Zengli Wang

The liquid film in the tooth tip clearance plays a critical role in reducing wear and sealing gas leakage in a single-screw compressor, yet its influence on shaft system dynamics has not been systematically quantified. In this paper, a comprehensive mathematical model of the liquid film in the star wheel tooth tip clearance is established, considering the conjugate geometry, the pressure governing equation, and the gas pressure equation. The finite difference method is employed to solve the pressure field, from which the bearing forces, frictional forces, axial/radial bearing loads, and rotating resistance torques are derived. The effects of the liquid film on the odd-groove and even-groove screw are compared, and a torque fluctuation ratio is introduced to quantify rotational stability. Results show that the liquid film in the odd-groove screw generates a larger frictional resistance torque on the star wheel, but induces smaller fluctuations in the rotating resistance torque on the screw rotor than in the even-groove screw. The axial load on the screw bearing in the even-groove case reaches approximately 154.8 N, which is about 26.2% higher than that in the odd-groove case. The radial load distributions on the bearings exhibit significant differences between the two configurations. The torque fluctuation ratio increases with viscosity and rotating speed, and decreases with suction temperature; with increasing discharge pressure, it decreases for the odd-groove rotor while showing a non-monotonic trend for the even-groove rotor. The even-groove rotor consistently exhibits higher values across all conditions, confirming the superior rotational stability of the odd-groove design. The findings provide quantitative guidance for single screw compressor design and bearing selection.

Solid oxide fuel cells (SOFCs) offer broad fuel flexibility and high overall energy-conversion efficiency. They are commonly integrated with gas turbines (GTs) or micro gas turbines (MGTs) to recover exhaust heat. However, incomplete heat recovery and poor thermal matching in bottoming cycles remain unresolved. To enable efficient cascade utilization of medium- and high-temperature flue-gas heat, this study proposed an SOFC-MGT-SRCO2-DPORC integrated power generation system. The system combines an SOFC-MGT topping cycle with a recuperative supercritical carbon dioxide cycle (SRCO2) and a dual-pressure organic Rankine cycle (DPORC). A thermodynamic model incorporating SOFC electrochemical behavior was established. The effects of operating parameters on thermodynamic performance were evaluated, followed by parameter optimization and comparisons under optimal conditions. The proposed system achieved the best overall performance among the investigated configurations. Its net power output and thermal efficiency reached 4.158 kW and 77.489%, respectively. Its exergy efficiency was 4.73% higher than that of the SOFC–MGT–SRCO2 system on a relative basis. These results provide a theoretical basis for improving the performance of integrated SOFC power systems.

Under ultra-high-pressure conditions, critical challenges are encountered for ionic liquid hydrogen compressors in hydrogen refueling stations, including cylinder heat dissipation difficulties and significant deviations in conventional macroscopic thermodynamic performance predictions based on the assumption of constant thermophysical properties. To address these challenges, a cross-micro/mesoscopic numerical simulation framework was developed in this study by integrating density functional theory (DFT) and molecular dynamics (MD). By bridging microscopic conformational analysis with mesoscopic property extraction, the microscopic interaction mechanisms of the ionic liquid–hydrogen system, the evolution characteristics of gas–liquid interfacial thermal resistance under variable operating conditions, and the corresponding heat transfer enhancement mechanisms were systematically investigated. The results demonstrated that hydrogen adsorption on the ionic liquid surface was identified as extremely weak physical adsorption, with absolute values of binding energy consistently remaining below 0.5 kcal·mol⁻¹. Furthermore, the system was found to exhibit favorable chemical stability throughout the pressurization process. The interfacial thermal resistance of the ionic liquid was observed to decrease nonlinearly with increasing pressure. The significant increase in collision flux, resulting from the elevated gas-phase number density at high pressures, more than compensated for the decrease in the energy accommodation coefficient per collision (from 1.0 to 0.3–0.4), thereby enhancing the overall interfacial energy exchange capability. Although temperature rise suppressed interfacial energy transfer, this effect remained limited under ultra-high-pressure conditions. The evolutionary behaviors of the thermophysical properties of ionic liquids and the anomalous interfacial heat transfer enhancement mechanisms under ultra-high-pressure and variable-temperature conditions, as revealed in this study, provide theoretical support for the elucidation of flow and heat transfer mechanisms and for the efficient and reliable design of ultra-high-pressure ionic liquid hydrogen compressors.

