本文在新型换热器冷通道内,对超临界状态下LNG的对流换热过程进行数值模拟,分别研究入口温度、入口质量流量和壁面热流密度对超临界甲烷流动与换热特性的影响,提出一种在直通道中加入凹槽结构的强化换热模型。首先采用Ansys Space Clai...本文在新型换热器冷通道内,对超临界状态下LNG的对流换热过程进行数值模拟,分别研究入口温度、入口质量流量和壁面热流密度对超临界甲烷流动与换热特性的影响,提出一种在直通道中加入凹槽结构的强化换热模型。首先采用Ansys Space Claim对换热通道进行几何建模,再使用Siemens STAR-CCM+仿真软件对模型进行网格划分和求解。研究发现:局部对流换热系数随着入口温度的升高有所降低,努塞尔数变化趋势与局部对流换热系数变化趋势大致相同,在斜通道内,超临界LNG具有更好的换热性能;当通道入口质量流量和壁面热流密度增加时,局部对流换热系数也随之增大;凹槽结构对换热器换热性能有较大的提升,对综合性能的提升较小。展开更多
The crushed-rock revetment, considered as a highly porous medium, is often applied to embankment slope to protect the underlying permafrost and ensure the thermal stability of roadway in permafrost regions. In this pa...The crushed-rock revetment, considered as a highly porous medium, is often applied to embankment slope to protect the underlying permafrost and ensure the thermal stability of roadway in permafrost regions. In this paper, in order to increase and optimize the cooling capacity of crushed-rock revetment in cold regions roadway engineering, based on the thermal convection theories, the practical geometry and the temperature characteristics of in-situ crushed-rock revetment, convective pattern and cooling effect of crushed-rock revetment are numerically studied, with a thickness of 1.0 m under different geometrical parameters, e.g. sloped angle and aspect ratio. The results indicate that, with a thickness of 1.0 m and a temperature difference of 10.0 ℃ between top and bottom boundaries, due to the existence of natural convection, the effective thermal conductivity of crushed-rock revetment can be increased and the thermal "semi-conductor" characteristics are endowed. However, the convective pattern changes with the variation of the sloped angle, namely, with the increase of the sloped angle, the convection cell number decreases; furthermore, when the flow changes from various cells to a single cell at a sloped angle, the Nu number is the smallest and the cooling effect is the worst, therefore, the corresponding sloped angle is considered as the worst cooling sloped angle. Besides, with the increase of the aspect ratio, the worst cooling sloped angle increases and tends to 32°, also approaching to the in-situ crushed-rock revetment angle 33.7°. Therefore, when the crushed-rock revetment em-bankment is too high, that is to say, the aspect ratio of the sloped crushed-rock revetment is too large, some measures should be taken to enhance its cooling effect, which have been researched and discussed in this paper. It is hoped that some scientific references can be supplied to the design and maintenance of the crushed-rock revetment embankment in cold regions.展开更多
The worldwide proven recoverable reserves of conventional oil are less than the amount of the heavy oil.Owing to weakly consolidated formation,sand production is an important problem encountered during oil production ...The worldwide proven recoverable reserves of conventional oil are less than the amount of the heavy oil.Owing to weakly consolidated formation,sand production is an important problem encountered during oil production in heavy oil reservoirs,for which frac-pack technique is one of the most common treatments.Hence,how to obtain the optimal fracture geometry is the key to increasing well production and preventing sand.Due to the faultiness that current optimization of the fracture geometry only depends on well productivity,fracture-flow fraction was used to describe the contribution of the fracture collecting and conducting fluids from the reservoir.The higher the fracture-flow fraction,the more likely bilinear flow pattern occurs,thus leading to smaller flow resistance and better results in oil productivity and sand prevention.A reservoir numerical simulation model was established to simulate the long-term production dynamic of a fractured well in rectangular drainage areas.In order to reach the aim of increasing productivity meanwhile preventing sand,a new method based on Unified Fracture Design was developed to optimize the fracture geometry.For a specific reservoir and a certain amount of proppant injected to the target layer,there exits an optimal dimensionless fracture conductivity which corresponds to the maximum fracture-flow fraction,accordingly we can get the optimal fracture geometry.The formulas of the optimal fracture geometry were presented on square drainage area conditions,which are very convenient to apply.Equivalent Proppant Number was used to eliminate the impact of aspect ratios of rectangular drainage area,then,the same method to optimize the fracture geometry as mentioned for square drainage areas could be adopted too.展开更多
