Pub Date : 2024-11-08DOI: 10.1016/j.applthermaleng.2024.124849
Entong Xia , Heping Xie , Licheng Sun , Xiting Long , Jun Wang , Tianyi Gao , Shuheng Li , Biao Li , Cunbao Li , Mingzhong Gao , Zhengyu Mo , Min Du
Thermoelectric generator (TEG) has been identified as a promising method for low-grade thermal energy recovery owing to its lack of moving parts, scalability, and compatibility with other devices generating waste heat. Heat exchanger, as one of the most important components of the modular TEG, plays a crucial role in improving the overall performance of the TEG. Nevertheless, flow maldistribution inside the heat exchanger results in uneven surface temperature field of the heat exchanger, which will ultimately limit the output capacity of the TEG. Achieving a homogeneous flow distribution within the heat exchanger while minimizing flow resistance is essential. To address this, optimization of a plate-shaped heat exchanger for the modular TEG is conducted using CFD analysis and the Taguchi method to identify the optimal combination of parameters. The optimized heat exchanger demonstrates a flow maldistribution intensity (ζ) of only 4.75 % and a low flow resistance of 1.16 kPa. Furthermore, a unit of the modular TEG is constructed using two optimized heat exchangers and commercial thermoelectric modules (TEMs), and its performance is analyzed via an analytical model. The results indicate that the power per module, net power density, and conversion efficiency reached 1.2 W, 51.4 kW/m3, and 1.92 %, respectively, at a temperature difference of 70 °C. These findings suggest that the optimized heat exchanger could provide high output performance compared with other literature, offering significant potential for low-grade heat energy recovery.
{"title":"Optimal design of a high-performance heat exchanger for modular thermoelectric generator towards low-grade thermal energy recovery","authors":"Entong Xia , Heping Xie , Licheng Sun , Xiting Long , Jun Wang , Tianyi Gao , Shuheng Li , Biao Li , Cunbao Li , Mingzhong Gao , Zhengyu Mo , Min Du","doi":"10.1016/j.applthermaleng.2024.124849","DOIUrl":"10.1016/j.applthermaleng.2024.124849","url":null,"abstract":"<div><div>Thermoelectric generator (TEG) has been identified as a promising method for low-grade thermal energy recovery owing to its lack of moving parts, scalability, and compatibility with other devices generating waste heat. Heat exchanger, as one of the most important components of the modular TEG, plays a crucial role in improving the overall performance of the TEG. Nevertheless, flow maldistribution inside the heat exchanger results in uneven surface temperature field of the heat exchanger, which will ultimately limit the output capacity of the TEG. Achieving a homogeneous flow distribution within the heat exchanger while minimizing flow resistance is essential. To address this, optimization of a plate-shaped heat exchanger for the modular TEG is conducted using CFD analysis and the Taguchi method to identify the optimal combination of parameters. The optimized heat exchanger demonstrates a flow maldistribution intensity (ζ) of only 4.75 % and a low flow resistance of 1.16 kPa. Furthermore, a unit of the modular TEG is constructed using two optimized heat exchangers and commercial thermoelectric modules (TEMs), and its performance is analyzed via an analytical model. The results indicate that the power per module, net power density, and conversion efficiency reached 1.2 W, 51.4 kW/m<sup>3</sup>, and 1.92 %, respectively, at a temperature difference of 70 °C. These findings suggest that the optimized heat exchanger could provide high output performance compared with other literature, offering significant potential for low-grade heat energy recovery.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"258 ","pages":"Article 124849"},"PeriodicalIF":6.1,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142659957","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 : 2024-11-08DOI: 10.1016/j.applthermaleng.2024.124855
Saeed Mahmoud AL Shurafa , Firas Basim Ismail , Hussein A. Kazem , Tareq Abdel Hameed Almajali , Tan Ee Sann
This study investigates a novel approach to enhancing photovoltaic-thermoelectric generator systems by utilizing advanced thermal interface materials in real-world conditions. The research compares two experimental systems under natural air cooling employing different thermal interface materials: one features a pyrolytic graphite sheet, while the other uses conventional thermal grease, alongside a photovoltaic-only system for reference. An Arduino-based data logger accurately monitored key environmental and operational parameters. At peak solar irradiation, the system with the pyrolytic graphite sheet achieved a surface photovoltaic temperature of 39.01 °C, generating 4.90 W and an overall efficiency of 17.95 %. In comparison, the system with thermal grease had a surface photovoltaic temperature of 48.88 °C, generating 4.67 W with an efficiency of 16.87 %, while the photovoltaic-only system reached a surface photovoltaic temperature of 55.37 °C, producing 4.54 W and an efficiency of 16.42 %. The experimental data’s accuracy and reliability were validated against simulations from previous work, revealing error margins between 1.20 % and 3.03 %. These findings underscore the potential of pyrolytic graphite sheets as effective thermal interface materials to significantly enhance the efficiency and power output of photovoltaic-thermoelectric generator systems, offering valuable insights for optimizing renewable energy technologies.
