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Numerical Comparisons on Heat-Source-Targeted and Large-Area Spray Cooling for an Impinging Jet at High Temperature in a Confined Space 1

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11th International Symposium on Heating, Ventilation and Air Conditioning, ISHVAC 2019

作者： Zhi, Chengqiang Huang, Yixiang Zhang, Qianru Ye, Wei Zhang, Xu School of Mechanical Engineering Tongji University Shanghai China Key Laboratory of Performance Evolution and Control for Engineering Structures of Ministry of Education Tongji University Shanghai China

ISBN: (数字)9789811395208

ISBN: (纸本)9789811395192

Impinging jets with high temperature can be commonly found among industrial applications, such as exhaust gas from turbine engines that used for ships, heavy trucks or aircrafts. When the heating source is in a confined space, i.e., a garage or a machine room, additional cooling method, e.g., spray cooling, usually needs to be applied to decrease the temperature of the impinging jet, to minimize damages to the interior structure. In this paper, numerical simulation is used to study the cooling effect of water spray on an impinging jet at ~800 K. The confined space also incorporates an exhaust fan to remove the generated gas. The cooling effect of both local cooling (i.e., directly spraying at the heat source) and large-area cooling (i.e., spraying spread out the whole space) are investigated. Six cases were designed. In the first case, there were no nozzles were set. In the next 5 cases, the total number of nozzles were 65 and remained unchanged, by changing the number of nozzles used for larger-area cooling and local cooling, the cooling effect of different installation scheme of nozzles was obtained thorough computational method. For all the cases, the flow rate of the flue gas is 28.0 kg/s, and hourly water consumption of each nozzle is ~0.8 m3/h. The results show that increasing the number of nozzles that used for local cooling result in a better cooling effect, but the increment of cooling effect will be slightly when the number of local cooling nozzles up to ~20. © 2020, Springer Nature Singapore Pte Ltd.

关键词： Cooling

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Modeling flexural and shear strength for corroded RC columns under seismic excitations

Modeling flexural and shear strength for corroded RC columns...

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2020 fib Symposium: Concrete structures for Resilient Society

作者： Gu, Xianglin Wouagabe, Justin Hua, Jingjing Key Laboratory of Performance Evolution and Control for Engineering Structures Ministry of Education Tongji University Shanghai China Department of Structural Engineering Tongji University Shanghai China

ISBN: (纸本)9782940643042

Corrosion of transverse reinforcements can decrease the flexure and shear capacity of reinforced concrete (RC) columns. Therefore, this paper introduces a new model for flexural and shear strengths of corroded RC columns under seismic excitations by considering the corrosion of stirrups. Based on aspect ratio, the result showed that all RC columns failed in flexure shear mode, the mass and diameter loss due to corrosion reduced the cross-sectional areas of stirrups, the larger the corrosion rate is, the larger is the slip value. Experimental results of twenty corroded RC columns were collected from the literature to verify the new model. These experiments involved different cross-sectional areas and corrosion degrees. The model predicted flexural and shear strengths were in good agreement with the collected experimental results, which demonstrated the validity of the new model. The proposed new model is useful in assessing the reliability of corroded RC columns in existing structures. © Proceedings of the fib Symposium 2020: Concrete structures for Resilient Society. All rights reserved.

关键词： Corrosion rate

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An Investigation on the Dynamic Response Property in an Underground Tunnel Space with Constant Temperature 11th

An Investigation on the Dynamic Response Property in an Unde...

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11th International Symposium on Heating, Ventilation and Air Conditioning, ISHVAC 2019

作者： Wu, Chao Zhang, Xu Huo, Jingtao Zhao, Wenxuan Ye, Wei School of Mechanical Engineering Tongji University Shanghai China Key Laboratory of Performance Evolution and Control for Engineering Structures of Ministry of Education Tongji University Shanghai China

ISBN: (纸本)9789811395277

The cutting-edge scientific research calls for the emergence of some special high-precision thermostatic chambers, which are characteristic of large space and many internal and external disturbances. These chambers mainly function by chilled water taking away most of the heat generated by the internal heat source and adjusting the air supply by air conditioners to ensure the constant temperature accuracy of the laboratory room. In order to improve this, the paper employs the numerical simulation method to study the temperature response characteristics of airflow organization under different air supply modes and the dynamic response characteristics of different air supply temperatures to constant-temperature region. The research finds the optimal airflow distribution pattern and the location of the optimal control point, which provides the reliable foundation for the high-precision control solutions for underground constant-temperature space. The research results show that the air distribution under the lower air supply mode is more resistant to interference than that under the side air supply. The delay time coefficient and system time constant of the control point located in the middle of the constant-temperature zone and equal to the design temperature are smaller than the conventional control point of the air outlet central. Therefore, the control point equal to the design temperature can make the system react faster and the sensitivity is higher, which will help to make the high-precision control of the constant-temperature space. © 2020, Springer Nature Singapore Pte Ltd.

