Investigation and prediction of slug flow characteristics in highly viscous liquid and gas flows in horizontal pipes

Slug flow characteristics in highly viscous liquid and gas flow are studied experimentally in a horizontal pipe with 0.074 m ID and 17 m length. Results of flow regime map, liquid holdup and pressure gradient are discussed and liquid viscosity effects are investigated. Applicable correlations which are developed to predict liquid holdup in slug body for low viscosity flow are assessed with high viscosity liquids. Furthermore, a mechanistic model is developed for predicting the characteristics of slug flows of highly viscous liquid in horizontal pipes. A control volume is drawn around the slug body and slug film in a slug unit. Momentum equations with a momentum source term representing the significant momentum exchange between film zone and slug body are applied. Liquid viscosity effects are considered in closure relations. The mechanistic model is validated by comparing available pressure gradient and mean slug liquid holdup data produced in the present study and those obtained from literature, showing satisfactory capabilities over a large range of liquid viscosity

The effect of tube diameter on vertical two-phase flow regimes in small tubes

Flow boiling flow patterns in four circular tubes with internal diameters of 1.10, 2.01, 2.88 and 4.26 mm were investigated in the present project. The experiments were conducted in vertical upward two-phase flow using R134a as the working fluid. The observed flow patterns include dispersed bubble, bubbly, confined bubble, slug, churn, annular and mist flow. The flow characteristics in the 2.88 and 4.26 mm tubes are similar to those typically described in normal size tubes. The smaller diameter tubes, 1.10 and 2.01 mm, exhibit strong "small tube characteristics" as described in earlier studies. The sketched flow maps show that the transition boundaries of slug-churn and churn-annular depend strongly on diameter. On the contrary, the dispersed bubble to churn and bubbly to slug boundaries are less affected. The transition boundaries are compared with existing models for normal size tubes showing poor agreement

R134a flow patterns in small diameter tubes

R134a vapour-liquid two-phase flow patterns were studied in vertical small diameter tubes. The observed flow patterns include bubbly, dispersed bubble, slug, churn, annular and mist flow. Six integrated flow pattern maps, derived for two internal diameters (2.01 and 4.26 mm) and three different pressures (6.0, 10.0, 14.0 bar), are presented. Some transition boundaries, such as slug-churn and churn-annular, were found to be very sensitive to diameter and pressure. On the contrary, the boundaries of dispersed bubble-churn and bubbly-slug are less affected. The transition boundaries are compared with the existing models for normal size tubes showing significant differences

The bubbly-slug transition in a high velocity two phase flow

A possible mechanism for the transition between bubbly and slug flow is proposed and tested in a simulated slug flow system. No sudden collapse of slug flow with increasing velocity is found and it is concluded that: a. Slug flow is generally stable at voids greater than 35%. b. Bubbly flow at voids higher than this is a result of entrance conditions. c. Visual observations of bubbly flow in unheated systems at higher voids are most likely faulty. No simple asymptote limit or criterion that would predict the location of the bubbly-slug transition was found.Sponsored by the U. S. Atomic Energy Commission DS

Slug flow

Introduction: When two phases flow concurrently in a pipe, they can distribute themselves in a number of different configurations. The gas could be uniformly dispersed throughout the liquid in the form of small bubbles. There could be large gas bubbles almost filling the tube. There could be an annulus of liquid and core of vapor with or without drops of liquid in it. The interface could be smooth or wavy. When one describes how the phases are distributed, one is specifying the flow regime. Such a description is necessary before any mathematical model can be constructed which will predict a quantity such as pressure drop It is naive to expect that a single mathematical model would adequately encompass all possible two-phase flow regimes, even for a single geometric configuration. Therefore, we shall begin by saying that for this work the results that have been obtained and the conclusions that have been drawn apply only to fully developed slug flow in a round vertical pipe. Slug flow is characterized by large bubblesalmost filling the tubewhich are separated by slugs of liquid. The nose of the bubble is rounded and the tail generally flat. One may or may not find small bubbles in the slug following the large bubble. A number of typical slug flow bubbles are pictured in Figures 4-10. Bubbles very similar to these have been studied by Dumistrescu (1), and Davis and Taylor (2). Both these references consider the same problem. How rapidly will a closed tube full of liquid empty when the bottom is suddenly opened to the atmosphere. The approach used by both authors is to assume that the asymptotic rise velocity (for large times) can be calculated from potential flow theory. The boundary condition at the pipe wall is that the velocity is axial. At the bubble boundary it is assumed that the pressure is constant, The problem is then to find the shape of the bobble that would satisfy the constant pressure boundary condition.(cont.) This was done approximately and in both cases the comparison with experiment was satisfactory though the deviations became large for small tubes. The work of Davis and Taylor, and Dumitrescu served as the starting point for this investigation. The boundary condition at the bubble wall for large bubbles, constant pressure, was still valid to an excellent approximation and the finiteness of the slug flow bubbles did not appear to make much difference in their rise velocity. In the next section, the fluctuation period, the mean density, and the pressure drop will be expressed in terms of the pipe area, the Taylor bubble rise velocity and the flow rates of the two phases. In subsequent sections the observations rade of bubble shape, length and velocity will be described and then a comparison of computed and measured pressure drops given.Office of Naval Research DSR Projec

