Pub Date : 2026-01-24DOI: 10.1016/j.csite.2026.107736
Akram Fadhl Al-mahmodi , Yamuna Munusamy , Hamada Esmaiel , Mahmood Riyadh Atta , Mohammed M. Alammar , Abdullah O. Baarimah
The increasing penetration of renewable energy sources requires reliable operational decision support for hybrid renewable energy systems operating under variable conditions. This study presents a physics-guided machine-learning framework for real-time operating-mode classification, distinguishing between grid-import and hydrogen-production states based on the system's energy balance. Ensemble models, including Random Forest and XGBoost, are trained using physically meaningful inputs such as solar power, wind power, load demand, and system losses. The framework is evaluated under nominal conditions and under physically motivated disturbances, including measurement noise, sensor bias, data loss, and marginal operating conditions near the surplus–deficit transition. Results show that ensemble-based models provide stable, consistent mode identification under uncertainty while maintaining alignment with physical energy-flow behavior. Scenario-based analysis reveals a marginal energy balance regime in which renewable generation approaches demand and losses, leading to increased decision sensitivity and switching instability in deterministic rule-based control. In this regime, the proposed surrogate reduces unnecessary mode transitions and improves decision stability without compromising physical fidelity. Explainability analysis using SHAP confirms that the model's decisions follow intuitive control logic, driven primarily by renewable availability. Overall, the study demonstrates that physics-guided machine learning enhances robustness, stability, and interpretability of operational mode decisions under realistic uncertainty.
{"title":"Explainable AI framework for operational mode classification in hybrid renewable energy systems","authors":"Akram Fadhl Al-mahmodi , Yamuna Munusamy , Hamada Esmaiel , Mahmood Riyadh Atta , Mohammed M. Alammar , Abdullah O. Baarimah","doi":"10.1016/j.csite.2026.107736","DOIUrl":"10.1016/j.csite.2026.107736","url":null,"abstract":"<div><div>The increasing penetration of renewable energy sources requires reliable operational decision support for hybrid renewable energy systems operating under variable conditions. This study presents a physics-guided machine-learning framework for real-time operating-mode classification, distinguishing between grid-import and hydrogen-production states based on the system's energy balance. Ensemble models, including Random Forest and XGBoost, are trained using physically meaningful inputs such as solar power, wind power, load demand, and system losses. The framework is evaluated under nominal conditions and under physically motivated disturbances, including measurement noise, sensor bias, data loss, and marginal operating conditions near the surplus–deficit transition. Results show that ensemble-based models provide stable, consistent mode identification under uncertainty while maintaining alignment with physical energy-flow behavior. Scenario-based analysis reveals a marginal energy balance regime in which renewable generation approaches demand and losses, leading to increased decision sensitivity and switching instability in deterministic rule-based control. In this regime, the proposed surrogate reduces unnecessary mode transitions and improves decision stability without compromising physical fidelity. Explainability analysis using SHAP confirms that the model's decisions follow intuitive control logic, driven primarily by renewable availability. Overall, the study demonstrates that physics-guided machine learning enhances robustness, stability, and interpretability of operational mode decisions under realistic uncertainty.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107736"},"PeriodicalIF":6.4,"publicationDate":"2026-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146047840","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Energy tunnels, which integrate underground construction with geothermal utilization, provide a promising approach for urban renewable energy development. However, in shielded energy tunnels, the asymmetry of heat exchanger arrangement and tunnel lining heat transfer conditions results in significant circumferential non-uniformity, and the heat flux dynamically varies with operating conditions, making traditional models based on constant heat flux and axisymmetric assumptions inadequate. This study proposes a segmental analytical heat transfer model for shielded energy tunnels, accounting for variable heat flux and asymmetric bidirectional heat transfer at the tunnel lining inner and outer surfaces. Under the assumption of uniform axial temperature, the model analytically predicts fluid temperature along the flow direction and the surrounding medium temperature field, and can be extended to multi-layer linings via superposition, enabling refined characterization of temperature and heat transfer in multi-ring energy tunnels. Validation against summer and winter field data shows that the root mean square errors of fluid temperature predictions are 0.40 °C in summer and 0.48 °C in winter, demonstrating high accuracy. Parametric analysis indicates that increasing inlet temperature or flow rate enhances circumferential heat flux non-uniformity and lining surface temperature differences, which may induce thermal stress. Increasing heat exchanger thermal conductivity improves overall heat transfer but has limited impact on circumferential non-uniformity. Multi-loop operation analysis shows that series operation maximizes heat transfer, achieving 1.52 % higher performance than parallel operation in summer and 2.76 % higher in winter. Parallel operation achieves higher system efficiency but limited heat transfer, while hybrid operation balances efficiency and heat transfer, offering the best overall performance. The proposed model overcomes limitations of existing analytical studies assuming constant heat flux and single-ring structures, providing a refined tool to describe circumferential non-uniformity and multi-ring effects, and offers a theoretical basis for optimizing energy tunnel design and thermo-mechanical coupling studies.
