This study explores the effects of nanofluids, used as a dense discrete two-phase system with nanoparticle volume fractions (ϕ) ranging from 0 to 3 %, on heat transfer in a ribbed microchannel with a porous medium. Key parameters such as rib angle, Darcy number, and Reynolds number were analyzed for their effect on heat transfer and particle migration. Results indicate that increasing the Darcy number from 0 to 1.883e-4 at a 30° angle and ϕ = 3 % raised the Nusselt number from 1.8235 to 2.0376 while increasing the Reynolds number from 10 to 1000 at a 30° angle and the same ϕ raised the Nusselt number from 2.1030 to 3.7519. The maximum Nusselt number observed was 3.9047 for a microchannel with 90° ribs, Reynolds number of Re = 1000, ϕ = 3 %, and a Darcy number of 7.533e-4. Conversely, the results show that increasing the ϕ also increases fluid density and relative viscosity, leading to higher kinetic energy and maximum flow velocity in the microchannel. Finally, the results revealed that in the presence of a porous medium with a Darcy number of 1.883e-4, for micro-ribs with an angle of 90°, Re = 10, and ϕ = 1 %, the value of the friction factor increases from 0.5956 to 0.9495.
{"title":"Simulation of water-graphene oxide two-phase nanofluid flow in a porous ribbed microchannel by considering heat transfer and particle migration","authors":"Ahmadreza Rezaei , Mohammadreza Niknejadi , Davood Toghraie , Soheil Salahshour","doi":"10.1016/j.csite.2026.107706","DOIUrl":"10.1016/j.csite.2026.107706","url":null,"abstract":"<div><div>This study explores the effects of nanofluids, used as a dense discrete two-phase system with nanoparticle volume fractions (ϕ) ranging from 0 to 3 %, on heat transfer in a ribbed microchannel with a porous medium. Key parameters such as rib angle, Darcy number, and Reynolds number were analyzed for their effect on heat transfer and particle migration. Results indicate that increasing the Darcy number from 0 to 1.883e-4 at a 30° angle and ϕ = 3 % raised the Nusselt number from 1.8235 to 2.0376 while increasing the Reynolds number from 10 to 1000 at a 30° angle and the same ϕ raised the Nusselt number from 2.1030 to 3.7519. The maximum Nusselt number observed was 3.9047 for a microchannel with 90° ribs, Reynolds number of Re = 1000, ϕ = 3 %, and a Darcy number of 7.533e-4. Conversely, the results show that increasing the ϕ also increases fluid density and relative viscosity, leading to higher kinetic energy and maximum flow velocity in the microchannel. Finally, the results revealed that in the presence of a porous medium with a Darcy number of 1.883e-4, for micro-ribs with an angle of 90°, Re = 10, and ϕ = 1 %, the value of the friction factor increases from 0.5956 to 0.9495.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107706"},"PeriodicalIF":6.4,"publicationDate":"2026-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146047839","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 : 2026-01-23DOI: 10.1016/j.csite.2026.107741
Nishab Ali , Osama Zaid , Abraham Teklay Gebremariam , Arun Chand , Andallib Tariq
For the advancement of sustainable and cleaner operation in concrete recycling, the Heating Air Classification System (HAS) requires replacing the existing diesel-fired burner with an electric heating technology. This study contributes to that transition by evaluating the suitability of electric hot air generators for HAS operational thermal needs. Through detailed numerical analysis, the thermal performance and flow behavior of HAS are assessed across single (Cases: A1–A4) and dual inlet (Cases: B1–B4) configurations, and for a range of hot air inlet temperatures (800–950 °C). Spatial distributions of normalized temperature, velocity, and turbulent kinetic energy (TKE) are examined on multiple planes to characterize flow behavior, heating uniformity, and mixing. The results show that an electric hot air generator can nearly match the mean bulk temperature (⟨T/T0⟩ ≈ 0.49–0.50) achieved with diesel systems, while providing notable improvements in thermal uniformity. Among all studied scenarios, the dual inlet configuration with lower hot air injection temperature (B1) achieves the lowest standard deviation (0.080) and coefficient of variation (0.162), ensuring the most consistent heating and minimal thermal gradients. These findings highlight that an electric hot air generator can be seen as one of the promising electrification pathways for HAS, supporting enhanced energy efficiency and cleaner production in concrete recycling applications.
