Low Superficial Liquid Velocities Research Articles

Biological treatment of mixed industrial wastewaters in a fluidised bed reactor

A study has been carried out on the operating parameters that influence the biodegradation of petroleum and brewery wastewaters, with a low-density biomass support. The biodegradation rate of a mixture of two wastes was compared with that of the separate wastes. A low aspect ratio reactor was employed, and this made it possible to operate at low superficial gas and liquid velocities. The gas distributor used created a fluid flow pattern similar to that of a draft tube, which enhanced axial mixing. At a particles loading of 12% (v/v), the optimum superficial gas velocity was 2.5 cm/s for the mixture. The interstice structure of the biomass-support particles, improved microbial attachment due to the resulting large surface area. There was a low biomass concentration when petroleum wastewater was treated alone, however, for a mixture of petroleum and brewery wastewaters, an increase in the concentration was observed. There was a higher gas hold up in the mixture than in the petroleum wastewater, but lower than in the brewery wastewater. An improved biodegradation was achieved when a mixture of brewery and petroleum wastewaters was treated, and this gave an indication that nutrient deficient wastes can be treated together with phosphate and nitrate rich food industry wastewaters.

Investigation of Paraffin Deposition During Multiphase Flow in Pipelines and Wellbores—Part 1: Experiments

Results are presented from two-phase flow wax deposition tests using a state-of-the-art, high-pressure, multiphase flow test facility. Wax deposition was found to be flow pattern specific and dependent on the flow velocities of the two-phase fluids. Wax deposition occurs only along the pipe wall in contact with a waxy crude oil. An increase in mixture velocity results in harder deposits, but with a lower deposit thickness. The wax buildup trend at low mixture velocities is similar to that observed in laminar single-phase flow tests. The wax buildup trend at high mixture velocities is similar to that observed in turbulent single-phase flow tests. Thinner and harder deposits at the bottom than at the top of the pipe were observed in horizontal and near-horizontal intermittent flow tests. For annular flow tests, thicker and harder deposits were observed at low superficial liquid velocity than at high superficial liquid velocity. In stratified flow tests, no wax deposition was observed along the upper portion of the pipe.

A Study of Flow Characteristics in Air-Water Two-Component Two-Phase Flow under Microgravity. Results of Flight Experiments.

In order to better understand the effect of gravity on two-phase flow, the microgravity experimental tests were conducted aboard MU-300 aircraft capable of parabolic trajectory flying. They are carried out in an air-water two-phase flow through 10 mm diameter adiabatic test section, which is 600 mm lengths of transparent acrylic resin horizontal tube. The obtained experimental data covered a range of liquid and gas flow rates with the liquid superficial velocity ranging from 0.095 m/s to 2.56 m/s, and the gas superficial velocity ranging from 0.032 m/s to 21.08 m/s. Flow pattern results obtained under μg, 1 g and 2 g conditions were compared with void fraction based flow pattern transition models developed by Bousman (1995). The effects of the gravity change on flow patterns were significantly large at low gas and liquid superficial velocities. In the comparisons of the microgravity void fraction results with the correlation proposed by Inoue-Aoki (1970), it was found that the micorgravity void fraction was greater than the model as 42% for bubbly flow region. Two-phase frictional pressure drops obtained under three g-levels were compared with each other, and it was also found that frictional pressure drop were well fitted with the Lockhart-Martinelli-Chisholm model. The effect of gravity change on the pressure drops was insignificant for the turbulent flow reginos.

Study of the Influence of Liquid Phase Viscosity on the Effective Surface Area of Arranged Packings with Vertical Walls at Low Liquid Superficial Velocity

Using the absorption of ammonia in aqueous sulfuric acid solutions, a model system to study ‘honeycomb’-type packings made of various materials (ceramics and plastics) is presented by the author. The experimental results are described by two equations, one for plastic and the other for ceramic packings. The proposed equations can also be used to determine the critical point after which the packing is completely wetted.

Flow Pattern, Holdup and Pressure Drop in Vertical and Near Vertical Two- and Three-Phase Upflow

Two-phase, air and water near vertical upflow showed significant differences to vertical and other greater inclinations. New relations are presented for prediction of holdup and transitions between fiow regimes for the near vertical case. Three-phase, oil, water and air near vertical upflow exhibit two new flow regimes which were not found in + 90° vertical upflow; a regime possessing a clear water stratified layer and semi-annular curl flow. Flow regime maps are presented and there was a significant difference between the near vertical case and the vertical upflow map in the low gas flow region where the superficial gas velocity was below V¯SG = 10ms−1 and around the inversion point between water dominated and oil dominated flows at higher gas flow rates. Relations are presented for the transitions between water and oil dominated regimes and two annular regimes in the water dominant area. In general, the liquid holdup for near vertical flow was greater than for vertical upflow, the exception being at low liquid superficial velocities of under 0.06 ms−1 and high superficial gas velocities of over 20 ms−1. Here the liquid holdup varied being sometimes below and other times above the corresponding vertical value. These variations of liquid holdup were shown to depend on the fine structure of the flow patterns present. The total pressure drop and its component parts showed significantly different patterns of behaviour depending on whether the superficial gas velocity was above or below the rise velocity of a Taylor bubble. The total pressure drop generally was greater for near vertical flow compared to the vertical up flow case and reflected changes in the fine structure of the flow patterns.