{"title":"An Analytical Model for Asymmetric Heat Transfer in Energy Tunnels with Segment Lining: Validation and Multi-Loop Analysis","authors":"Xue Wang, Xiaozhao Li, Xueyin Zhu, Huiyuan Wang, Haifeng Qing, Yanyu Zhao, Rongying Liu, Qingru Wu, Peng Zhao","doi":"10.1016/j.csite.2026.107743","DOIUrl":"https://doi.org/10.1016/j.csite.2026.107743","url":null,"abstract":"Energy tunnels, which integrate underground construction with geothermal utilization, provide a promising approach for urban renewable energy development. However, in shielded energy tunnels, the asymmetry of heat exchanger arrangement and tunnel lining heat transfer conditions results in significant circumferential non-uniformity, and the heat flux dynamically varies with operating conditions, making traditional models based on constant heat flux and axisymmetric assumptions inadequate. This study proposes a segmental analytical heat transfer model for shielded energy tunnels, accounting for variable heat flux and asymmetric bidirectional heat transfer at the tunnel lining inner and outer surfaces. Under the assumption of uniform axial temperature, the model analytically predicts fluid temperature along the flow direction and the surrounding medium temperature field, and can be extended to multi-layer linings via superposition, enabling refined characterization of temperature and heat transfer in multi-ring energy tunnels. Validation against summer and winter field data shows that the root mean square errors of fluid temperature predictions are 0.40 °C in summer and 0.48 °C in winter, demonstrating high accuracy. Parametric analysis indicates that increasing inlet temperature or flow rate enhances circumferential heat flux non-uniformity and lining surface temperature differences, which may induce thermal stress. Increasing heat exchanger thermal conductivity improves overall heat transfer but has limited impact on circumferential non-uniformity. Multi-loop operation analysis shows that series operation maximizes heat transfer, achieving 1.52 % higher performance than parallel operation in summer and 2.76 % higher in winter. Parallel operation achieves higher system efficiency but limited heat transfer, while hybrid operation balances efficiency and heat transfer, offering the best overall performance. The proposed model overcomes limitations of existing analytical studies assuming constant heat flux and single-ring structures, providing a refined tool to describe circumferential non-uniformity and multi-ring effects, and offers a theoretical basis for optimizing energy tunnel design and thermo-mechanical coupling studies.","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"7 1","pages":""},"PeriodicalIF":6.8,"publicationDate":"2026-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146047837","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study examines the influence of magnetic field and thermal radiation on the onset of mixed convection instability in a horizontal porous layer saturated by a viscoelastic Kelvin-Voigt fluid with a special focus on applications to renewable energy and geothermal science. Many geothermal reservoirs underground heat-storage units, and solar assisted porous heat exchangers involve complex fluids whose rheology depart from Newtonian behavior due to presence of polymers, suspended particles or bio-geochemical interaction. Understanding the stability of thermally driven flow in such environments is crucial for optimizing heat extraction, improving long-term reservoir performance, and preventing undesired thermal stratification. A linear stability analysis is conducted to determine the critical Reynolds number as a function of Hartmann number, Darcy number, Kelvin-Voigt parameter, radiative parameter, Richardson number and Prandtl number. The results show that increasing the Darcy number enhances the effective permeability to the porous matrix, strengthens viscous dissipation, and therefore stabilizes the flow by raising the critical threshold of instability. Similarly, a stronger magnetic field, represented by the Hartmann number, generates a Lorentz damping force that suppresses transverse perturbations, acting as a major MHD stabilizing mechanism. The radiation parameter also contributes to flow stabilization by increasing effective thermal diffusion and weakening temperature gradients. In addition, the