{"title":"Thermal behavior of a concrete recycling unit during the transition from diesel-fired to electric hot air generator","authors":"Nishab Ali , Osama Zaid , Abraham Teklay Gebremariam , Arun Chand , Andallib Tariq","doi":"10.1016/j.csite.2026.107741","DOIUrl":"10.1016/j.csite.2026.107741","url":null,"abstract":"<div><div>For the advancement of sustainable and cleaner operation in concrete recycling, the Heating Air Classification System (HAS) requires replacing the existing diesel-fired burner with an electric heating technology. This study contributes to that transition by evaluating the suitability of electric hot air generators for HAS operational thermal needs. Through detailed numerical analysis, the thermal performance and flow behavior of HAS are assessed across single (Cases: A1–A4) and dual inlet (Cases: B1–B4) configurations, and for a range of hot air inlet temperatures (800–950 °C). Spatial distributions of normalized temperature, velocity, and turbulent kinetic energy (<em>TKE</em>) are examined on multiple planes to characterize flow behavior, heating uniformity, and mixing. The results show that an electric hot air generator can nearly match the mean bulk temperature <em>(⟨T/T</em><sub><em>0</em></sub><em>⟩ ≈ 0.49–0.50</em>) achieved with diesel systems, while providing notable improvements in thermal uniformity. Among all studied scenarios, the dual inlet configuration with lower hot air injection temperature (B1) achieves the lowest standard deviation (<em>0.080</em>) and coefficient of variation (<em>0.162</em>), ensuring the most consistent heating and minimal thermal gradients. These findings highlight that an electric hot air generator can be seen as one of the promising electrification pathways for HAS, supporting enhanced energy efficiency and cleaner production in concrete recycling applications.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107741"},"PeriodicalIF":6.4,"publicationDate":"2026-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146033040","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 : 2026-01-23DOI: 10.1016/j.csite.2026.107732
Qiang Gao , Zhe Zhang , Dong Liu
The dependable operation and effective thermal management of transformers are essential to power-system stability. To tackle this, a numerical model for the buoyancy-driven oil-immersed transformer cooling system is established, focusing on the heat transfer and flow characteristics within the transformer and its influencing factors. A figure of merit (FOM) is proposed to guide the coolants' selection and development for immersion liquid cooling systems under natural convection conditions. The results show that due to the competitive interaction mechanism between local natural convection and global natural convection, the convective heat transfer capability near the left windings decreases, resulting in the left windings' temperature being significantly higher. In static mode, the oil-immersed transformer's hotspot temperature is positively correlated with the load, with a critical load of 107 %. Furthermore, the magnitude of FOM is positively correlated with the mineral insulating oil's heat dissipation performance, and its evaluation of insulating oil performance in static mode is reliable. Notably, based on the FOM's importance, the thermal properties for different mineral insulating oils are ranked as dynamic viscosity > density > thermal expansion coefficient > thermal conductivity > specific heat capacity. With the increase in temperature, only the dynamic viscosity's weight factor rises, while the other thermal properties' weight factors reduce. Moreover, compared to mineral insulating oil 2 and mineral insulating oil 3, the service life of the transformer using mineral insulating oil 1 is increased by 1.11 and 1.53 times, respectively.
