吹氩流量对结晶器流场影响的插钉工业试验

 结晶器吹氩流量对流场分布有明显影响，因此明确吹氩流量对结晶器内流场分布的影响规律对提高铸坯质量有重要意义。通过插钉法工业试验研究了吹氩流量对结晶器内流场分布的影响，并且定量分析了液位波动的变化。结果表明，随着吹氩流量的增大，流场形态从双环流逐步转变为复杂流和单环流。结晶器内流场形态从双环流转变为复杂流和单环流的过程中，水口附近速度逐渐增大，液位逐渐升高，弯月面速度分布逐渐转变为从水口流向窄面，液位波动也相应增大。因此，生产过程中应选择合适的吹氩流量，避免产生复杂流和单环流，以提高铸坯质量。     

Short‐term effects in a reduced flow stretch: The case of the Antas River in South Brazil

The building of adduction channels (penstocks) that conduct water from reservoirs to turbines, which are located kilometres from the dam, is becoming common, optimizing the electricity generation in small dams. This design creates a river stretch with reduced discharge between the dam and the powerhouse. This study evaluates the short‐term impacts of the below‐dam decrease in river flow on fish assemblages. Samples were collected in the reduced flow stretch of the Castro Alves Hydropower Plant (Antas River, Rio Grande do Sul, Brazil) before the reservoir started operating (January 2008; mean discharge of 103.7 m³/s) and immediately after operation began (March 2008; mean discharge of 12.4 m³/s). Sampling was conducted in distinct habitats of the reduced flow stretch (slow waters—gillnets, sand beaches—seining nets, structured littoral—electrofishing, and fast waters—cast nets) with a strongly standardized effort. The attributes of the fish assemblages were not negatively affected by the flow reduction in any habitat sampled. However, distinct changes in the spatial structure were observed considering the different types of habitat predominantly used by the species, which represents an entire reorganization of the fish assemblages in the short term. It is fundamental that these short‐term aspects be considered in the licensing of hydropower plants in addition to the long‐term changes.     

Mathematical model for coal conversion in supercritical water: reacting multiphase flow with conjugate heat transfer

Providing heat for supercritical water gasification (SCWG) of coal by coupling subsequent products oxidation in integrated supercritical water reactor (ISWR) provides an effective method for directional control of temperature field and avoids excessive hot spots caused by uniform heating. An exploratory numerical model incorporating particle-fluid flow dynamics, multispecies transport and thermal coupling between endothermic coal gasification and exothermic product oxidation was established to simulate the reacting multiphase flow process of coal conversion in a novel lab-scale ISWR. An eleven-lump kinetic model was proposed for the prediction of chemical reactions. And the thermal coupling relationship was described by conjugate heat transfer boundary conditions (BC). Detailed physical and chemical field distribution in ISWR were analyzed and influence factors were discussed. The results showed that oxidation of gas products as inner heat source could promote the gasification reaction with only slight or even little maximum temperature increase of the pressure-bearing wall. Coal feeding rate and oxygen supply method significantly affected the field distribution. The multi-injection compressed-air supply method provided a more uniform temperature field but would reduce heat transfer temperature difference. The carbon gasification efficiency (CGE) in the gasification zone could easily reach up to 97% under mild conditions (less than 650 °C).     

气瓶内部淬火过程的流动换热特性

 大直径厚壁气瓶内部淬火时的流动换热过程极其复杂，受到多种因素的影响，而研究气瓶内部压强和温度的变化规律对改善流动换热效果、提高产品组织性能具有重要的理论指导意义。以914 mm厚壁气瓶和瓶内流体为研究对象，建立了二维等效流 固耦合模型；采用多喷嘴系统对气瓶内外进行喷水淬火，研究了气瓶总长、喷水流速及淬火时间对瓶内压强及内壁温度的影响，通过间歇淬火试验验证了数学模型的正确性。结果发现，气瓶长度对瓶内压强和瓶壁温度的影响显著，喷水流速次之，当喷水流速大于8 m/s后，水量对瓶壁的冷却效果大大降低；气瓶内壁长度方向的温度梯度分别随气瓶总长的增加和淬火时间的延长而减小，但基本不受喷水量的影响。     

Probabilistic tree-based representation for solving minimum cost integer flow problems with nonlinear non-convex cost functions

The minimum cost flow problem (MCFP) is the most generic variation of the network flow problem which aims to transfer a commodity throughout the network to satisfy demands. The problem size (in terms of the number of nodes and arcs) and the shape of the cost function are the most critical factors when considering MCFPs. Existing mathematical programming techniques often assume the cost functions to be linear or convex. Unfortunately, the linearity and convexity assumptions are too restrictive for modelling many real-world scenarios. In addition, many real-world MCFPs are large-scale, with networks having a large number of nodes and arcs. In this paper, we propose a probabilistic tree-based genetic algorithm (PTbGA) for solving large-scale minimum cost integer flow problems with nonlinear non-convex cost functions. We first compare this probabilistic tree-based representation scheme with the priority-based representation scheme, which is the most commonly-used representation for solving MCFPs. We then compare the performance of PTbGA with that of the priority-based genetic algorithm (PrGA), and two state-of-the-art mathematical solvers on a set of MCFP instances. Our experimental results demonstrate the superiority and efficiency of PTbGA in dealing with large-sized MCFPs, as compared to the PrGA method and the mathematical solvers.     