Kelvin-Voigt viscoelastic parameter introduces a memory-driven elastic resistance that absorbs perturbations and significantly delays the onset of instability. The Prandtl number plays a critical role in modulating the competition between thermal diffusion, shear and viscoelasticity, producing a Reynolds-dependent dual effect at low wavenumbers, but an exclusively stabilizing effect in high wavenumber regimes. Conversely, the Richardson number, which measures the competition between buoyancy and shear, exhibits a destabilizing effect: higher buoyancy forces intensify natural convection motions, making the system more sensitive to disturbance and facilitating the transition to instability. Quantitatively, we find that an increase in Hartmann number raises the stability threshold by 25 %, whereas changes in Darcy number and viscoelastic coefficient modify the threshold by 10 %. Thermal radiation increases the threshold by 12 %. Increasing the Richardson number decreases the critical threshold by approximately 25 %, with a typical reduction ranging between 20 % and 30 % depending on wavenumber domain. Theses findings provide valuable insight for the design and optimization of geothermal heat exchangers, porous thermal-energy storage units, and bio-energy and renewable energy systems, where controlling thermal and hydrodynamic stability is essential for improved efficiency, enhanced heat transfer, and safe long-term operation.
{"title":"Mixed-convection instability in a horizontal Brinkman porous layer saturated with a viscoelastic fluid under magnetic-field and thermal-radiation effects: Application to renewable energy systems","authors":"Cédric Gervais Njingang Ketchate , Pascalin Tiam Kapen , Alain Dika , Didier Fokwa","doi":"10.1016/j.csite.2026.107745","DOIUrl":"10.1016/j.csite.2026.107745","url":null,"abstract":"<div><div>This study examines the influence of magnetic field and thermal radiation on the onset of mixed convection instability in a horizontal porous layer saturated by a viscoelastic Kelvin-Voigt fluid with a special focus on applications to renewable energy and geothermal science. Many geothermal reservoirs underground heat-storage units, and solar assisted porous heat exchangers involve complex fluids whose rheology depart from Newtonian behavior due to presence of polymers, suspended particles or bio-geochemical interaction. Understanding the stability of thermally driven flow in such environments is crucial for optimizing heat extraction, improving long-term reservoir performance, and preventing undesired thermal stratification. A linear stability analysis is conducted to determine the critical Reynolds number as a function of Hartmann number, Darcy number, Kelvin-Voigt parameter, radiative parameter, Richardson number and Prandtl number. The results show that increasing the Darcy number enhances the effective permeability to the porous matrix, strengthens viscous dissipation, and therefore stabilizes the flow by raising the critical threshold of instability. Similarly, a stronger magnetic field, represented by the Hartmann number, generates a Lorentz damping force that suppresses transverse perturbations, acting as a major MHD stabilizing mechanism. The radiation parameter also contributes to flow stabilization by increasing effective thermal diffusion and weakening temperature gradients. In addition, the Kelvin-Voigt viscoelastic parameter introduces a memory-driven elastic resistance that absorbs perturbations and significantly delays the onset of instability. The Prandtl number plays a critical role in modulating the competition between thermal diffusion, shear and viscoelasticity, producing a Reynolds-dependent dual effect at low wavenumbers, but an exclusively stabilizing effect in high wavenumber regimes. Conversely, the Richardson number, which measures the competition between buoyancy and shear, exhibits a destabilizing effect: higher buoyancy forces intensify natural convection motions, making the system more sensitive to disturbance and facilitating the transition to instability. Quantitatively, we find that an increase in Hartmann number raises the stability threshold by 25 %, whereas changes in Darcy number and viscoelastic coefficient modify the threshold by 10 %. Thermal radiation increases the threshold by 12 %. Increasing the Richardson number decreases the critical threshold by approximately 25 %, with a typical reduction ranging between 20 % and 30 % depending on wavenumber domain. Theses findings provide valuable insight for the design and optimization of geothermal heat exchangers, porous thermal-energy storage units, and bio-energy and renewable energy systems, where controlling thermal and hydrodynamic stability is essential for improved efficiency, enhanced heat transfer, and safe long-term operation.