{"title":"Experimental study of photovoltaic-thermoelectric systems using thermal interface materials and natural cooling","authors":"Saeed Mahmoud AL Shurafa , Firas Basim Ismail , Hussein A. Kazem , Tareq Abdel Hameed Almajali , Tan Ee Sann","doi":"10.1016/j.applthermaleng.2024.124855","DOIUrl":"10.1016/j.applthermaleng.2024.124855","url":null,"abstract":"<div><div>This study investigates a novel approach to enhancing photovoltaic-thermoelectric generator systems by utilizing advanced thermal interface materials in real-world conditions. The research compares two experimental systems under natural air cooling employing different thermal interface materials: one features a pyrolytic graphite sheet, while the other uses conventional thermal grease, alongside a photovoltaic-only system for reference. An Arduino-based data logger accurately monitored key environmental and operational parameters. At peak solar irradiation, the system with the pyrolytic graphite sheet achieved a surface photovoltaic temperature of 39.01 °C, generating 4.90 W and an overall efficiency of 17.95 %. In comparison, the system with thermal grease had a surface photovoltaic temperature of 48.88 °C, generating 4.67 W with an efficiency of 16.87 %, while the photovoltaic-only system reached a surface photovoltaic temperature of 55.37 °C, producing 4.54 W and an efficiency of 16.42 %. The experimental data’s accuracy and reliability were validated against simulations from previous work, revealing error margins between 1.20 % and 3.03 %. These findings underscore the potential of pyrolytic graphite sheets as effective thermal interface materials to significantly enhance the efficiency and power output of photovoltaic-thermoelectric generator systems, offering valuable insights for optimizing renewable energy technologies.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"258 ","pages":"Article 124855"},"PeriodicalIF":6.1,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142659915","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 : 2024-11-08DOI: 10.1016/j.applthermaleng.2024.124852
Ahmet Dogan , Nurullah Kayaci , Aykut Bacak
The research introduces an artificial neural network model that predicts temperature and assesses thermal comfort metrics for a cooling room, demonstrating how machine learning advancements can enhance thermal efficiency and cost-effectiveness in building design. The study utilized the Levenberg-Marquardt (LM) artificial neural network (ANN) approach to derive the average temperature and thermal comfort metrics collected under actual operating settings. The Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD)values were measured at three distinct sites and then compared to the trial findings. The model uses a dataset of 205 observations, with 143 cases used for training and 31 examples for testing and validation. The ANN model demonstrated effective training, with negligible errors in estimated error values. The mean squared error values for average temperature and thermal comfort parameters were 0.0342, 0.0376, 0.0571, 0.0029, and 0.2296. The R values for temperature measurements are 0.9947 and 0.9923, 0.9847 and 0.9437, and 0.9737, demonstrating a highly effective engineering method. The ANN model provided precise predictions for temperature and thermal comfort metrics, such as PMV and PPD in a cooling chamber, with a tolerance of ± 15 %. The LM approach, a machine learning methodology, produced excellent outcomes, particularly at lower temperatures, with 15 % of the data exceeding this range.
