The Experts below are selected from a list of 132507 Experts worldwide ranked by ideXlab platform
Mingyi Zhang - One of the best experts on this subject based on the ideXlab platform.
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enhancement of convective Cooling of the porous crushed rock layer in cold regions based on experimental investigations
International Communications in Heat and Mass Transfer, 2017Co-Authors: Mingyi Zhang, Shuangyang LiAbstract:Abstract A crushed-rock layer, because of its pore-air convective Cooling Effect, has been widely used to adjust the geotemperature of the permafrost stratum in cold regions. To optimize the control measure, a series of experiments have been conducted. The convective heat transfer capability of crushed-rock layers with different thicknesses is evaluated. The experimental results indicate that: 1) forced convection occurs during warm period and mixed convection occurs during cold period. The Cooling performance is mainly determined by the forced convective heat transfer process; 2) pore-air flow pattern can change thermal resistance of the crushed-rock layer. Larger thermal resistance can reduce heat accumulation during the warm period and smaller thermal resistance can strengthen heat transfer during the cold period; and 3) there exists an optimal thickness to enhance the convective Cooling Effect. Under the experimental conditions, the optimum thickness is close to 1.3 m. These findings are helpful to the construction of cold regions engineering. If the thickness of crushed rock revetment could be reasonably designed, the well convective Cooling Effect can be achieved and the construction costs will also be reduced.
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experimental study on influence of particle size on Cooling Effect of crushed rock layer under closed and open tops
Cold Regions Science and Technology, 2007Co-Authors: Mingyi Zhang, Yuanming Lai, Zhijun HuangAbstract:Abstract A series of Laboratory studies were carried out on the Cooling Effects of crushed rock layers with different particle sizes under closed and open tops. The thicknesses of crushed-rock layers are 130 cm and the mean particle sizes are 8.3 cm, 14.8 cm, 22.1 cm and 27.1 cm, respectively. The experimental results indicate that the Cooling Effects of the crushed-rock layers with open tops are less than those with closed tops under the same experimental conditions. Under closed top, the crushed-rock layers with different particle sizes have a similar Cooling tendency and good Cooling Effects on the underlying soil layers; however, the Cooling Effect is best when the mean particle size is 22.1 cm. Under open top, the crushed-rock layers have some Cooling Effects and their bottom mean periodic temperatures are below 0 °C when their mean particle sizes are from 14.8 to 27.1 cm; however, the crushed-rock layer with mean particle size of 8.3 cm does not result in its bottom mean periodic temperature lower than the ambient temperature (about 0.5 °C) in the model box. The periodic temperature ranges at the bottoms of crushed-rock layers under open top are far larger than those under closed top. The particle size has little influence on the bottom periodic temperature range under closed top, however, the influence is more obvious under open top. Therefore, if the Cooling characteristics of crushed-rock layers with different particle sizes under open and closed tops can be reasonably utilized in cold regions engineering, the underlying permafrost can be Effectively protected and cost can been reduced.
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numerical analysis for Cooling Effect of open boundary ripped rock embankment on qinghai tibetan railway
Science China-earth Sciences, 2006Co-Authors: Yuanming Lai, Mingyi Zhang, Zhiqiang LiuAbstract:The heat convection of fluid inside the ballast layer and ripped-rock layer, which are regarded as porous media in railway embankment, is a process of heat and mass transfer. At present, the ripped-rock embankment, as a new type of embankment structure, has widely been used in the construction of Qinghai-Tibetan railway. However, because its ripped-rock layer is almost open in two bilateral boundaries and closed at top and bottom, and air can flow into/out of the ballast layer and ripped-rock layer, the convection and transfer heat patterns are very complicated in the embankment. Therefore, based on the temperature and geology conditions of the Qinghai-Tibetan Plateau, a numerical approach of the unsteady two-dimensional continuity, momentum (non-Darcy flow) and energy equations of heat convection for incompressible fluid in porous media is provided to analyze the velocity and temperature characteristics of the ripped-rock embankment with different embankment heights under open boundary condition for the coming 50 years in this paper. The calculated results indicate that, due to the influence of the outside wind, the convective heat transfer mainly relies on the forced convection in the open ripped-rock embankment. Even if the air temperature will be warmed up by 2.6°C in the coming 50 years, it still has a better Cooling Effect on the underlying soils and a low temperature frozen-soil core is formed in the permafrost below it if the embankment is constructed in the regions whose present mean annual air temperature is −4.0°C. Furthermore, the Cooling Effect of high ripped-rock embankment is better than that of low embankment. This is because the wider bottom of high embankment has a more influence dimension on the underlying frozen soil. However, cardinal winds on the Qinghai-Tibetan Plateau disturb its convection pattern, so that an asymmetric temperature distribution occurs under high embankment and it is possible to induce a transverse uneven deformation of embankment, but no similar situation occurs under low embankment. This asymmetric temperature field problem should be considered when ripped-rock embankment is designed and constructed.
