GAS-NON-NEWTONIAN LIQUID FLOW THROUGH GLOBE AND GATE VALVES

Experimental investigations have been carried out to evaluate the two-phase pressure drop across half-inch globe and gate valves for gas-non-Newtonian liquid flow. The non-Newtonian liquids used were different concentrations of dilute solutions of the sodium salt of carboxymethyl cellulose (SCMC), which behaved as pseudoplastic liquids. Generalized correlations in terms of the various physical and dynamic variables of the system have been developed for prediction of the two-phase frictional pressure drop for each valve. Statistical analysis of the correlations suggest that they are of acceptable accuracy.     

GAS-NON-NEWTONIAN LIQUID FLOW THROUGH ELBOWS

Experimental investigations have been carried out to evaluate the two-phase pressure drop across different types of elbows in the horizontal plane for gas-non-Newtonian pseudoplastic liquid flow. A generalised correlation have been developed to predict The two-phase pressure drop as a function of various physical and dynamic variables of the system. Statistical analysis of the correlation suggests that the correlation is of acceptable accuracy.     

气液两相流流经环形狭缝通道的流动特性

引言动力、能源、石油化工等领域中广泛应用着各类管壳式换热器,此类换热器的管子与折流板之间、折流板与壳体之间在制造与装配中存在着一定的间隙。这些间隙对壳侧的压降及换热系数有较大影响。对于单相流体,这些间隙产生的泄漏量可占总流量的15％～60％~［1～4]．根据文献报道~［5],大约有50％以上的管壳式换热器涉及气液两相流,迄今为止对气液两相流体流经环形狭缝通道的流动特性研究尚未见有文献报道．本文在水平放置环形狭缝通道中,对空气一水两相混合物流经3种不同间隙环形狭缝通道的流动特性进行了研究,并应用分相模型提出了计…     

DISPERSE PHASE STRESS IN TWO-PHASE FLOW

The usual two-fluid models for disperse two-phase flows feature an average disperse-phase stress in the disperse-phase momentum equation. It is shown that it is possible to derive an expression for this quantity without considering the detailed nature of the constitutive relation of the disperse phase. The result, which is more general than other relations of the same nature, is illustrated with a number of examples. It is also shown that a new formulation of the averaged equations recently proposed by the authors is equivalent to the more usual one.     

STOKES FLOW THROUGH A BARRIER WITH DISTRIBUTED PORES

The Stokes flow through a barrier with multiple pores is solved using a cylinder approximation and eigenfunction expansions. The effect of the proximity of neighboring pores on the resistance is determined.     

环形狭缝通道内气液两相环状流流动特性

建立了环形狭缝通道内气液两相环状流的理论模型 ,该模型计及环状流气芯流动的可压缩性、气液两相间的相滑移、气相对液滴的夹带作用等因素 .考察了两相流质量流量和干度对压降、液滴速度相对变化和狭缝喉部气芯通流面积的影响 .用建立的理论模型对空气 -水两相环状流通过环形狭缝的两相压降进行预测 ,预测值和试验值吻合良好     

PRESSURE LOSSES IN TWO-PHASE GAS-NON-NEWTONIAN LIQUID FLOW IN A VERTICAL TUBE

Experimental data on pressure drop for two-phase gas-non-Newtonian ps:udoplastic liquid vertical slug flow have been analysed. Correlation have been proposed for predicting the two-phase friction factor as a function of the physical and dynamic variables of the system.     

