Study of vapor liquid two-phase frictional pressure drop in a vertical heated spirally internally ribbed tube

Experiments of vapor liquid two-phase frictional pressure drop of upward flow boiling in a smooth tube and in a spirally internally ribbed tube were conducted, respectively. The spirally internally ribbed tube has an outside diameter of 22 mm and an inside diameter of 11 mm (an equivalent inside diameter of 11.6 mm) and the smooth tube has an outside diameter of 19 mm and an inside diameter of 15 mm. The test tubes were vertically installed and uniformly heated by electricity to achieve flow boiling test conditions. The available heated length of both test tubes is 2500 mm. The working fluids are water and kerosene, respectively. The experimental pressure is 6 bar for flow boiling of water and 3 bar for flow boiling of kerosene. The exit vapor quality of the test sections is about 0.3. The two-phase Reynolds number ranges from 8000 to 28,000. The experimental two-phase frictional pressure drops in the smooth tube are compared with the predicted results by the two-phase flow homogeneous model and the Friedel formula (Friedel, 1979. Improved friction pressure drop correlation for horizontal and vertical two-phase pipe flow. European Two-phase Flow Group Meeting, Ispra, Italy), respectively. It shows that the experimental results agree with the Friedel formula better than the two-phase flow homogenous model. By comparison, the two-phase frictional pressure drops in the spirally internally ribbed tube are 1.6-2.7 times greater than that in the smooth tube. A physical explanation of the increase of the two-phase frictional pressure drop in the spirally internally ribbed tube is given. According to the two-phase flow homogeneous model, a correlation of two-phase friction factor is proposed for the spirally internally ribbed tube and it is applicable to pressures up to 6 bar.     

上升管内环状流含液体积分数与压降预测模型

对垂直上升管中气液二相环状流的含液体积分数及压降预测进行了研究,在充分考虑了环状流的流型特征以及合理假设的前提下,以二相流动力学理论和Wallis有关经验式为基础,推导出了环状流的数学模型。通过求解力学方程,获得了含液体积分数及压降预测的新模型,将新模型及已有模型与实验数据进行对比,结果表明,新模型不仅与实验结果符合良好,还具有计算速度快的特点,从而为垂直上升管内气液二相环状流含液体积分数与压降的预测提供了一种新的有效方法。     

Gas entrainment rate and flow pattern of vertical plunging liquid jets

For a vertical plunging liquid jet system using various liquids, the effects of the operating conditions including the nozzle length-to-diameter ratio on the gas entrainment rate Q_g were evaluated experimentally. The differences in Q_g were related to the changes in the jet shape before plunging and the velocity of the plunging liquid jet at the point where the gas sheath breaks up. Empirical relationships were also presented to predict the maximum depth Z of bubbles entrained by the diffusing jet. The changes of Z were further discussed in terms of the downward liquid velocity distribution in the submerged two-phase region, which depends mainly on the size of entrained bubbles.     

新型导向桥阀塔板的雾沫夹带和塔板压降

在φ1000mm的圆塔内,采用空气–水系统对新型导向桥阀塔板的流体力学性能进行了测试,考察了液流强度、出口堰高等因素对雾沫夹带和塔板压降的影响,并且与标准的F1型浮阀进行了对比实验。结果表明:新型导向桥阀塔板上气体分散均匀,泡沫层高度稳定,气液接触充分,在相同条件下压降比F1浮阀低10%～30%。具有较好的流体力学性能。     

Analysis of pressure drop in vertical pneumatic conveying. Generalized approach for gas—particle and liquid—particle systems

A simple model has been developed for estimating the pressure drop in the steady zone of a vertical pneumatic lifter. As distinct from the earlier developments, the model does not introduce any friction factors which are specific to pneumatic conveying but it makes use of the generalized correlations developed for explaining the fluid—particle interactions. The concept has also been extended to incorporate collisions among particles when a binary mixture is conveyed. The validity of the generalized model has been tested with experimental data and information available in the literature, for both gas—particle and liquid—particle systems.     

