This study focuses on developing an electric propulsion platform that utilizes liquid hydrogen (LH2) as both fuel and coolant. The cooling system aims to cryogenically cool the rotor of a high-temperature superconductor (HTS) motor with LH2while supplying the discharged hydrogen to the fuel cell. By omitting an additional cryocooler for the HTS motor, this approach enhances efficiency and overall performance. The research includes the thermohydraulic and structural design of the HTS magnet rotor, incorporating LH2and a triple tube-magnetic fluid seal. A prototype cooling system was fabricated, and its performance evaluated using liquid nitrogen (LN2) as an alternative refrigerant to ensure safety. LN2verified the flow and boiling heat transfer characteristics of the HTS rotor cooling system, with the flow rate controlled by the pressure build-up (PBU) method in the LN2vessel, relying on ambient heat load.

Gas turbine blade cooling typically uses a cooling air passage with a sharp 180° turn in the midchord area of the airfoil. Its geometric shape and dimensions are strictly constrained within the airfoil to ensure both aerodynamic and cooling performance. These characteristics imply the importance of understanding the relationships between the geometric dimensions and the cooling channel performance. In this study, we validated a numerical method using the commercial software, Ansys Fluent 2021 R2, by predicting a total pressure loss coefficient with less than 6% deviation from the experimental results of Metzger et al. for four different Reynolds numbers. Through parameter studies, the divider tip-to-wall clearance was found to be the most significant parameter influencing the pressure loss. Parameter correlations and predictive models between the design variables and the pressure loss were derived by regression analysis using the R language; the regression model predicted the pressure loss to within 2.29% of the numerical method. As the geometries changed, the response surface and the adjoint solver improved the pressure loss by approximately 20.87% and 25.96%, respectively, at the representative Reynolds number of 24,230; this showed that the adjoint solver was a relatively simple and effective method with minimal geometric changes.

Abstract Rare-earth Barium Copper Oxide (REBCO) high-temperature superconducting (HTS) magnets are typically fabricated by winding REBCO tapes into coils. During operation, these magnets experience compressive stresses induced by winding tension, electromagnetic forces, and thermal contraction, which can cause mechanical deformation and fracture. Conventional approaches estimate the mechanical properties of REBCO tapes based on the behavior of individual constituent materials; however, such estimates are valid only for single tapes. In practical applications, stacked or wound tapes exhibit markedly different mechanical responses due to interfacial effects. Therefore, investigating the mechanical behavior of stacked HTS tapes is essential for reliable structural design and analysis. In this study, five types of REBCO tapes were selected and cut into uniform dimensions to fabricate stacked specimens. Compression experiments were conducted in a liquid-nitrogen-filled vacuum chamber at two maximum stress levels to simulate typical stresses experienced during magnet cool-down and operation. Two stacking configurations were considered: one consisting solely of REBCO tapes and the other composed of alternating REBCO and stainless-steel tapes, commonly referred to as metal insulation. Precision cutting tools were employed to minimize edge effects, and custom specimen guides and load transfer blocks were designed to ensure proper transversal loading. A cryogenically compatible universal testing machine was used to apply compressive stress, while an extensometer measured the displacement. Each specimen underwent three loading–unloading cycles to evaluate hysteresis behavior after local post-yield. Stress–strain curves were obtained, and the effective tangent modulus was determined. Under maximum compressive stress, the measured modulus varied significantly depending on the specimen, ranging from 1.3 GPa to 62.9 GPa, and exhibited clear stress-dependent behavior. The copper stabilizer thickness ratio, associated with low stiffness, strongly influenced both the strain and tangent modulus. These results provide key mechanical properties necessary for the structural evaluation and modeling of HTS magnets.

This study analyzed the particle collection characteristics of an electrostatic precipitator (ESP) based on three performance-influencing parameters: applied voltage, volumetric flow rate, and collection plate type. We employed the flat, tilt, half-tilt, and expand type collection plates. Compared with the flat type, the tilt and half-tilt type exhibited enhanced corona discharge. The half-tilt type exhibited a 9 % higher collection efficiency than the flat type at φ = 12 kV and Q = 0.15 m³/s. Additionally, the expand type exhibited the same electric-field trend as the flat type; however, it developed a separation region in the flow-velocity distribution. Consequently, its efficiency was higher under φ = 9 kV than that at φ = 12 kV because the separation region prevented the particles from attaching to the collection plates. Using the results, we developed an prediction model with a single hidden layer comprising 18 neurons. The predictions agreed well with the numerical simulation results, exhibiting errors within ±10 %.

This article presents a partial-depth impregnation method using electrically conductive epoxy composites in high-temperature superconductor (HTS) coils. In a previous study, we proposed a wet winding technique using electrically-conductive epoxy composites to control the contact resistance of no-insulation (NI) HTS coils. In that method, the epoxy composites were applied across the entire contact surface between winding turns, allowing the contact resistance to be controlled by adjusting the mixing ratio of electrically-conductive powder. However, this approach led to significant current degradation due to delamination caused by thermal contraction mismatch between the epoxy composites and the HTS tape. The partial-depth impregnation method addresses this issue by allowing the epoxy composites to penetrate only partway between winding turns, thereby minimizing critical current degradation. In this study, HTS coils were dry-wound with 4.1 mm-wide HTS tape and insulated with 3 mm-wide polyimide tape on each turn. By applying the electrically-conductive epoxy composites to the edge of the HTS coil, the epoxy composite penetrated to a depth of 1.1 mm. This configuration allows the current to bypass through the edge of the insulated coil, providing self-protection characteristics. Additionally, the contact resistance can be controlled by adjusting the mixing ratio of the electrically-conductive powders. The feasibility of the proposed impregnation technique was demonstrated through over-current and sudden-discharge tests on the partial-depth impregnated coils with different mixing ratios of electrically conductive powders.

This study focuses on developing an electric propulsion platform that utilizes liquid hydrogen (LH2) as both fuel and coolant. The cooling system aims to cryogenically cool the rotor of a high-temperature superconductor (HTS) motor with LH2while supplying the discharged hydrogen to the fuel cell. By omitting an additional cryocooler for the HTS motor, this approach enhances efficiency and overall performance. The research includes the thermohydraulic and structural design of the HTS magnet rotor, incorporating LH2and a triple tube-magnetic fluid seal. A prototype cooling system was fabricated, and its performance evaluated using liquid nitrogen (LN2) as an alternative refrigerant to ensure safety. LN2verified the flow and boiling heat transfer characteristics of the HTS rotor cooling system, with the flow rate controlled by the pressure build-up (PBU) method in the LN2vessel, relying on ambient heat load.

Gas turbine blade cooling typically uses a cooling air passage with a sharp 180° turn in the midchord area of the airfoil. Its geometric shape and dimensions are strictly constrained within the airfoil to ensure both aerodynamic and cooling performance. These characteristics imply the importance of understanding the relationships between the geometric dimensions and the cooling channel performance. In this study, we validated a numerical method using the commercial software, Ansys Fluent 2021 R2, by predicting a total pressure loss coefficient with less than 6% deviation from the experimental results of Metzger et al. for four different Reynolds numbers. Through parameter studies, the divider tip-to-wall clearance was found to be the most significant parameter influencing the pressure loss. Parameter correlations and predictive models between the design variables and the pressure loss were derived by regression analysis using the R language; the regression model predicted the pressure loss to within 2.29% of the numerical method. As the geometries changed, the response surface and the adjoint solver improved the pressure loss by approximately 20.87% and 25.96%, respectively, at the representative Reynolds number of 24,230; this showed that the adjoint solver was a relatively simple and effective method with minimal geometric changes.