Pub Date : 2026-01-27DOI: 10.1016/j.csite.2026.107758
Long Wang , Wenhao Wang , Liuying Wang , Lijun Yang , Gu Liu , Chaoqun Ge , Tonghao Liu , Bin Wang , Yuanxi Chang , Cuiping Zhang , Haoqiang Ai , Xiaohu Wu
Multispectral camouflage faces growing urgency due to multimodal detection threats. To meet the spectral requirements for different bands, artificially designed selective spectral properties are needed. However, achieving a balance among simplicity of configuration, durability, spectral selectivity, and large-scale potential remains challenging, as well as achieving passive radiative cooling for effective thermal management. Here, we present a Ge (635 nm)/ZnS (1152 nm)/Ge (1260 nm)/ZnS (1141 nm)/Ge (656 nm) heterogeneous photonic crystal (HPC) selective thermal emitter for achieving low thermal emissivity camouflage ( = 0.28, = 0.24), low laser reflection at 10.6 μm (0.29), and radiative cooling within non-atmospheric window (0.70 at 5–7.5 μm). This emitter shows a 25 °C radiative cooling reduction than traditional low-emissivity Cu films at 350 °C. The emitter also has good angle and polarization independence, environmental durability, and can be manufactured on a large scale. This technology offers a cost-effective way for multispectral-compatible camouflage design and creates new opportunities for combining camouflage with thermal management.
{"title":"Heterostructure photonic crystal selective thermal emitter for laser and infrared camouflage with heat dissipation","authors":"Long Wang , Wenhao Wang , Liuying Wang , Lijun Yang , Gu Liu , Chaoqun Ge , Tonghao Liu , Bin Wang , Yuanxi Chang , Cuiping Zhang , Haoqiang Ai , Xiaohu Wu","doi":"10.1016/j.csite.2026.107758","DOIUrl":"10.1016/j.csite.2026.107758","url":null,"abstract":"<div><div>Multispectral camouflage faces growing urgency due to multimodal detection threats. To meet the spectral requirements for different bands, artificially designed selective spectral properties are needed. However, achieving a balance among simplicity of configuration, durability, spectral selectivity, and large-scale potential remains challenging, as well as achieving passive radiative cooling for effective thermal management. Here, we present a Ge (635 nm)/ZnS (1152 nm)/Ge (1260 nm)/ZnS (1141 nm)/Ge (656 nm) heterogeneous photonic crystal (HPC) selective thermal emitter for achieving low thermal emissivity camouflage (<span><math><mrow><msub><mi>ε</mi><mrow><mn>3</mn><mo>−</mo><mn>5</mn></mrow></msub></mrow></math></span> = 0.28, <span><math><mrow><msub><mi>ε</mi><mrow><mn>8</mn><mo>−</mo><mn>14</mn></mrow></msub></mrow></math></span> = 0.24), low laser reflection at 10.6 μm (0.29), and radiative cooling within non-atmospheric window (0.70 at 5–7.5 μm). This emitter shows a 25 °C radiative cooling reduction than traditional low-emissivity Cu films at 350 °C. The emitter also has good angle and polarization independence, environmental durability, and can be manufactured on a large scale. This technology offers a cost-effective way for multispectral-compatible camouflage design and creates new opportunities for combining camouflage with thermal management.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107758"},"PeriodicalIF":6.4,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146072381","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 : 2026-01-27DOI: 10.1016/j.csite.2026.107760
Ahmad Rajani, Dalila Mat Said, Zulkarnain Ahmad Noorden, Nasarudin Ahmad, Muhammad Subhan Arifin, Tinton Dwi Atmaja, Nia Nuraeni Suryaman, Muslizainun Mustapha, Hilmi Abyan Muzhaffar, Ahmad Fudholi, Randy Erfa Saputra
{"title":"Electrical and Thermal Performance of Double-Pass Bifacial Photovoltaic Thermal System in Tropical Climate","authors":"Ahmad Rajani, Dalila Mat Said, Zulkarnain Ahmad Noorden, Nasarudin Ahmad, Muhammad Subhan Arifin, Tinton Dwi Atmaja, Nia Nuraeni Suryaman, Muslizainun Mustapha, Hilmi Abyan Muzhaffar, Ahmad Fudholi, Randy Erfa Saputra","doi":"10.1016/j.csite.2026.107760","DOIUrl":"https://doi.org/10.1016/j.csite.2026.107760","url":null,"abstract":"","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"3 1","pages":""},"PeriodicalIF":6.8,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146072382","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}
