Low Flow Rate Conditions Research Articles

B209 垂直上昇環状二相流における液滴飛散特性に及ぼす壁面濡れ性の影響(OS8 熱流動),動力エネルギーシステム部門20周年,次の20年への新展開)

To evaluate the effect of wall surface wettability on the characteristics of upward gas-liquid annular two-phase flow in a vertical pipe, an experimental study was performed using two test pipes: an acrylic pipe and a FEP pipe. Measured contact angles on the acrylic and FEP pipe surfaces were 60° and 80°, respectively. Basic flow characteristics such as liquid film thickness and liquid entrainment ratio were respectively measured by a laser focus displacement meter and a suction method. At relatively high gas flow rate and low liquid flow rate conditions, a reduction of the surface wettability by the FEP pipe enhanced the interfacial waves on liquid film, and caused an increase in the liquid entrainment ratio and a decrease in the liquid film thickness.

Bubble formation on a submerged micronozzle

This work investigates detailed formation of air bubbles on a submerged micrometer-sized nozzle. The experimental study is conducted on a submerged nozzle of radius of 55 μm under low gas flow rate conditions (0.015 ∼ 0.83 ml/min). The bubble formation is recorded by a high-speed optical camera and detailed characteristics of bubble formation such as the variations of instantaneous contact angles, bubble heights and the radii of contact lines are obtained, which shows a weak dependence on the flow rate under the conditions of current work. Using experimentally captured values of the height of bubble and the radius of contact line, the Young–Laplace equation is solved, which is found to be able to predict the bubble evolution quite well until the last milliseconds before the detachment. A force analysis of bubble formation reveals that the observed variations of contact angles and other characteristics during the bubble growth period are associated with the relative contribution of surface tension, buoyancy force and gravitational force.

Flow-field dynamics during droplet formation by dripping in hydrodynamic-focusing microfluidics

Using microscopic particle image velocimetry, we examine the flow field around an oil droplet as it is formed by hydrodynamic focusing in an aqueous solution using a pressure-driven cross-channel microfluidic device. By detecting the temporal dependence of the instantaneous flow fields of the continuous phase in the dripping regime, we show that shear is not the primary mechanism that initiates droplet formation in our low flow rate and moderate capillary number experimental conditions. Instead, the advancing finger of oil partially and temporarily plugs the outlet channel, creating a pressure difference that builds up and is released when water from the side channels pushes the tip of the finger into the outlet channel, thereby facilitating the birth of the droplet by interfacial pinch-off that is primarily initiated by an extensional flow.

Experimental study and CFD modelling of a two-phase slug flow for an airlift tubular membrane

The aim of the present study was to develop a computational fluid dynamics (CFD) model to study the effect of slug flow on the surface shear stress in a vertical tubular membrane. The model was validated using: (1) surface shear stresses, measured using an electrochemical shear probe and (2) gas slug (Taylor bubble) rising velocities, measured using a high speed camera. The length of the gas slugs and, therefore, the duration of a shear event, was observed to vary substantially due to the coalescing of gas slugs as they travelled up the tube. However, the magnitude of the peak surface shear stress during a shear event was not observed to vary significantly. The experimental conditions significantly affected the extent to which the gas slugs coalesced. More coalescing between gas slugs was typically observed for the experiments performed with higher gas flow rates and lower liquid flow rates. Therefore, the results imply that the frequency of shear events decreases at higher gas flow rates and lower liquid flow rates. Shear stress histograms (SSH) were used as a simple approach to compare the different experimental conditions investigated. All conditions resulted in bi-modal distributions: a positive surface shear peak, caused by the liquid slug, and a negative shear peak caused by the gas slugs. At high gas flow rates and at low liquid flow rates, the frequency of the shear stresses in both the negative and positive peaks were more evenly distributed. For all cases, increasing the liquid flow rate and decreasing the gas flow rate tends to result in a predominant positive peak. These results are of importance since conditions that promote evenly distributed positive and negative peaks, are likely to promote better fouling control in membrane system. At high liquid and low gas flow rates, the frequencies obtained numerically and experimentally were found to be similar, deviating by less than approximately 10%. However, at high gas and low liquid flow rates, the differences were slightly higher, exceeding 20%. Under these conditions, the CFD model simulations over predicted the shear stresses induced by gas slugs. Nonetheless, the results indicate that the CFD model was able to accurately simulate shear stresses induced by gas slugs for conditions of high liquid and low gas flow rates.