{"title":"Thermal behavior of a buoyancy-driven oil-immersed transformer and coolant performance assessment","authors":"Qiang Gao , Zhe Zhang , Dong Liu","doi":"10.1016/j.csite.2026.107732","DOIUrl":"10.1016/j.csite.2026.107732","url":null,"abstract":"<div><div>The dependable operation and effective thermal management of transformers are essential to power-system stability. To tackle this, a numerical model for the buoyancy-driven oil-immersed transformer cooling system is established, focusing on the heat transfer and flow characteristics within the transformer and its influencing factors. A figure of merit (FOM) is proposed to guide the coolants' selection and development for immersion liquid cooling systems under natural convection conditions. The results show that due to the competitive interaction mechanism between local natural convection and global natural convection, the convective heat transfer capability near the left windings decreases, resulting in the left windings' temperature being significantly higher. In static mode, the oil-immersed transformer's hotspot temperature is positively correlated with the load, with a critical load of 107 %. Furthermore, the magnitude of FOM is positively correlated with the mineral insulating oil's heat dissipation performance, and its evaluation of insulating oil performance in static mode is reliable. Notably, based on the FOM's importance, the thermal properties for different mineral insulating oils are ranked as dynamic viscosity > density > thermal expansion coefficient > thermal conductivity > specific heat capacity. With the increase in temperature, only the dynamic viscosity's weight factor rises, while the other thermal properties' weight factors reduce. Moreover, compared to mineral insulating oil 2 and mineral insulating oil 3, the service life of the transformer using mineral insulating oil 1 is increased by 1.11 and 1.53 times, respectively.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107732"},"PeriodicalIF":6.4,"publicationDate":"2026-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146033042","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}
Altermagnets represent a recently discovered class of magnetic materials that combine fully compensated magnetic order with nonrelativistic spin-split electronic bands, enabling unique charge, spin, and valley transport properties. Here, using first-principles calculations, we systematically investigate the structural, electronic, thermoelectric, valleytronic, and piezoelectric properties of monolayer Ca(CoN)2. The system is found to be intrinsically altermagnetic and semiconducting with a direct band gap of 0.432 eV and symmetry-protected degenerate valleys at the X and Y points. High carrier mobility and a large Seebeck coefficient (∼1.3 mV K−1 at 300 K) lead to an excellent thermoelectric performance, with a maximum ZT of 1.8 at 500 K under hole doping. Uniaxial strain efficiently lifts the valley degeneracy, generating a sizable spin-valley polarization with a valley splitting of up to 112 meV at 4 % strain. Additionally, the monolayer possesses high piezoelectricity having d31 of 1.18 p.m./V. The results show Ca(CoN)2 is a promising multifunctional material. It is suitable for future thermoelectric, valleytronic, and piezo-spintronic applications.
{"title":"Strain-tunable spin-valley polarization and high thermoelectric performance in a two-dimensional Ca(CoN)2 altermagnet","authors":"Mohamed Bouzidi , Salhah Hamed Alrefaee , Tatyana Orlova , Aeshah Alrubayyi , Vineet Tirth , Ali Algahtani , Tawfiq Al-Mughanam , Naseem Akhter , Abid Zaman","doi":"10.1016/j.csite.2026.107737","DOIUrl":"10.1016/j.csite.2026.107737","url":null,"abstract":"<div><div>Altermagnets represent a recently discovered class of magnetic materials that combine fully compensated magnetic order with nonrelativistic spin-split electronic bands, enabling unique charge, spin, and valley transport properties. Here, using first-principles calculations, we systematically investigate the structural, electronic, thermoelectric, valleytronic, and piezoelectric properties of monolayer Ca(CoN)<sub>2</sub>. The system is found to be intrinsically altermagnetic and semiconducting with a direct band gap of 0.432 eV and symmetry-protected degenerate valleys at the X and Y points. High carrier mobility and a large Seebeck coefficient (∼1.3 mV K<sup>−1</sup> at 300 K) lead to an excellent thermoelectric performance, with a maximum ZT of 1.8 at 500 K under hole doping. Uniaxial strain efficiently lifts the valley degeneracy, generating a sizable spin-valley polarization with a valley splitting of up to 112 meV at 4 % strain. Additionally, the monolayer possesses high piezoelectricity having d<sub>31</sub> of 1.18 p.m./V. The results show Ca(CoN)2 is a promising multifunctional material. It is suitable for future thermoelectric, valleytronic, and piezo-spintronic applications.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107737"},"PeriodicalIF":6.4,"publicationDate":"2026-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146033039","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 : 2026-01-23DOI: 10.1016/j.csite.2026.107730
