With the recent trend toward higher integration density and enhanced performance in semiconductor devices, thermal management and the analysis of localized heat transfer characteristics have become increasingly important. Scanning Thermal Microscopy has been widely recognized as an effective technique for investigating the thermal properties of thin films and nanostructures owing to its high spatial resolution. However, quantitative thermal conductivity analysis remains challenging due to the contact thermal resistance generated at the probe–sample interface. In this study, the thermal conductivity of thin films was quantitatively analyzed using a simple analytical model based on a thermal resistance network. First, the effective thermal contact radius at the probe–sample interface was calculated using reference samples with known thermal conductivities, namely Si and Pyrex. Based on the obtained contact parameter, the thermal conductivities of TEOS SiO2, SiON, and AlN thin films with different thicknesses and conditions (500 nm, 1000 nm, and 1000 nm after annealing at 200 °C) were evaluated. The effective thermal contact radius used in this study was defined not as the actual mechanical contact radius, but as an effective thermal contact parameter representing the heat transfer behavior between the probe and the sample. The proposed approach establishes a practical analytical framework in which an effective thermal contact radius is quantitatively determined from reference samples using a thermal resistance network and subsequently applied to the thermal conductivity characterization of thin films with different materials and thicknesses.
Solar salt is widely used as a high-temperature thermal energy storage (TES) material; however, its relatively low specific heat limits its heat-storage density. In this study, solar salt nanofluids containing 1 wt% Al2O3, graphene nanoplatelets (GNPs), and SiO2 nanoparticles, were prepared using an aqueous-assisted dispersion method to investigate the influence of nanoparticle type on thermal storage performance. Differential scanning calorimetry (DSC) was employed to evaluate phase-transition behavior, specific heat, and total TES capacity. The results showed that the specific heat of the base salt was increased with the addition of nanoparticles, and the degree of enhancement was strongly dependent on the type of nanoparticles. The Al2O3 nanocomposite showed the greatest improvement, with specific heat increases of 30.5% and 40.4% in the solid and liquid phases, respectively, while SiO2 produced a moderate enhancement and GNPs a comparatively limited one. The TES capacity, calculated from both sensible and latent heat contributions over the temperature range of 150-300°C, reached a maximum of 341.3 kJ·kg-1 for the Al2O3 nanocomposite, an increase of 17.3% over the base solar salt. The results suggest that nanoparticle-dependent morphology and particle-salt interfacial effects may contribute to the observed differences in TES performance.
We experimentally investigate the thermal performance of thermal-link configurations between the second-stage cold head of a compact GM cryocooler and a sample stage for wide-range temperature control. To quantify the cooling performance, heaters were installed on the first and second stage of the cold-head, and a cooling-capacity map was obtained under various heat-load conditions. Sapphire, fiber-reinforced plastic (FRP) with Cu-plated through holes (Cu PTHs), and their hybrid stack were employed as thermal interface materials (TIMs) with different temperature-dependent thermal conductivities. The temperature difference between the second-stage cold head and the sample stage was systematically compared among TIM configurations under steady-state heating. Sapphire provided efficient cooling at low temperatures but generated only a limited temperature difference at elevated temperatures. In contrast, FRP with Cu PTHs produced a larger thermal resistance, and the hybrid configuration achieved a temperature difference of 102.5 K, raising the sample stage to 430.2 K. These results provide practical guidelines for TIM selection and sample-stage design in compact conduction-cooled systems.
Low-velocity airflow produces only subtle changes in convective heat transfer, making it difficult to resolve with compact thermal sensors. This study investigates the frequency-dependent thermal response of a 3ω microheater supported on a SiNₓ membrane. Removal of the silicon beneath the heater exposes the membrane to gas on both sides and enhances the influence of flow-induced heat transfer on the sensor response. The sensor was characterized in a rectangular chamber under no-flow and finite low-velocity airflow conditions over a broad excitation-frequency range. The temperature amplitude decreased with increasing frequency and airflow, with the clearest separation among the flow conditions occurring in the low-frequency regime. The low-frequency response was interpreted using a lumped thermal-resistance framework that combines a baseline heat-transfer pathway with an additional forced-convection conductance that increases with flow velocity. The resulting correlation captured the nonlinear decrease in temperature amplitude under finite-flow conditions, whereas the no-flow condition was retained as a separate reference rather than imposed on the finite-flow regression. These results show that the low-frequency 3ω temperature amplitude provides a quantitative response to changes in low-velocity airflow within the present sensor–chamber configuration and supports the use of membrane-based 3ω microheaters as compact thermal flow sensors.
Multiple REBCO tapes are often assembled into stacked or parallel conductors to achieve high transport current capacity. However, the current-carrying capability of stack–parallel REBCO conductors cannot be estimated by simply multiplying the critical current of a single tape by the total number of tapes, because self-field effects and current redistribution cause nonuniform critical-current degradation inside the conductor. In this study, the critical current of stack–parallel REBCO conductors was calculated by considering the arrangement-dependent self-field degradation and current redistribution, and a fitting equation was proposed for practical critical-current estimation. The proposed fitting equation showed good agreement with the calculated results, with a mean absolute percentage error of 1.45%. Transient thermal analysis of terminal Joule heating was also performed to determine suitable test conditions under liquid nitrogen cooling, and the temperature rise was limited to less than 0.5 K at the selected current level. Experimental validation was conducted using stack–parallel REBCO conductors immersed in liquid nitrogen, and the measured critical currents and burn-out currents generally followed the calculated trend. These results indicate that the proposed calculation method and fitting equation can provide a practical reference for evaluating fabrication-induced degradation in stack–parallel REBCO conductors.
