Confluence and cold shut computation based on time field in casting simulation

Numerical simulation technology has been widely used in the foundry industry to analyze and improve casting processes.During the casting filling process,many filling-related defects form easily at the confluences of liquid metal streams.The main filling-related defects are cold shut defects.To calculate the positions of casting defects,the characteristics of liquid metal confluences were analyzed.The flow front of liquid metal was captured by the volume-of-fluid algorithm to obtain a time field,which was used to calculate the time derivatives of the liquid front position and the confluences of liquid metal streams.To distinguish small confluences from the main confluences,the concept of confluent scale was developed,which was used to filter the small confluences based on a threshold.The calculation process was demonstrated through the post-processing of numerical simulation.A "W" shaped casting and a steering wheel casting were calculated to validate the accuracy of the method developed in this study.The positions of cold shut defects were predicted by calculating the confluences of liquid metal streams.The method was proved to be practical by comparing the calculation results with the positions of cold shut defects in an end cover casting.The computation of confluences and cold shut defects can improve the analysis efficiency and provide assurance for the optimization of a casting process plan.

Transient Hydraulic Performance and Numerical Simulation of a Centrifugal Pump with an Open Impeller during Shutting Down

In this paper, the transient behavior of a low specific speed centrifugal pump with straight blades during shutting down is studied through the experimental test, theoretical calculation, and numerical simulation. The variations of the rota- tional speed, flow rate, and head with time are obtained in experiment. Based on the experimental results of the rota- tional speed and flow rate, the additional theoretical heads are quantitatively calculated and analyzed. The experimental results of the rotational speed and flow rate are worked as the boundary conditions to accurately accomplish the nu- merical simulation of the transient flow during shutting down. The experimental results show that the decrease history of the flow rate evidently lags behind that of the rotational speed, while the rotational speed slightly lags behind the head. Theoretical analysis shows that there exists a clear negative head impact phenomenon in the process of stopping. The transient behavior of the centrifugal pump with straight blades mainly comes from the rotation deceleration of im- peller, and has nothing to do with the fluid deceleration. The numerical simulations show that a large area backflow can be seen when the rotational speed decreases to zero due to the flowing inertia. In conclusion, the numerical simulation of the flow field is in good agreement with the internal flow theory of centrifugal pumps.

Leak-off behavior and water shut-off performance of a polymer/chromium(Cr^(3+)) gel in fractured media

During gel treatments for fractures, the leak-off behavior of gelant has a great effect on the water shut-off performance of gel. Experiments were carried out using a polymer/chromium(Cr^(3+)) gel system to explore the leak-off behavior and the water shut-off performance of gel in fractured media. Results of the gelant leak-off study show that the gelant leak-off from fracture into matrix contributes to the formation of the gelant leak-off layer during the gelant injection. Moreover, because of the gradual formation of the gelant leak-off layer along fracture, the initial leak-off ratio of gelant is relatively high, but it declines and finally levels off with the increase of the injection volume. The polymer concentration of gelant has a great effect on the chromium output in fluids produced from fractures. With the increase of the polymer concentration, the chromium concentration first decreases and then increases, and the leak-off depth of gelant into matrix is gradually reduced. Results of the water shut-off study present that the decrease of the chromium concentration inside the fracture greatly reduces the water shut-off performance after the gel formation. Therefore, because of the relatively high degree of chromium leak-off, enough injection volume of gelant is essential to ensure the sufficient chromium concentration inside the fracture and to further achieve a favorable water shut-off performance. On the premise of gel strength assurance inside the fracture, the water shut-off performance of gel gradually declines with the extension of the distance from the fracture inlet, and different leak-off degrees of gelant along the fracture are responsible for this phenomenon. Therefore, a proper degree of gelant leak-off contributes to enhancing the water shut-off performance of gel for fractures.

Analysis of Factors Influencing Shut in Pressure Cone in Offshore Strong Bottom Water Reservoir

X oilfield is an offshore strong bottom water reservoir with water cut up to 96% at present, and liquid extraction has become one of the main ways to increase oil production. However, the current liquid production of the oilfield reaches 60,000 m3/d due to the limitation of offshore platform, well trough and equipment, the oilfield is unable to continue liquid extraction. In order to maximize the oil production of the oilfield, it is necessary to study the strategy of shut in and cone pressure. Through numerical simulation, this paper analyzes the influence of different factors, such as crude oil density, viscosity, reservoir thickness, interlayer, permeability and so on, on the drop height of water cone and the effect of precipitation and oil increase after well shut in. At the same time, the weight of each factor is analyzed by combining the actual dynamic data with the fuzzy mathematics method, and the strategy of well shut in and cone pressure is formulated for the offshore strong bottom water reservoir. It provides the basis and guidance for the reasonable use of shut in pressure cone when the reservoir with strong bottom water meets the bottleneck of liquid volume.