Hai Wang , Yuandi Chen , Chen Wang , Weijian He , Haojie Xu , Jiameng Tian , Shuqian Zhang , Taizeng Yu , Zheyi Gu , Titi Zhang , Junfeng Wang
Engineered surfaces for nucleate boiling enhancement have attracted increasing attention owing to distinctive characteristics of manipulate bubble behaviors. In this study, superhydrophilic porous surfaces with varying pore structures were fabricated on copper spherical particles (size range: 2–8 mm) via chemical etching and electrodeposition methods. A tightly packed monolayer of copper spherical hybrid particles was coated on the heated surface, and experimental results confirmed that this configuration significantly improves boiling performance. Specifically, the porous architectures of the hybrid particles and the narrow corner gaps generated between the particles and boiling surface provide abundant nucleation sites, thereby initiating the early onset of nucleate boiling (ONB). Among all samples, the HP-2 particles yielded the largest ONB reduction of 68.2 %. Furthermore, the in-situ oscillation of 4 mm-diameter hybrid particles periodically generates numerous transient gaps, which promote bubble detachment and liquid replenishment. This dynamic mechanism enables the HP-5 particle-modified surface to achieve a maximum critical heat flux (CHF) of 1870 kW/m2, corresponding to a CHF enhancement ratio of 1.76 relative to the plain copper surface. Additionally, pool boiling heat transfer performance exhibits a distinct non-monotonic dependence on the pore size of hybrid particles, with peak performance attained at a pore size of 100 μm.
{"title":"Heat transfer characteristics of nucleate boiling on surfaces by addition of hybrid superhydrophilic and porous copper particles","authors":"Hai Wang , Yuandi Chen , Chen Wang , Weijian He , Haojie Xu , Jiameng Tian , Shuqian Zhang , Taizeng Yu , Zheyi Gu , Titi Zhang , Junfeng Wang","doi":"10.1016/j.csite.2026.107730","DOIUrl":"10.1016/j.csite.2026.107730","url":null,"abstract":"<div><div>Engineered surfaces for nucleate boiling enhancement have attracted increasing attention owing to distinctive characteristics of manipulate bubble behaviors. In this study, superhydrophilic porous surfaces with varying pore structures were fabricated on copper spherical particles (size range: 2–8 mm) via chemical etching and electrodeposition methods. A tightly packed monolayer of copper spherical hybrid particles was coated on the heated surface, and experimental results confirmed that this configuration significantly improves boiling performance. Specifically, the porous architectures of the hybrid particles and the narrow corner gaps generated between the particles and boiling surface provide abundant nucleation sites, thereby initiating the early onset of nucleate boiling (ONB). Among all samples, the HP-2 particles yielded the largest ONB reduction of 68.2 %. Furthermore, the in-situ oscillation of 4 mm-diameter hybrid particles periodically generates numerous transient gaps, which promote bubble detachment and liquid replenishment. This dynamic mechanism enables the HP-5 particle-modified surface to achieve a maximum critical heat flux (CHF) of 1870 kW/m<sup>2</sup>, corresponding to a CHF enhancement ratio of 1.76 relative to the plain copper surface. Additionally, pool boiling heat transfer performance exhibits a distinct non-monotonic dependence on the pore size of hybrid particles, with peak performance attained at a pore size of 100 μm.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107730"},"PeriodicalIF":6.4,"publicationDate":"2026-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146033038","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 : 2026-01-23DOI: 10.1016/j.csite.2026.107731
Tomáš Ficker
Convenient thermal comfort in indoor spaces is a standard requirement that is commonly asked and expected by occupants. Although the notion of thermal comfort seems to be understandable, its monitoring and maintenance are not easy. In 1970, Fanger defined six parameters to quantify thermal comfort. Among these parameters, the so-called mean radiant temperature characterizes the temperature state of the room envelope and strongly influences the apparent temperature perceived by the occupants. The mean radiant temperature can be measured or computed. For its computation, Fanger's classical equation is frequently used. Unfortunately, this equation holds only for absolutely black surfaces that are free of reflections, but such surfaces do not exist in practice. Real non-black surfaces are accompanied by varying degrees of heat reflections; consequently, with such surfaces, Fanger's