The flow of sand/water slurries in horizontal pipes with internal spiral ribs — effect of rib height

The effect of secondary flows created by an internal spiral rib in an otherwise conventional smooth 2-inch pipe on the transportability of “settling” suspensions of sand in water was investigated with emphasis on the effect of rib height. While the ribs were found to be a disadvantage at relatively high average mixture velocities because of increased pressure gradients, they were advantageous at low velocities. The deposit velocity and the pressure gradient at the deposit velocity in ribbed pipes of several pitch to diameter ratios and rib heights were correlated with respect to the corresponding smooth pipe values. These correlations are useful in pipeline design. The optimum rib geometry was estimated to be a pitch to diameter ratio of about 8 and a rib height in the range of 10–15% of the pipe diameter for the solid-liquid mixtures investigated.     

The entry length for slurries in horizontal pipeline flow

The entry length for horizontal slurry pipeline flows has been determined experimentally using a pipeline of diameter 50 mm. Concentration and velocity distributions have been measured in the vertical direction at positions 6, 50 and 185 diameters downstream of the entrance. The measurements show that the entry length is of the order of 50 pipe diameters for sand slurries. High particle settling velocities give somewhat shorter lengths than intermediate settling velocities. With lower density polystyrene particles for which dispersive effects are important, the entry length is significantly greater than 50 diameters. The velocity distributions show that the velocity profiles develop concurrently with the concentration profiles. For sand slurries, a two-dimensional simulation gives a satisfactory representation of the developing concentration profiles.     

Wasserlösliche hochpolymere als strömungsbeschleuniger

Soluble high polymers drastically reduce the friction or drag of turbulent wall flows; this effect is widely known as drag reduction. In practical applications drag reducing polymers also bring about an increase in flow rate. That is why we have introduced the term flow enhancer for this type of polymer. Drag reduction by polymers was discovered in 1948. The addition of very small amounts (ppm) of a high polymer reduces the pressure drop in turbulent pipe flow by up to 80 % or increases the flow rate by up to 100 %. These rheological effects are demonstrated with the aid of laboratory experiments. A physical model is presented which describes the interference of the coiled macromolecule in turbulent boundary layers with elongational velocity gradients. From this theory are derived a number of requirements for particularly effective macromolecules, such as molar mass, conformation, linearity and electrical charges in the molecule. The well-known water soluble drag reducing polymers are presented and the influence of pH, electrolytes and temperature described. Finally a survey of practical applications with experiments describing the operation of a specially designed flow enhancer for hydrotransport of sand slurries is given.     

内壁填充环状金属泡沫的管内流动凝结换热

通过采用在圆管内壁填充环状金属泡沫的方法强化管内对流凝结换热,实验研究了制冷剂R134a在内壁填充环状金属泡沫管内的流动凝结的压降和换热,克服了完全填充金属泡沫管流动阻力大的缺点。用于计算传热系数的管壁温度通过热电偶测量得到。综合分析了质量流速和两相流体干度对流动凝结压降及传热系数的影响。研究结果表明内壁填充环状金属泡沫管压降远大于光管,压降随质量流速和干度的增加而迅速增大且呈非线性。通过壁面温度分布和温度波动对内壁填充环状金属泡沫管内的两相流型进行判别,发现影响该类强化管凝结换热的两种主要流型：分层流和环状流。内壁填充环状金属泡沫管的凝结传热系数大于光管,且随着质量流速和干度的增加传热系数增大,该类强化管流动凝结传热系数是光管的2倍左右。     

Predicting pressure gradients in heavy oil—water pipelines

Experimental investigations of the flow of water‐heavy oil mixtures at velocities typical of oil‐field gathering systems show that continuous water assisted flow at very low pressure gradients can be achieved. The principal criterion to be satisfied in establishing this desirable flow regime appears to be use of sufficient water, with the velocity also playing a role. It also appears that oil viscosity and water fraction effects on pressure gradient are small provided the beneficial flow regime is established. The flows resemble core‐annular flow, which has been observed previously in Bitumen froth and water‐heavy oil flows, with an oil layer on the pipe wall. However, the correlation for pressure gradient is somewhat different from that reported previously for Bitumen froth flows.     

