Experimental Flow Data Research Articles

Two-phase flow performance prediction for minichannel solar collectors

High thermal efficiencies reported in the literature for non-evacuated minichannel-based solar collectors open up the possibility to explore their operation under two-phase flow conditions for low-grade steam generation and energy storage. In this article, a mathematical model is developed to analyze the performance of a minichannel solar collector under two-phase flow conditions. Six published two-phase frictional pressure drop correlations and six two-phase heat transfer correlations are utilized, and the results compared against experimental two-phase flow data from the literature. The most accurate correlations are later on used for simulating the operation of the minichannel solar collector. Results show that for two phase flow conditions, the pressure drop is found to increase dramatically with mass flux, while the outlet quality is found to remain near saturated liquid at mass fluxes higher than 54.58 kg/m2s. In addition, inlet temperature at saturated liquid conditions and constant mass flux did not have a significant effect on outlet quality. Applications that require low-grade steam, such as food-drying, steam-cleaning, or sterilization, among others, could benefit from the two-phase flow operation of this type of collectors.

Constitutive equations with pressure-dependent rheological parameters for describing ice creep

ABSTRACTExperimental data from creep tests on polycrystalline ice samples highlight not only the non-Newtonian behavior of ice but also suggest a critical dependence of the various rheological parameters upon the applied hydrostatic pressure. We propose a new modeling framework, based on implicit theories of continuum mechanics, that generalizes two well-known constitutive models by taking into account the effect of the pressure in the description of ice in creep. To ascertain the validity of the proposed models, we fit the physical parameters with experimental data for the elongational flow of ice samples. The results show good agreement with the experimental creep curves. In particular, the proposed generalized models reproduce the increase of the creep rate due to the presence of hydrostatic pressure.

A methodology for simulating 2D shock-induced dynamic stall at flight test-based fluctuating freestream

A comprehensive methodology for simulating 2D dynamic stall at fluctuating freestream is proposed in this paper. 2D CFD simulation of a SC1095 airfoil exposed to a fluctuating freestream of Mach number 0.537 ± 0.205 and Reynolds number 6.1 × 106 (based on the mean Mach number) and undergoing a 10° ± 10° pitch oscillation with a frequency of 4.25 Hz was conducted. These conditions were selected to be representative of the flow experienced by a helicopter rotor airfoil section in a real-life fast forward flight. Both constant freestream dynamic stall as well as fluctuating freestream dynamic stall simulations were conducted and compared. The methodology was carefully validated with experimental data for both transonic flow and dynamic stall under fluctuating freestream. Overall, the results suggest that the fluctuating freestream alters the dynamic stall mechanism documented for constant freestream in a major way, emphasizing that inclusion of this effect in the prediction of dynamic stall related rotor loads is imperative for rotor performance analysis and blades design.

Single and multiphase CFD simulations for designing cavitating venturi

Hydrodynamic cavitation (HC) is becoming a popular process intensification tool for many industrial processes. It has its applications in emulsification, advanced oxidation processes, nano-material synthesis etc. Venturi is one of the most commonly used device to generate hydrodynamic cavitation at laboratory as well as industrial scale. Recently researchers have taken interest to find the effect of the geometric design parameters of the venturi on cavitating flows.In the present work, cavitating flow in a venturi is simulated using Computational Fluid Dynamics (CFD). Optimum mesh size and suitable turbulence model for this such a flow were selected using a preliminary study. Single phase as well as multiphase simulations were carried out and the results were validated using experimental data of pressure drop and flow rate.Further, discrete phase model (DPM) was used to predict the possible path taken by multiple cavities, and the pressure and turbulence data along these paths was extracted to solve the Keller–Miksis equation for cavity dynamics simulations. Parameters like bubble radius, collapse pressure and collapse temperature of the cavity during its dynamic behavior were estimated from this model. A comparison between the results for single phase and multiphase models is made to propose a numerically inexpensive and reasonably accurate method to model cavitating flows in a venturi.

Characterization and Modeling of Hot Deformation Behavior of a Copper-Bearing High-Strength Low-Carbon Steel Microalloyed with Nb

This study investigates hot deformation behavior of a newly developed Cu-bearing high-strength low-carbon steel microalloyed with Nb (Nb-HSLC). A computational method based on experimental data was employed to design the chemical composition of the alloy. Compression tests were carried out in the temperature range of 850-1100 °C as well as strain rates of 0.001-10 s−1 using BAHR Dil 805 A/D thermo-analyzer equipment. The Arrhenius-type constitutive equations were used to model the hot working behavior of the designed steel. Effects of friction and temperature rise during deformation were corrected to obtain the actual stresses. The results showed that the peak flow stress was increased with increasing Zener–Hollomon parameter. The obtained flow curves at strain rates lower than 0.1 s−1 and temperatures above 950 °C represented the typical dynamic recrystallization (DRX) behavior, while the flow curves at temperatures lower than 950 °C at all strain rates were associated with continuous strain hardening. This feature is in good agreement with the precipitation temperature range of Nb(C, N) particles, i.e., 800-1000 °C. Moreover, the flow curves showed the serrations during hot deformation at strain rates of 0.001 and 0.01 s−1, indicating that the dynamic strain aging (DSA) phenomenon occurred at low strain rates. The best fit between “peak stress” and “deformation conditions” was obtained by a hyperbolic sine-type equation (R2 = 0.993). Therefore, the average activation energy was determined as 348 kJ mol−1. The agreement between the achieved model and experimental flow data was verified using the results of additional tests at a strain rate of 5 s−1. The maximum difference between the measured and predicted “peak stresses” was calculated as 5 Mpa.