SUSPENSION MODEL FOR BLOOD FLOW THROUGH ARTERIAL CATHETERIZATION

This article is concerned with the analysis of a dusty model for the axi-symmetric flow of blood through coaxial tubes such that the outer tube with an axially nonsymmetreic but radially symmetric mild stenosis and the inner tube have a balloon (assumed that is axi-symmetric in nature). The mild stenosis approximation is used to solve the problem. To estimate the effect of the stenosis shape, a suitable geometry has been considered such that the axial shape of the stenosis can be changed easily just by varying a parameter (referred to as the shape parameter). The model is also employed to study the effect of the volume fraction density of the particles C, the maximum height attained by the balloon δ₂, the radius of the inner tube, which keeps the balloon in position κ, and the axial displacement of the balloon x _d . Flow parameters such as velocity, the resistance to flow (the resistance impedance), the wall shear stress distribution in the stenotic region and its magnitude at the maximum height of the stenosis (stenosis throat) have been computed numerically for different shape parameters n, C, δ₂, κ, and x _d . It is shown that the resistance to flow decreases with increasing values of the parameter determining the stenosis shape n and the axial displacement of the balloon x _d , while the resistance to flow increases with the volume fraction density of the particles C, the radius of the inner tube, which keeps the balloon in position κ, and the maximum height attained by the balloon δ₂. The magnitudes of the resistance to flow are higher in the case of a dusty fluid model than in the case of a Newtonian fluid model. The wall shear stress distribution in the stenotic region and its magnitude at the maximum height of the stenosis possess a character similar to the resistance to flow with respect to C, δ₂, κ, and x _d . Finally, the effect of the volume fraction density of the particles C, δ₂, and x _d on the velocity profile are discussed.     

UNSTEADY CONVECTIVE DIFFUSION IN BLOOD FLOW THROUGH A TUBE

The paper presents an exact analysis of unsteady convective dispersion of a solute in a Casson fluid (assumed as the non-Newtonian behaviour of blood) flowing in a tube. Using a generalized dispersion model, which is valid for all time after the injection of the solute in the flow, we evaluate the axial dispersion coefficients as functions of time. The variation of the asymptotic dispersion coefficient K₂* with y₀ (the dimensionless radius of the plug flow region) shows that K₂* first increases with y₀, reaches a maximum and then decreases. The behaviour of the dimensionless dispersion coefficient K₂(T) - Pe^-2 with time T is also shown graphically.     

A MODEL FOR PULSING FLOW IN COCURRENT DOWN-FLOW TRICKLE-BED REACTORS

Based on macroscopic mass and momentum balances, a model is developed to characterize the hydrodynamic behavior of pulsing flow in cocurrent down-flow trickle-bed reactors. Predictions of the model regarding liquid saturation, length and velocity of both the liquid rich slug and gas rich pulse are reported. Also presented are experimental data of an air-water system for the effects of varying gas and liquid flow rates on pulse frequency, total pulse length and apparent slug velocity. To confirm the theory, predictions are compared with measured overall pressure gradient. Agreement is reasonably good.     

水平直圆管内油气两相流的压降

对水平放置的内径为40 mm的有机玻璃管内的油气两相流进行了详细的实验研究,实验工质为46^＃机械油和空气.油相和气相折算速度分别为0.051～0.612 m•s^-1和0.024～50.64 m•s^-1,实验在室温下进行.采用Lockhart-Martinelli关联方法对各典型流型下的实验数据进行了整理,结合流动的具体情况对其中的关联参数C进行了重新定义,提出了基于典型流型的压力梯度计算模型,并对水平管内油气两相流的压降变化规律进行了分析和讨论.理论计算值与实验测量值吻合良好.     

CHARACTERISTICS OF PULSING FLOW IN TRICKLE BEDS. IMPROVEMENTS OF A MACROSCOPIC MODEL

A rather simple macroscopic model, originally proposed by Dimenstein and Ng (1986), is examined by comparison with results of experimental work carried out in this laboratory recently. Several improvements are proposed relying either on new correlations or in better physical understanding obtained from the recent experiments. The model, despite its simplicity, is considered quite comprehensive and reliable (for the range of physical properties examined) providing good estimates of essentially all the significant time averaged characteristics of pulsing flow.     

被动应力状态下非流态化颗粒流通过孔口的流率

讨论了非流态化气固流通过孔口流率的理论模型中主动应力状态及被动应力状态模型参数符号的选取原则,导出被动应力状态下颗粒流通过孔口流率的理论方程.将理论计算结果与大量实验数据比较,归纳出被动应力状态下孔口流率的数值解法与简化积分解法的修正系数经验方程.     

COMPTON PROFILE MEASUREMENT OF TWO-PHASE FLOW DISTRIBUTION

To improve the proposed technique of Compton profile measurements and develop an accurate density distribution measurement technique, the detected scattered spectrum in a system of collimated source and uncollimated detector is expressed in terms of the density distribution and a multiple-scattering factor.

A particular experimental approach to this technique is outlined. Multiple-scattering is carefully considered in the analytical-numerical interpretation of the problem. The proposed technique is shown to be clearly valuable for stochastically steady flows in which relatively low frame rates for local time average two-phase flow parameters are acceptable.     