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107745"},"PeriodicalIF":6.4,"publicationDate":"2026-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146047835","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-24DOI: 10.1016/j.csite.2026.107751
Osama Abd Al-Munaf Ibrahim , Saif Ali Kadhim , Ali M. Ashour , Abdallah Bouabidi , Ravishankar Sathyamurthy
This study presents an experimental investigation aimed at improving the thermal performance of a solar box cooker using metallic fibers and a booster mirror. Three identical cookers were fabricated and tested under two operating conditions: without and with a reflective mirror. Each cooker contained an equal mass of copper, aluminum, or steel fibers distributed around the cooking pot to enhance internal heat transfer. Experiments were conducted under natural solar radiation from 7:00 a.m. to 5:00 p.m., and temperatures were monitored continuously. The cooker containing copper fibers and equipped with a booster mirror achieved the best overall performance, reaching a maximum water temperature of 92.2 °C, and maintaining temperatures above 90 °C for nearly 1 h under peak solar conditions, with a second figure of merit of 0.303, a thermal efficiency of 27.34 %, and an exergy efficiency of 3.07 %. These results confirm the strong influence of copper's high thermal conductivity on energy absorption and temperature uniformity. The addition of the booster mirror increased heat gain and reduced cooking time by approximately 17 % compared with the non-reflective case. The proposed modification demonstrates that combining conductive enhancement and optical intensification can substantially improve the thermal behavior of solar box cookers, providing an effective and sustainable option for clean energy cooking applications.
{"title":"Improvement solar box cooker thermal performance using metal fibers","authors":"Osama Abd Al-Munaf Ibrahim , Saif Ali Kadhim , Ali M. Ashour , Abdallah Bouabidi , Ravishankar Sathyamurthy","doi":"10.1016/j.csite.2026.107751","DOIUrl":"10.1016/j.csite.2026.107751","url":null,"abstract":"<div><div>This study presents an experimental investigation aimed at improving the thermal performance of a solar box cooker using metallic fibers and a booster mirror. Three identical cookers were fabricated and tested under two operating conditions: without and with a reflective mirror. Each cooker contained an equal mass of copper, aluminum, or steel fibers distributed around the cooking pot to enhance internal heat transfer. Experiments were conducted under natural solar radiation from 7:00 a.m. to 5:00 p.m., and temperatures were monitored continuously. The cooker containing copper fibers and equipped with a booster mirror achieved the best overall performance, reaching a maximum water temperature of 92.2 °C, and maintaining temperatures above 90 °C for nearly 1 h under peak solar conditions, with a second figure of merit of 0.303, a thermal efficiency of 27.34 %, and an exergy efficiency of 3.07 %. These results confirm the strong influence of copper's high thermal conductivity on energy absorption and temperature uniformity. The addition of the booster mirror increased heat gain and reduced cooking time by approximately 17 % compared with the non-reflective case. The proposed modification demonstrates that combining conductive enhancement and optical intensification can substantially improve the thermal behavior of solar box cookers, providing an effective and sustainable option for clean energy cooking applications.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107751"},"PeriodicalIF":6.4,"publicationDate":"2026-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146047832","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-24DOI: 10.1016/j.csite.2026.107744
Wugang Huang , Xiwen Lei , Jianing Wang