{"title":"Effect of swirl and hot streak on unsteady thermal performances of film-cooled high pressure turbine rotor","authors":"Shenghui Zhang, Shuiting Ding, Chuangkai Liu, Xiaojun Yang, Tian Qiu, Chenyu Gan","doi":"10.1016/j.csite.2026.107753","DOIUrl":"https://doi.org/10.1016/j.csite.2026.107753","url":null,"abstract":"","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"15 1","pages":"107753"},"PeriodicalIF":6.8,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146072383","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}
{"title":"Similarity simulation study on coal mine goaf temperature field dynamic evolution influenced by initial stop-mining temperature","authors":"Yueping Qin, Jinchuan Sun, Chenyu Wang, Zhenming Ren, Yulong Li, Hairong Wang, Yi Xu","doi":"10.1016/j.csite.2026.107748","DOIUrl":"https://doi.org/10.1016/j.csite.2026.107748","url":null,"abstract":"","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"35 1","pages":""},"PeriodicalIF":6.8,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146072380","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 paper presents a numerical optimisation of an air-forced heat sink design for application in cooling systems for power electronic devices. A three-phase inverter is a typical power electronic circuit which commonly employs three or six power semiconductor modules installed in a row on an air-forced heat sink. When power loss is evenly distributed among the modules, the temperature increases along the heat sink in the direction from the air inlet to the outlet, creating a thermal gradient across the power semiconductors. This thermal gradient is a negative factor, leading to mechanical stress in the semiconductor structure and reducing the device's reliability and lifespan. To improve the temperature gradient, the study proposes a modification to the standard heat sink design by introducing a V-shaped cut in the fin area near the inlet. This modification creates an inconstant distribution of thermal resistance along the length of the heat sink reducing temperature variation. Numerical simulations were conducted to identify the optimal V-shaped cut configuration providing minimal temperature differences between modules. The optimal value of the V-shaped cut was determined to be 0.255pu, while the standard deviation of the temperature difference between the power semiconductor modules was reduced from 2.194 to 0.183 at a heat flux of 100W per module. The results show that the optimised design significantly reduces the thermal gradient, ensuring a more uniform temperature distribution across the semiconductor modules.
{"title":"Design optimisation of air-forced heat sink to improve temperature gradient in power semiconductor modules","authors":"Andrew Sharp , Shafiul Monir , Valentine Dumeril , Cedric Belloc , Mobayode Akinslou , Yuriy Vagapov","doi":"10.1016/j.csite.2026.107746","DOIUrl":"10.1016/j.csite.2026.107746","url":null,"abstract":"<div><div>This paper presents a numerical optimisation of an air-forced heat sink design for application in cooling systems for power electronic devices. A three-phase inverter is a typical power electronic circuit which commonly employs three or six power semiconductor modules installed in a row on an air-forced heat sink. When power loss is evenly distributed among the modules, the temperature increases along the heat sink in the direction from the air inlet to the outlet, creating a thermal gradient across the power semiconductors. This thermal gradient is a negative factor, leading to mechanical stress in the semiconductor structure and reducing the device's reliability and lifespan. To improve the temperature gradient, the study proposes a modification to the standard heat sink design by introducing a V-shaped cut in the fin area near the inlet. This modification creates an inconstant distribution of thermal resistance along the length of the heat sink reducing temperature variation. Numerical simulations were conducted to identify the optimal V-shaped cut configuration providing minimal temperature differences between modules. The optimal value of the V-shaped cut was determined to be 0.255pu, while the standard deviation of the temperature difference between the power semiconductor modules was reduced from 2.194 to 0.183 at a heat flux of 100W per module. The results show that the optimised design significantly reduces the thermal gradient, ensuring a more uniform temperature distribution across the semiconductor modules.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107746"},"PeriodicalIF":6.4,"publicationDate":"2026-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146045235","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.2026.107738