{"title":"Machine learning-based predictive model for temperature and comfort parameters in indoor enviroment using experimantal data","authors":"Ahmet Dogan , Nurullah Kayaci , Aykut Bacak","doi":"10.1016/j.applthermaleng.2024.124852","DOIUrl":"10.1016/j.applthermaleng.2024.124852","url":null,"abstract":"<div><div>The research introduces an artificial neural network model that predicts temperature and assesses thermal comfort metrics for a cooling room, demonstrating how machine learning advancements can enhance thermal efficiency and cost-effectiveness in building design. The study utilized the Levenberg-Marquardt (LM) artificial neural network (ANN) approach to derive the average temperature and thermal comfort metrics collected under actual operating settings. The Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD)values were measured at three distinct sites and then compared to the trial findings. The model uses a dataset of 205 observations, with 143 cases used for training and 31 examples for testing and validation. The ANN model demonstrated effective training, with negligible errors in estimated error values. The mean squared error values for average temperature and thermal comfort parameters were 0.0342, 0.0376, 0.0571, 0.0029, and 0.2296. The R values for temperature measurements are 0.9947 and 0.9923, 0.9847 and 0.9437, and 0.9737, demonstrating a highly effective engineering method. The ANN model provided precise predictions for temperature and thermal comfort metrics, such as PMV and PPD in a cooling chamber, with a tolerance of ± 15 %. The LM approach, a machine learning methodology, produced excellent outcomes, particularly at lower temperatures, with 15 % of the data exceeding this range.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"259 ","pages":"Article 124852"},"PeriodicalIF":6.1,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142658191","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 : 2024-11-08DOI: 10.1016/j.applthermaleng.2024.124799
Elias Vieren , Kenny Couvreur , Michel De Paepe , Steven Lecompte
Industrial heat significantly contributes to global primary energy use and primarily relies on fossil-fuel combustion. Recovering residual heat in the industry offers a means to reduce overall energy use. However, the temperature and amount of residual heat available varies widely across industrial sites. Some may have a large amount of residual heat available at relatively high temperatures, while others may not have any residual heat available. Furthermore, for most industries, the residual heat available is at temperatures below 100 °C, while the heat demands are at higher temperatures. Hence, clustering these industries by industrial heating networks, using high-temperature heat pump integration, could offer a promising solution. Research on this concept regarding energy use, emissions and economics is however lacking in the literature. This study however distinguishes and subsequently compares three different heat network configurations in terms of their energy use, carbon emissions and financial appraisal. These configurations include a ‘consumer based heat upgrading network’, a ‘supplier based heat upgrading network’ and a ‘supplier based heat upgrading network with an additional hot water network’. For this purpose a generic methodology is developed, using first and second law principles completed with empirical data for performance and costs. The methodology is applied to data collected from ten companies clustered within the North Sea Port, Ghent (Belgium). The results indicate that the first configuration exhibits the most efficient use of energy and consequently also has the lowest carbon emissions. In addition it also has the lowest levelized cost of heat. This configuration shows, depending on maximum supply temperature of the heat pump, a potential reduction in carbon emissions ranging from 70 % to 80 % in comparison to natural gas boilers. Considering low gas prices, a positive financial appraisal is difficult without carbon taxation. On the other hand, an evaluation during the energy crisis of 2021–2022 indicates that the even without carbon taxation, the levelized cost of heat decreases by 19 % compared to a gas boiler at a maximum heat pump temperature of 160 °C. It was also found that in scenarios of dynamic energy prices a hybrid configuration of a consumer based heat upgrading network and a natural gas boiler could lower the LCOH compared to the individual solutions, by up to 7.6 % compared to the best individual solution. This is done by activating the technology with the lowest operational cost in each time frame.
{"title":"High-temperature heat pumps in industrial heating networks: A study on energy use, emissions, and economics","authors":"Elias Vieren , Kenny Couvreur , Michel De Paepe , Steven Lecompte","doi":"10.1016/j.applthermaleng.2024.124799","DOIUrl":"10.1016/j.applthermaleng.2024.124799","url":null,"abstract":"<div><div>Industrial heat significantly contributes to global primary energy use and primarily relies on fossil-fuel combustion. Recovering residual heat in the industry offers a means to reduce overall energy use. However, the temperature and amount of residual heat available varies widely across industrial sites. Some may have a large amount of residual heat available at relatively high temperatures, while others may not have any residual heat available. Furthermore, for most industries, the residual heat available is at temperatures below 100 °C, while the heat demands are at higher temperatures. Hence, clustering these industries by industrial heating networks, using high-temperature heat pump integration, could offer a promising solution. Research on this concept regarding energy use, emissions and economics is however lacking in the literature. This study however distinguishes and subsequently compares three different heat network configurations in terms of their energy use, carbon emissions and financial appraisal. These configurations include a ‘consumer based heat upgrading network’, a ‘supplier based heat upgrading network’ and a ‘supplier based heat upgrading network with an additional hot water network’. For this purpose a generic methodology is developed, using first and second law principles completed with empirical data for performance and costs. The methodology is applied to data collected from ten companies clustered within the North Sea Port, Ghent (Belgium). The results indicate that the first configuration exhibits the most efficient use of energy and consequently also has the lowest carbon emissions. In addition it also has the lowest levelized cost of heat. This configuration shows, depending on maximum supply temperature of the heat pump, a potential reduction in carbon emissions ranging from 70 % to 80 % in comparison to natural gas boilers. Considering low gas prices, a positive financial appraisal is difficult without carbon taxation. On the other hand, an evaluation during the energy crisis of 2021–2022 indicates that the even without carbon taxation, the levelized cost of heat decreases by 19 % compared to a gas boiler at a maximum heat pump temperature of 160 °C. It was also found that in scenarios of dynamic energy prices a hybrid configuration of a consumer based heat upgrading network and a natural gas boiler could lower the LCOH compared to the individual solutions, by up to 7.6 % compared to the best individual solution. This is done by activating the technology with the lowest operational cost in each time frame.