关键词： Dynamic response

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performance analysis of a hybrid solar energy, heat pump, and desiccant wheel air-conditioning system in low energy consumption building 11th

Performance analysis of a hybrid solar energy, heat pump, an...

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11th International Symposium on Heating, Ventilation and Air Conditioning, ISHVAC 2019

作者： Tian, Shaochen Su, Xing School of Mechanical Engineering Tongji University Shanghai China Key Laboratory of Performance Evolution and Control for Engineering Structures of Ministry of Education Tongji University Shanghai China

ISBN: (纸本)9789811395239

In hot and humid climate zone of China, a huge amount of building energy is consumed by conventional air-conditioners (CACs) in dehumidification especially in low energy consumption buildings where sensible load can be largely reduced by adopting high-performance building envelopes, but the moisture load is not changed. In this paper, a hybrid solar energy, heat pump, and desiccant wheel (HSHDW) system was proposed and the performance of the system was analyzed based on simulation studies. It was found that the evaporation temperature of the system should be kept at 12.8 and 9.7 °C on a typical day of summer and transition season separately. Compared with CACs, HSHDW system can provide a more comfortable thermal and humid indoor environment. The daily energy consumption of the HSHDW system is lower than that of the CAC, achieving great energy savings, especially for a typical weekday in summer, when a 16.8% daily energy saving is obtained. © Springer Nature Singapore Pte Ltd 2020.

关键词： Solar energy

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A Deep Learning Method for Building Façade Parsing Utilizing Improved Solov2 Instance Segmentation

SSRN

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SSRN 2023年

作者： Lu, Yujie Wei, Wei Li, Peixian Zhong, Tao Nong, Yuanjun Shi, Xing College of Civil Engineering Tongji University Shanghai200092 China Key Laboratory of Performance Evolution and Control for Engineering Structures of Ministry of Education Tongji University Shanghai200092 China Shanghai Institute of Intelligent Science and Technology Tongji University Shanghai200092 China College of Architecture and Urban Planning Tongji University Shanghai200092 China

Energy consumption simulation and renovation of existing buildings require accurate acquisition of building façade features which mostly relies on time-consuming manual calculations based on architectural drawings. In this article, we proposed an automated deep learning-based approach based on the SE module and BiFPN to achieve precise and efficient façade feature extraction. The approach eliminated the image distortion of building façades and then enabled accurate segmentation of windows and accessory structures even under the situation of occlusion and reflection. The improved SOLOv2 algorithm resulted in a high mean average precision of 93% for window segmentation, leading to a more precise window-to-wall ratio estimation with a mean absolute error of 2.9% than the experts’ estimation and existing deep learning-based methods. Considering the accurate results of façade parsing, our method can be utilized for city-level building feature extraction, providing theoretical and practical references for urban building energy simulation, urban renewal, and building health examination. © 2023, The Authors. All rights reserved.

关键词： Energy utilization

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CFD Simulations on Temperature control for an Organic Glass Sphere with High-Heat-Flux Sources 11th

CFD Simulations on Temperature Control for an Organic Glass ...

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11th International Symposium on Heating, Ventilation and Air Conditioning, ISHVAC 2019

作者： Zhao, Wenxuan Ye, Wei Wu, Chao Zhang, Xu School of Mechanical and Energy Engineering Tongji University Shanghai China Key Laboratory of Performance Evolution and Control for Engineering Structures of Ministry of Education Tongji University Shanghai China

ISBN: (纸本)9789811395192

A sphere-shaped experimental setup is assembled by organic glass via mass polymerization in a layer-by-layer manner from top (north pole) to bottom (south pole) in a cylindrical experimental hall. For each layer, the thermal bonding joints of both inner and outer surfaces need to be annealed by a heating belt with heat flux density of approximately 4200 W/m2. Due to the requirements of the experiment, the temperature should be controlled within the range of 21 ± 1 °C to avoid physical deformation. In this paper, rapid release and diffuse process of high heat (0–300 s) is simulated using transient CFD method and the applicability of two ventilation schemes, e.g., general ventilation and push–pull ventilation, is investigated. The temperature distributions of all the areas above the layer under polymerization and heat exhaust efficiency are used to evaluate the effects of different ventilation schemes on heat dilution. The results show that, first, the high heat release and diffusion results in rapid buoyancy and general ventilation alone cannot maintain temperature increment. Second, the push–pull ventilation can effectively minimize the buoyancy caused by the heating sources and maintain thermal environment and increase the heat exhaust efficiency. © 2020, Springer Nature Singapore Pte Ltd.

关键词： Ventilation

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A Deep Learning Method for Building Façade Parsing Utilizing Improved SOLOv2 Instance Segmentation

SSRN

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SSRN 2023年

Energy consumption simulation and renovation of existing buildings require accurate acquisition of building façade features which mostly relies on time-consuming manual calculations based on architectural drawings. In this article, we proposed an automated deep learning-based approach based on the SE module and BiFPN to achieve precise and efficient façade feature extraction. The approach eliminated the image distortion of building façades and then enabled accurate segmentation of windows and accessory structures even under the situation of occlusion and reflection. The improved SOLOv2 algorithm resulted in a high mean average precision of 93% for window segmentation, leading to a more precise window-to-wall ratio estimation with a mean absolute error of 2.9% than the experts' estimation and existing deep learning-based methods. Considering the accurate results of façade parsing, our method can be utilized for city-level building feature extraction, providing theoretical and practical references for urban building energy simulation, urban renewal, and building health examination. © 2023, The Authors. All rights reserved.