Mehmet Ali Kallioğlu , Hakan Karakaya
This study aims to improve diesel engine performance and reduce harmful emissions by adding multiwall carbon nanotubes (MWCNT) to Eurodiesel fuel. The experiments were conducted using four different engine loads (0.3, 1.0, 2.0 and 3.0 BMEP) and five different MWCNT concentrations (0, 25, 50, 75 and 100 ppm). Fuel combustion characteristics, engine efficiency and exhaust emissions were extensively analyzed. The experimental findings were modeled and optimized by response surface method (RSM) and central composite design (CCD) based on three different operating conditions. It was observed that MWCNT doping improves combustion characteristics by increasing combustion homogeneity due to its high surface area and thermal conductivity. Especially at 3.0 BMEP load condition and 75 ppm MWCNT content, 26.47 % increase in brake thermal efficiency and 21.88 % reduction in specific fuel consumption were achieved. Furthermore, CO and HC emissions were reduced by 28.57 % and 27.27 %, respectively. On the other hand, due to the increase in in-cylinder temperature and more efficient combustion, NOx emissions increased by 9.30 % and CO2 emissions increased by 12.5 %. According to the RSM analysis, the optimal MWCNT concentration was determined as 74.74 ppm and the ideal engine load as 1.71 BMEP. The generated models exhibited high accuracy; the lowest R2 value was 80.60 % and the composite desirability value was 0.64. Overall, MWCNT nanoparticles stand out as an innovative additive that improves the efficiency of diesel engines and reduces emissions by improving fuel atomization and combustion quality.
{"title":"Influence of MWCNT-enhanced diesel fuels on engine thermal efficiency and emission behavior: Experimental and multivariate analysis","authors":"Mehmet Ali Kallioğlu , Hakan Karakaya","doi":"10.1016/j.csite.2026.107738","DOIUrl":"10.1016/j.csite.2026.107738","url":null,"abstract":"<div><div>This study aims to improve diesel engine performance and reduce harmful emissions by adding multiwall carbon nanotubes (MWCNT) to Eurodiesel fuel. The experiments were conducted using four different engine loads (0.3, 1.0, 2.0 and 3.0 BMEP) and five different MWCNT concentrations (0, 25, 50, 75 and 100 ppm). Fuel combustion characteristics, engine efficiency and exhaust emissions were extensively analyzed. The experimental findings were modeled and optimized by response surface method (RSM) and central composite design (CCD) based on three different operating conditions. It was observed that MWCNT doping improves combustion characteristics by increasing combustion homogeneity due to its high surface area and thermal conductivity. Especially at 3.0 BMEP load condition and 75 ppm MWCNT content, 26.47 % increase in brake thermal efficiency and 21.88 % reduction in specific fuel consumption were achieved. Furthermore, CO and HC emissions were reduced by 28.57 % and 27.27 %, respectively. On the other hand, due to the increase in in-cylinder temperature and more efficient combustion, NO<sub>x</sub> emissions increased by 9.30 % and CO<sub>2</sub> emissions increased by 12.5 %. According to the RSM analysis, the optimal MWCNT concentration was determined as 74.74 ppm and the ideal engine load as 1.71 BMEP. The generated models exhibited high accuracy; the lowest R<sup>2</sup> value was 80.60 % and the composite desirability value was 0.64. Overall, MWCNT nanoparticles stand out as an innovative additive that improves the efficiency of diesel engines and reduces emissions by improving fuel atomization and combustion quality.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107738"},"PeriodicalIF":6.4,"publicationDate":"2026-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146047838","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.2026.107736
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}
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