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"259 ","pages":"Article 124799"},"PeriodicalIF":6.1,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142657650","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 : 2024-11-07DOI: 10.1016/j.applthermaleng.2024.124841
Huakun Huang , Jingxuan He , Qingmo Xie , Tiezhi Sun , Guiyong Zhang , Peng Yu
Jet impingement heat transfer in the transitional type involves the occurrence and disappearance of the secondary maximum heat transfer, which is challenging for numerical simulation. In the paper, the effects of the nozzle-plate spacing H/D on heat transfer and flow fields in the range of 57 within the transitional type are investigated. In this type, the secondary maximum heat transfer rate gradually vanishes. In addition, the transitional properties of jet impingement are further discussed. It is found that the heat transfer rate at the stagnation point shows an important relationship with the arriving stream Reynolds number and turbulence intensity. Additionally, three heat transfer modes, i.e., the peak (), swelling (), and linear modes (), are identified in the transitional type based on the analysis of the heat transfer rate, development of the intermittency, and the wall shear stress. For the latter two aspects, the laminar zone and the turbulence zone are discussed in detail for different . In the peak mode, heat transfer rate is largely influenced by the transition process, resulting in a secondary peak. While in the swelling mode, the second peak evolves to a swelling and the effect of transition becomes weak. As a result, the influences of the laminar region will extend to downstream. However, in the linear mode, the swelling vanishes with a mild change of intermittency in the boundary layer and the sudden mutation of heat transfer mainly takes place in the stagnation region.
{"title":"Flow field and heat transfer in the transitional type of turbulent round jet impingement","authors":"Huakun Huang , Jingxuan He , Qingmo Xie , Tiezhi Sun , Guiyong Zhang , Peng Yu","doi":"10.1016/j.applthermaleng.2024.124841","DOIUrl":"10.1016/j.applthermaleng.2024.124841","url":null,"abstract":"<div><div>Jet impingement heat transfer in the transitional type involves the occurrence and disappearance of the secondary maximum heat transfer, which is challenging for numerical simulation. In the paper, the effects of the nozzle-plate spacing <em>H</em>/<em>D</em> on heat transfer and flow fields in the range of 5<span><math><mrow><mspace></mspace><mo>≤</mo><mspace></mspace><mtext>H</mtext><mtext>/</mtext><mtext>D</mtext><mo>≤</mo></mrow></math></span>7 within the transitional type are investigated. In this type, the secondary maximum heat transfer rate gradually vanishes. In addition, the transitional properties of jet impingement are further discussed. It is found that the heat transfer rate at the stagnation point shows an important relationship with the arriving stream Reynolds number and turbulence intensity. Additionally, three heat transfer modes, i.e., the peak (<span><math><mrow><mtext>5</mtext><mo><</mo><mtext>H</mtext><mtext>/</mtext><mtext>D</mtext><mo>≤</mo><mtext>5.5</mtext></mrow></math></span>), swelling (<span><math><mrow><mtext>5.5</mtext><mo><</mo><mtext>H</mtext><mtext>/</mtext><mtext>D</mtext><mo>≤</mo><mtext>6.6</mtext></mrow></math></span>), and linear modes (<span><math><mrow><mtext>6.6</mtext><mo><</mo><mtext>H</mtext><mtext>/</mtext><mtext>D</mtext><mo>≤</mo><mtext>7</mtext></mrow></math></span>), are identified in the transitional type based on the analysis of the heat transfer rate, development of the intermittency, and the wall shear stress. For the latter two aspects, the laminar zone and the turbulence zone are discussed in detail for different <span><math><mrow><mspace></mspace><mtext>H</mtext><mtext>/</mtext><mtext>D</mtext></mrow></math></span>. In the peak mode, heat transfer rate is largely influenced by the transition process, resulting in a secondary peak. While in the swelling mode, the second peak evolves to a swelling and the effect of transition becomes weak. As a result, the influences of the laminar region will extend to downstream. However, in the linear mode, the swelling vanishes with a mild change of intermittency in the boundary layer and the sudden mutation of heat transfer mainly takes place in the stagnation region.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"259 ","pages":"Article 124841"},"PeriodicalIF":6.1,"publicationDate":"2024-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142657835","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 : 2024-11-07DOI: 10.1016/j.applthermaleng.2024.124743
Haonan Cai , Chongsheng Cheng , Lilin Wang , Hong Zhang , Jianting Zhou , Ri Na , Bo Wu
Debonding in Concrete-Filled Steel Tubes (CFST) can reduce bridges’ overall load-bearing capacity and thus threaten the bridge’s structural safety. Infrared thermography (IRT) is widely used for CFST debonding detection due to its efficiency and non-contact advantages. However, IRT is often affected by complex environmental factors and faces challenges in achieving quantitative evaluation only based on thermal contrast. This study aims to reveal the relationship between thermal indicators and thermal contrast through numerical and experimental investigations of CFST debonding under varied mimicked climatic conditions. A 3-dimensional (3-D) heat transfer transient model of CFST is established to simulate the evolution of thermal contrast of debonding under different daily temperature variations and seasonal solar irradiance. Based on the finite element analysis results, the internal interface heat flux is found as a strong linear indicator correlating the thermal contrast to environmental factors. Model experiments then were conducted to verify the validity of this indicator. Finally, an infrared evaluation method for CFST debonding is proposed, which can linearly quantify the relationships among debonding sizes, environmental factors, and thermal contrast.