equation can provide only compromised values. So far, nobody has improved Fanger's equation to include reflections of low-emissive room envelopes. In this paper, the generalized equation is derived to compute the mean radiant temperature of room envelopes with arbitrary emissivities. The equation is derived based on the so-called algebraic radiosity method and uses the entire matrix of view factors, while Fanger's equation uses only one row of that matrix. The classical Fanger equation and the new generalized equation have been applied to a common living room with variable surface emissivities, and the results have been compared. Such a comparison enables quantification of the influence of heat reflections on mean radiant temperatures. Both equations show similar temperatures for emissivities in the range between 1 and 0.9, but with surfaces of lower emissivity, they yield different results due to non-negligible heat reflections. When the emissivities of room surfaces approach 0.8, the temperature differences reach 0.6 °C. When the emissivities are close to 0.6, the temperature difference is 1.6 °C, and at emissivities 0.1, a large temperature difference appears, reaching 8.3 °C. This fact has direct consequences for measuring temperatures with radiometers and thermocouples. Measurements with thermocouples that are attached to surfaces are almost insensitive to heat reflections, whereas measurements with radiometers placed apart from the surfaces suffer from heat reflections.
{"title":"Ab initio computations of the mean radiant temperature of indoor spaces","authors":"Tomáš Ficker","doi":"10.1016/j.csite.2026.107731","DOIUrl":"10.1016/j.csite.2026.107731","url":null,"abstract":"<div><div>Convenient thermal comfort in indoor spaces is a standard requirement that is commonly asked and expected by occupants. Although the notion of thermal comfort seems to be understandable, its monitoring and maintenance are not easy. In 1970, Fanger defined six parameters to quantify thermal comfort. Among these parameters, the so-called mean radiant temperature characterizes the temperature state of the room envelope and strongly influences the apparent temperature perceived by the occupants. The mean radiant temperature can be measured or computed. For its computation, Fanger's classical equation is frequently used. Unfortunately, this equation holds only for absolutely black surfaces that are free of reflections, but such surfaces do not exist in practice. Real non-black surfaces are accompanied by varying degrees of heat reflections; consequently, with such surfaces, Fanger's equation can provide only compromised values. So far, nobody has improved Fanger's equation to include reflections of low-emissive room envelopes. In this paper, the generalized equation is derived to compute the mean radiant temperature of room envelopes with arbitrary emissivities. The equation is derived based on the so-called algebraic radiosity method and uses the entire matrix of view factors, while Fanger's equation uses only one row of that matrix. The classical Fanger equation and the new generalized equation have been applied to a common living room with variable surface emissivities, and the results have been compared. Such a comparison enables quantification of the influence of heat reflections on mean radiant temperatures. Both equations show similar temperatures for emissivities in the range between 1 and 0.9, but with surfaces of lower emissivity, they yield different results due to non-negligible heat reflections. When the emissivities of room surfaces approach 0.8, the temperature differences reach 0.6 °C. When the emissivities are close to 0.6, the temperature difference is 1.6 °C, and at emissivities 0.1, a large temperature difference appears, reaching 8.3 °C. This fact has direct consequences for measuring temperatures with radiometers and thermocouples. Measurements with thermocouples that are attached to surfaces are almost insensitive to heat reflections, whereas measurements with radiometers placed apart from the surfaces suffer from heat reflections.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107731"},"PeriodicalIF":6.4,"publicationDate":"2026-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146033041","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 : 2026-01-22DOI: 10.1016/j.csite.2026.107725
Mehdi Tavakoli , Jeong Tae Kim , Su Il Park , Man Yeong Ha , June Kee Min
