In this study, the penetration behavior of pure water into a porous layer of copper nanoparticles which was formed on a copper substrate by a thermal treatment was experimentally investigated. The amount of liquid-water penetrating into the porous layer was calculated by measuring the volume change of pure water dropped on the surface of porous layer using a high-speed camera. For the penetration behavior of liquid-water in the porous layer, the Lucas-Washburn equation, Darcy's law, and Kozeny-Carman equation were used to estimate the effective pore radius, penetration coefficient, and specific surface area, respectively. Furthermore, observational study was conducted by a scanning electron microscopy to investigate the surface structure of nanoparticles in detail. As a result, it was confirmed that the thermal treatment not only changed the size of the nanoparticles aggregates, but also created new nanostructures on the surface of copper nanoparticles. The experimental results showed that the newly formed nanostructures on the nanoparticles’ surface also affected the penetration behavior of liquid-water.

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This study investigates the use of an ultrasonic visualization technique to visualize the working fluid in pulsating heat pipes (PHPs). A flat-plate aluminum alloy PHP used with R1336mzz(Z) hydrofluoroolefins as the working fluid was visualized by measuring the reflected intensity at the boundary between the flow channel wall and its inside. Vapor plugs and liquid slugs were identified by the difference of the reflected intensity. Results showed that when the working fluid in the PHP pulsated with the equivalent thermal conductivity of 2100 W/(mK), the pulsation exhibited low-frequency components equivalent to those reported in previous studies. These findings demonstrate that the ultrasonic visualization technique is useful for visualizing PHPs with multi-layer flow channel structures for measurements over a long period of time.

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