TWO-PHASE FLOW PRESSURE CHANGE ACROSS SUDDEN EXPANSIONS IN DUCT AREAS

A new model to calculate the two-phase flow pressure change across a sudden expansion in a duct area was developed and checked against data measured with mixtures of air and water, aqueous glycerol, watery calcium nitrate and with refrigerant R 12. In the model all relevant physical parameters are included and, in contrast to equations in the literature, the entrainment of liquid in the gas stream is considered. The predictions are validated for a wide range of conditions, pipe diameters and physical properties typically encountered in industrial pipe line systems: Calculations based on the new approach are sufficiently accurate for engineering purposes.     

BASIC EQUATION OF TURBULENCE AND MODELING OF INTERFACIAL TRANSFER TERMS IN GAS-LIQUID TWO-PHASE FLOW

Turbulence is one of the most important phenomena in analyzing thermohydrodynamic characteristics of gas-liquid two-phase flow. For the purpose of accurate prediction of the turbulence phenomena, a basic conservation equation of Reynolds stress was derived based on the local instant formulation of mass and momentum conservations of two-phase flow. In this equation, interfacial transfer terms of turbulence appear as source terms. Detailed considerations on these transport terms were carried out. It was shown that they consist of a viscous damping term due to small scale interfacial structures, a drag induced turbulence generation term due to large scale interfacial structures and a term representing the exchange between surface energy and turbulence. Based on the mechanistic modeling and turbulence modulations, carried out were physical interpretations of interfacial area concentrations of small and large scale interfacial structures, a viscous damping term due to small scale interface and turbulence generation term due to large scale interface.     

多孔介质中流体流动的格子气自动机模拟

介绍了 13-Bit正六边形多速格子气自动机模型的特点 ,讨论了多孔介质流体流动的格子气自动机模型的渗透率等参量算方法 ,应用该模型对计算机产生的多孔介质几何构型和焦炭多孔介质中的流体流动进行了模拟 ,其结果既可以给出多孔介质中的流动细节 ,也可统计得到表征多孔介质宏观流动特征的物理参量 .初步研究表明 :格子气自动机模型可用于模拟复杂边界条件下多孔介质的流体流动     

APPLICATION OF HOT-FILM ANEMOMETRY TO AIR-WATER FLOW IN AERATED STIRRED TANKS

The subject of this paper is the evaluation of the applicability of constant temperature anemometry (CTA) with a modified version of Delhaye's method to aerated stirred tanks. A calibration technique that takes into account the variation in medium temperature was developed and verified experimentally. The directional sensitivity of the conical film probe was investigated in a streamline flow field as well as in the impeller discharge stream in an stirred tank.

The reliability of the setup and the technique was verified through the comparison of the vertical and radial velocity profiles of water in a stirred tank with those obtained from the literature. The directional response of the conical probe follows the cosine law for intersection angles smaller than 45° in a streamline flow field, but the directional sensitivity in the impeller discharge stream is rather poor, owing to the rolling characteristics of flow in this region. Due to the inability to detect bubbles smaller than the sensing element of the conical probe, the CTA usually gives lower values of local gas holdup. However, this discrepancy is considered to have no influence on the velocity measurement.     

A NEW CORRELATION FOR TWO-PHASE PRESSURE DROPS IN FULLY DEVELOPED DILUTE SLURRY UP-FLOWS THROUGH AN ANNULUS

The prediction of two-phase pressure drops is important in the design of fluidized beds, heat exchangers, slurry transport lines, annular risers in reactors, driers, and other applications of particulate flows. Experimental data for liquid-solid up-flows through annuli are very limited. In this study, a correlation was developed for predicting two-phase pressure drops via Euler number (Eu _tp ) for liquid-solid suspension up-flows in the fully developed flow region of an annulus in terms of mixture Reynolds number (Re _m ), solid particle Froude number (Fr _p ), ratio of particle diameter to hydraulic diameter, and ratio of area-averaged solids density in the tested cross-sectional flow area of the annulus to the average density of the feed slurry entering the annulus. The proposed correlation, having an accuracy of almost ±25%, was obtained for water-feldspar dilute suspension up-flows in an annulus with a hydraulic diameter of 79.8 mm and with feldspar particles (2400 kg/m³ in material density and 0.072–0.138 mm in average diameter) at low concentrations.