Gas entrainment behavior of vertical plunging liquid jets in terms of changes in jet surface length

For a vertical jet system using various liquids, the shape change of liquid jets discharged from nozzles having different nozzle aspect ratios was evaluated in terms of the surface length l_m of the jet flow, and the relation between the change of l_m and the gas entrainment behavior was investigated. It was found that the way of changing of l_m with varying operating conditions or the liquids corresponded well to that of changing of the gas entrainment rate Q_g, that is, the change of l_m of the jet before plunging could be closely related to the change of Q_g.     

Effect of impeller geometry on drop break-up in a stirred liquid—liquid contactor

Drop size measurements were made in the break-up zone at the tip of three 6 bladed disc turbines of different geometries in a 0·30 m dia. vessl. Three systems kerosene, methyl iso-butyl ketone (MIBK) and n-butanol at a volumetric fractional hold-up of 0·05 in water were examined. Power input and circulation time characteristics were determined and a new dimensionless group (?^{?$\text{1}\text{3}$}t_c/T^{$\text{2}\text{3}$}) is proposed to account for the effect of geometric parameters in the correlation of the drop size.     

Characteristics of a hydro-filter pressure drop,liquid hold-up and liquid overflow rate

An experimental study of the effect of operating conditions on the characteristics of a hydro-filter (Marble bed scrubber) has been performed. There are stable operating regions of a hydro-filter with respect to the gas flow rate, the packed bed height and the height of an overflow pipe above the bed. The total pressure is mainly composed of the pressure drops in two sections, the packed section and the bubble section. The pressure drop in the packed section can be estimated from the correlation for a cocurrent gas-liquid upward flow packed bed given by Turpin ad Huntington.     

Liquid–liquid slug flow: Hydrodynamics and pressure drop

In this paper, the hydrodynamics and the pressure drop of liquid–liquid slug flow in round microcapillaries are presented. Two liquid–liquid flow systems are considered, viz. water-toluene and ethylene glycol/water-toluene. The slug lengths of the alternating continuous and dispersed phases were measured as a function of the slug velocity (0.03–0.5 m/s), the organic-to-aqueous flow ratio (0.1–4.0), and the microcapillary internal diameter (248 and 498 μm). The pressure drop is modeled as the sum of two contributions: the frictional and the interface pressure drop. Two models are presented, viz. the stagnant film model and the moving film model. Both models account for the presence of a thin liquid film between the dispersed phase slug and the capillary wall. It is found that the film velocity is of negligible influence on the pressure drop. Therefore, the stagnant film model is adequate to accurately predict the liquid–liquid slug flow pressure drop. The influence of inertia and the consequent change of the slug cap curvature are accounted for by modifying Bretherton’s curvature parameter in the interface pressure drop equation. The stagnant film model is in good agreement with experimental data with a mean relative error of less than 7%.     

Hydrodynamic characteristic of Conical Cap tray: Experimental studies on dry and total pressure drop,weeping and entrainment

This paper addresses an experimental investigation in the hydrodynamic behavior of a new type of cap trays called Conical Cap tray (ConCap tray). The hydrodynamics of the tray was investigated in a commercial scale air–water column with an internal diameter of 1.2 m. The experimental liquid loads were 29.9, 44.4, 60 and 74.4 (m³/h)/m of weir length and gas flow in terms of F_s in the range of 0.2–1.5 m/s (kg/m³)^0.5. The dry pressure drop, total pressure drop, weeping and entrainment for the ConCap tray and a valve tray were measured and compared. Correlations for pressure drop, weeping and entrainment of the ConCap tray were provided using regression analysis method. Standard deviations of correlations, R², are quoted. The ConCap tray was compared with a bubble cap tray using correlations. The pressure drop of the ConCap tray was less than the bubble cap and close to the valve tray. The weeping rate of the ConCap tray was less than the valve tray. Its entrainment is more than the valve tray and less than the bubble cap tray. Good turndown ratio is important characteristic of the ConCap tray which is achieved without having too much pressure drop.     