{"title":"Numerical and experimental study on the evolution of thermal contrast for infrared detection of debonding in concrete filled steel tubular structure","authors":"Haonan Cai , Chongsheng Cheng , Lilin Wang , Hong Zhang , Jianting Zhou , Ri Na , Bo Wu","doi":"10.1016/j.applthermaleng.2024.124743","DOIUrl":"10.1016/j.applthermaleng.2024.124743","url":null,"abstract":"<div><div>Debonding in Concrete-Filled Steel Tubes (CFST) can reduce bridges’ overall load-bearing capacity and thus threaten the bridge’s structural safety. Infrared thermography (IRT) is widely used for CFST debonding detection due to its efficiency and non-contact advantages. However, IRT is often affected by complex environmental factors and faces challenges in achieving quantitative evaluation only based on thermal contrast. This study aims to reveal the relationship between thermal indicators and thermal contrast through numerical and experimental investigations of CFST debonding under varied mimicked climatic conditions. A 3-dimensional (3-D) heat transfer transient model of CFST is established to simulate the evolution of thermal contrast of debonding under different daily temperature variations and seasonal solar irradiance. Based on the finite element analysis results, the internal interface heat flux is found as a strong linear indicator correlating the thermal contrast to environmental factors. Model experiments then were conducted to verify the validity of this indicator. Finally, an infrared evaluation method for CFST debonding is proposed, which can linearly quantify the relationships among debonding sizes, environmental factors, and thermal contrast.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"258 ","pages":"Article 124743"},"PeriodicalIF":6.1,"publicationDate":"2024-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142660061","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 : 2024-11-07DOI: 10.1016/j.applthermaleng.2024.124764
Agnieszka Ciesielska, Adam Klimanek, Sławomir Sładek, Jakub Tumidajski, Andrzej Szlęk, Wojciech Adamczyk
The goal of the current work is to develop a combustion chamber that can operate on recirculated steam produced by burning hydrogen in oxygen under conditions of Moderate or Intense oxygen Dilution (MILD) in atmospheric and stoichiometric conditions. The study investigates several configurations of combustor with nozzles, taking into account the overall temperature, OH radicals, and heat release rate distribution throughout the combustor’s domain. Thermal power variations of the steam generator (5 to 20 kW) were examined in conjunction with different oxygen dilutions with steam, down to 3% of O2 (by mol.). The outcomes reveal that a rise in dilution degree promotes a drop in the mean temperature across every case and reagents’ recirculation with homogeneous temperature field, suggesting the presence of MILD combustion. The highest temperature values were observed at the stoichiometric mixture fraction. Higher dilution degree revealed more efficient heat release across the domain with low fluctuations from the reference MILD combustion data. Of the two combustion models studied, the Partially Stirred Reactor model did not show flame extinction at the highest dilution degrees, unlike the Eddy Dissipation model. The selected final design of the combustion chamber was used for constructing the actual combustor dedicated for lab-scale operation.
