Showing papers on "Slug flow published in 1984"

Hydrodynamics and mass transfer in non‐Newtonian solutions in a bubble column

Abstract: Until now the oxygen transfer in viscous non-Newtonian solutions has been studied only in bubble columns of about 0.14-m diameter. Recently Godbole et al. (1982) reported much smaller gas holdups in Carboxy Methyl Cellulose solutions (CMC) for a large-diameter column. Therefore, the gas holdups, volumetric mass transfer coefficients, and specific gas-liquid interfacial areas are measured in CMC solutions using a bubble column of diameter 0.305 m and height 3.4 m. The transition from churn-turbulent to slug flow regime occured at higher viscosities and the gas holdups and volumetric mass transfer coefficients were lower in both flow regimes than reported for smaller column diameters. Empirical correlations are presented for the gas holdup, volumetric mass transfer coefficient, and specific gas-liquid interfacial area which would be suitable for the design of fermentors.

Studies of mixing in a concentric tube air-lift reactor containing xanthan gum by means of an improved flow follower

Abstract: The influence of a pseudoplastic non-Newtonian fluid upon the hydrodynamic performance and mixing parameters of a concentric tube air-lift fermenter has been studied using a range of dilute xanthan gum solutions (0-0.5% weight by volume). Liquid circulation times vary in a complex pattern with increasing gum concentration. At low concentrations, circulation was more; rapid due to drag reduction whilst at the highest concentrations circulation times were increased. The column voidage decreased with increasing gum concentration and bubbly flow in the riser was replaced by slug flow. For all gum concentrations the effective dispersion coefficient for a single passage around the loop was increased relative to tap water. An improved radio-pill flow follower system for hydrodynamic studies is described.

Electrochemical Method for Measuring Turbulent Characteristics of Gas-Liquid Flows

Abstract: Electrochemical method of studying the hydrodinamic characteristics of two-phase flow based on the measurement of the diffusion current to a microelectrode placed in the solution ofthe special electrolyte is a diffusional analog of the constant-temperature hot-wire technique. Application of this method to measurements of wall shear stress, liquid velocity and local void fraction, fluctuational characteristics including components of velocity is described. Some results showing the efficiency of the application of the electrochemical technique to complex studies of gas-liquid flow are presented.

Comparison of measured and predicted pressure drops in tubing for high-water-cut gas wells

Abstract: A considerable number of deep (10,000 plus feet) high volume gas wells in Northern Germany show signs of increasing water production (up to 125 BBL/MMscf). To predict well behavior and optimize recovery from these wells it is not only necessary that one is able to realistically describe the two-phase flow in the reservoir but also flow in the wellbore up the tubing. In particular one must be able to: - Predict the pressure drop in the tubing with reasonable accuracy, and - estimate the benefit from operational changes such as changing tubing size, etc. Since none of the available calculation procedures was found capable of handling the problem, an extensive gas well-testing program was initiated and actual two-phase (gas/water) pressure drops measured in the field for a wide range of operating parameters. The evaluation of the test results and comparison with calculated pressure drops provide the following conclusions: Unmodified, the multi-flow-regime calculation procedures significantly overpredict the actual tubing pressure drop in reasonably high to high water-cut gas wells. Unmodified, the much simpler no-flow-regime calculation procedures, while underpredicting the actual pressure drop, provided far better estimates over the range of parameters considered. In using the multi-flow-regime procedures, pressure drop calculations assumingmore » mist flow yielded very accurate values for the pressure drop over a much wider range of flow parameters than suggested by the available flow regime definitions. Using the available data to redefine the flow regime boundary separating the mist from the slug flow regime, the multi-flow-regime pressure drop calculation procedures could be significantly improved.« less

Analysis of low-Peclet heat transfer during slug flow in tubes with axial wall conduction

Abstract: An exact solution is presented for the temperature distribution during slug flow inside an infinitely long tube with a finite heated length. The solution takes into consideration axial conduction in the fluid and tube wall, which are characterized by Peclet number and a wall conduction parameter, respectively. Results of bulk and wall temperatures, convective heat flux and Nusselt number are presented for low and high Peclet numbers using a range of values for the wall conduction parameter. It is concluded that wall conduction can have substantial effects on the heat transfer characteristics in the areas surrounding the beginning and end of direct heating. These effects can be much more pronounced than the effects of fluid conduction.

Combinated Flow Pattern Map for Cocurrent and Countercurrent Air-Water Flows in Vertical Tube

Abstract: Flow patterns for cocurrent and countercurrent air-water flows in vertical tubes (40 and 80mm I.D.) at volumetric flux densities of air and water in the ranges −115–158 and −100–102 cm/s were observed. A flow pattern map presenting the entire data of the observed flow patterns, i.e. bubbly, slug and annular flow for each mode of flow operation (upflow, countercurrent flow and downflow) were presented on the jl vs. jg plane. The flow pattern maps showed significant difference of flow pattern transition boundaries with upflow, countercurrent flow and downflow. Flow pattern transition curves were smoothly continuous with the change of the direction of water flow, on the other hand the change of flow direction of air showed complicated effect on flow pattern transition near zero jg . Comparison of the present flow pattern data with the reported general flow pattern maps for upflow showed that the correlation of Taitel et al. for bubble-slug flow transition is applicable to both cocurrent and countercurrent ai...