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influence of boundary conditions on the Cooling Effect of crushed rock embankment in permafrost regions of qinghai tibetan plateau
Cold Regions Science and Technology, 2006Co-Authors: Mingyi Zhang, Wenbing YuAbstract:Abstract The crushed-rock layer is a highly porous medium that has been used to ensure the stability of embankment in permafrost regions. At present, depending on different boundary conditions (impermeable and permeable) of crushed-rock layer in embankment, the crushed-rock embankments are divided into two kinds of structures in the construction of Qinghai–Tibetan railway in China. One is a closed-boundary crushed-rock embankment; the other is an open-boundary crushed-rock embankment. In order to investigate the influence of boundary conditions (impermeable and permeable) on the Cooling Effect of a crushed-rock embankment, two numerical models of the unsteady two-dimensional hydrokinetic equations for incompressible fluid are presented to analyze the velocity and temperature characteristics of crushed-rock embankment with different embankment heights under impermeable and permeable boundary conditions for a period of 50 years. The results indicate: (1) the boundary conditions (impermeable and permeable) of crushed-rock embankment can have a very large impact on the heat transfer pattern within it in windy permafrost regions of Qinghai–Tibetan Plateau. The Cooling Effect of the closed crushed-rock embankment mainly relies on natural convection within crushed-rock layer, which is caused by the thermal boundary condition, but the Cooling Effect of the open crushed-rock embankment is due to the heat transfer enhancement because of internal forced convection induced by the external low temperature air flow (wind); (2) from the temperature distributions of crushed-rock embankments, it can be found that, under the assumption that the air temperature will be warmed up by 2.6 °C in a period of 50 years and in the areas where the mean annual air temperature is − 4.0 °C, when embankment is low, the Cooling Effects of crushed-rock embankment have no obvious difference under the two boundary conditions, and the Cooling Effect of closed crushed-rock embankment is only a little better than that of open one; however, when embankment is high, the boundary conditions cause a distinct influence on the temperature distribution of crushed-rock embankment, and the Cooling Effect under the permeable boundary condition is far better than that under the impermeable boundary condition. However, the asymmetric temperature distribution problem of the high crushed-rock embankment, caused by permeable boundary and external wind, must be considered when it is designed and constructed.
Jing Dong - One of the best experts on this subject based on the ideXlab platform.
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quantitative study on the Cooling Effect of green roofs in a high density urban area a case study of xiamen china
Journal of Cleaner Production, 2020Co-Authors: Jing DongAbstract:Abstract Green roofs are thought to be an Effective measure to solve the contradiction between land shortages and ecological construction, especially address urban heat island (UHI) Effects in high-density urban areas. However, few empirical studies have focused on the Cooling Effect of green roof projects at urban scales. This study quantified the Cooling Effect of green roofs in Xiamen Island, China, where 540,000 m2 of green roofs were implemented between 2015 and 2017, in order to address the two research questions: (1) do green roofs in high-density urban areas have a significant Cooling Effect at the city scale and (2) what is the extent of the Cooling? The relative difference between the average land surface temperature (LST) of Xiamen Island and the green roofs stemmed from Landsat 8 remote sensing image in the summers of 2014 and 2017 were calculated in geographic information systems (GIS) to represent the Cooling Effect of green roof project. Results showed that: (1) the average LST difference between green roofs and Xiamen Island decreased by 0.91 °C, indicating that green roofs could Effectively alleviate UHI Effects in high-density urban areas; (2) The Cooling Effect was significant up to 100 m from the green roof installation in Xiamen Island, we called it as characteristic Cooling buffer zone; (3) Regression analysis revealed that for every 1000 m2 increase in green roof area, the average LST of the roof and its characteristic Cooling buffer zone decreased by 0.4 °C. These findings provide the empirical proof for the Cooling Effect of green roofs on the surrounding environment in high-density urban areas and important insights for urban planners and government agencies for the Effective mitigation of UHI impacts.
Shuangyang Li - One of the best experts on this subject based on the ideXlab platform.