The claw compressor is one of the most promising hydrogen circulation pumps, featuring high reliability, oil-free operation and compact structure. However, the conventional claw hydrogen circulation pump adopts a point-to-point meshing approach at the pitch circle for its two mutually meshing rotors, resulting in severe hydrogen leakage, which is a bottleneck limiting its development. In order to solve this problem, in this study, the authors proposed a novel gear double-claw rotor, which uses arcs, cycloids and parabolas. This novel rotor contains a type of tortuous meshing structure between the claw rotors to increase the gas sealing. Furthermore, a corresponding geometric model for the gear double-claw rotor was constructed, and its cross-sectional profile equations were derived. During operation, the unsteady flow of the internal gas in the novel gear double-claw hydrogen circulation pump that has complicated geometric boundaries was numerically simulated; the pressure distributions and transient flows of the novel pump were compared with those of the conventional pump. The numerical simulation results were experimentally verified. Results show that the proposed gear double-claw rotor is able to significantly enhance the sealing performance; and the gas leakage velocity of the novel rotor during operation decrease by 35.15%.

Liquid film phase change is a critical factor in the performance degradation of mechanical seals. However, experimental data regarding the evolution of phase change and groove-type differences for typical hydrodynamic grooves such as inner herringbone and inner spiral grooves remain scarce. In this study, phase change experiments were conducted on mechanical seals with these two groove types using high-temperature hot water as the working medium. The effects of rotational speed and medium temperature on phase change evolution were systematically investigated, the temperature distribution on the back surface of the stationary ring was synchronously measured, and the influence of film thickness on sealing performance was analyzed using a numerical model. The numerical predictions show good agreement with the experimental data. The results demonstrate that, compared with the inner spiral groove seal, the inner herringbone groove seal exhibits a 6.44%–33.61% higher phase change rate, an 18.4%–35.4% lower leakage rate, and an average back-surface temperature up to 4.88 K lower. Phase change in the inner spiral groove seal concentrates at the low-pressure inner-diameter side and propagates outward along the spiral grooves, whereas in the inner herringbone groove seal it is additionally distributed on the leeward side of the grooves. This difference arises from the coupled effects of non-uniform liquid film thickness between the groove and dam regions and localized low-pressure zones. The phase change rate decreases with increasing rotational speed but increases significantly with medium temperature. Film thickness analysis reveals a stable operating interval and a phase-change-sensitive interval. The dimensionless friction torque gradually attenuates and plateaus as film thickness increases, while the leakage rate exhibits a continuous upward trend.

Liquid film phase change critically degrades mechanical seal performance. Experimental data on phase change evolution and groove-type differences for typical hydrodynamic grooves remain scarce. In this study, phase change experiments were conducted on mechanical seals with these two groove types using high-temperature hot water as the working medium. The effects of rotational speed and medium temperature on phase change were investigated, back-surface temperature was synchronously measured, and film thickness effects were analyzed numerically. The numerical predictions agree well with experimental data. The results demonstrate that, compared with the inner spiral groove seal, the inner herringbone groove seal exhibits a 6.44%–33.61% higher phase change rate, an 18.4%–35.4% lower leakage rate, and an average back-surface temperature up to 4.88 K lower. Phase change in the inner spiral groove seal concentrates at the low-pressure inner-diameter side and propagates outward along the spiral grooves, whereas in the inner herringbone groove seal it is additionally distributed on the leeward side of the grooves. This difference arises from the coupled effects of non-uniform liquid film thickness between the groove and dam regions and localized low-pressure zones. The phase change rate decreases with increasing rotational speed but increases significantly with medium temperature. Film thickness analysis reveals a stable operating interval and a phase-change-sensitive interval. The dimensionless friction torque gradually attenuates and plateaus as film thickness increases, while the leakage rate exhibits a continuous upward trend.