Case Studies in Thermal Engineering最新文献

{"title":"Oil transport mechanisms in piston ring assembly: CFD analysis with consideration of ring motion and deformation","authors":"Yuping Hu, Rui Su, Xiaoqing Tian, Shiying Liu, Jian Sun, Jun Wang, Yong Cheng, Yong Hu","doi":"10.1016/j.csite.2026.108040","DOIUrl":"https://doi.org/10.1016/j.csite.2026.108040","url":null,"abstract":"The dynamic design of piston rings and cylinder liners critically influences engine performance, durability, and reliability. While experimental validation of blow-by gas and oil transport remains challenging due to high costs and limited visualization capabilities, numerical analysis has emerged as a robust alternative. This study investigates oil transport in the piston ring assembly using a fluid model driven by prescribed ring deformation and motion. A refined 2D CFD framework, incorporating piston ring dynamics, deformations, and localized mesh refinement, was developed and validated using a 4.5L diesel engine under rated conditions. Key findings reveal: (1) During ring flutter, intensified gas flow through the back clearance facilitates oil renewal, removing carbon deposits. (2) Ring collapse disrupts the oil wedge on the ring-liner interface, increasing oil stripping and degrading lubrication. (3) Ring twist enhances axial stability by promoting line contact with the liner and oil wedge formation at angular regions, improving run-in and lubrication. (4) Further analysis of a throttle-equipped diesel engine under low load demonstrates that in-cylinder negative pressure induces a 6.3% rise in oil accumulation during intake, directly linking throttling-induced vacuum to elevated oil consumption. This study establishes a fluid modeling methodology driven by prescribed deformation and motion of the piston ring assembly, aiming to optimize ring dynamic characteristics and address critical challenges in oil control and lubrication for advanced engine designs.","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"22 1","pages":""},"PeriodicalIF":6.8,"publicationDate":"2026-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681259","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":"Flow enhancement strategies for reducing flow interference and improving in-cylinder flow in multi-cylinder GDI engines under low-speed low-temperature operating condition","authors":"Dongwoo Kang, Geonwoo Ko, Yubeen Yang, Sangjae Park, Yousang Son, Sungwook Park","doi":"10.1016/j.csite.2026.108017","DOIUrl":"https://doi.org/10.1016/j.csite.2026.108017","url":null,"abstract":"Gasoline direct injection (GDI) engines face challenges during low-temperature conditions, primarily due to high hydrocarbon and particulate emissions and unstable combustion. The objective of this work is to investigate in-cylinder flow variations for enhancing combustion stability in multi-cylinder GDI engines under low-temperature operation conditions. First, the analysis revealed that cylinder-to-cylinder flow variations arise from interference between the back flow of a preceding cylinder and the intake flow of the subsequent cylinder, with the extent of interference governed by the distance between firing-adjacent cylinders. Second, optimization of injection timing demonstrated that early injection at BTDC 300° effectively sustained tumble flow, leading to a 17% increase in TKE (turbulent kinetic energy) and a 7% reduction in wall film accumulation. Third, the introduction of an intake port tumble insert effectively suppressed flow structures that disrupt tumble development (counter-flow) while reinforcing those that sustain rotational structure (co-flow), thereby enhancing in-cylinder tumble flow. As a result, TKE increased by 32%, and wall film formation was reduced by 11%. Finally, modifying the firing order to eliminate long-distance cylinder pairs mitigated in-cylinder flow imbalances and improved the overall uniformity of tumble intensity. These findings highlight that appropriate design and operational strategies, such as injection strategy, tumble insert in intake port, and firing order adjustments, can substantially improve flow dynamics, mixture preparation, and ultimately, performance of low-speed low-temperature conditions in multi-cylinder GDI engines.","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"5 1","pages":""},"PeriodicalIF":6.8,"publicationDate":"2026-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681287","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":"Assessment of thermal uniformity in bottom freezer refrigerators through combined experimental measurements and transient CFD simulations","authors":"Gökhan Bozkula","doi":"10.1016/j.csite.2026.108041","DOIUrl":"https://doi.org/10.1016/j.csite.2026.108041","url":null,"abstract":"This study presents a comprehensive investigation aimed at improving thermal uniformity within the freezer compartment of a bottom-freezer domestic refrigerator by achieving a more homogeneous temperature distribution and reducing temperature variations among stored packaged items. Two different design configurations were developed and comparatively analyzed using Computational Fluid Dynamics (CFD) simulations conducted in STAR-CCM+, under identical boundary conditions derived from experimental test data to ensure a reliable comparison, with the initial design serving as the reference case. The numerical results were validated through experimental measurements, showing a strong agreement between simulated