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enhancement of convective Cooling of the porous crushed rock layer in cold regions based on experimental investigations
International Communications in Heat and Mass Transfer, 2017Co-Authors: Mingyi Zhang, Shuangyang LiAbstract:Abstract A crushed-rock layer, because of its pore-air convective Cooling Effect, has been widely used to adjust the geotemperature of the permafrost stratum in cold regions. To optimize the control measure, a series of experiments have been conducted. The convective heat transfer capability of crushed-rock layers with different thicknesses is evaluated. The experimental results indicate that: 1) forced convection occurs during warm period and mixed convection occurs during cold period. The Cooling performance is mainly determined by the forced convective heat transfer process; 2) pore-air flow pattern can change thermal resistance of the crushed-rock layer. Larger thermal resistance can reduce heat accumulation during the warm period and smaller thermal resistance can strengthen heat transfer during the cold period; and 3) there exists an optimal thickness to enhance the convective Cooling Effect. Under the experimental conditions, the optimum thickness is close to 1.3 m. These findings are helpful to the construction of cold regions engineering. If the thickness of crushed rock revetment could be reasonably designed, the well convective Cooling Effect can be achieved and the construction costs will also be reduced.
Jan Carmeliet - One of the best experts on this subject based on the ideXlab platform.
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parametric study of the influence of environmental factors and tree properties on the transpirative Cooling Effect of trees
Agricultural and Forest Meteorology, 2018Co-Authors: Lento Manickathan, Thijs Defraeye, Jonas Allegrini, Dominique Derome, Jan CarmelietAbstract:Abstract Vegetation can provide transpirative Cooling in cities and is therefore being increasingly integrated as an essential part of Urban Heat Island (UHI) mitigation strategies. However, the behaviour of vegetation must be accurately understood to determine the Effectiveness of vegetation based solutions. In this study, vegetation is modelled as a porous medium in a computational fluid dynamics model for flow of moist air, where a leaf energy balance model is used to determine the heat fluxes. We study the Cooling Effect of a single row of trees at noon with solar altitude at 90° for various environmental factors (wind speed, air temperature, relative humidity and solar radiation intensity) and tree properties (leaf size, stomatal resistance and leaf area density). Furthermore, the influence of tree height and number of tree rows on the Cooling Effect are studied. The Universal Thermal Climate Index (UTCI) around the trees is estimated to determine the impact of transpirative Cooling on pedestrian thermal comfort. The study shows that, at low wind speeds, pedestrians would only perceive a local benefit of transpirative Cooling. However, vegetation extracts overall more heat from the flow at higher wind speeds. A study on the influence of environmental conditions quantifies to which extent a single row of trees provide maximum Cooling during hot and dry conditions. The shading provided by trees improves thermal comfort more that transpirative Cooling of a single row of trees. Furthermore, taller trees are more beneficial as the vegetation canopy with high leaf temperatures is further away from the pedestrian level.
Xiang Dong Xiao - One of the best experts on this subject based on the ideXlab platform.
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the influence of the spatial characteristics of urban green space on the urban heat island Effect in suzhou industrial park
Sustainable Cities and Society, 2018Co-Authors: Xiang Dong Xiao, Li Dong, Nan Yang, Yimei XiongAbstract:Abstract Urban green spaces can mitigate urban warming problems to some extent. However, the Cooling Effect of plants differs spatially and temporally, and with plant features. To understand how plants affect urban surface and air temperature, 15 urban green spaces in Suzhou Industrial Park were selected to study the diurnal variation of summer air temperature. At the same time, the mitigation Effect of different types of green spaces on the urban heat island (UHI) Effect was investigated and further research was undertaken on the Effect of green space area, perimeter area ratio, green space average canopy density, average leaf area index (LAI), and other factors influencing the Cooling Effect. Based on these studies, three representative parks were selected as samples to investigate the Cooling Effect of urban green space in terms of the water and wind environment. It was found that in the summer, large green spaces had a stable Cooling and humidifying Effect, while small green spaces had the opposite Effect. The Cooling and humidifying Effect of large green spaces was more obvious and stable, and the Cooling Effect of small green spaces was more variable, with a heat preservation phenomenon occurring in some cases. The Cooling Effect of each green area was positively correlated with the green area, the average LAI of green space, and the average canopy density of green space. The Cooling Effect of each green area was significantly negatively correlated with the green area perimeter. Water bodies within green spaces did not contribute to Cooling; however, the Cooling Effect was related to the wind environment. From the perspective of the planning and construction of city green spaces it is important to increase the green area and the reasonable planning green perimeter area ratio; however, suitable tree species should be selected in the greening process. The Effect of urban greening in improving the urban ecological environment has been established. It was concluded that the Cooling Effects of such green areas are largely determined by plant type, canopy density, and park shapes. Therefore, it is suggested that a stronger emphasis is placed on the selection of plant species and the design of park shapes to achieve environmental Cooling Effects.