Local formulation of interfacial area concentration and its measurements in two-phase flow

Abstract: The interfacial area concentration is one of the most important parameters in analyzing two-phase flow based on the two-fluid model. The local instantaneous formulation of the interfacial area concentration is introduced here. Based on this formulation, time and spatial averaged interfacial area concentrations are derived, and the local ergodic theorem (the equivalency of the time and spatial averaged values) is obtained for stationary developed two-phase flow. On the other hand, the global ergodic theorem is derived for general two-phase flow. Measurement methods are discussed in detail in relation to the present analysis. The three-probe method, with which local interfacial area concentration can be measured accurately, has been proposed. The one-probe method under some statistical assumptions has also been proposed. In collaboration with the experimental data for the interfacial velocity, radial profiles of the local interfacial area concentration are obtained based on the one-probe method. Result indicates that the local interfacial area concentration has a peak value near the tube wall in bubbly flow, while in slug flow it shows a higher value in the central region of the tube for that particular set of data.

Velocity Measurement with Electrical Double-Sensing Devices in Two-Phase Flow

Abstract: A computer-aided-data-processing method was developed to enable the velocity and liquid holdup measurements of liquid lumps having a wide range of velocities from forward and backward flow. Furthermore, an algorithm for the development of a relatively simple microprocessor was produced with aiming the measurement of forward flow. The features of these were discussed with comparing the conventional methods by means of cross-correlation, cross-spectrum-coherence and manual reading for determining transit time.

Measurement of Transient Flow Pattern by High Speed Scanning X -Ray Void Fraction Meter

Abstract: In order to measure void distributions across pipe flow and to determine the transient flow pattern during blowdown from a high pressure water vessel to atmosphere, we have developed a high-speed scanning X-ray void fraction meter. The scanning X-ray beam is collimated by 8 hole-slits on a rotating disc. An X-ray beam scans across a pipe from top to bottom, according to the hole-slit movement. The maximum scanning frequency is 200 Hz. A void distribution curve can be obtained every 5.0 ms. Void signals are sent to a void distribution color display system that make it easy to recognize even a slug flow. Experimental results show that the system is very effective to determine how flow patterns change during blowdown.

Effect of grid spacers on reflood heat transfer in PWR-LOCA

Abstract: Experiments were performed in order to clarify the effect of the grid spacers on reflood heat transfer in PWR-LOCA The flow pattern, the thermal responses and the water accumulation near the grid spacer were investigated by shifting the grid spacer at the midplane of the simulated core The heat transfer coefficient before the quenching was about 20 to 50% higher just above the grid spacer than just below the grid spacer The decrease of the droplet diameter due to the grid spacer was observed in the droplet dispersed flow regime In the slug flow regime, the grid spacer was rewetted early in the reflood transient and the increased water accumulation near the grid spacer was observed Hence, the heat transfer enhancement due to the grid spacer is mainly attributed to the increased interfacial surface area of droplets in the dispersed flow and also to the increased film boiling heat transfer in the slug flow The thermo-hydraulic behavior near the grid spacer was well predicted with the model developed ba

Wall Shear Measurements by Electrochemical Probes in Two-Phase Flow - Bubble and Slug Regimes

Abstract: Frictional pressure drop is an important parameter to consider for the design of equipment concerned by two-phase flow. In most cases the wall friction is obtained from the momentum balance which can induce some uncertainty. Another way is offered by local and instantaneous measurements of the wall shear giving a more precise evaluation of the pressure drop and valuable information about the flow near the wall. The electrochemical probes appeared to be very convenient for that purpose in liquid flow; their use has been extended in gas-liquid flow for two important regimes: bubbly flow and sluggish flow.

Full-scale cold-flow modelling of the SRC-I slurry fired heater at Creare, Inc. mixing and 1/sup 0/ downslope studies