文摘本文在新型换热器冷通道内,对超临界状态下LNG的对流换热过程进行数值模拟,分别研究入口温度、入口质量流量和壁面热流密度对超临界甲烷流动与换热特性的影响,提出一种在直通道中加入凹槽结构的强化换热模型。首先采用Ansys Space Claim对换热通道进行几何建模,再使用Siemens STAR-CCM+仿真软件对模型进行网格划分和求解。研究发现:局部对流换热系数随着入口温度的升高有所降低,努塞尔数变化趋势与局部对流换热系数变化趋势大致相同,在斜通道内,超临界LNG具有更好的换热性能;当通道入口质量流量和壁面热流密度增加时,局部对流换热系数也随之增大;凹槽结构对换热器换热性能有较大的提升,对综合性能的提升较小。
基金Supported by the National Natural Science Foundation of China (Grant Nos.40601023 and 40730736)the Special Funding for "Prize for Excellent Student" (to Dr. ZHANG Mingyi),awarded by the President of the Chinese Academy of Sciencesthe Western Program of the Chinese Academy of Sciences (Grant No.KZCX2-XB2-10)
文摘The crushed-rock revetment, considered as a highly porous medium, is often applied to embankment slope to protect the underlying permafrost and ensure the thermal stability of roadway in permafrost regions. In this paper, in order to increase and optimize the cooling capacity of crushed-rock revetment in cold regions roadway engineering, based on the thermal convection theories, the practical geometry and the temperature characteristics of in-situ crushed-rock revetment, convective pattern and cooling effect of crushed-rock revetment are numerically studied, with a thickness of 1.0 m under different geometrical parameters, e.g. sloped angle and aspect ratio. The results indicate that, with a thickness of 1.0 m and a temperature difference of 10.0 ℃ between top and bottom boundaries, due to the existence of natural convection, the effective thermal conductivity of crushed-rock revetment can be increased and the thermal "semi-conductor" characteristics are endowed. However, the convective pattern changes with the variation of the sloped angle, namely, with the increase of the sloped angle, the convection cell number decreases; furthermore, when the flow changes from various cells to a single cell at a sloped angle, the Nu number is the smallest and the cooling effect is the worst, therefore, the corresponding sloped angle is considered as the worst cooling sloped angle. Besides, with the increase of the aspect ratio, the worst cooling sloped angle increases and tends to 32°, also approaching to the in-situ crushed-rock revetment angle 33.7°. Therefore, when the crushed-rock revetment em-bankment is too high, that is to say, the aspect ratio of the sloped crushed-rock revetment is too large, some measures should be taken to enhance its cooling effect, which have been researched and discussed in this paper. It is hoped that some scientific references can be supplied to the design and maintenance of the crushed-rock revetment embankment in cold regions.
基金supported by the National Science and Technology Major Projects of China (Grant No. 2008ZX05024-03-003-004)
文摘The worldwide proven recoverable reserves of conventional oil are less than the amount of the heavy oil.Owing to weakly consolidated formation,sand production is an important problem encountered during oil production in heavy oil reservoirs,for which frac-pack technique is one of the most common treatments.Hence,how to obtain the optimal fracture geometry is the key to increasing well production and preventing sand.Due to the faultiness that current optimization of the fracture geometry only depends on well productivity,fracture-flow fraction was used to describe the contribution of the fracture collecting and conducting fluids from the reservoir.The higher the fracture-flow fraction,the more likely bilinear flow pattern occurs,thus leading to smaller flow resistance and better results in oil productivity and sand prevention.A reservoir numerical simulation model was established to simulate the long-term production dynamic of a fractured well in rectangular drainage areas.In order to reach the aim of increasing productivity meanwhile preventing sand,a new method based on Unified Fracture Design was developed to optimize the fracture geometry.For a specific reservoir and a certain amount of proppant injected to the target layer,there exits an optimal dimensionless fracture conductivity which corresponds to the maximum fracture-flow fraction,accordingly we can get the optimal fracture geometry.The formulas of the optimal fracture geometry were presented on square drainage area conditions,which are very convenient to apply.Equivalent Proppant Number was used to eliminate the impact of aspect ratios of rectangular drainage area,then,the same method to optimize the fracture geometry as mentioned for square drainage areas could be adopted too.