Effect of flow-induced vibration on local flow parameters of two-phase flow

A preliminary study was conducted experimentally in order to investigate the effect of flow-induced vibration on flow structure in two-phase flow. Two kinds of experiments were performed, namely ‘reference’ (no vibration) and ‘vibration’ experiments. In the reference experiment, an experimental loop was fixed tightly by three structural supports, whereas the supports were loosen a little in the vibration experiment. In the vibration experiment vibration was induced by flowing two-phase mixture in the loop. For relatively low superficial liquid velocity, flow-induced vibration promoted the bubble coalescence but liquid turbulence energy enhanced by the vibration might not be enough to break up the bubble. This leaded to the marked increase of Sauter mean diameter, and the marked decrease of interfacial area concentration. Accordingly, flow-induced vibration changed the void fraction profile from ‘wall peak’ to ‘core peak’ or ‘transition’, which increased distribution parameter in the drift-flux model. For high superficial liquid velocity, shear-induced liquid turbulence generated by two-phase flow itself might be dominant for liquid turbulence enhanced by flow-induced vibration. Therefore, the effect of flow-induced vibration on local flow parameters was not marked as compared with that for low superficial liquid velocity. Since it is anticipated that flow structure change due to flow-induced vibration would affect the interfacial area concentration, namely interfacial transfer term, further study may be needed under the condition of controlled flow-induced vibration.

Modeling of Vertical Bubble-Driven Flows

Bubbly flows comprise a large number of different flow situations, e.g., dispersed pipe flows, flows in multiphase agitated tanks, flows in multiphase fixed- and fluidized-bed reactors, and typical bubble-column and loop-reactor flows. This paper focuses on bubble-driven flows. These are flow situations were the bubble movement itself is the main source of momentum to the flow field and are often characterized by low superficial liquid velocities, relatively high superficial gas velocities, and no mechanical support of the flow (e.g., agitation). Only vertical flow situations are considered. An overview of the verified forces acting on bubbles is given, and examples of both classical and more recent modeling approaches are shown. This include gravity, buoyancy, centrifugal forces, conventional Magnus and Saffman forces, form and friction drag, and added mass as well as turbulent migration and other instability mechanisms. Special emphasis is placed on mechanisms creating bubble movement in the radial direction. Important literature on the subject with regard to the use of computational fluid dynamics to model gas-driven bubbly flows is reviewed, and the various approaches are evaluated, i.e., dynamic vs steady-state descriptions and Euler/Lagrange vs Euler/Euler formulations. Results from steady-state Euler/Euler simulations are given and discussed, and the demand for amplified modeling including more accurate and stable numerical solution schemes and algorithms is stressed.

Heat transfer and pressure drop for air-water mixtures in an isoflux vertical annulus / Wärmeübertragung und Druckabfall für Strömungen von Luft-Wasser-Gemischen in einem vertikalen Ringraum

Heat transfer and pressure drop in flows of air-water mixtures have been investigated experimentally in an isoflux vertica annulus. The superficial liquid Reynolds number as a refer ence parameter, varied from 4500 to 30000, at different values of gas-to-liquid superficial velocity ratios up to 20 and surface heat fluxes from 50 to 240 kW/m 2 . Enhancement of the two phase heat transfer coefficient is pronounced particularly a low liquid superficial velocities. The results are correlated an compared with some models of two-phase, two-componen flows for air-water mixtures within their range of validity.

Thermal dispersion in vertical gas-liquid flows with foaming and non-foaming liquids

Heat transfer experiments have been performed in gas-liquid upwards flow in a vertical column with non-foaming (water) and foaming (kerosene) liquids. The main purpose of the experiments has been to characterize the degree of thermal mixing in the system. For the range of conditions employed, the non-foaming liquid exhibits complete mixing at low liquid superficial velocities. An increase in liquid velocity leads to incomplete mixing. In the latter case, the thermal dispersion coefficient at low gas superficial velocities is larger than what correlations in the literature predict. For the foaming liquid, when foaming and bubbling regions coexist in the bubble column, each region behaves as a completely-mixed subsystem.

Measuring and modelling mass transfer at bends in annular two phase flow

Mass transfer measurements at 180° bends under annular two phase flow conditions have been successfully carried out using the dissolution of copper in acid ferric chloride solutions. It appears that the enhancement of mass transfer at bends relative to straight tubes increases with superficial gas velocities and is constant with low superficial liquid velocities. A model has been formulated which accounts for the effect of bend geometry on mass transfer and relates the results to mass transfer at two phase annular impinging jets.

Casing Heading in Flowing Oil Wells

Summary Casing heading, an unsteady flow in oil wells completed without packers, occurs when both gas and liquid superficial velocities are low. A hydrodynamic model is presented that simulates laboratory data for the cases considered. Results confirm that heading occurs for low superficial gas and liquid velocities and that choking re-establishes stability.