The electron temperature and the density of argon arc plasma plume injected into water were observed through optical emission spectroscopic measurement. Argon arc plasma jets were generated with a DC arc current of 40–200 A by a non‐transferred arc discharge plasma torch under atmospheric pressure, and ejected through a nozzle on the anode into water or gas‐phase argon. The electron temperature of the plasma plume was determined by the Boltzmann plot with line intensity measurement of atomic argon lines, while the electron density is examined with the Stark broadening measurement of Hα line. It was found that the electron temperature increased from approximately 6500–8000 K, and the electron density also increased up to the order of 1016cm−3, as the discharge current increased for the underwater argon arc plasma plume, both of which were observed at 20 mm in the downward direction from the plasma generator nozzle. In addition, the electron temperature of the underwater plasma plume was slightly lower than that of the gas‐phase argon plasma plume, while the electron density of the underwater plasma was slightly higher than that of the gas‐phase plume. Longitudinal variation of the electron temperature and density of the underwater plasma plume was also observed, and the lowering rate was found to depend on the arc discharge current. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Understanding the relationships between the thermal conductivity and carrier density in thin films is of great importance for the thermal management of flexible thin film electronics. Here, we report a robust measurement technique to tune the carrier density in thin films and to evaluate their cross-plane thermal conductivities simultaneously. We employed the time-domain thermoreflectance method using an Au transducer and evaluated the thin film thermal conductivity in situ using electrolyte gating with an ionic gel. The robust measurement technique proposed in this study elucidated the relationships among the above-mentioned parameters in semiconducting single-walled carbon nanotubes.

Precise evaluation of the thermophysical properties of thin films is crucial for realizing high-performance flexible electrical and energy devices. The ultrafast laser-based time-domain thermoreflectance (TDTR) method is one of the most effective methods for examining the thermophysical properties of thin films attached to metals; however, conventional TDTR methods are mainly employed for an aluminum transducer layer, which is not used for conventional metal electrodes. Here, we developed a TDTR system designed for a gold transducer, which is a typical metal electrode in electronic devices, and evaluated the thermophysical properties of a carbon nanotube thin film adhered on a gold surface.

The flow and thermohydraulic characteristics of an atmospheric‐pressure argon arc jet plume injected into water were investigated. The temperature of the underwater plasma plume was measured using optical emission spectroscopy, and the water with a thermocouple. The velocity field of the water induced by the arc‐jet injection was observed using the particle image velocimetry method, which demonstrated that as the discharge current increased, the water flow velocity also increased. The diameter of the plasma plume was observed to be approximately the same as that of the anode nozzle, 6.7 mm. The heat transfer characteristics of the injected arc jet plume to the surrounding water were also investigated. The average velocity of the arc jet plume in the water was estimated based on mass balance to be in the range of 280–2500 m/s as a monotonically decreasing function of the flow distance. The velocity of the underwater arc is found to be subsonic over the entire volume of the plasma plume, however, it is larger than the sound velocity of the water up to 10 mm downward from the plasma nozzle. The resultant Reynolds number of the plasma flow was found to be between 1000 and 2800, indicating the flow was turbulent only at the most upstream region up to 3 mm downward from the nozzle, while it was almost laminar over the whole observed area of the underwater arc plasma plume. The heat transfer characteristics were discussed in terms of the dimensionless numbers. The Nusselt number ranges from approximately ∼3.8 to ∼6.5, which is a reasonable value. Although the existing theories of correlation heat transfer cannot fully explain the relationship between these dimensionless numbers, the correlation proposed by Fiszdon and the one by Lee–Pfender can qualitatively explain the observed results for the upstream region, which include the effects of the variation in the mass density, the viscosity, and the specific heat for a constant pressure of the argon arc plasma. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Understanding the relationship between electrical and thermal characteristics of thin films is crucial for their thermal management. However, there are hardly any reliable experimental data on this relationship because measurement methods that can evaluate both characteristics in the same direction are very limited. Here, we report a measurement technique that can simultaneously evaluate electrical and thermal characteristics by combining time-domain thermoreflectance and vertical electrolyte-gated transistors. We demonstrate that the thermal conductivity of single-walled carbon nanotube films is independent of the vertical current density, which is modulated over 4 orders of magnitude, indicating a route to improve thermoelectric conversion efficiencies.