Thermal behavior of a copolymer PV/Th solar system in low flow rate conditions

A simulation model of finite differences describing a water heating system using a Hybrid Photovoltaic–Thermal collector manufactured in a copolymer material and running in low flow rate conditions has been developed. It includes the essential thermal transfers. The thermal and electrical performances of this solar system have been studied. The choice of the material and the structure of the solar collector are described. The temperatures evolution is modeled in various parts of the solar system and the stratification of the tank is shown. Average electrical, thermal and global efficiencies are calculated each month. We note the importance of thermal recuperation which can catalyze the development of such systems. The utilization of a copolymer for the total design of the solar collector has numerous advantages as reducing the weight, facilitating the manufacturing and reducing the cost.

Occurrence Mechanism and Oscillation Characteristics of Pulsation Phenomenon Arising in Cavitation Surge in Cascade

In this study, numerical analysis of cavitating three-blade cyclic flat-plate cascade is performed with paying attention to cavitation surge which is a type of cavitation instabilities. A numerical method employing “locally homogeneous model for compressible gas-liquid two-phase medium” is applied to solve the unsteady cavitating flowfield. From results of numerical analysis, few typical tendency of cavitation surge which is well known in experiments was reproduced numericaly, that frequency of cavitation surge decreases with lowering σ, and that cavitation surge is easy to occur at low flow rate condition. Additionaly, mechanism of pulsation phenomenon of cavitation surge in flat-plate cascade was clarified, that collapse pressure of cloud cavity in downstream of cascade propagates upstream on contact with re-entrant jet which is flowing backward inside a sheet cavity and causes oscillation in upstream pressure, also that negative angle of attack and choking of cascade throat are considered to cause of oscillation in flow rate. About dynamic transfer function of cavitation, certain degree of possibility is confirmed in quasi-steady mass flow gain factor Mquasi and cavitation compliance Kquasi for prediction of occurrence limit of cavitation instabilities. Additionally, for prediction of frequency of cavitation surge, it was confirmed that local cavitation compliance Klocal is more available than quasi-steady one.

Chiral separation of tryptophan by single-pass affinity inclined ultrafiltration using hollow fiber membrane module

The principle of inclined ultrafiltration, which can remove the filter cake continuously, was applied to the chiral separation of tryptophan enantiomers with bovine serum albumin (BSA) as the stereospecific macroligand by operating with the mode of single-pass using the hollow fiber membrane module vertically placed. The increase in the BSA concentration and the decrease in the racemic tryptophan concentration in the feed solution caused the increase in the separation factor of d-tryptophan, which preferentially permeated through the membrane, because of the strong stereospecific binding of the l-isomer to BSA at pH 7. The separation factor in affinity ultrafiltration was well evaluated based upon the Freundlich equation, in which the empirical constants were determined from the static binding experiments. The filtration rate was decreased with the BSA concentration, but was little influenced by the mass flow rate of the concentrate because BSA cake deposited on the membrane was efficiently removed by the gravitational effect even at the extremely low flow rate. Consequently, the decrease in the flow rate of the concentrate brought about the dramatic increase in the concentration ratio of BSA in the concentrate, serving the purpose of the performance increase of the next stage eluting the bound l-tryptophan from BSA. The concentration ratio of BSA was accurately estimated by considering the mass balance of BSA in the module at the steady state condition where the growth of the BSA cake on the membrane ceased. It is concluded that the method of single-pass ultrafiltration at the extremely low flow rate condition using the module placed vertically is distinctly efficient also in chiral separation by affinity ultrafiltration using the stereospecific macroligand. Additionally, the two-stage affinity ultrafiltration in which both the binding process of enantiomers to BSA and the elution process of the bound enantiomers were included was efficient for recovery of each tryptophan enantiomer.