弯曲内肋换热管综合换热性能的数值模拟

基于纵向涡强化换热理论提出了新型的强化换热管--弯曲内肋强化换热管。运用数值计算的方法,在Re=500～40000研究了新型强化换热管结构参数肋宽a、导程p、肋深e和Re数对Nu、f及换热性能评价指标PEC的影响,并拟合出换热管Nu、f的量纲为1关联式。结果表明:由于内肋的作用,在换热管的近壁面区域能够有效诱导产生沿纵向的涡旋结构,破坏壁面边界层,实现强化换热;导程p和肋深e对综合换热性能影响较大,肋宽a对综合换热性能影响较小,在Re=500～40000范围内,新型换热管较优的结构参数为p=10mm、e=0.6mm、a=1.8mm;与普通平滑圆管相比,当Re<2300,其换热性能Nu可达到普通圆管的2.9～7.0倍,沿程阻力系数f约为普通圆管的1.4～3.6倍;当500< Re <2300,其综合换热评价指标PEC可以达到2.6～4.6;当2300 <Re <40000时,其PEC可以达到1.2～2.3。     

水煤浆在渐缩管中局部阻力特性的数值试验

针对质量浓度为57.08%神华水煤浆,利用管流法和旋转粘度计法测得其流变模型。运用FLUENT软件提供的非牛顿流体模块对水煤浆流经渐缩管进行模拟计算,比较计算压差和实验压差,证明计算模型的正确性。基于计算模型的正确性,对水煤浆在渐缩管中不同流速、不同渐缩角度的工况下进行数值试验,得出局部损失系数与雷诺数和渐缩角度的经验公式;在渐缩角度不变的情况下,改变渐缩管长度与渐缩管进口端直径比率,得出各个相应比率下的局部损失系数与雷诺数的关系。     

高效复合强化换热器的管程性能

通过搭建内螺纹扭曲椭圆管复合强化管换热器传热与压降性能测试平台,对内螺纹扭曲椭圆管复合强化管换热器的管程传热和流阻性能进行了实验研究,以实验数据为基础拟合得到其对流传热系数和流动摩擦阻力系数与管内流体Reynolds数的计算准则关系式,将内螺纹扭曲椭圆管与光滑圆管、内螺纹圆管、光滑扭曲管的管程传热、流阻以及综合性能进行对比分析,结果显示内螺纹扭曲管流动阻力略高于其他类型的换热管,传热效果和综合性能明显优于其他类型换热管。内螺纹扭曲管作为一种内螺纹和扭曲扁管强化传热技术的叠加技术,强化传热效果明显,具有重要的工程应用价值。     

Experimental investigation of some hydrodynamic factors affecting slurry pipeline wall erosion

Using a non-intrusive technique, particle velocities and concentrations have been measured as functions of position on the pipe wall for water slurries of two different sands. The experimental conditions correspond to both low (fine particles) and high contact load flows. Although the velocity and concentration distributions for the two sands were quite different, flux distributions computed from the product of velocity and concentration were similar. The flux distributions are used to interpret wall erosion distributions for sands of these sizes. In the case of the coarser sand, there is evidence that the contact load mechanism contributes significantly to abrasive wear. In this case, scaleup of erosion test results may be possible, using concepts provided by mechanistic flow models. For the finer sand, wall erosion rates appear to be reduced by a lubrication force.     

Heat transfer and friction factor of Therminol liquid phase heat transfer fluid in a ribbed tube

Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch and rib height of 4.5 and 1.0 mm.respectively.Experimental results show that the heat transfer and thermal performance of Therminol-55 liquid phase heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube.The Nusselt number increase with the increase of Reynolds number.The increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times.Also,the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.4 and 2.8 times over the smooth tube.Numerical simulations of three-dimensional flow behavior of Therminol-55 liquid phase heat transfer fluid are carried out using three different turbulence models in the ribbed tube.The numerical results show that the heat transfer of ribbed tube is improved because vortices are generated behind ribs,which produce some disruptions to fluid flow and enhance heat transfer compared with smooth tube.The numerical results prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.     

