This research introduces and optimizes a novel multi-generation power system integrating a steam Rankine cycle (SRC), a gas turbine (GT), an absorption refrigeration cycle (ARC), a proton exchange membrane (PEM) electrolyzer, and a CO2 separation unit. This system is designed to improve energy efficiency while simultaneously capturing CO2 and producing hydrogen through electrolysis. Two configurations-with and without ARC-are evaluated using a genetic algorithm-based multi-objective optimization framework, which considers exergetic efficiency, CO2 emission reduction, and total cost rate. The findings demonstrate that the proposed system improves exergetic efficiency by up to 71% and reduces CO2 emissions by up to 3.9% compared to a standalone GT system. Furthermore, the system without ARC achieves higher hydrogen production, while the system with ARC provides valuable cooling. These findings demonstrate the feasibility and environmental advantages of integrated power, CO2 capture, and H 2 blending systems for sustainable energy generation.
Carbon dioxide (CO2) has emerged as a promising natural refrigerant for electric vehicle (EV) heat pump systems because of its low environmental impact and strong heating capability at low ambient temperatures. However, its high operating pressure, low critical temperature, and transcritical behavior continue to hinder practical vehicle implementation. This review critically examines recent developments in CO2-based heat pump systems for EV thermal management, covering key components, advanced cycle configurations, and auxiliary performance-enhancement strategies. Unlike previous reviews that focused mainly on general CO2 systems or EV heat pumps using multiple refrigerants, the present study provides a dedicated synthesis of CO2-based EV heat pump technologies from an EV-oriented system-level perspective. Advanced configurations, including dual heat exchangers, secondary loops, ejector cycles, vapor injection, intercooled compression, and auto-cascade systems, are reviewed together with waste heat recovery, operating control, refrigerant mixtures, and defrosting strategies. The reviewed evidence indicates that advanced cycle configurations can improve low-temperature heating capability, reduce compressor burden, and expand the operating range, while auxiliary technologies can enhance energy utilization, adaptability, and operational stability. However, these benefits are frequently accompanied by increased packaging requirements, control complexity, cost, and reliability concerns. Therefore, the selection and integration of CO2 heat pump technologies should account for the trade-offs between thermodynamic performance and practical vehicle implementation under different operating conditions. This review provides a structured technical basis for developing high-efficiency and reliable CO2-based thermal management systems for next-generation EVs.
One of the key challenges in the hospitality industry is managing workforce schedules in response to seasonal fluctuations in demand. To address this, organizations often adopt flexible scheduling approaches that adjust working hours across different periods. The Flexible Work Hours System (FWHS) in South Korea enables employees to work longer hours during peak seasons and fewer hours during off-seasons, while ensuring compliance with national regulations on average working hours. Despite its potential, FWHS adoption in the hospitality industry remains limited, and empirical evidence on its practical and economic impact is scarce. This study examines the applicability of FWHS in hotel operations through quantitative and economic analysis. A mathematical optimization model is developed, incorporating labor regulations and industry-specific operational constraints. Four distinct scheduling scenarios are constructed considering peak and off-seasons, with and without FWHS, and are analyzed from both employer and employee perspectives. The results suggest that FWHS can serve as an effective workforce management tool in environments with fluctuating demand. For employers, the system reduces total labor costs by requiring fewer employees. For employees, although workloads intensify during peak seasons, overall compensation improves due to increased allowances and greater scheduling flexibility in the off-season. These features make FWHS particularly appealing to individuals who prioritize income or adaptable work patterns. By presenting a practical and replicable modeling framework, this study offers insights for both researchers and practitioners seeking to evaluate the potential benefits and trade-offs of FWHS in service-oriented industries.
SA508 low-alloy steel is a candidate material for main steam line piping, and its microstructure and mechanical properties are significantly influenced by the cooling rate after austenitizing. This study quantitatively analyzed the effect of cooling rate–induced microstructural changes on J -R fracture resistance. As the cooling rate increased, the fraction of coarse ferrite and pearlite decreased, while the formation of low-temperature transformation microstructure increased. As a result, the strength increased, whereas the J -R fracture resistance increased up to the air cooling (AC) and subsequently decreased with a further increase in the cooling rate. These changes in mechanical properties are considered to be associated with these low-temperature microstructures induced by the increased cooling rate. The relationship between microstructure and J Ic was quantitatively evaluated using a predictive model incorporating grain size and strength. For specimens with mixed microstructures of ferrite, pearlite, and bainite (FC, AC, AQ), the predicted values of J Ic showed good agreement with experimental results. However, for WQ, the experimental J Ic was approximately 140 kJ/m 2 lower than the predicted value.