{"title":"The design of a combustion chamber operated in MILD regime — Numerical modeling of hydrogen combustion in oxygen–steam mixtures","authors":"Agnieszka Ciesielska, Adam Klimanek, Sławomir Sładek, Jakub Tumidajski, Andrzej Szlęk, Wojciech Adamczyk","doi":"10.1016/j.applthermaleng.2024.124764","DOIUrl":"10.1016/j.applthermaleng.2024.124764","url":null,"abstract":"<div><div>The goal of the current work is to develop a combustion chamber that can operate on recirculated steam produced by burning hydrogen in oxygen under conditions of Moderate or Intense oxygen Dilution (MILD) in atmospheric and stoichiometric conditions. The study investigates several configurations of combustor with nozzles, taking into account the overall temperature, OH radicals, and heat release rate distribution throughout the combustor’s domain. Thermal power variations of the steam generator (5 to 20 kW) were examined in conjunction with different oxygen dilutions with steam, down to 3% of O<sub>2</sub> (by mol.). The outcomes reveal that a rise in dilution degree promotes a drop in the mean temperature across every case and reagents’ recirculation with homogeneous temperature field, suggesting the presence of MILD combustion. The highest temperature values were observed at the stoichiometric mixture fraction. Higher dilution degree revealed more efficient heat release across the domain with low fluctuations from the reference MILD combustion data. Of the two combustion models studied, the Partially Stirred Reactor model did not show flame extinction at the highest dilution degrees, unlike the Eddy Dissipation model. The selected final design of the combustion chamber was used for constructing the actual combustor dedicated for lab-scale operation.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"259 ","pages":"Article 124764"},"PeriodicalIF":6.1,"publicationDate":"2024-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142657849","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-07DOI: 10.1016/j.applthermaleng.2024.124844
Hengyuan Wang, Qiyu Xuan, Hailin Lei, Xi Li, Zhibin Li, Huixiong Li
Helically-coiled tube steam generator has been widely used in nuclear reactor, energy power, petrochemical and other systems. In the liquid metal reactor, the liquid metal on the primary side of the helically-coiled tube steam generator exchanges heat with the water on the secondary side. Due to the coupled heat transfer between liquid metal and water, the distribution of the wall temperature or heat transfer coefficient of helically-coiled tube are significant different in the circumferential direction of the tube cross-section. An experimental system of helically-coiled tube steam generator was set up in this paper. The non-uniform heat transfer characteristics of secondary side fluid of helically-coiled tube steam generator were studied under the coupled heat transfer conditions between the heat transfer of primary side and secondary sides fluid. It was found that the wall temperature or heat transfer coefficient in the circumferential direction of tube cross-section were significantly different, the maximum and minimum wall temperature appeared on the inside and bottom of the tube cross-section, respectively, the maximum and minimum heat transfer coefficient appeared on the outside and top of the tube cross-section, respectively. The effect of secondary side refrigerant pressure, secondary side refrigerant supercooling degree, mass flux of secondary side refrigerant, primary side heating water temperature and mass flux of primary side heating water on the maximum wall temperature, minimum wall temperature, maximum heat transfer coefficient, minimum heat transfer coefficient were obtained. Beside, The local and overall non-uniformity of the wall temperature and heat transfer coefficient in the circumferential direction of tube cross-section were obtained and the influence of each parameter on the local and overall non-uniformity were revealed, respectively. Finally, it was concluded that the non-uniformity of heat transfer coefficient in the circumferential direction of tube cross-section under coupled heat transfer conditions was more obvious than that under constant heat flux conditions. And the the overall non-uniformity of heat transfer coefficient (δh) obtained in our experimental were larger than the δh of Chang et al. [33], Zheng et al. [38], Kong et al. [34], Yao et al. [36] and Niu et al. [37] by 130.67%, 48.10%, 289.48%, 151.28% and 271.67%, respectively.