and measured package temperatures, which confirms the accuracy of the simulation methodology. The optimized design demonstrated a significant enhancement in thermal uniformity, reducing the maximum temperature difference among the packages from 3.7 °C to 1.6 °C, thereby substantially improving the overall thermal performance and storage efficiency of the freezer compartment.","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"16 1","pages":""},"PeriodicalIF":6.8,"publicationDate":"2026-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681292","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":"Numerical study on unsteady heat transfer characteristics of phase change plates optimized by fin structure","authors":"Shiyu Liao, Xiang Li, Jiri Zhou, Xiaoyan Yi, Ruiyong Mao, Hongwei Wu, Zujing Zhang","doi":"10.1016/j.csite.2026.108042","DOIUrl":"https://doi.org/10.1016/j.csite.2026.108042","url":null,"abstract":"The energy crisis has heightened the importance of phase change energy storage technology as a key enabler for orderly energy transformation. However, the density variation of phase change materials during phase transition is often overlooked, leading to issues such as reduced heat transfer efficiency and local overheating. In previous studies, the inhibition effect of phase transition stratification has been found as an incidental result of thermal performance studies. There are few studies have systematically analyzed it. Therefore, in this study, the fin structure is studied by numerical simulation to mitigate the resulting stratification phenomenon. The results can reduce the thermal efficiency loss of the phase change plate and the risk of local overheating of the system. Specifically, the inhibitory effects of fin length, the number of transverse fins, and the presence of longitudinal fins on melting stratification are analyzed. The phase change plate melting rate is calculated as the total melting mass divided by the total melting time. The melting uniformity of the phase change plate was determined by the liquid phase component gradient. The temperature inhomogeneity coefficient is used to determine the air uniformity after passing through the phase change plate. The main results are as follows: (1) The plain phase change plate (without fins) showed an abrupt temperature rise followed by stabilization during melting, with a concurrent shift in its liquid fraction curve; (2) Increases in fin length, transverse fin number, and longitudinal fin number all improved the plate's melting rate and temperature uniformity, with maximum improvements of 10.86% and 293%, respectively; (3) The PCP of the optimized method 1 has better melting uniformity, but the initial cost is higher than that of the optimized method 2.","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"24 1","pages":""},"PeriodicalIF":6.8,"publicationDate":"2026-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681286","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":"Flow-field evolution and transient load characteristics during separation in an integrated solid rocket–ramjet combined nozzle","authors":"Shilin Yang, Wenyan Song, Jianru Wang, Yanfang Li, Kaibin Zheng, Nan Niu, Yongtao Zhao, Yuyan Wu","doi":"10.1016/j.csite.2026.108003","DOIUrl":"https://doi.org/10.1016/j.csite.2026.108003","url":null,"abstract":"This study addresses the transient separation of a combined nozzle in an integrated solid rocket ramjet (ISRR) subjected to strong coupling among structural displacement, compressible flow, and unsteady aerodynamic loading. An experimental–numerical coupled framework was developed. A two-dimensional axisymmetric model incorporating dynamic mesh techniques and fluid–structure interaction (FSI) was established and validated against ground-test measurements, with deviations in axial separation velocity and displacement maintained within ≤15.1%.The results indicate that the separation process follows a three-stage evolution pattern characterized by pressure attenuation, control response, and fluid–structure destabilization. At the instant of detachment, nozzle motion induces a localized choking phenomenon, generating a pressure perturbation with a peak magnitude of 0.783 MPa. These observations suggest that separation cannot be adequately described as a quasi-static pressure-difference-driven event. Instead, it arises from flow destabilization and structural reconfiguration governed by dynamically evolving boundary constraints. Furthermore, asymmetric pressure redistribution caused by internal–external flow interaction during the late separation stage is identified as the primary source of potential lateral loading. From a multiphysics dynamical perspective, this work reconstructs the theoretical framework of transient nozzle separation and provides mechanistic guidance for separation control optimization and high-fidelity simulation improvement.","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"144 1","pages":""},"PeriodicalIF":6.8,"publicationDate":"2026-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681288","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":"Influence of structural defects in nanocubes on solar photothermal conversion","authors":"Shijiang Guo, Xinrong Zhang, Chen Xu, Jia Liu, Xiaohu Wu","doi":"10.1016/j.csite.2026.108028","DOIUrl":"https://doi.org/10.1016/j.csite.2026.108028","url":null,"abstract":"The structure of nanoparticles plays a crucial role in tuning optical