Inhibitor Performance on Corrosion and Erosion/Corrosion Under Turbulent Flow With Sand and CO2—An AC Impedance Study

Summary Erosion/corrosion is a severe problem in oil and gas producing wells because of high flow velocity and sand particles entrained in the system. Using corrosion inhibitors to reduce erosion/corrosion has recently been proposed as an economically viable solution for carbon-steel piping systems (Smart 1991). In the literature, most studies using inhibitors to mitigate corrosion have been conducted under stagnant or low flow rate (<1 m/s) conditions. However, severe erosion/corrosion may occur when inhibitor films are removed from the steel by high liquid shear forces under actual oil and gas production conditions. The inhibiting effect of a commercial inhibitor [named Inhibitor A (Wang et al. 2005)] on the behavior of carbon steel in CO2-saturated media has been examined under high flow velocity with sand by electrochemical and gravimetric measurements. Experiments were performed using a Rotating Cylinder Electrode (RCE). The alternate current (AC) impedance technique was used to study the effect of inhibitor adsorption onto the metal surface. The study clearly reveals that the addition of the inhibitor moves the corrosion potential toward positive values and reduces the corrosion rate. Changes in impedance parameters (Rct and Cdl) are indicative of adsorption of inhibitor on the metal surface leading to the formation of protective films.

Investigation and numerical simulation of inner-flow of an axial mineflow fan under low flow rate conditions

Because of unstable properties of axial mine flow fans working under conditions of low flow rates, the safety and reliability of fans in their operational zone is reduced. At times, serious vibration may bring about the destruction of equipment or even jeopardize the safety of entire factories. By means of oil flow visualization techniques and numerical simulation, we have investigated the inner-flow of an axial mine flow fan working under low flow rate conditions. The fundamental reasons of complex flow phenomena of the inner-flow of the flow fan under these stated conditions were revealed. At the same time and in order to improve the inner-flow under conditions of low flow rates, a blade separator and air separator were designed. From our tests we found that the blade separator and air separator are two kinds efficient methods to improve the unstable working characteristics of the axial mine flow fan operating under low flow rate conditions. The effect of the improvement of the air separator is stronger than that of the blade separator.

In vitro hemorheological study on the hematocrit effect of human blood flow in a microtube

In vitro experiments to investigate the hematocrit effect on human blood flow in microcirculation were carried out using a micro-PIV technique. The micro-PIV system consisted of a 2 head Nd:YAG laser as a illumination light, a cooled CCD camera, a delay generator and a personal computer for control and data processing. Human blood with a hematocrit of 20, 30 and 40% was supplied into a microtube of 100 microM in diameter using a syringe pump. Fluorescent particles of 1.0 microM in mean diameter were seeded in the blood flow as tracers to measure instantaneous velocity fields by applying a cross-correlation PIV algorithm. The mean velocity field information was obtained by ensemble averaging the instantaneous velocity field data obtained. The hemorheological characteristics related with the blood flow in the microtube were also evaluated as functions of flow rate and hematocrit using the PIV data. The blood flow has a cell-free layer near the tube wall and this layer's thickness is increased with the increasing flow speed due to the radial migration. As the hematocrit increases, the velocity profile starts acquiring non-Newtonian features under low flow rate conditions. The hemorheolgical characteristics were found to influence largely on the viscosity and shear rate of blood flow.

D12 半開放型軸流ファンの低流量域流れに関する研究(流体工学I)

D12 半開放型軸流ファンの低流量域流れに関する研究(流体工学I)

Occurrence Mechanism and Oscillation Characteristics of Pulsation Phenomenon Arising in Cavitation Surge in Cascade

In this study, numerical analysis of cavitating three-blade cyclic flat-plate cascade is performed with paying attention to cavitation surge which is a type of cavitation instabilities. A numerical method employing “locally homogeneous model for compressible gas-liquid two-phase medium” is applied to solve the unsteady cavitating flowfield. From results of numerical analysis, few typical tendency of cavitation surge which is well known in experiments was reproduced numericaly, that frequency of cavitation surge decreases with lowering σ, and that cavitation surge is easy to occur at low flow rate condition. Additionaly, mechanism of pulsation phenomenon of cavitation surge in flat-plate cascade was clarified, that collapse pressure of cloud cavity in downstream of cascade propagates upstream on contact with re-entrant jet which is flowing backward inside a sheet cavity and causes oscillation in upstream pressure, also that negative angle of attack and choking of cascade throat are considered to cause of oscillation in flow rate. About dynamic transfer function of cavitation, certain degree of possibility is confirmed in quasi-steady mass flow gain factor Mquasi and cavitation compliance Kquasi for prediction of occurrence limit of cavitation instabilities. Additionally, for prediction of frequency of cavitation surge, it was confirmed that local cavitation compliance Klocal is more available than quasi-steady one.