非晶Fe粉掺杂Al-12Si合金的高温压缩变形行为

为提高Al-12Si合金的热变形抗力,并探索非晶Fe粉掺杂对Al-12Si合金热压缩行为的影响和掺杂非晶Fe粉热压缩中的晶化温度等,采用连续挤压技术制备了掺杂10wt%非晶Fe粉与不掺杂非晶Fe粉的Al-12Si合金试样,对试样进行了不同温度和应变速率下的热压缩试验,分析了试样在热压缩中的组织转变,以及采用双曲正弦关系构建了试样的热流变应力方程。结果表明:非晶Fe掺杂试样在450 ℃及以下的热压缩时,Fe维持非晶态,500 ℃时,则已发生晶化;掺杂10wt%非晶Fe粉使Al-12Si合金的热抗变形能力显著提高,其热压缩激活能Q=211.29 kJ/mol,比未掺杂非晶Fe粉的Al-12Si合金试样高40.78 kJ/mol,且热压缩过程中存在动态回复和动态再结晶;利用双曲正弦关系构建试样的热流变应力方程为ε·=4.42×10¹⁴[sinh(0.016 6σ)]^6.13exp(-211 290/RT),线性回归系数高达0.99,即可为非晶Fe粉掺杂试样的热加工提供一定的理论指导。     

A system for time-fluctuating flow rate measurements in a single-blade pump circuit

Commonly used flow rate measurement systems provide an accurate and stable output value of the quasi-stationary flow rate. In some pump types as e.g. single-blade pumps significant flow rate fluctuations may occur even in steady operation points due to rotor-stator interaction. For the analysis of the time-resolved flow rate a new measurement and evaluation method is presented based on an electromagnetic flow meter. Internal averaging of the flow meter is deactivated and the raw signal is evaluated directly with a sampling rate of 3 kHz. With ensemble-averaging in combination with an impeller position detection, interfering signals acting on the time-resolved measurement signal are filtered out. Accompanying numerical simulations of the pump flow circuit are carried out with a 1D method of characteristics and validated against well-established time-resolved pressure measurements of the pump flow. Experiment and simulation show a resembling trend of pressure as well as flow rate fluctuations over the entire operation range of the pump. Thus, by the combined utilisation of measurement and simulation technique, we assure the validity of the ensemble-averaged flow rate fluctuation results. We find that the flow rate fluctuations show a consistent phase shift to the pressure fluctuations that increases towards overload. The flow rate amplitude is an order of magnitude smaller than the amplitude of the pressure fluctuations.     

机械密封腔流场内粒子对密封腔壁面及波纹管冲蚀分析

为研究机械密封腔内混有固体颗粒的流体,在复杂工况下对密封腔壁面及波纹管表面冲蚀的影响,以CFD理论及方法,采用k-ε湍流模型和离散项DPM模型,对固液混合流场进行模拟分析,获得密封腔内流体中介质作用下密封腔壁面及波纹管外表面的压力场分布,分析不同工作状态下固体颗粒作用下密封腔内壁和波纹管外表面的冲蚀区域分布、固体颗粒在流场中的运动轨迹,以及机械密封工作过程中流场内固体颗粒的逃逸量、运动状态的变化。结果表明:粒子主要受颗粒阻力、浮重力、压力梯度力及波纹管和密封腔表面反作用力的影响;在旋转流场中,粒子作与旋转方向一致的螺旋方式前进;无转速时,冲蚀多发生在靠近入口处的波纹管外表面,旋转流场中,冲蚀多发生在密封腔靠后位置的壁面;随着转速增加,粒子逃逸率下降。研究结论为机械密封腔的设计布局及机械密封装置的优化提供理论依据。     

Polyoctadecylacrylate (POA) and resin-stabilized asphaltene synergistically improve the flow behavior of model waxy oils

In this paper, the effect of POA PPD together with resin-stabilized asphaltenes on the flow behavior of model waxy oils was investigated through rheological test, DSC, microscopic observation and asphaltenes precipitation test. Compared to the POA or asphaltenes alone, POA/asphaltenes cannot further decrease the wax appearance temperature of oils, but can dramatically decrease the pour point, gelation point, G′, G″ and apparent viscosity of oils. POA molecules can adsorb on the surface of asphaltenes, thus inhibiting the asphaltenes precipitation and forming the POA/asphaltenes composite particles. The composite particles can act as wax crystallization templates and then greatly change the wax crystals' morphology into large and spherical-like, thus improving the waxy oil flow behavior.