were observed at room temperature. Consequently, the strain effects (either compression or elongation), which originated from the interactions between the coating and the liquid, were thoroughly analyzed. The findings of this study are important for proper undisturbed measurement by Rayleigh-based OFDR when designing fiber sensor setups that work in different fluids.