Compact designs in engineering devices such as refrigeration systems often require heated components installed within corners of flow paths. While extensive Nusselt number correlations exist for a heated sphere in straight flows, curvature and flow path features in such configurations can significantly affect heat transfer, making conventional correlations potentially inaccurate. As a result, one of the most common curvatures is the 90° bend, yet the effect of 90°-bent rectangular ducts on sphere heat transfer remains largely unexplored. This study addresses this gap by numerically developing Nusselt number correlations for a heated sphere in 90°-bent duct flows using three-dimensional CFD simulations. Simulations were conducted at various dimensionless sphere-to-vertical gap distances (0.1 ≤ ≤ 0.9), sphere-to-horizontal gap distances (0.1 ≤ ≤ 0.9), Reynolds numbers (1000 ≤ ≤ 5000), and Prandtl numbers (0.71 ≤ ≤ 1) considering both buoyancy and radiation effects to develop a comprehensive correlation. Results reveal a significant increase in average Nusselt numbers in bent ducts compared to straight flows, with mixed convection and radiation influencing heat transfer by up to 3.5 % and 30.7 % at Ri = 0.25, respectively. A detailed parametric study was performed based on the major parameters , , , and to analyze flow structure and heat transfer behavior under varying conditions. New correlations for the Nusselt number and friction factor are proposed for practical applications and compared to straight-flow correlations using the thermal performance factor (TPF), which can be 60 % higher at lower Reynolds and gradually decreases at higher Reynolds numbers.
{"title":"Development of Nusselt number correlation for iso flux sphere in 90°-bent rectangular duct flow","authors":"Mehdi Tavakoli , Jeong Tae Kim , Su Il Park , Man Yeong Ha , June Kee Min","doi":"10.1016/j.csite.2026.107725","DOIUrl":"10.1016/j.csite.2026.107725","url":null,"abstract":"<div><div>Compact designs in engineering devices such as refrigeration systems often require heated components installed within corners of flow paths. While extensive Nusselt number correlations exist for a heated sphere in straight flows, curvature and flow path features in such configurations can significantly affect heat transfer, making conventional correlations potentially inaccurate. As a result, one of the most common curvatures is the 90° bend, yet the effect of 90°-bent rectangular ducts on sphere heat transfer remains largely unexplored. This study addresses this gap by numerically developing Nusselt number correlations for a heated sphere in 90°-bent duct flows using three-dimensional CFD simulations. Simulations were conducted at various dimensionless sphere-to-vertical gap distances (0.1 ≤ <span><math><mrow><msub><mi>r</mi><mi>v</mi></msub></mrow></math></span> ≤ 0.9), sphere-to-horizontal gap distances (0.1 ≤ <span><math><mrow><msub><mi>r</mi><mi>h</mi></msub></mrow></math></span> ≤ 0.9), Reynolds numbers (1000 ≤ <span><math><mrow><mi>R</mi><msub><mi>e</mi><mi>s</mi></msub></mrow></math></span> ≤ 5000), and Prandtl numbers (0.71 ≤ <span><math><mrow><mi>Pr</mi></mrow></math></span> ≤ 1) considering both buoyancy and radiation effects to develop a comprehensive correlation. Results reveal a significant increase in average Nusselt numbers in bent ducts compared to straight flows, with mixed convection and radiation influencing heat transfer by up to 3.5 % and 30.7 % at Ri = 0.25, respectively. A detailed parametric study was performed based on the major parameters <span><math><mrow><msub><mi>r</mi><mi>h</mi></msub></mrow></math></span>, <span><math><mrow><msub><mi>r</mi><mi>v</mi></msub></mrow></math></span>, <span><math><mrow><msub><mtext>Re</mtext><mi>s</mi></msub></mrow></math></span>, and <span><math><mrow><mi>Pr</mi></mrow></math></span> to analyze flow structure and heat transfer behavior under varying conditions. New correlations for the Nusselt number and friction factor are proposed for practical applications and compared to straight-flow correlations using the thermal performance factor (TPF), which can be 60 % higher at lower Reynolds and gradually decreases at higher Reynolds numbers.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"78 ","pages":"Article 107725"},"PeriodicalIF":6.4,"publicationDate":"2026-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146023484","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 : 2026-01-22DOI: 10.1016/j.csite.2026.107726
Jing Nie , Tong-Zheng Guo , Jin-Chen Xu , Xin-Yao Ruan , Li-Yao-Min Nie , Xiao Guo
The Inner Mongolia Autonomous Region characterized by abundant solar radiation, extended sunshine hours, and vast land areas, offers significant potential for the development of solar chimney power plants (SCPPs) to provide electricity to remote pastoral and rural areas. This study presents a year-long performance and techno-economic evaluation of SCPPs at six representative sites using CFD simulations (Fluent) coupled with a theoretical model. Carbon reduction benefits are also quantified under two accounting frameworks. The results show that the output power in the Inner Mongolia Autonomous Region is between 414 and 460 kW. Among the sites, Bayannur achieves the highest output (52 kW), while Ejin Banner records the highest collector efficiency (31.6 %). Bayannur is identified as the most suitable site, with generation capacity meeting the annual demand of approximately 135 people. In addition, by using the correlation coefficient R2, where the R2 value is always greater than 0.9, the size of the Gr number can reflect the change in power. Economic analysis indicates that when considering the average lifecycle, carbon credits, and electricity revenues, the effective LCOE decreases to $0.144 - $0.172/kWh. Under a 4.1 % inflation and discount rate, these values converge, highlighting the sensitivity of cost-effectiveness to financial parameters. The findings confirm the technical feasibility and long-term economic potential of SCPPs as a decentralized clean energy solution tailored to Inner Mongolia's environmental context.