properties due to flexible surface modification and geometry-dependent spectrum response. Previous studies show that introducing structural defects can enhance plasmonic absorption. Here, we investigate the effects of Au nanocubes and structural defects on optical and photothermal performance. Compared with Au nanospheres, nanocubes red-shift absorption into the near-infrared and support multiple plasmonic resonances, increasing absorption by 6.63% over 300-1500 nm and achieving a solar-weighted absorption fraction of 97.11%, much higher than 80.97% for nanospheres, highlighting their potential for solar applications. Corner defects induce a blue shift of the resonance peak, weaken the second resonance, and increase scattering, reducing near-infrared absorption and solar-weighted absorption to ∼93%. Mid-side defects exhibit higher structural tolerance, enabling multiple resonances, broadening the absorption bandwidth (300-1100 nm), and suppressing scattering, with solar-weighted absorption decreasing slightly to 95.74%–96.92%. Analysis of electric and magnetic fields and thermal power shows local defects enhance fields and excite multiple resonances but do not necessarily increase peak photothermal output, revealing a trade-off between local plasmon excitation and overall performance. This work provides guidance for structural design, defect engineering, and application of Au nanocubes in direct solar thermal absorption systems.","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"68 1","pages":""},"PeriodicalIF":6.8,"publicationDate":"2026-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681469","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":"Research on intelligent control strategy of active grille shutters of hybrid vehicle based on low energy consumption","authors":"Yingchao Zhang, Ruizhuo Zhou, Guohua Wang, Mingzhe Liu, Xiaowen Zang, Zhe Zhang","doi":"10.1016/j.csite.2026.108026","DOIUrl":"https://doi.org/10.1016/j.csite.2026.108026","url":null,"abstract":"How to coordinate the heat dissipation and heating requirements of each subsystem of the thermal management system and its components is an important research direction of the hybrid electric vehicle. Active Grille Shutters (AGS) can reduce the internal flow resistance, balance the heat dissipation requirements of thermal management system and reduce the wind resistance to reduce fuel consumption, and has become an important component of vehicle thermal management system (TMS). Although AGS control strategies have been applied in the automotive industry, there is still a lack of mature and comprehensive control solutions for energy efficiency optimization. In this paper, three-dimensional Computational Fluid Dynamics (CFD) simulation software STAR-CCM+ is used to establish a three-dimensional vehicle model and analyze the changes of the flow field in the engine compartment under the steady-state condition of full open and full closed active grille. Then, a one-dimensional engine compartment model is introduced into the vehicle TMS of GT-SUITE, and a new AGS opening control strategy considering the coupling of aerodynamic and thermal management is proposed for low SOC initial value. The results show that when the initial SOC values are 0.2 and 0.3, the average resistance coefficient of the AGS control strategy is significantly lower than that without active grid, and the fuel consumption can be reduced by 0.65% and 0.89%, respectively.","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"5 1","pages":""},"PeriodicalIF":6.8,"publicationDate":"2026-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681471","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":"An experimental investigation of a greenhouse solar dryer integrated with a solar air heater and a rock bed thermal storage material","authors":"Yared A. Demissie, Muluken Temesgen, Rewla E. Abreham, Mulat S. Alem, Hailemariam M. Wassie, Muluken Z. Getie","doi":"10.1016/j.csite.2026.108033","DOIUrl":"https://doi.org/10.1016/j.csite.2026.108033","url":null,"abstract":"Efficient postharvest curing of onion bulbs requires controlled thermal and humidity conditions to reduce moisture effectively while maintaining product quality, especially in rural areas with limited access to conventional energy. In this context, this study aims to experimentally evaluate the thermal performance of a modified Quonset-shaped solar greenhouse dryer covered with a polycarbonate sheet under active and passive modes at Bahir Dar Institute of Technology. To achieve this objective, the active system incorporated a solar air heater with a rock bed thermal storage unit, extended surfaces to enhance heat transfer, and a suction blower for forced convection. Performance was assessed by monitoring temperature, relative humidity, and air velocity from 9:00 a.m. to 5:00 p.m. using onion bulbs as the test crop. The results revealed that moisture content decreased from 83% to 77.2% (wet basis), with curing completed in 10 h under active mode, 22 h in passive mode, and 36 h under open sun conditions. Zeolite desiccants at the air inlet reduced relative humidity to as low as 10%, enhancing drying efficiency. Maximum temperatures reached 61 °C in the greenhouse and 108 °C in the solar air heater. The solar air heater achieved an average efficiency of 53.78%, while the overall system efficiency reached 31.74%. All cured bulbs exhibited full neck tightness, confirming effective curing. These findings