Subway platform fires have the characteristics of rapid smoke spread, difficulties in smoke exhaust and in evacuating personnel. To investigate the impact of collaborative smoke exhaust design with rail-top system on the smoke exhaust performance during subway platform fires, a series of full-scale numerical simulations were conducted by taking a real subway station as an example. The variation patterns of downward velocity at stairway, as well as temperature, CO concentration and visibility at the clear height were revealed. The results indicate that the downward velocity at stairway gradually increases as the rail-top exhaust system airflow increases. The relationship between downward velocity and rail-top exhaust system velocity was proposed. When the rail-top exhaust system velocity reaches 70 m3/s, it can meet the requirement of a 1.5 m/s downward velocity at stairway. Based on the result of temperature, CO concentration, visibility indicators and the calculated smoke exhaust volume of the exhaust system according to specifications, using a rail-top fan airflow of 70 m3/s (252,000 m3/h) for collaborative smoke exhaust can meet the requirements for personnel evacuation. The results can give insights for the emergency evacuation planning, smoke control and firefighting activities in subway stations.
{"title":"Numerical investigation on cooperative platform smoke exhaust technology of rail-top exhaust system in subway station fires","authors":"Wugang Huang , Xiwen Lei , Jianing Wang","doi":"10.1016/j.csite.2026.107744","DOIUrl":"10.1016/j.csite.2026.107744","url":null,"abstract":"<div><div>Subway platform fires have the characteristics of rapid smoke spread, difficulties in smoke exhaust and in evacuating personnel. To investigate the impact of collaborative smoke exhaust design with rail-top system on the smoke exhaust performance during subway platform fires, a series of full-scale numerical simulations were conducted by taking a real subway station as an example. The variation patterns of downward velocity at stairway, as well as temperature, CO concentration and visibility at the clear height were revealed. The results indicate that the downward velocity at stairway gradually increases as the rail-top exhaust system airflow increases. The relationship between downward velocity and rail-top exhaust system velocity was proposed. When the rail-top exhaust system velocity reaches 70 m<sup>3</sup>/s, it can meet the requirement of a 1.5 m/s downward velocity at stairway. Based on the result of temperature, CO concentration, visibility indicators and the calculated smoke exhaust volume of the exhaust system according to specifications, using a rail-top fan airflow of 70 m<sup>3</sup>/s (252,000 m<sup>3</sup>/h) for collaborative smoke exhaust can meet the requirements for personnel evacuation. The results can give insights for the emergency evacuation planning, smoke control and firefighting activities in subway stations.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107744"},"PeriodicalIF":6.4,"publicationDate":"2026-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146047836","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Thermal interface materials consisting of low-melting-point liquid metal indicate excellent thermal conductivity and good deformation capabilities, thereby displaying important role in thermal management applications under extreme conditions. This study introduces the molecular dynamics simulation to investigate the thermal transport and wetting behavior of Ga-Diamond and Ga-Cu solid-liquid interfaces. From 323 to 1023 K, the interfacial thermal resistance of both assemblies drops sharply as rising temperature boosts phonon coupling efficiency. Notably, analysis on the phonon participation ratio shows that Ga at the Ga-Cu interface indicates a high extended phonon share of 20 %, which is larger than that at the Ga-Diamond system (16.1 %). The interfacial phonon match illustrates dominant effect on the thermal transport difference. Moreover, the wettability analysis reveals that the contact angle θ of gallium at the two interfaces shows opposite tendency. The contact angle increases with temperature by 9.3 % on the diamond surface, whereas it reduces by 79.6 % on the Cu surface. In addition, a strong linear correlation between interfacial thermal resistance interfacial thermal resistance and cosθ is fitted, showing positive relation in the Ga-Diamond system and negative relation in the Ga-Cu system.