{"title":"CFD-based multi-location analysis of power output and LCOE for solar chimneys in arid regions of Inner Mongolia","authors":"Jing Nie , Tong-Zheng Guo , Jin-Chen Xu , Xin-Yao Ruan , Li-Yao-Min Nie , Xiao Guo","doi":"10.1016/j.csite.2026.107726","DOIUrl":"10.1016/j.csite.2026.107726","url":null,"abstract":"<div><div>The Inner Mongolia Autonomous Region characterized by abundant solar radiation, extended sunshine hours, and vast land areas, offers significant potential for the development of solar chimney power plants (SCPPs) to provide electricity to remote pastoral and rural areas. This study presents a year-long performance and techno-economic evaluation of SCPPs at six representative sites using CFD simulations (Fluent) coupled with a theoretical model. Carbon reduction benefits are also quantified under two accounting frameworks. The results show that the output power in the Inner Mongolia Autonomous Region is between 414 and 460 kW. Among the sites, Bayannur achieves the highest output (52 kW), while Ejin Banner records the highest collector efficiency (31.6 %). Bayannur is identified as the most suitable site, with generation capacity meeting the annual demand of approximately 135 people. In addition, by using the correlation coefficient R<sup>2</sup>, where the R<sup>2</sup> value is always greater than 0.9, the size of the Gr number can reflect the change in power. Economic analysis indicates that when considering the average lifecycle, carbon credits, and electricity revenues, the effective LCOE decreases to $0.144 - $0.172/kWh. Under a 4.1 % inflation and discount rate, these values converge, highlighting the sensitivity of cost-effectiveness to financial parameters. The findings confirm the technical feasibility and long-term economic potential of SCPPs as a decentralized clean energy solution tailored to Inner Mongolia's environmental context.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"79 ","pages":"Article 107726"},"PeriodicalIF":6.4,"publicationDate":"2026-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146033925","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 : 2026-01-21DOI: 10.1016/j.csite.2026.107717
Xintong Ye , Zhongzhi Hu , Haiwen Xiong , Pu Liu , Shanquan Fan , Hui Huang
To address the issues of high energy consumption, difficulty in continuous monitoring, and system complexity associated with active heating methods (e.g., cable heating) for oil-water interface monitoring during salt cavern leaching, this study proposes a novel passive monitoring method based on geothermal-driven thermal perturbation. This method eliminates the need for an active heat source, utilizing the stable underground geothermal field, introducing natural thermal perturbation by injecting low-temperature fluid, and achieving passive interface identification by leveraging the differences in thermophysical properties between oil and water. By establishing a multi-physics numerical model coupled with the geothermal field, the study finds that under baseline conditions (water injection rate: 100 m3/h, temperature: 308.15 K, tubing shoe distance H: 14.7 m), a significant temperature step exceeding 2 K can be generated at the oil-water interface. Furthermore, the slopes of the temperature-depth curves for the oil and water phases show distinct differences (approximately −0.42 K/m for oil and −0.19 K/m for water), with their ratio reaching 2.2. The Distributed Temperature Sensing (DTS) system can effectively capture this dual characteristic. Sensitivity analysis indicates that the characteristic interface temperature difference is positively correlated with the injection flow rate and the tubing shoe distance H, and negatively correlated with the injection temperature. Additionally, the study proposes an adaptive strategy involving channel switching via an optical switch, using the maximization of the interface temperature difference as the criterion, which theoretically can reduce the localization error to 0 m. This research confirms the feasibility of geothermal-driven passive monitoring, providing a new paradigm for establishing a green, low-energy-consumption intelligent monitoring system.