{"title":"Experimental study on flow boiling and circumferential non-uniform heat transfer characteristics in helically-coiled tube under coupled heat transfer conditions","authors":"Hengyuan Wang, Qiyu Xuan, Hailin Lei, Xi Li, Zhibin Li, Huixiong Li","doi":"10.1016/j.applthermaleng.2024.124844","DOIUrl":"10.1016/j.applthermaleng.2024.124844","url":null,"abstract":"<div><div>Helically-coiled tube steam generator has been widely used in nuclear reactor, energy power, petrochemical and other systems. In the liquid metal reactor, the liquid metal on the primary side of the helically-coiled tube steam generator exchanges heat with the water on the secondary side. Due to the coupled heat transfer between liquid metal and water, the distribution of the wall temperature or heat transfer coefficient of helically-coiled tube are significant different in the circumferential direction of the tube cross-section. An experimental system of helically-coiled tube steam generator was set up in this paper. The non-uniform heat transfer characteristics of secondary side fluid of helically-coiled tube steam generator were studied under the coupled heat transfer conditions between the heat transfer of primary side and secondary sides fluid. It was found that the wall temperature or heat transfer coefficient in the circumferential direction of tube cross-section were significantly different, the maximum and minimum wall temperature appeared on the inside and bottom of the tube cross-section, respectively, the maximum and minimum heat transfer coefficient appeared on the outside and top of the tube cross-section, respectively. The effect of secondary side refrigerant pressure, secondary side refrigerant supercooling degree, mass flux of secondary side refrigerant, primary side heating water temperature and mass flux of primary side heating water on the maximum wall temperature, minimum wall temperature, maximum heat transfer coefficient, minimum heat transfer coefficient were obtained. Beside, The local and overall non-uniformity of the wall temperature and heat transfer coefficient in the circumferential direction of tube cross-section were obtained and the influence of each parameter on the local and overall non-uniformity were revealed, respectively. Finally, it was concluded that the non-uniformity of heat transfer coefficient in the circumferential direction of tube cross-section under coupled heat transfer conditions was more obvious than that under constant heat flux conditions. And the the overall non-uniformity of heat transfer coefficient (δ<sub>h</sub>) obtained in our experimental were larger than the δ<sub>h</sub> of Chang et al. <span><span>[33]</span></span>, Zheng et al. <span><span>[38]</span></span>, Kong et al. <span><span>[34]</span></span>, Yao et al. <span><span>[36]</span></span> and Niu et al. <span><span>[37]</span></span> by 130.67%, 48.10%, 289.48%, 151.28% and 271.67%, respectively.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"258 ","pages":"Article 124844"},"PeriodicalIF":6.1,"publicationDate":"2024-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142659845","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 : 2024-11-07DOI: 10.1016/j.applthermaleng.2024.124842
Kai Deng , Aidi He , Zhenyu Liu , Shiheng Ye , Wentao Lin , Weiwei Kang , Qinglu Lin , Junjie Zhu , Zhirong Liang
Carbon-free fuels such as ammonia and hydrogen have attracted much attention in response to tackling with climate problem of global warming, but their high NOX emissions limit practical applications unavoidably. Currently, very few studies have addressed the inter-relationship between flame structures and NOX formation. In addition, few previous studies have analyzed ammonia-hydrogen combustion with low hydrogen mixing ratio through in-depth NOX formation mechanisms. In this work, NOX formation of ammonia-hydrogen swirl flame with different equivalence ratios and hydrogen mixing ratios (<30 %) has been comprehensively investigated, and the connection between flame structures and NOX has been reflected based on PLIF technique. The analytical results showed that as equivalence ratio (Φ = 0.6–1.2) increased, NOX concentration increased firstly and then decreased subsequently, and peak NOX value was observed between Φ = 0.7–0.8. Besides, NOX increased as the hydrogen mixing ratio increased from 10 % to 25 %, being capable of reaching up to 2795 ppm. Furthermore with flame structure analysis, the flame structure could be classified into single-front flame, transition flame, and double-front flame, in which transition flame featured with the largest decomposition reaction region contributing to NH3 oxidation to form NOX (intensive OH radicals propagation); while double-front flame characterized by smallest decomposition reaction region inhibiting the NOX formation via OH suppression (weak OH radicals propagation). Based on systematically flame surface density and chemical kinetics analysis, lean combustion benefited the NOX pathway, whilst rich combustion favored the N2 pathway. In addition, as the hydrogen ratio increased, and the reducibility of NH/NH2 to NOX was weakened, which ultimately promoted the production of NOX. The findings achieved suggest that future combustion techniques by the ammonia-hydrogen dual fuel should avoid the occurrence of transition flame, and prone to the generation of double-front flame, which could thus implement effective suppression on NOX formation.
