This study experimentally investigated the performance and operating characteristics of four expanders repurposed from automotive air-conditioning compressors—a double-acting rotary vane expander (DRVE), modified DRVE (MRVE), single-acting rotary vane expander (SRVE), and scroll expander (SE)—in a microscale organic Rankine cycle system using R134a as the working fluid. The MRVE and SRVE included a vapor pressure-assisted mechanism to enhance vane-tip sealing. Under the same chamber architecture, this mechanism enabled the MRVE to achieve lower minimum permeability (α) than the DRVE did (0.100 kg/s·MPa vs. 0.120 kg/s·MPa), which increased the peak isentropic efficiency (ηexp,is) and electrical power output (Ẇelec) by 18.1 percentage points and 404 W, respectively. As the pressure ratio (σ) was increased, α decreased for the SRVE and MRVE, with the SRVE consistently demonstrating lower α values, reflecting reduced clearance leakage. When σ exceeded 2.5, the SRVE maintained superior performance, whereas the MRVE exhibited a marked decline in ηexp,is, a deterioration reasonably attributed to increased mechanical friction at the vane tips and secondary slot leakage. Although the SE achieved the highest peak Ẇelec (1128 W) and net system efficiency (5.1%) values among all expanders, its performance degraded sharply at elevated σ values because of underexpansion associated with its fixed built-in volume ratio. Overall, expander performance reflected the combined effects of expander architecture, vane count, pressure-assisted sealing, friction, and internal flow paths. The findings highlight the viability of compressor-derived expanders and emphasize the importance of matching their configuration to the intended operating pressure ratio and thermal conditions.
This study experimentally investigates the thermal implications of geometric compactness in vertical earth–air heat exchangers (EAHEs) under space-constrained conditions. Two vertical U-type EAHE systems connected in series and differing only in internal pipe spacing (25 and 15 cm) were evaluated under warm–humid climatic conditions. Reducing pipe spacing intensified localized transient soil thermal accumulation near the inlet section, producing soil temperature differences between configurations of 0.7–1.2 °C at 5 cm from the pipe. At 15 cm, these differences decreased to 0–0.3 °C, while the radial attenuation of the soil thermal disturbance within individual configurations ranged from 61.5–88.9%. Heat transfer was spatially non-uniform, with approximately 53–63% of the total inlet-to-outlet temperature reduction occurring within the first well. Statistical analysis of daily mean values confirmed higher local soil temperatures in the compact configuration, whereas paired two one-sided tests demonstrated practical equivalence of outlet air temperatures within a predefined ±0.5 °C margin. The compactness-induced thermal differences were progressively attenuated both radially through the surrounding soil and longitudinally along the airflow path, resulting in comparable global thermal responses despite measurable local effects. This behavior provides experimental evidence of thermal decoupling between localized subsurface thermal dynamics and the outlet response under the evaluated operating conditions. The findings provide experimental evidence of the spatial attenuation mechanisms governing compact vertical EAHEs and contribute to the development of practical design guidelines for applications with limited installation space.
The efficient exploitation of low-enthalpy geothermal resources requires Organic Rankine Cycle (ORC) systems that can adapt to unavoidable fluctuations in the source. While previous studies have focused on static multi-objective optimization using Genetic Algorithms (NSGA-II), these often lack the computational speed required for real-time operational adjustments. This study investigates a custom Multi-Objective Particle Swarm Optimization (MOPSO) algorithm to optimize a low-GWP zeotropic mixture (Pentane/Isobutane) under quasi-dynamic geothermal conditions. Net electrical power output and cycle thermodynamic efficiency were simultaneously optimized, with the Levelized Cost of Energy (LCOE) mapped as a post-processed techno-economic metric along the Pareto frontier, incorporating the degree of superheating ΔTsh as a critical decision variable for turbine protection. The results indicate that the MOPSO algorithm identified a high-performing configuration with a peak net power output of 4,432.68 kW and a minimum LCOE of 0.0472 €/kWh. Under the evaluated nominal conditions, the optimization converged toward a 0 K superheating degree. Furthermore, MOPSO generated a denser Pareto solution set while reducing the number of objective-function evaluations by 75% relative to NSGA-II. Under a simulated 30 °C reduction in geothermal source temperature (from 150 °C to 120 °C), the swarm-based approach enabled adaptive Power Point Tracking and maintained a 7.9% higher power output than the corresponding static operating strategy. These findings suggest that MOPSO-based frameworks can enhance operational adaptability and support thermo-economic performance under varying geothermal resource conditions.
The suitability of lithium-ion battery thermal management strategies (TMSs) varies substantially across operating conditions and engineering constraints, limiting the effectiveness of single-metric or fixed-weight evaluation methods. This study develops a scenario-adaptive framework integrating the Analytic Hierarchy Process and Fuzzy Comprehensive Evaluation (AHP-FCE). The framework comprises four primary criteria (technical performance, economic viability, environmental safety, and sustainability) and 15 secondary indicators, with scenario-specific weights and evaluation boundaries established for energy storage systems (ESS), electric supercars (ESC), and electric propulsion ships (EPS). Among the evaluated candidates, single-phase immersion cooling, two-phase immersion cooling, and single-phase cold-plate cooling rank first for ESS, ESC, and EPS, with adaptability scores of 0.894, 0.930, and 0.885, respectively, highlighting the scenario dependence of TMS selection. Robustness analyses confirm the overall stability of these recommendations, although the ESC ranking is more sensitive to the weighting method. An external techno-economic benchmark further supports the engineering plausibility of the ESS recommendation. The proposed framework provides a transparent and interpretable quantitative basis for preliminary TMS screening and scenario-specific engineering decision-making.
The thermal reliability of polymer gears operating under dry-running conditions is governed by the interaction between friction-induced heat generation, conductive heat dissipation, and localized thermal accumulation. However, the relationship between intrinsic thermal transport and component-level thermal reliability remains insufficiently understood. In this study, the transient thermal behavior of polyoxymethylene (POM) gears reinforced with carbon black (CB) and nano-calcium carbonate (NCC) was investigated through an integrated experimental–numerical approach. Thermal conductivity, specific heat capacity, transient temperature evolution, cooling behavior, wear, and surface degradation were experimentally characterized, while three-dimensional finite element simulations were used to analyze localized temperature fields and heat-transfer pathways. A cooling-stage-based validation strategy was introduced to evaluate the component-level cooling response under controlled conditions while excluding active friction-induced heating. Furthermore, localized heat-flux analysis, thermal hotspot localization, cooling-time-constant evaluation, and a Heat-Flow Intensity (HFI) index were employed to quantitatively characterize internal heat transport within the gear tooth, while a normalized Thermo-Tribological Performance Index (TTPI) was developed to provide a unified comparative assessment of thermal transport, cycle-normalized wear performance, and service durability. Thermal conductivity increased from 0.29 to 0.449 W m⁻1 K⁻1 with increasing nanofiller loading, leading to faster cooling and enhanced heat transport. However, the highest thermal conductivity did not provide the best thermal reliability because excessive nanoparticle loading was associated with increased friction-induced heating and surface degradation. Instead, the POM/CB/3NCC composite exhibited the best overall performance, combining efficient heat dissipation, reduced operating temperature, superior wear resistance, and the longest service life. The proposed framework, together with the HFI and TTPI indices, provides quantitative comparative tools for evaluating internal heat transport and integrated thermo-tribological performance of polymer nanocomposite gears and offers a potentially transferable basis for the thermal and tribological design of polymer transmission components.