{"title":"Molecular dynamics study on temperature-dependent interfacial thermal resistance and wettability at Ga-Diamond/Cu interfaces","authors":"Jiaqing Zhang , Abdulmajeed Mohamad , Qiuwang Wang , Wenxiao Chu","doi":"10.1016/j.csite.2026.107747","DOIUrl":"10.1016/j.csite.2026.107747","url":null,"abstract":"<div><div>Thermal interface materials consisting of low-melting-point liquid metal indicate excellent thermal conductivity and good deformation capabilities, thereby displaying important role in thermal management applications under extreme conditions. This study introduces the molecular dynamics simulation to investigate the thermal transport and wetting behavior of Ga-Diamond and Ga-Cu solid-liquid interfaces. From 323 to 1023 K, the interfacial thermal resistance of both assemblies drops sharply as rising temperature boosts phonon coupling efficiency. Notably, analysis on the phonon participation ratio shows that Ga at the Ga-Cu interface indicates a high extended phonon share of 20 %, which is larger than that at the Ga-Diamond system (16.1 %). The interfacial phonon match illustrates dominant effect on the thermal transport difference. Moreover, the wettability analysis reveals that the contact angle <em>θ</em> of gallium at the two interfaces shows opposite tendency. The contact angle increases with temperature by 9.3 % on the diamond surface, whereas it reduces by 79.6 % on the Cu surface. In addition, a strong linear correlation between interfacial thermal resistance interfacial thermal resistance and cos<em>θ</em> is fitted, showing positive relation in the Ga-Diamond system and negative relation in the Ga-Cu system.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107747"},"PeriodicalIF":6.4,"publicationDate":"2026-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146047833","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-24DOI: 10.1016/j.csite.2026.107750
Minho Kim , Beungyong Park , Dongsu Kim , Sung Lok Do
This study proposes an economizer integrated with ground-coupled air duct system (EGAS) to expand the range of outdoor air (OA) conditions suitable for economizer operation and to maximize cooling energy savings under Korean climate (4A climate zone). The EGAS features an OA duct buried underground, allowing heat exchange with the relatively stable and lower-temperature soil before determining the OA intake rates of economizer. Therefore, this study aims to evaluate the cooling energy savings potential by using EGAS in the Korean climate. To achieve this, the EGAS control algorithm was developed and integrated into the Base model to conduct building energy simulations. The results showed that EGAS increased OA intake rates, extended the operating hours of economizer. Accordingly, mixed air temperatures and cooling coil loads were reduced. Specifically, the annual cumulative cooling coil loads decreased by approximately 15.9 % compared to the Basecase, HVAC energy usage was reduced by about 13 %. Additionally, the indoor dry-bulb temperature and relative humidity remained within the comfort range, indicating no degradation of thermal comfort. These findings suggest that using EGAS for OA intake is an effective strategy for cooling energy savings.