Dynamic Model and Performance of Absorption Heat Pump in Shut-down Process

The dynamic model of LiBr absorption heat pump in shut-down process is established. The simulation results show good agreement with the experiments. The dynamic performance of high-pressure generator, low-pressure generator and heat exchanger are analyzed in detail. The proper shut-down mode of the heat pump is presented,which, in consideration of solution parameters, has a great effect on the possibility of crystallization of some components.

Geothermal Investigations in Permafrost Regions—The Duration of Temperature Monitoring after Wellbores Shut-In

The most important data on the thermal regime of the Earth’s interior come from temperature measurements in deep boreholes. The drilling process greatly alters the temperature field of formations surrounding the wellbore. In permafrost regions, due to thawing of the formation surrounding the wellbore during drilling, representative data can be obtained only by repeated observations over a long period of time (up to 10 years). Usually a number of temperature logs (3 - 10) are taken after the well’s shut-in. Significant expenses (manpower, transportation) are required to monitor the temperature regime of deep wells. In this paper we show that in most of the cases (when the time of refreezing formations is less than the shut-in time) two temperature logs are sufficient to predict formations temperatures during shut-in, to determine the geothermal gradients, and to evaluate the thickness of the permafrost zone. Thus the cost of monitoring the temperature regime of deep wells after shut-in can be drastically reduced. A simple method to process field data (for the well sections below and above the permafrost base) is presented. Temperature logs conducted in two wells were used to demonstrate utilization of this method.

Mechanism and prevention method of drill string uplift during shut-in after overflow in an ultra-deep well

Drill string will sustain large uplift force during the shut-in period after gas overflow in an ultra-deep well, and in serious case, it will run out of the wellhead. A calculation model of uplift force was established to analyze dynamic change characteristics of the uplift force of drill string during the shut-in period, and then a management procedure for the uplift risk during the shut-in period after gas overflow in the ultra-deep well was formed. Cross section method and pressure area method were used to analyze the force on drill string after shut-in of well, it was found that the source of uplift force was the "fictitious force" caused by the hydrostatic pressure in the well. When the fictitious force is in the opposite direction to the gravity, it is the uplift force. By adopting the theory of annular multiphase flow, considering the effects of wellbore afterflow and gas slippage, the dynamic change of the pressure and fluid in the wellbore and the uplift force of drill string during the shut-in period were analyzed. The magnitude and direction of uplift force are related to the length of drill string in the wellbore and shut-in time, and there is the risk of uplift of drill string when the length of drill string in the wellbore is smaller than the critical drill string length or the shut in time exceeds the critical shut in time. A set of treatment method and process to prevent the uplift of drill string is advanced during the shut-in period after overflow in the ultra-deep well, which makes the risk management of the drill string uplift in the ultra-deep well more rigorous and scientific.

Open and Shut Up

Doctor: Please open your wouth,madam.Lady:Thank you

Shutting the Door

China pledges to crack down on counterfeit products to Africa MANY people who have traveled in Africa and visited some of many Chinese retail outlets across the continent have encountered cheap fake items on the shelves,which not only present a bad image of China’s manufacturing abilities but also infringe on the intellectual property rights of others.

Study on durability of Pt supported on graphitized carbon under simulated start-up/shut-down conditions for polymer electrolyte membrane fuel cells