Modelling Heterogeneous Slurry Flows at High Velocities

Experiments have been conducted with sand slurries of median diameter 0.09 mm and 0.27 mm in a laboratory test pipeline 0.103 m in diameter. In addition to pressure gradient measurements as functions of mean velocity and in‐situ solids concentration, concentration and velocity profiles have been obtained. The measurements show that the pipeline friction is lower than expected at high velocities. This deviation is of the type that has been predicted in recent theoretical work by Wilson and coworkers. A correlation for the slurry friction at high velocities has been obtained. This correlation has been used to modify the model for predicting friction of heterogeneous slurries at velocities above the deposition condition.     

Flow regimes and vertical solids conveying in a spout‐fluid bed with a draft tube

Pressure fluctuation data were obtained in a semi‐cylindrical spout‐fluid bed with draft tube, and statistical analyses of them were employed to recognise flow regimes. Also, the effects of spouting‐gas and auxiliary‐gas velocities, and length of entrainment zone on solids loading ratio in a draft tube were examined. As a result, five flow regimes appeared by changing spouting‐gas and auxiliary‐gas velocities and it was found that the simplest method to determine flow regime is to measure pressure fluctuations in a draft tube. Moreover, solids loading ratio could be controlled flexibly by auxiliary‐gas velocity and length of entrainment zone.     

Anomalous friction in slurry flows

Experiments conducted with water slurries of 1 mm particles of specific gravity 1.59 in a laboratory pipeline 0.105 m in diameter have provided evidence of a change in the friction mechanism at velocities above 3 m/s. These flows were stratified and at low velocities the frictional pressure gradients were in satisfactory agreement with the predictions of the conventional two‐layer model. However at higher velocities the friction is substantially lower than predicted. Measurements of concentration and velocity distributions within the pipe show that no major change in flow regime occurs concurrently with the change in the friction mechanism. It appears that the effect is due to a change in the nature of the particle‐wall interaction, of a type which suggests that an inward‐acting force affects the particles adjacent to the wall.     

减弱节流器中颗粒冲蚀破坏措施的数值模拟

井下节流器是水力加砂压裂施工中的重要元件之一。对在节流器内壁面设置肋条以提高其抗冲蚀性能的方法,采用考虑颗粒-颗粒碰撞的离散颗粒硬球模型进行了数值模拟,并采用半实验关联式计算了节流器内壁面的冲蚀速率,进一步对肋条的几何参数进行了优化。结果表明,设置肋条不仅可以在壁面附近形成类似滚动轮子的流场结构,减弱连续相的流速,还可以将90%以上冲击颗粒的速度降低到0.5 m/s以下,从而明显地提高了节流器的抗冲蚀性能;同时,当肋条高度H为3 mm、宽度B与间距L相同(5 mm),布置4个肋条时可以达到相对最佳的抗冲蚀效果。     

An improved two layer model for horizontal slurry pipeline flow

A model for predicting head losses for coarse-particle or settling slurries has been obtained. Experimental data for isothermal flows of sand, gravel and coarse coal slurries in pipes of industrial scale have been used to obtain the correlations in the model. The model differs from previous versions in the way it deals with the concentration of the lower layer and in the role ascribed to the finest (–74 μm) particles. The fraction of contact load, which contributes sliding friction at the pipe wall, is found to be primarily a function of the ratio of the mean flow velocity to the settling velocity of the mass median particle size in the (+74 μm) fraction. The correlations are restricted to mixtures containing less than 35% (+ 74 μm) particles by volume.     