indicate that combining thermal storage, humidity control, and enhanced airflow significantly improves drying rate and product quality, offering a practical and sustainable solution for agricultural processing in rural areas, contributing to food security and clean energy access in line with the Sustainable Development Goals.","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"68 1","pages":""},"PeriodicalIF":6.8,"publicationDate":"2026-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681290","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":"Sustainable bio-oil generation from Chlorella vulgaris: Catalytic hydrothermal liquefaction and predictive modeling using RSM, ANN, and machine learning","authors":"J. Mozas Santhose Kumar, Prakash Ramakrishnan, Padmanathan Panneerselvam, C.G. Mohan, Cataldo De Blasio","doi":"10.1016/j.csite.2026.108032","DOIUrl":"https://doi.org/10.1016/j.csite.2026.108032","url":null,"abstract":"The catalytic hydrothermal liquefaction (HTL) of <ce:italic>Chlorella vulgaris</ce:italic> algal (CVA) biomass was systematically investigated to advance sustainable biofuel production by maximizing bio-oil yield and minimizing biochar generation. Potassium carbonate (K<ce:inf loc=\"post\">2</ce:inf>CO<ce:inf loc=\"post\">3</ce:inf>) served as an alkaline catalyst to exploit the inherent benefits of CVA, such as its high hydrogen-to-carbon ratio and superior calorific value, for enhanced biofuel conversion. Response Surface Methodology (RSM) combined with Central Composite Design (CCD) was employed to optimize key process variables, including operating temperature, residence time, biomass-to-solvent ratio, and catalyst dosage. The regression model demonstrated strong predictive accuracy for bio-oil and biochar yields (R<ce:sup loc=\"post\">2</ce:sup> = 0.9355), identifying optimal conditions with 15 g catalyst loading and a 10.573 wt% biomass-to-solvent ratio, leading to a bio-oil yield of 35.019 wt% at reduced residence time. The predictive robustness of the model was further validated using Artificial Neural Network (ANN) and Support Vector Machine (SVM) methods. The ANN demonstrated a Mean Squared Error of 0.2276 and an R<ce:sup loc=\"post\">2</ce:sup> value of 0.99, while the SVM exhibited a Root Mean Square Error of 0.537 and an R<ce:sup loc=\"post\">2</ce:sup> of 0.97. Characterization of the bio-oil through FTIR and GC-MS analysis confirmed that K<ce:inf loc=\"post\">2</ce:inf>CO<ce:inf loc=\"post\">3</ce:inf> catalysis effectively reduced nitrogen content and enhanced the conversion of proteins and lipids into valuable bio-products, such as indole and pyrrolic derivatives. The resulting bio-oil was rich in phenolics, aliphatic hydrocarbons, ketones, aromatics, and carboxylic acids. K<ce:inf loc=\"post\">2</ce:inf>CO<ce:inf loc=\"post\">3</ce:inf>-catalyzed conversion emerges as an efficient and sustainable strategy for producing high-grade bio-oil from algal biomass, contributing significantly to renewable energy advancement under SDG 7.","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"83 1","pages":""},"PeriodicalIF":6.8,"publicationDate":"2026-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681291","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":"Thermo-hydraulic evaluation of perforated hourglass pin-fin designs in micro pin fin heat sinks","authors":"Hatem Gasmi, Zakarya Ahmed, As'ad Alizadeh, Adel Almarashi, Abdellatif M. Sadeq, Husam Rajab, Khalil Hajlaoui, Narinderjit Singh Sawaran Singh","doi":"10.1016/j.csite.2026.108039","DOIUrl":"https://doi.org/10.1016/j.csite.2026.108039","url":null,"abstract":"Efficient thermal management is crucial for next-generation microelectronic systems operating under increasingly high heat flux conditions. This work presents a comprehensive numerical study to evaluate the thermo-hydraulic performance of advanced micro pin-fin heat sink configurations, including innovative hourglass-shaped and hybrid geometries, under laminar forced convection. The governing equations for mass, momentum, and energy are solved using the finite volume method (FVM) implemented in ANSYS Fluent, with all models validated against experimental data from the literature. The effects of fin shape, fin arrangement, and Reynolds number on heat transfer enhancement, pressure drop, temperature uniformity, and overall performance are systematically analyzed. Results indicate that hourglass configurations significantly promote fluid mixing, disrupt boundary layers more effectively, and increase the heat transfer coefficient by up to 67% compared to simple geometries. Although there is a moderate increase in pressure drop, the hourglass circular design offers the best overall performance, demonstrating superior thermal resistance reduction and more uniform temperature distribution. This study illustrates the delicate balance between geometric modifications and hydraulic penalties and emphasizes the importance of an optimized pin-fin topology for compact, high-heat-flux cooling solutions. Overall, this work provides new insights into the design of micro pin-fin heat sinks and establishes a detailed thermo-hydraulic performance benchmark for emerging micro-scale cooling technologies.","PeriodicalId":9658,"journal":{"name":"Case Studies in Thermal Engineering","volume":"130 1","pages":""},"PeriodicalIF":6.8,"publicationDate":"2026-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681289","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}