The primary issue for the commercialization of proton exchange membrane fuel cell(PEMFC) is the carbon corrosion of support under start-up/shut-down conditions. In this study, we employ the nanostructured graphitized carbon induced by heat-treatment. The degree of graphitization starts to increase between 900 and 1300 ℃ as evidenced by the change of specific surface area, interlayer spacing, and ID/IG value. Pt nanoparticles are deposited on fresh carbon black(Pt/CB) and carbon heat-treated at 1700 ℃(Pt/HCB17) with similar particle size and distribution. Electrochemical characterization demonstrates that the Pt/HCB17 shows higher activity than the Pt/CB due to the inefficient microporous structure of amorphous carbon for the oxygen reduction reaction. An accelerating potential cycle between 1.0 and 1.5 V for the carbon corrosion is applied to examine durability at a single cell under the practical start-up/shutdown conditions. The Pt/HCB17 catalyst shows remarkable durability after 3000 potential cycles. The Pt/HCB17 catalyst exhibits a peak power density gain of 3%, while the Pt/CB catalyst shows 65% loss of the initial peak power density. As well, electrochemical surface area and mass activity of Pt/HCB17 catalyst are even more stable than those of the Pt/CB catalyst. Consequently, the high degree of graphitization is essential for the durability of fuel cells in practical start-up/shut-down conditions due to enhancing the strong interaction of Pt and π-bonds in graphitized carbon.

On-site raw gas cut-off during the shut down of Baosteel phaseⅠcoke ovens

The preparation and implementation of rawcoke oven gas cut-off,which was the key process involved with shutting down the Baosteel phase I coke ovens,were investigated,and the main technical points and countermeasures are presented.

华龙一号安注系统电动截止阀可靠性试验及评估研究

作为核反应堆系统中的关键设备,阀门在核反应堆系统中起着至关重要的作用,其可靠性直接决定着核反应堆安全以及人员安全。本文针对华龙一号安注系统电动截止阀,采用3个试验样机开展可靠性试验,通过模拟使用工况下的冷热态寿命试验,获得了该型阀门的典型失效——阀座内漏,并基于试验数据采用小子样试验的半经验评估方法完成了可靠性评估,确定该安注系统电动截止阀全寿期无故障动作360次的可靠度大于0.99。

核级典型电动截止阀FMECA及试验验证

作为核反应堆系统中的关键能动设备,阀门在核反应堆系统中起着至关重要的作用,其安全性直接决定着核反应堆安全及人员安全。本文针对安注系统电动截止阀,基于使用特点对其开展故障模式、影响及危害性分析(FMECA),找出其结构中潜在的故障模式及其原因与影响,并根据失效分析结果有针对性地开展寿命试验,以激发潜在的故障,验证分析结果并获得该阀最为典型的失效模式。

中国固定式燃气内燃机环境管理的形势、问题和对策

固定式燃气内燃机是实现碳减排富有成效的技术方案之一,但其相应的环境管理略滞后,应尽快制定固定式燃气内燃机排放标准,且在环境管理体系中明确固定式燃气内燃机“非正常情况”下的达标判定依据。典型机组在线监测结果显示,监测期间NO_(x)排放小时质量浓度介于0~305 mg/m^(3);NO_(x)与CO均出现不同程度的排放超标现象,超标小时数分别为61、4 h,分别占有效小时数的9.8%、0.6%;NH_(3)质量浓度为0.94 mg/m^(3),排放达标。结果表明,选择性催化还原技术(SCR)系统与生产设备不同步投运是造成内燃机启动、停机阶段NO_(x)超标的主要原因;SCR催化剂老化是正常运行时段NO_(x)排放超标的主要原因。通过优化SCR系统停机控制调整逻辑、增加SCR催化床层厚度有望解决以上两个原因引起的NO_(x)超标问题。“调峰模式”“调负荷不停机”两种运行情景的NO_(x)日排放量分别为9.5、11.4 kg,前者环境效益明显。研究结果能为生态环境部门提高固定式燃气内燃机NO_(x)排放监管的科学性、有效性提供参考。

京西关停矿井开发利用规划研究

京西矿井关停后将形成71万m3的可利用特殊地下空间和77.4万m2的地面工业广场,近千亿资产被闲置。针对京西矿井现状,响应北京总体规划,通过建设国家级安全生产事故预控与应急处置技术实验实训和科普基地(一期)作为京西关停矿井开发利用的首期工程。京西基地建设内容包括防灾减灾救灾技术支撑平台、应急管理能力培养课程体系、基础条件建设、应急管理信息化研发实训平台、应急管理特色学历教育课程体系、应急实训演练与知识文化科普平台6部分,具体由26个建设模块组成,共需要配置专业仪器设备1827台、开发课程54门、图书文献156套、引进培训师资180人次、改扩建工程设施1609套(项),利用千军台井地下巷道约3147 m,最终建成服务安全生产和应急管理的国际一流科教培基地。