Gas-liquid flow through coils

Experimental investigations have been carried out to evaluate the two-phase pressure drop and the holdup for flow through helical coils. The coils were made of thick wall transparent PVC tube of diameter 0.01 m and 0.013 m. 24 coils were made at different coil diameter and different helix angles (0° to 12°). Three different liquids were used for the experimental studies and air was the gas. Empirical correlations have been developed to predict the two-phase friction factor and the liquid holdup as functions of the physical and dynamic variables of the system. Statistical analyses of the correlations suggest that they are of acceptable accuracy.     

立式螺旋管气液两相流摩擦阻力特性研究

分别以油 气、气 水为工质,对立式螺旋管内气液两相流的摩擦阻力特性进行实验研究。实验用螺旋管完全由内径为３９ｍｍ的有机玻璃管弯制而成,其螺旋直径２６５ｍｍ,全长４４９０ｍｍ。在对实验结果和前人有关研究进行分析的基础上,给出了两种流动条件下摩擦阻力的计算公式,并与实验结果进行了比较,两种流动条件下,预测值与实验数据的最大偏差分别在３０％和２０％之内。     

垂直管中气,液两相上升流动摩擦压降测定的改进

本文研究了气、液两相垂直上升流动的摩擦压降，改进了两相液中流体的压差与持液量的测定技术，实验在内径为１９ｍｍ、高度为１５００ｍｍ的垂直玻璃管中完成，实验介质采用空气与水，两相流摩擦压了值通过测定压差与持液量实验数据计算得到，流型通过观察决定。     

水蒸汽在蛇管内分层流膜状冷凝

对水蒸汽在蛇管内分层流膜状态冷凝传热进行了理论分析和实验研究。根据数学模型研究了蛇管的倾斜角，曲率半径等因素对膜状冷凝传热系数的影响，由实验测定了蛇管内水蒸汽膜水冷凝传热系数，并与理论值进行了对比，两者吻合较好。     

Vertical two-phase flow: Part II. Holdup and pressure drop

Two-phase gas-liquid flow has been investigated in a 1-inch internal diameter vertical tube coil containing two risers and a downcomer all connected by “U” bends. Pressure drop, holdup and flow pattern data were successfully obtained simultaneously in the three vertical tubes, each 17.30 ft. long, for five different air-liquid systems at about 25 psia and 50°F-80°F over flow ranges of 0–700 lb_m air/min-ft² and 140--25300 lb_m liquid/min-ft². Pressure drops and liquid holdups were plotted against gas volume flowrate with liquid flowrate as a parameter. From these plots it was found that for a combination of an increase in liquid viscosity and density, and a decrease in surface tension, the frictional pressure drop increased in down flow and decreased in upflow. Holdup, on the other hand, increased for both types of vertical flow with respect to the same combination of parameters. The Lockhart-Martinelli scheme was satisfactory in correlating frictional pressure drop and holdup in all the flow regimes except the frothy-slug regime in upflow. In downflow however, the Lockhart-Martinelli scheme met with limited success because of a strong influence of liquid flowrate, physical properties and pipe orientation. Holdup in the falling film and falling bubbly film regimes in downflow were satisfactorily treated by the drift flux approach which emphasizes the relative motion of the two phases.     

惯性管盘绕方式对脉管制冷机性能的影响

为了研究惯性管盘绕方式对脉管制冷机性能的影响,揭示不同盘绕结构时惯性管调相能力及制冷机性能变化规律,为实际应用提供必要的实验数据或理论支持,结合湍流因素影响,计算了不同盘绕惯性管的压降损失,分析对调相能力的影响。研究发现,绕圈数越多,压降越大,惯性管调相能力越小。最后,选用了不同盘绕方式的惯性管进行了实验研究,实验结果显示随着惯性管盘绕圈数增加,压缩机效率略微减小,相同冷量下制冷机输入功率显著增大。对惯性管型脉管制冷机盘管方式的实际应用具有重要指导意义。     

Experimental Investigation on the Holdup Distribution of Oil‐Water Two‐Phase Flow in Horizontal Parallel Tubes

An experimental investigation was conducted to study the holdup distribution of oil and water two‐phase flow in two parallel tubes with unequal tube diameter. Tests were performed using white oil (of viscosity 52 mPa s and density 860 kg/m³) and tap water as liquid phases at room temperature and atmospheric outlet pressure. Measurements were taken of water flow rates from 0.5 to 12.5 m³/h and input oil volume fractions from 3 to 94 %. Results showed that there were different flow pattern maps between the run and bypass tubes when oil‐water two‐phase flow is found in the parallel tubes. At low input fluid flow rates, a large deviation could be found on the average oil holdup between the bypass and the run tubes. However, with increased input oil fraction at constant water flow rate, the holdup at the bypass tube became close to that at the run tube. Furthermore, experimental data showed that there was no significant variation in flow pattern and holdup between the run and main tubes. In order to calculate the holdup in the form of segregated flow, the drift flux model has been used here.     