{"title":"Resolving NOX formation of ammonia-hydrogen flame utilizing PLIF technique collaborated with flame structures and chemical kinetics analysis","authors":"Kai Deng , Aidi He , Zhenyu Liu , Shiheng Ye , Wentao Lin , Weiwei Kang , Qinglu Lin , Junjie Zhu , Zhirong Liang","doi":"10.1016/j.applthermaleng.2024.124842","DOIUrl":"10.1016/j.applthermaleng.2024.124842","url":null,"abstract":"<div><div>Carbon-free fuels such as ammonia and hydrogen have attracted much attention in response to tackling with climate problem of global warming, but their high NO<sub>X</sub> emissions limit practical applications unavoidably. Currently, very few studies have addressed the inter-relationship between flame structures and NO<sub>X</sub> formation. In addition, few previous studies have analyzed ammonia-hydrogen combustion with low hydrogen mixing ratio through in-depth NO<sub>X</sub> formation mechanisms. In this work, NO<sub>X</sub> formation of ammonia-hydrogen swirl flame with different equivalence ratios and hydrogen mixing ratios (<30 %) has been comprehensively investigated, and the connection between flame structures and NO<sub>X</sub> has been reflected based on PLIF technique. The analytical results showed that as equivalence ratio (<em>Φ</em> = 0.6–1.2) increased, NO<sub>X</sub> concentration increased firstly and then decreased subsequently, and peak NO<sub>X</sub> value was observed between <em>Φ</em> = 0.7–0.8. Besides, NO<sub>X</sub> increased as the hydrogen mixing ratio increased from 10 % to 25 %, being capable of reaching up to 2795 ppm. Furthermore with flame structure analysis, the flame structure could be classified into single-front flame, transition flame, and double-front flame, in which transition flame featured with the largest decomposition reaction region contributing to NH<sub>3</sub> oxidation to form NO<sub>X</sub> (intensive OH radicals propagation); while double-front flame characterized by smallest decomposition reaction region inhibiting the NO<sub>X</sub> formation via OH suppression (weak OH radicals propagation). Based on systematically flame surface density and chemical kinetics analysis, lean combustion benefited the NO<sub>X</sub> pathway, whilst rich combustion favored the N<sub>2</sub> pathway. In addition, as the hydrogen ratio increased, and the reducibility of NH/NH<sub>2</sub> to NO<sub>X</sub> was weakened, which ultimately promoted the production of NO<sub>X</sub>. The findings achieved suggest that future combustion techniques by the ammonia-hydrogen dual fuel should avoid the occurrence of transition flame, and prone to the generation of double-front flame, which could thus implement effective suppression on NO<sub>X</sub> formation.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"259 ","pages":"Article 124842"},"PeriodicalIF":6.1,"publicationDate":"2024-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142657655","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}
Public transport buses and other large vehicles are facing increasing engine fire issues stemming from higher operating temperatures, phonic insulation and low maintenance time. The fire suppression systems currently employed or considered for vehicles could be used for the protection of buses. Water mist is one of these technologies. One of the challenges a water mist faces for the fire protection of small enclosures is the ventilation. Inside a full scale engine compartment of a truck, the interaction and heat transfer between a n-heptane pool fire and water mist droplets are studied using velocimetry techniques. Most notably, the influence of the nozzle operating pressure and a variable cross-flow ventilation on the extinguishing performance is explored. In this preliminary study without clutter, the results show the importance of the ventilation flow on the performance of the water mist. Moderate ventilation speeds up to 3.2 m s-1 show an improvement of the extinguishing time over natural ventilation while a higher ventilation speed of 6.4 m s-1 degrades the extinguishing performance of the mist. For low-pressure water mists, the momentum of the spray is the most important factor for water mist extinguishing performance.
{"title":"Case study on thermal and flow analysis of a water mist on a pool fire in a ventilated engine compartment","authors":"Antonin Robinet , Khaled Chetehouna , Ilyas Sellami , Souria Hamidouche , Nicolas Gascoin , Denis Guedal","doi":"10.1016/j.applthermaleng.2024.124694","DOIUrl":"10.1016/j.applthermaleng.2024.124694","url":null,"abstract":"<div><div>Public transport buses and other large vehicles are facing increasing engine fire issues stemming from higher operating temperatures, phonic insulation and low maintenance time. The fire suppression systems currently employed or considered for vehicles could be used for the protection of buses. Water mist is one of these technologies. One of the challenges a water mist faces for the fire protection of small enclosures is the ventilation. Inside a full scale engine compartment of a truck, the interaction and heat transfer between a <em>n</em>-heptane pool fire and water mist droplets are studied using velocimetry techniques. Most notably, the influence of the nozzle operating pressure and a variable cross-flow ventilation on the extinguishing performance is explored. In this preliminary study without clutter, the results show the importance of the ventilation flow on the performance of the water mist. Moderate ventilation speeds up to 3.2<!--> <!-->m<!--> <!-->s<sup>-1</sup> show an improvement of the extinguishing time over natural ventilation while a higher ventilation speed of 6.4<!--> <!-->m<!--> <!-->s<sup>-1</sup> degrades the extinguishing performance of the mist. For low-pressure water mists, the momentum of the spray is the most important factor for water mist extinguishing performance.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"258 ","pages":"Article 124694"},"PeriodicalIF":6.1,"publicationDate":"2024-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142659843","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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