垂直上升内螺纹管内流动沸腾传热特性

在压力9～22 MPa,质量流速450～2000 kg·m^-2·s^-1,内壁热负荷200～700 kW·m^-2的参数范围内,试验研究了用于1000 MW超超临界锅炉φ28.6 mm×5.8 mm垂直上升内螺纹水冷壁管内汽水流动沸腾传热。研究表明：内螺纹管内壁螺纹的漩流作用可抑制偏离核态沸腾（DNB）传热恶化,内螺纹管在高干度区发生蒸干型（DO）传热恶化。增大质量流速可推迟壁温飞升,壁温飞升幅度随质量流速增大而降低。热负荷越大管壁温越高,随热负荷增大管壁壁温飞升提前,且传热恶化后壁温飞升值增大。随着压力增加,壁温飞升发生干度值减小。内螺纹管汽水流动沸腾传热系数呈π形分布,传热系数峰值出现在汽水沸腾区。文中还给出了亚临界压力区内螺纹管单相区和汽水沸腾区的传热系数试验关联式。     

Effect of the annulus aeration on annulus leakage and particle circulation in a three-phase spout-fluid bed with a draft tube

The distribution of flow between the annulus and the draft tube sections of a liquid spout-fluid bed with a draft tube was analyzed in the presence of air flow through the annulus using a tracer response technique.The responses of the tracer injections prove that part of the flow originating from the annulus liquid inlet leaks into the draft tube when any amount of annulus liquid inlet flow is present and this annulus leakage increases when air flow is introduced into the annulus. This finding extends the recently acquired knowledge about the annulus leakage and cross flow in the entrance region below the draft tube in liquid spout-fluid beds to three phase spout-fluid beds with a draft tube where the annulus is aerated.The experimental system studied consisted of a semi-circular column of 80 mm diameter equipped with a semi-circular draft tube of 20 mm diameter. Liquid and air flows coexisted in the annulus. The liquid velocities were well above the minimum fluidization velocity and the particles were glass beads of 3 mm diameter.Experimentally determined values of the superficial annulus and draft tube liquid velocities from the tracer response analyses together with the experimental draft tube pressure gradients were used as input into Grbavcic et al.'s [Z.B. Grbavcic, R.V. Garic, D.V. Vukovic, Dz.E. Hadzismajlovic, H. Littman III, M.H. Morgan, S.Dj. Jovanovic, Hydrodynamic modeling of vertical liquid-solids flow. Powder Technol. 72, (1992)183-191] variational model for vertical non-accelerating liquid-solids flow to calculate the draft tube voidage and the particle mass flux assuming an air free draft tube. Results indicate that annulus aeration lowers the particle mass flux in this particular column geometry.     

Enhanced Heat Transfer Characteristics of Upward Flow Boiling of Kerosene in a Vertical Spirally Internally Ribbed Tube

Experiments of upward flow boiling of kerosene in a vertical spirally internally ribbed tube and a vertical smooth tube were conducted, respectively, in the present study. The spirally internally ribbed tube has an inner diameter of 11 mm (an equivalent inner diameter of 11.6 mm) and an outer diameter of 22 mm. The smooth tube has an inner diameter of 15 mm and an outer diameter of 19 mm. The test tubes were uniformly heated by passing an electrical current along the tubes with an available heated length of 2500 mm. At the outlet of the test section, the experimental pressure was 3 bars. The experimental heat flux ranged from 28.5 to 93.75 kW/m². The experimental mass flux was 410, 610, and 810 kg/m²s, respectively. Both local and average flow boiling heat transfer coefficients were measured in the test tubes. The enhanced heat transfer characteristics of the flow boiling of kerosene in the spirally internally ribbed tube are presented by comparing the experimental heat transfer coefficients with those obtained in the smooth tube. It shows that the flow boiling heat transfer coefficients in the spirally internally ribbed tube are 1.6 to 2 times greater than those in the smooth tube. The physical mechanisms of the enhanced heat transfer characteristics of flow boiling in the spirally internally ribbed tube are analyzed. According to the experimental data, an expression for the flow boiling heat transfer coefficient of kerosene was found in terms of the Martinelli number for the spirally internally ribbed tube. The correlation is applicable to the design of heat exchange equipment, using the spirally internally ribbed tube as a heat transfer element under these test conditions.     

Startup of a pipeline containing settled solid particles

Experimental studies have shown that, provided a threshold velocity is exceeded, bed of solid particles can be displaced from pipelines at low pressure gradients using fluid velocities near the limit-deposit velocity. The time scale of the process depends upon three factors: fluid acceleration, bed erosion and displacement. Results are reported for water slurries of a silica send of d₅₀ = 0.43 mm. A simple model for the transient response is proposed.