关键词： Energy utilization

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A preliminary field study on using air cleaners to substitute mechanical ventilation in an open office in Shanghai 16

A preliminary field study on using air cleaners to substitut...

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16th Conference of the International Society of Indoor Air Quality and Climate: Creative and Smart Solutions for Better Built Environments, Indoor Air 2020

作者： Fan, Yujie Zhi, Chengqiang Chen, Zean Ye, Wei Zhang, Xu School of Mechanical Engineering Tongji University Shanghai201804 China Key Laboratory of Performance Evolution and Control for Engineering Structures Ministry of Education Tongji University Shanghai200092 China

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Modelling the effect of fatigue damage on chloride diffusion coefficient of concrete

Modelling the effect of fatigue damage on chloride diffusion...

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2020 fib Symposium: Concrete structures for Resilient Society

作者： Fang, Jing Jiang, Chao Gu, Xiang-Lin Key Laboratory of Performance Evolution and Control of Engineering Structures of Ministry of Education Tongji University Shanghai China Department of Structural Engineering College of Civil Engineering Tongji University Shanghai China

ISBN: (纸本)9782940643042

Concrete bridges usually undergo repeated vehicle or train loads which will cause fatigue growth of micro-cracks of concrete and hence accelerate the penetration of chloride ions into concrete. In this paper, a multi-scale method is proposed to characterize the effect of fatigue damage on the chloride diffusivity of concrete. First, concrete is considered as a two-phase composite material composed of mortar and coarse aggregates. Residual strain of concrete is used to characterize the effects of fatigue loads and the generalized self-consistent model is implemented to determine residual strains of aggregates and surrounding mortar in concrete. The fatigue damage of concrete is then assumed to reside in both the damaged mortar matrix and the cracked/crushed zones between the damaged mortar matrix and coarse aggregates. Furthermore, through elastic mechanical analysis, the volume of cracked/crushed zone is estimated as a function of residual strain of concrete caused by fatigue loads. Then the fatigue-damaged concrete is further considered as a three-phase composite material composed of coarse aggregates, damaged mortar matrix and cracked/crushed zone between them. With the specific chloride diffusion coefficients of all three components reported by the literature and their respective volume fractions calculated by the authors, the chloride diffusion coefficient of fatigue damaged concrete can be calculated by the generalized self-consistent scheme. Several chloride penetration tests on fatigue damaged concrete are collected to validate the proposed chloride diffusion coefficient model. It is found that the predicted values of chloride diffusion coefficient in fatigue damaged concrete are in acceptable agreement with those reported by experimental results. In summary, the proposed model of chloride diffusion coefficient in fatigue damaged concrete will contribute to more accurate predictions for chloride ion penetration into concrete in bridges. Moreover, the multi-sc

关键词： Fatigue damage

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Macro-Cell Corrosion between Crossed Steel Bars in Cracked Concrete

SSRN

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SSRN 2022年

作者： Jin, Zhi-Hao Jiang, Chao Gu, Xiang-Lin Dong, Zheng Key Laboratory of Performance Evolution and Control for Engineering Structures Ministry of Education Tongji University Shanghai200092 China Department of Structural Engineering College of Civil Engineering Tongji University Shanghai200092 China College of Civil Engineering Zhejiang University of Technology Hangzhou310023 China

To investigate the corrosion behavior of coupled crossed steel bars in cracked concrete, a study on the influence of crack width [[EQUATION]] and crack location [[EQUATION]] on the microcell and macro-cell corrosion of coupled crossed steels in cracked concrete is presented. The corrosion process of crossed steel bars in concrete specimens with crack widths of 0, 0.1, 0.2, 0.5 and 1.0 mm, respectively, were continuously monitored in an artificially created chloride environment for 26 weeks. The results showed that the corrosion of steel bars in cracked areas was much severer than that of steel bars in uncracked areas. Both microcell corrosion current ( [[EQUATION]] ) and macro-cell corrosion current [[EQUATION]] of coupled active steel bars in a cracked area increased with the increase of the transverse crack width, and [[EQUATION]] was found to be more sensitive to the change of crack width. The [[EQUATION]] ratio decreased with time, which meant that while macro-cell corrosion made a fair contribution, microcell corrosion played a dominant role in the whole corrosion period. In addition, the distance between the concrete crack and the intersection of the crossed steel bars, defined as the crack location [[EQUATION]] in the study, was proved to have a significant impact on the value and the direction of total macro-cell corrosion current [[EQUATION]] . © 2022, The Authors. All rights reserved.

关键词： Bars (metal)

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