{"title":"Research on passive monitoring mechanisms and optimization for oil-water interface in salt cavity reservoirs based on geothermal-driven thermal perturbations","authors":"Xintong Ye , Zhongzhi Hu , Haiwen Xiong , Pu Liu , Shanquan Fan , Hui Huang","doi":"10.1016/j.csite.2026.107717","DOIUrl":"10.1016/j.csite.2026.107717","url":null,"abstract":"<div><div>To address the issues of high energy consumption, difficulty in continuous monitoring, and system complexity associated with active heating methods (e.g., cable heating) for oil-water interface monitoring during salt cavern leaching, this study proposes a novel passive monitoring method based on geothermal-driven thermal perturbation. This method eliminates the need for an active heat source, utilizing the stable underground geothermal field, introducing natural thermal perturbation by injecting low-temperature fluid, and achieving passive interface identification by leveraging the differences in thermophysical properties between oil and water. By establishing a multi-physics numerical model coupled with the geothermal field, the study finds that under baseline conditions (water injection rate: 100 m<sup>3</sup>/h, temperature: 308.15 K, tubing shoe distance H: 14.7 m), a significant temperature step exceeding 2 K can be generated at the oil-water interface. Furthermore, the slopes of the temperature-depth curves for the oil and water phases show distinct differences (approximately −0.42 K/m for oil and −0.19 K/m for water), with their ratio reaching 2.2. The Distributed Temperature Sensing (DTS) system can effectively capture this dual characteristic. Sensitivity analysis indicates that the characteristic interface temperature difference is positively correlated with the injection flow rate and the tubing shoe distance H, and negatively correlated with the injection temperature. Additionally, the study proposes an adaptive strategy involving channel switching via an optical switch, using the maximization of the interface temperature difference as the criterion, which theoretically can reduce the localization error to 0 m. This research confirms the feasibility of geothermal-driven passive monitoring, providing a new paradigm for establishing a green, low-energy-consumption intelligent monitoring system.</div></div>","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"78 ","pages":"Article 107717"},"PeriodicalIF":6.4,"publicationDate":"2026-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146023483","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 : 2026-01-20DOI: 10.1016/j.csite.2026.107718
M.F. Ismail, M.Z. Sharif, M.M. Sulhan
{"title":"Energy and Performance Improvement of R32-Based Residential Air Conditioning using SiO2 and TiO2 Nanolubricants","authors":"M.F. Ismail, M.Z. Sharif, M.M. Sulhan","doi":"10.1016/j.csite.2026.107718","DOIUrl":"https://doi.org/10.1016/j.csite.2026.107718","url":null,"abstract":"","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"1 1","pages":""},"PeriodicalIF":6.8,"publicationDate":"2026-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146014336","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}
扫码关注我们
求助内容：
应助结果提醒方式：
京公网安备 11010802042870号