The Colloidal Approach. A Promising Route for Asphaltene Deposition Modelling

It is now widely recognized that asphaltene exist in crude oils both as dissolved and particulate matter and that asphatenic crude oils behave as colloidal systems. The objective of this research work is to check if, in porous media and under dynamic conditions, asphaltene also behave as colloids. In this case, their deposition kinetic should obey the classical laws for colloid deposition in porous media. To achieve this, asphaltene deposition kinetics has been investigated as a function of the main controlling parameters such as flow rate, asphaltene aggregation state, resin content and crude origin. The study has been performed, first under well controlled condition using model fluids and porous media, and then under more representative conditions using actual crude oils and outcrop sandstones. The results confirmed that, indeed, the kinetics of asphaltene deposition in porous media obeys the general scaling low of colloid deposition. They allowed us to propose general scaling laws for the deposition kinetics in the form , η is the capture efficiency and γ the shear rate. The exponents s are universal exponents that are characteristic of the deposition regimes while the power law pre-factors A encompass all the specific features of the system considered (asphaltene and porous media). These kinetic laws show that the thickness of the deposit increases rapidly with decreasing shear rate. Accordingly and under favourable conditions, a thick deposit is expected to form during heavy oil extraction from high permeability formations and under low flow rate conditions. Such deposition could then have significant impact on the efficiency of heavy oil recovery. Therefore, its impact on permeability and on flow properties of reservoir fluids needs to be assessed as a part of process optimisation and evaluation. The Colloidal approach provides a new and promising route for asphaltene deposition and associated permeability damage modelling.

Performance of a Sequential Reactive Barrier for Bioremediation of Coal Tar Contaminated Groundwater

Following a thorough site investigation, a biological Sequential Reactive Barrier (SEREBAR), designed to remove Polycyclic Aromatic Hydrocarbons (PAHs) and BTEX compounds, was installed at a Former Manufactured Gas Plant (FMGP) site. The novel design of the barrier comprises, in series, an interceptor and six reactive chambers. The first four chambers (2 nonaerated-2 aerated) were filled with sand to encourage microbial colonization. Sorbant Granular Activated Carbon (GAC) was present in the final two chambers in order to remove any recalcitrant compounds. The SEREBAR has been in continuous operation for 2 years at different operational flow rates (ranging from 320 L/d to 4000 L/d, with corresponding residence times in each chamber of 19 days and 1.5 days, respectively). Under low flow rate conditions (320-520 L/d) the majority of contaminant removal (>93%) occurred biotically within the interceptor and the aerated chambers. Under high flow rates (1000-4000 L/d) and following the installation of a new interceptor to prevent passive aeration, the majority of contaminant removal (>80%) again occurred biotically within the aerated chambers. The sorption zone (GAC) proved to be an effective polishing step, removing any remaining contaminants to acceptable concentrations before discharge down-gradient of the SEREBAR (overall removals >95%).

An experimental study of the fluid flow and heat transfer characteristics in micro-condensers with slug-bubbly flow

Experiments were conducted to study the condensation flow pattern in silicon micro-condensers using water as the medium. Slug-bubbly flow was found to be one of the dominant flows in the micro-condenser and it was a major factor in determining the heat transfer and pressure drop properties of the fluid inside the micro-condenser. The transition from the slug-bubbly flow to a mixed flow pattern was studied. A correlation was obtained to predict when the transition of the flow pattern would occur. Only slug-bubbly flow existed under low steam mass flow rate and high heat transfer rate conditions. As the steam mass flow rate increased or the heat transfer rate dropped, the mixed flow pattern would then appear. In the slug-bubbly flow regime, the heat transfer coefficient and pressure drop in the micro-condensers were investigated in detail. It was found that micro-condensers with smaller channels could exhibit higher heat transfer coefficients with the same Reynolds number. The condensation heat transfer coefficient was higher than that in the tubes with the diameter of centimeter. Pressure drops in the micro-condensers with smaller channels were higher due to the increased transition loss. At the same time, the pressure drop in the micro-condenser was found to be lower than what could be predicted using the macro-scale correlation. Increasing the heat flux would create a longer bubble–film region and fewer unit cells in the micro-condenser resulting in an increased heat transfer coefficient and a decreased pressure drop.