Effect of solid monodisperse particles on the pressure drop of fibrous filters

The increase in pressure drop across glass HEPA filters has been measured as a function of particle mass loading using polystyrene latex particles (PSL). PSL particles in several different sizes were generated as challenge aerosols. For each particle size distribution, the specific resistance (K₂) was calculated by measuring the mass of PSL particles loaded per unit area of filter and the pressure drop across the filters at a given filtration velocity. In all cases, the specific resistance of the filter cake increased as the aerodynamic mean particle diameter decreased at the same mass loading. This correlation equation was modified by using the lognormal conversion method suggested by Raabe [1971] for a polydisperse particle size distribution; then the modified equation was expressed as a function of geometric mean particle diameter and standard deviation which could be obtained by the measuring instruments (PDS 3603; TSI Inc.). The advantage of this approach over other methods is the use of a more convenient prediction of pressure drop, if we know the geometric mean particle diameter and standard deviation, which could be easily measured. The values of porosities, obtained from the pressure drop responses of loading in the filters using the Rundnick and First equation, were compared with other researches.     

Designing for pressure drop in Venturi scrubbers: the importance of dry pressure drop

An industrial scale Venturi scrubber pilot plant has been used to provide detailed measurements of pressure drop as a function of a broad range of operating conditions. Modelling approaches suitable for design predictions of ΔP have been examined. While numerical models provide clearer understanding of the phenomena occurring in scrubbers, analytical models offer the most promise of improving industrial design practice. These models concentrate on the work done on the liquid phase and ignore turbulence-induced gas phase accelerational (dry pressure drop) losses. However, the experiments show that the latter are important even in well-designed, classical Venturi shapes. Available models are compared, for the first time, with actual wet pressure drop data and agreement is shown to be good. By isolating the dry pressure drop effect, design models can be applied to a wider range of Venturi geometries.     

矩形截面螺旋细通道内气液两相流液相分布及压降特性

为探究不同操作参数及结构下矩形截面螺旋细通道内气液两相流的液相分布及压降特性,建立了光滑螺旋通道及内置矩形涡发生器的螺旋通道2种模型,在进口速度u_(in)=0.22～0.32 m/s,进口含气率α=0.55～0.59的条件下,以空气-水两相流为工质进行了数值模拟。结果表明,在研究的范围内通道内液体受离心力的影响被甩向螺旋通道外侧,而气体分布于通道内侧。进口含气率的增加会减少通道外壁面的液膜厚度。通道内置的矩形涡发生器可使内部工质产生二次流从而增强混合,有效提升截面含气率。除此之外,进口速度的增大、进口含气率的减小及矩形涡发生器的加入均会使矩形螺旋细通道内两相压降增大。     

Gas—liquid pressure drop studies in a reciprocating plate column

Two-phase pressure drop in a 93 mm diameter reciprocating plate column (RPC) was studied for the air-water system, and to a lesser extent for air-kerosene. Amplitudes (strokes) in the range 14 to 63.5 mm and frequencies from 0.75 to 4.0 Hz were investigated for between 2 and 10 brass plates with hole diameters from 3 to 8 mm and free flow area between 0.09 and 0.306. Continuous phase velocity was varied from 1.24 to 3.72 cm s^?1 and dispersed phase velocity varied from 0.04 to 5.10 cm s^?1. The measured pressure head was subjected to a static head correction based on the measured holdup of the dispersed phase and densities of the phases. The data were correlated by regression analysis as a friction factor expressed in terms of loading ratio, Reynolds number and Froude number; they were also compared with an earlier theoretical prediction by Noh and Baird for single phase flow in a RPC. The two-phase pressure drop was found to increase with agitation both in the mixer-settler and emulsion regions and reached a maximum at vibrating speeds around 10 cm s^?1. Beyond this point, it decreased in the unstable region preceding flooding. It was concluded that the RPC could be effectively used in the emulsion region for optimum performance.     

Effect of heat flux on pressure drop in low pressure flow boiling in a horizontal tube

There has been a lack of research specifically examining the effect of heat addition on frictional pressure drop in two phase flow systems. The work presented herein is a result of a series of experiments, using a low pressure steam-water loop to investigate this effect. It was found that the application of constant heat flux results in a significant increase in frictional pressure drop at certain qualities. It was also found that increasing mass flux or decreasing system pressure shifts the maximum pressure drop towards lower qualities. The observed phenomenon is believed to be the result of liquidvapour interactions at the slug-annular flow regime transition. This has been confirmed by flow pattern analysis using Mandhane's flow map.