Frictional Pressure Drop of Air Non‐Newtonian Liquid Flow through Helical Coils in Horizontal Orientation

Investigations have been carried out to evaluate the two‐phase frictional pressure drop for air non‐Newtonian liquid flow through helical coils in horizontal orientation. The experiments performed using 36 different helical coils and 4 different concentrations of sodium salt of carboxymethyl—cellulose (SCMC) as non‐Newtonian liquids. The effects of air and liquid flow rate, coil diameter, helix angle and liquid properties‐ on two‐phase frictional pressure drop have been discussed. An attempt has been made to fit the experimental two‐phase frictional pressure drop data by the Lockhart and Martinelli, Chem. Eng. Prog. 45 , 39–48 (1949) correlation and the modified Lockhart‐Martinelli correlation as presented by different authors. In another approach, friction factor method was adopted to correlate the experimental data by dimensional analysis. The correlation developed predicts the two‐phase frictional pressure drop with acceptable statistical accuracy.     

Experiments on the suspension of spheres in inclined tubes—II. Suspension by air

Data are presented on the suspension of single spheres by air, in inclined tubes ranging in diameter from 0·97 to 5·13 cm. The angle of inclination of the tubes to the horizontal axis varied from 0 to 90°. The data, which relate the pressure drop and suspending velocity to the geometric and physical parameters of the system, are compared with data generated previously using water as the suspending fluid. Dimensionless expressions are presented which correlate both sets of data for pressure drop and suspending velocity in terms of sphere/tube diameter ratio, tube diameter, density of solid and fluid and angle of inclination of the tube.     

Flow regimes,hold–up and pressure drop for two phase flowin helical coils

Experimental results on flow pattern, hold–up and pressure drop are presented for cocurrent upward and downward air water flow in helical coils. A tube of 0.01 m internal diameter was used and the ratio of coil to tube diameter was varied from 11 to 156.5. Water flow rate was varied from 4.9 × 10-⁶ m³/s to 92 × 10-⁶ m³/s while the range of gas flow rate covered was 83 × 10-⁶ m³/s to 610 × 10-⁶ m³/s. A new mechanistic approach is proposed to correlate pressure drop data in coils. The proposed model retains the identity of each phase and separately accounts for the effects of curvature and tube inclination resulting from the torsion of the tube. This makes it possible to use a single model to predict pressure drop for both upward and downward two–phase flow in coiled tubes. Required correlations for hold–up, interfacial friction factor and friction factors for individual phases are provided.     

固液分布器中主分布器的实验研究

在不同结构形式的主分布器条件下，研究了表观液速对换热管中固含率、下管箱内床层高度、静压降及平均固含率的影响。利用体积容积法测量了换热管束中的固含率、刻度尺测量了下管箱中的床层高度、U形管测量了下管箱的静压降，并运用差压法测量了下管箱中平均固含率。采用不均匀度函数衡量了不同结构条件下管束间固含率的不均匀程度。实验结果表明：在换热管下方增加优化后的主分布器可以均匀分布固液两相；主分布器直径变化时对下管箱内流动特性的影响大于主分布器轴向位置改变时的影响。     

螺旋管丙烷流动沸腾换热特性

丙烷作为自然工质具有良好的换热性能并且对环境影响较小,是替代传统制冷剂的选择。目前对于丙烷在螺旋管中沸腾传热的研究较少。实验测量了丙烷在管内径8 mm、螺旋半径42 mm、螺距21.5 mm的螺旋管中的流动沸腾传热系数。实验采用套管的形式,在螺旋管外用恒温水对丙烷进行加热,调整水入口温度与水流量得到不同的热通量。实验表明,螺旋管对流动沸腾换热具有一定的强化作用。实验数据与已有的螺旋管流动沸腾换热关联式进行了比较,在6 kW·m⁻²以下的低热通量时,Guo（1998）换热关联式比Ji（2015）预测准确度更高,推荐使用Guo（1998）关联式。     