{"title":"Cooling energy savings potential from economizer integrated with ground-coupled air duct system in Korean climate","authors":"Minho Kim , Beungyong Park , Dongsu Kim , Sung Lok Do","doi":"10.1016/j.csite.2026.107750","DOIUrl":"10.1016/j.csite.2026.107750","url":null,"abstract":"<div><div>This study proposes an economizer integrated with ground-coupled air duct system (EGAS) to expand the range of outdoor air (OA) conditions suitable for economizer operation and to maximize cooling energy savings under Korean climate (4A climate zone). The EGAS features an OA duct buried underground, allowing heat exchange with the relatively stable and lower-temperature soil before determining the OA intake rates of economizer. Therefore, this study aims to evaluate the cooling energy savings potential by using EGAS in the Korean climate. To achieve this, the EGAS control algorithm was developed and integrated into the Base model to conduct building energy simulations. The results showed that EGAS increased OA intake rates, extended the operating hours of economizer. Accordingly, mixed air temperatures and cooling coil loads were reduced. Specifically, the annual cumulative cooling coil loads decreased by approximately 15.9 % compared to the Basecase, HVAC energy usage was reduced by about 13 %. Additionally, the indoor dry-bulb temperature and relative humidity remained within the comfort range, indicating no degradation of thermal comfort. These findings suggest that using EGAS for OA intake is an effective strategy for cooling energy savings.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107750"},"PeriodicalIF":6.4,"publicationDate":"2026-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146047834","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-24DOI: 10.1016/j.csite.2026.107749
Suraj Krishnamurti, James Tancabel, Vikrant Aute
Plate-fin heat exchangers (PFHX) have a very high surface area to volume ratio (>1000 m2/m3), which falls under the class of compact heat exchangers. Due to their high compactness, flexibility, and low cost, they are used in a wide variety of applications, including but not limited to the process industry, cryogenics, heating, ventilation, air-conditioning and refrigeration (HVAC&R), and aviation. This paper reviews the state of the art in the modeling and design of plate-fin heat exchangers. We first describe recent advances in performance enhancement techniques for PFHX, which are largely passive in nature, by means of novel fin structures and/or vortex generators. A systematic analysis of the physical phenomena associated with PFHXs was conducted using the Phenomenon Identification and Ranking Table (PIRT) approach, which is commonly used for modeling critical devices across a wide array of applications and can also be used to guide PFHX model development. Modeling approaches used in the literature have been summarized and categorized into 4 types: (i) Lumped, (ii) Layer stacking, (iii) Distributed and (iv) CFD. Verification, validation and uncertainty quantification of these modeling approaches are also discussed. The models available in the literature are often used to optimize PFHXs, which is a complex problem containing both continuous and discrete design variables and the existence of multiple objectives and constraints depending on the design requirements. This is an interesting area of active research, and we have reviewed the latest developments thereof. Finally, research gaps and future directions for research are discussed. We hope that this review will serve as a guide for future researchers in the modeling and optimization of PFHX.
{"title":"Review of the state of the art in modeling and optimization of plate fin type heat exchangers","authors":"Suraj Krishnamurti, James Tancabel, Vikrant Aute","doi":"10.1016/j.csite.2026.107749","DOIUrl":"10.1016/j.csite.2026.107749","url":null,"abstract":"<div><div>Plate-fin heat exchangers (PFHX) have a very high surface area to volume ratio (>1000 m<sup>2</sup>/m<sup>3</sup>), which falls under the class of compact heat exchangers. Due to their high compactness, flexibility, and low cost, they are used in a wide variety of applications, including but not limited to the process industry, cryogenics, heating, ventilation, air-conditioning and refrigeration (HVAC&R), and aviation. This paper reviews the state of the art in the modeling and design of plate-fin heat exchangers. We first describe recent advances in performance enhancement techniques for PFHX, which are largely passive in nature, by means of novel fin structures and/or vortex generators. A systematic analysis of the physical phenomena associated with PFHXs was conducted using the Phenomenon Identification and Ranking Table (PIRT) approach, which is commonly used for modeling critical devices across a wide array of applications and can also be used to guide PFHX model development. Modeling approaches used in the literature have been summarized and categorized into 4 types: (i) Lumped, (ii) Layer stacking, (iii) Distributed and (iv) CFD. Verification, validation and uncertainty quantification of these modeling approaches are also discussed. The models available in the literature are often used to optimize PFHXs, which is a complex problem containing both continuous and discrete design variables and the existence of multiple objectives and constraints depending on the design requirements. This is an interesting area of active research, and we have reviewed the latest developments thereof. Finally, research gaps and future directions for research are discussed. We hope that this review will serve as a guide for future researchers in the modeling and optimization of PFHX.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107749"},"PeriodicalIF":6.4,"publicationDate":"2026-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146048052","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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