Compact fluid-flow restrictor

Fluid-flow restrictor has degree of restriction easily and accurately controlled during manufacture. Restrictor's flow channel is machined square thread around a solid slug which is shrink-fitted to cylindrical case. One end of case is closed, open end capped, and both ends tapped for tube fittings for fluid flow

Vertical upward flow patterns in small diameter tubes

Two-phase flow patterns were studied in vertical small diameter tubes using R134a as the working fluid. The observed flow patterns include bubbly, dispersed bubble, confined bubble, slug, churn, annular and mist flow. Twelve flow pattern maps, derived from four internal diameters (1.10, 2.01, 2.88 and 4.26 mm) and three different pressures (6, 10, 14 bar), are presented. The flow patterns exhibit strong “small tube characteristics” described in earlier studies when the tube diameter is 2 mm or less. Slug-churn and churn-annular boundaries depend on diameter and pressure. Dispersed bubble-churn and bubbly-slug are less affected. The transition boundaries are compared with existing models for normal size tubes showing poor agreement. Various coordinate systems were considered for the flow maps. The results show that the Lockhard-Martinelli Parameter and mass flow flux can account for the effect of fluid pressure on flow patterns

Patterns of cell movement within the Dictyostelium slug revealed by cell type-specific, surface labeling of living cells

There are cells acattered in the rear, prespore region of the Dictyostelium slug that share many of the properties of the prestalk cells and that are therefore called anterior-like cells (ALCs). By placing the gene encoding a cell surface protein under the control of an ALC-specific promoter and immunologically labeling the living cells, we analyze the movement of ALCs within the slug. There is a posterior to anterior cellular flow, and the ALCs change their movement pattern as they enter the prestalk zone. Prestalk cells are periodically shed from the migrating slug. They must be replaced if the correct ratio of prestalk to prespore cells is to be maintained, and we present evidence for the trans-differentiation of prespore into prestalk cells, with ALCs functioning as intermediates in the transition. The slug has, therefore, a surprisingly dynamic structure, both with respect to cellular differentiation and cell movement

Thermal exchange effects on steel thixoforming processes

Steel thixoforging is an innovative semi-solid forming process. It allows the manufacturing of complex parts and minimises the forming load. This work aims to identify and characterise the main feature zones of a thixoforging part. The material flow and the forging load are dependent on the thixoforging speed, the tool temperature and the initial temperature of the slug. The data are obtained for C38 thixoforging steel. A specific extrusion tool was designed that integrates the heating of the tool and the slug. This tool was set up on a high-speed hydraulic press. This work highlights the effects of heat exchange on the microstructure, the internal flow and the mechanical characteristics of thixoforging material. These heat exchanges depend primarily on the working speed and tool temperature. The internal flow is composed of three distinct zones. Among them, only semisolid zone is observed during working. The microstructures of thixoforming C38 steel consist of ferrite, pearlite and bainite

Numerical Investigation of Bubble Movement in Magnetic Nanofluids

Department of Mechanical EngineeringIn this study, the idea to generate electrical energy by using waste heat is suggested. In this idea, the electrical energy can be generated by a magnetic nanofluid and bubble movement. Thus, bubble movement in a magnetic fluid is numerically investigated using the commercial CFD package COMSOL Multiphysics for effective energy generation. The slug characteristics are also investigated because it can be generated by merging each bubble. The level-set method and phase-field method are used to simulate the bubble and slug movement, respectively. For the investigation, EFH1 and EFH3 are selected as working fluidsthey are commercial magnetic fluids manufactured by Ferrotec, and each fluid contains different amounts of magnetic particles. The solvers are validated by comparing the numerical results with previous research studies and experimental data for reliable results. The properties of a fluid can be changed by solid particles if the particles are dispersed in the fluid. These particles can affect the bubble and slug characteristics, such as shape, velocity and wake. Thus, the effect of solid particles is first studied by observing the bubble and slug movement in each magnetic fluid. In the slug investigation, the effects of some parameters are also studied, such as slug length and liquid backflow. The patterns of bubble and slug movement are investigated to predict the effective condition for the energy generation. The effective bubble and slug movements are predicted by evaluating the disturbance of the surrounding magnetic fluid for each flow pattern. A magnetic force can be created, and it can affect any phenomena when the magnetic field is applied to the system. Thus, the effect of the magnetic force is also investigated because the magnetic field should be applied to the system for the electrical energy generation. Finally, the important factor for energy generation is identified by comparing the results.ope