Performance Comparison of Scanning Electrical Mobility Spectrometers

Scanning electrical mobility spectrometers (SEMS) are commonly used for near real-time ultrafine particle size distribution measurements. Analysis of SEMS measurements to calculate particle size distributions requires detailed understanding of instrument characteristics and operation. Varying instrument designs are used in the different commercial SEMS systems, and data analysis with these instruments requires accurate knowledge of their relative performance. In this study, an experimental approach to evaluate and reconcile differences between different SEMS instruments is established. This approach is used to characterize the relative performance of two SEMS systems—TSI's SMPS 3936-L22 and MSP's WPS XP1000—for particle sizes in the range of 20 to 300 nm. In these tests, the instruments were operated under a low flowrate condition with aerosol and sheath air flows of 0.3 and 3 LPM, respectively. Measurements show that the particle sizing characteristics of the instruments are very consistent with each oth...

Numerical simulation of periodic bubble formation at a submerged orifice with constant gas flow rate

Extensive numerical simulations were carried out to study the problem of bubble formation at submerged orifices under constant inflow conditions. A combined volume-of-fluid and level-set method was applied to simulate the formation process, the detachment and the bubble rise above the orifice in axisymmetric coordinates. On the one hand, the operating conditions of the formation process such as orifice flow rate, orifice radius and wettability of the orifice plate were investigated for the working fluids of air and water at 20 °C. On the other hand, the influence of the variation of fluid properties (liquid density and viscosity, surface tension) was examined individually. In this frame, the present work focused on low and medium flow rate conditions, at which the formation takes place in a periodic manner, in contrast to aperiodic or double periodic modes. The results of the computations provide information on the influence of various conditions on the bubble shapes, the bubble volume and the transition from a single to a double periodic formation process. The numerical results were extensively validated with experimental data available in the literature.

Simultaneous nitrification and denitrification in step feeding biological nitrogen removal process

The simultaneous nitrification and denitrification in step-feeding biological nitrogen removal process were investigated under different influent substrate concentrations and aeration flow rates. Biological occurrence of simultaneous nitrification and denitrification was verified in the aspect of nitrogen mass balance and alkalinity. The experimental results also showed that there was a distinct linear relationship between simultaneous nitrification and denitrification and DO concentration under the conditions of low and high aeration flow rate. In each experimental run the floe sizes of activated sludge were also measured and the results showed that simultaneous nitrification and denitrification could occur with very small size of floe.

Detecting the Blockage of the Sensing Lines of a Differential-Pressure Flow Sensor in a Dynamic Process Using Wavelet Transform Techniques

The blockage of the sensing lines of a differentialpressure (DP) flow sensor has been found to be the main cause of a malfunction of a flow measurement system in many industrial applications. In this paper, the blockage of the sensing lines under dynamic process conditions is investigated using wavelet transform techniques. The results obtained show that the blockage in a fast changing process is only detectable when the severity of the blockage is over 90%. This outcome differs from that when the sensor operates under a slow varying process. The main reason resulting in the discrepancy between slow and fast varying processes is that a process with high flow rates produces more noise energy in the output of the sensor than a process with low flow rates does. This means that the noise energy generated by the blockage of the sensor under low flow-rate conditions is indistinguishable with that from the output of the sensor working under the sensor normal operating conditions but a process with high flow rates

Quantifying Ground Water Inputs along the Lower Jordan River

The flow rate of the Lower Jordan River has changed dramatically during the second half of the 20th century. The diversion of its major natural sources reduced its flow rate and led to drying events during the drought years of 2000 and 2001. Under these conditions of low flow rates, the potential influence of external sources on the river discharge and chemical composition became significant. Our measurements show that the concentrations of chloride, calcium, and sodium in the river water decrease along the first 20-km section, while sulfate and magnesium concentrations increase. These variations were addressed by a recent geochemical study, suggesting that ground water inflow plays a major role. To further examine the role of ground water, we applied mass-balance calculations, using detailed flow rate measurements, water samplings, and chemical analyses along the northern (upstream) part of the river. Our flow-rate measurements showed that the river base-flow during 2000 and 2001 was 500 to 1100 L s(-1), which is about 40 times lower than the historical flow rates. Our measurements and calculations indicate that ground water input was 20 to 80% of the river water flow, and 20 to 50% of its solute mass flow. This study independently identifies the composition of possible end-members. These end-members contain high sulfate concentration and have similar chemical characteristics as were found in agricultural drains and in the "saline" Yarmouk River. Future regional development plans that include the river flow rate and chemistry should consider the interactions between the river and its shallow ground water system.