Abstract: One of the major pieces of equipment in the SRC-I Demonstration Plant is the slurry fired heater. Because of the absence of any plant data at comparable combinations of operating severity, a cold-flow modelling experimental program was initiated at Creare, Inc. The first phase of the test program confirmed the fired heater design and established reliable boundaries of flow rates for proper operation of the fired heater. An experimental setup was designed and built at Creare to duplicate the piping arrangement and flow conditions of the fired heater. The pipe dimensions, flow rates, and fluid properties were selected to minimize areas of scale-up and extrapolation. This follow-up test program was developed to resolve concerns raised from the observations made in the first phase. Tests were conducted to establish the extent of mixing between the liquid carpet and the fast-moving liquid slugs above it. The other segment of the test program was designed to develop the flow regime and pressure drop data in the 1/sup 0/ downslope configuration. The results demonstrated a significant amount of mixing between the liquid carpet and the liquid slugs for water and the 400-cP fluid at the design flow conditions. The extent of mixing improved withmore » increasing liquid and gas velocities and decreasing liquid viscosities. Adequate mixing was observed at liquid flow rates as low as 50% of the design flow conditions. Slug flow was observed at design conditions in the 1/sup 0/ downslope configuration. Although adequate mixing is expected in heater pipes, different techniques should be investigated to improve the extent of mixing, especially near the transition boundary. 4 references, 5 figures, 8 tables.« less

The Measurement of Liquid Phase Velocity Profiles in Vertical Two-Phase Flow

Abstract: A non-disturbing photochromic dye tracing flow visualisation technique has been applied to measure velocity profiles in two-phase flow in a 10 mm diameter pipe, using trichloroethylene and air as working fluids. Measurements are presented for vertical annular and slug flows.

Slug Flow Transition in Horizontal Gas-Liquid Flow

Abstract: We investigated a horizontal two-phase flow transition from separated flow to slug flow without a phase change. A transition model is presented in this paper, based on the experimental results obtained in the air-water system. The model is derived from the growth condition of a wave on a stratified water layer. It agrees reasonably well with Mandhane's map of flow patterns. If disturbances enter the system, the slug flow transition is sometimes enhanced. To examine this transition enhancement, a test tube was attached to a water tank with a weir to regulate the initial water depth in the tube. When a water slug flows out of the tube, a bore goes upstream in the tube, and occasionally causes formation of a next slug. The theoretical model is used to predict the conditions of continual slug formation. The hydrodynamic behavior of slug flow is also examined.

Gas-liquid flow and heat transfer

Abstract: This book covers almost the total field of gas-liquid flow and heat transfer, reviewing and collating recent information. Contents (partial): Introduction. Regimes of flow. General analytical and empirical relationships in two phase flow. Interfacial waves. Creation and behaviour of entrained droplets. Bubble flow. Plug flow. Hydrodynamics of co-current vertical annular flow. Hydrodynamics and limits of counter-current flows. Stratified wavy and slug flow in horizontal tubes. Hydrodynamics of annular flows in nonvertical channels and complex. Introduction to two phase heat transfer. Heat transfer in annular flow. Burnout. Post burnout heat transfer. Rewetting and reflooding. Experimental techniques.

Correlations of characteristic parameters with reference to horizontal gas-liquid transient slug flow.

Abstract: Simplified correlations for estimating characteristic parameters are presented with reference to a transient slug flow, which is induce by an abrupt increase in a volumetric gas flux in a horizontal two-phase shear flow. The correlations are available in the range of tube diameter : 20-40 mm, initial gas flux : 0.3-1.0 m/s, final gas flux : 0.9-3.2 m/s. and liquid flux : 0.04-0.08 m/s.

Measurement of Void Distribution in Transient Flows

Abstract: By means of X-ray Beam Scanning Method, void distributions in horizontal pipes during blowdown were measured for various conditions. Two types of X-ray void fraction meters were used; One was scanning upward and downward across the pipes, and the other was highspeed scanning type using a rotating disc. Highspeed scanning type had a void distribution color display system that made it easy to recognize even a slug flow. The data were plotted on the flow regime map and compared with available data. For high mass flux. the flow pattern became annular and was weakly dependent on pressure. For low mass flux, the flow pattern became stratified due to gravity.

Effect of Gas Introduction on Temperature Distribution for Tube Flow with Internal Heat Sources

Abstract: An experimental study has been conducted to investigate the effect of gas introduction on the heat transfer characteristics for turbulent flow of a heat generating liquid in an adiabatic tube 20 mm in inside diameter. Heat generation within the fluid was brought about by passing an alternating current through the working fluid, which was an aqueous solution of sodium chloride mixed with air bubbles. The superficial liquid Reynolds number ranged 3,700–11,000. The quality was varied from 2.6×10−5 to 3.3×l0−3. Measurements were made of the temperature distributions in the fluid as well as on the tube wall. The experimental results were compared with theoretical analyses. In bubbly flow; the introduction of air into liquid brought forth a flat temperature distribution due to a considerable increase of turbulence and a saddle-shaped void distribution, which had a maximum near the tube wall. In slug flow, however, the void distribution changed to a dome-shaped profile with a maximum at the tube center and the r...

Development of flow boiling following depressurisation

Abstract: An electrically heated stainless steel strip initially cooled by flowing water at 670 kPa was subjected to rapid blowdown to atmospheric pressure. The development of nucleate boiling and slug flow is described. It is shown that steady-state flow boiling conditions are not applicable and that there are large departures from equilibrium between the phases under these transient conditions.