不同倾角放置螺旋管汽波两相摩擦阻力特性

在宽广的参数范围内试验研究了螺旋管在不同倾角放置时的单相及汽液两相摩擦阻力特性,获得了螺旋管放置方向及各主要系统参数对汽液两相摩擦阻力特性的影响规律。在对试验结果及前人研究结果进行详细分析的基础上,获得了第一个能适用于不同倾角放置螺旋管的单相及汽液两相摩擦阻力计算式,从而为汽液两相摩擦阻力及螺旋管的进一步研究和应用提供了依据。     

连续螺旋折流板换热器流动与传热性能及熵产分析

采用数值模拟的方法,研究了螺旋角对连续螺旋折流板换热器流动与传热性能的影响,并以熵产数为指标对换热器性能进行了基于热力学第二定律的分析评价。结果表明,相同质量流量时壳程传热系数和压降均随螺旋角的增大而降低,且后者降低的幅度大于前者。连续螺旋折流板换热器壳程横截面上切向速度分布较弓形折流板换热器更加均匀。在靠近中心假管的内层区域,同一径向位置的轴向速度随螺旋角的增大而降低,而在靠近壳体壁面的外层区域则相反。螺旋角越大,不同径向位置的换热管间的换热量分布均匀性越好。壳程质量流量相等时,换热器中传热引起的熵产占总熵产的比重随着螺旋角的增大而增加,熵产数随着螺旋角的增大而降低。     

Hydrodynamics of a flowing gas-solids suspension in a tube at high angles of inclination

A study was made of pneumatic transport of particles of sand suspended in air in a 31.8 mm diameter Plexiglas tube inclined at either 72 or 90 degrees with respect to the horizontal plane. The solids holdup, pressure gradient and pressure drop fluctuations over a 4.55 m test section were measured as functions of the air velocity and the solids flux. Previously observed sudden changes in slope of plots of solids holdup versus solids flux at constant gas velocity in a vertical tube (Mok et al., 1989), which were identified as transition points between dilute and dense phases, were confirmed and extended to inclined tubes. Breaks were also found in plots of pressure drop fluctuations versus solids flux at constant gas velocity.     

An Analysis of Pressure Drop and Holdup for Liquid‐Liquid Upflow through Vertical Pipes

The present study has attempted to investigate pressure drop and holdup during simultaneous flow of two liquids through a vertical pipe. The liquids selected were kerosene and water. The measurements were made for phase velocities varying from 0.05–1.2 m/s for both liquids. The pressure drop was measured with a differential pressure transducer while the quick closing valve (QCV) technique was adopted for the measurement of liquid holdup. The measured holdup and pressure drop were analyzed with suitable theoretical models according to the existing flow patterns. The analysis reveals that the homogeneous model is suitable for dispersed bubbly flow whereas bubbly and churn‐turbulent flow pattern is better predicted by the drift flux model. On the other hand, the two fluid flow model accurately predicts the pressure drop in core annular flow.     

移动容器加热结构对流体分布影响的研究

利用数值模拟的方法,研究了一种典型的移动式压力容器外置式加热管连接处开孔对管内流动性能的影响。开孔的目的是为了均衡不同纵向加热管内的流量,充分发挥每根加热管的传热性能。分析了不同小孔直径对加热管内流量和压降的影响。结果表明,孔径的减小使流体分布更加对称,但同时也使管内压降剧增。因此孔径的选取需要综合考虑流量和压降两种因素的影响。     

不同倾角放置螺旋管汽波两相摩擦阻力特性

在宽广的参数范围内试验研究了螺旋管在不同倾角放置时的单相及汽液两相摩擦阻力特性,获得了螺旋管放置方向及各主要系统参数对汽液两相摩擦阻力特性的影响规律。在对试验结果及前人研究结果进行详细分析的基础上,获得了第一个能适用于不同倾角放置螺旋管的单相及汽液两相摩擦阻力计算式,从而为汽液两相摩擦阻力及螺旋管的进一步研究和应用提供了依据。     

Experimental studies on flow boiling in inclined tubes: In the regions encountered in solar collectors

Flow boiling in inclined tubes is encountered in solar collectors, but there is no literature on inclined flow boiling on which to base their design. Experimental studies have been carried out on heat transfer, pressure drop and flow maps for flow boiling of water in a circular tube. The angle of inclination was varied from 0° to 90°. The inclination was found to influence the transport processes in the bubbly and the intermittent flow regimes. The correlation of Chen (1966) has been extended to correlate the heat-transfer data to account for the angle of inclination. The Baroczy (1965) and the Lockhart-Martinelli (1949) correlations were adapted to correlate the frictional pressure gradient in the inclined flow boiling. The observed flow patterns were presented as flow maps.