The elements of fluid mechanics of bile flow through biliary drainage catheters

Obstructive jaundice in the biliary tract can infect blood and result in mortality with a high rate. Percutaneous transhepatic biliary drainage (PTBD) with catheters is a useful solution discharging the obstructive jaundice. However, the elements of fluid mechanics showing clinical performance of a PTBD catheter have been documented little so far. In the article, empirical relationships between bile flow rate and pressure gradient in PTBD catheters were studied in terms of equivalent friction factor for the first time. Firstly, an equivalent friction factor in a catheter was raised and determined based on existing in vitro experimental data of bile flow through the catheters with different materials, various inner diameters and lengths under various pressure differences. Then, an empirical correlation of bile flow rate through a catheter was established based on pressure gradient, inner diameter and bile viscosity. The correlation was used to identify effects of catheter inner diameter and bile viscosity on the bile flow rate under the physiological bile pressure difference across obstructed common bile ducts. The feature of minor hydraulic losses in the catheters was clarified, too. The proposed equivalent friction factor was proportional to Reynolds number in a power of -0.654 in comparison with a power of -1 for the fully developed laminar flow in circular pipes. The bile flow rate through a catheter was proportional to inner diameter, kinematic viscosity, and pressure gradient in the powers of 3.2, -0.5 and 0.74, respectively. The minor hydraulic losses could be significant when Reynolds number was greater than 100.

Experimental Investigation of the Aerodynamic Roughness Length for Flexible Plants

The aerodynamic roughness length z0 is modelled as a function of the zero-plane displacement d, plant drag coefficient CdR, the ratio β of the drag coefficient for an isolated roughness element and the surface drag coefficient, and the lateral cover λ. The model is investigated using wind-tunnel experiments on a ground surface covered by artificial plastic flexible plants of very small basal-to-frontal area ratios (0.001–0.007). The plant drag coefficient at different plant densities is inferred from measurements of the total shear stress and the average surface shear stress for five plant heights at four plant densities. The aerodynamic roughness length and zero-plane displacement are estimated by logarithmic regression of the measured velocity profile with a predetermined friction velocity. With the increase of lateral cover λ, the plant drag coefficient can be considered as a constant for λ 0.01. With an increase in the friction velocity, the roughness length z0 generally decreases because of plant flexibility, while with increases in plant density and plant height, the value of z0 increases because the surface becomes physically rougher. Our model for the roughness length z0 is verified using experimental data for flow over flexible plants. Compared with rigid roughness elements, such as cylinders, cubes and blocks, the normalized roughness z0/h (where h is the plant height) for the flexible plants is smaller because of the porosity and the larger value of the ratio d/h.

Dilute gas-particle flow through thin and thick orifice: a computational study through two fluid model

The present work deals with the three-dimensional computational study of dilute gas-particle suspension through thin and thick orifice. The objective of the study is to predict the two phase pressure drop across an orifice for relatively higher solid loading but within the limit of dilute phase flow situation. The study involves the investigation of effect of five pertinent parameters namely area ratio, thickness of orifice, particle phase volume fraction, particle size, and particle phase density on the two phase pressure drop across orifice. The Eulerian–Eulerian model (Two fluid model) has been used for this purpose. The numerical procedure adopted in the present work has been validated with the experimental data for gas-particle flow through a horizontal sudden expansion pipe and good agreement has been revealed. The study reveals that the two phase pressure drop across orifice increases with increases in solid volume fraction and particle density, whereas it decreases with increase in particle diameter and area ratio of the pipe. Moreover, slight increase in pressure drop across orifice is observed with increase in thickness of orifice. Thus, higher pressure drop is observed for thick orifice as compared to thin orifice.

Subcooled flow boiling of water in a copper microchannel: Experimental investigation and assessment of predictive methods

The current study presents experimental pressure drop and heat transfer data for subcooled flow boiling of water in a 1.0 mm wide × 0.49 mm deep × 40 mm long aged copper microchannel. The experiments were performed for three inlet temperatures: 30o C, 50o C and 70o C, each with mass flux range of 528–1188 kg/m2 s and heat flux range of 260–1100 kW/m2. The trends observed in experimental subcooled boiling heat transfer and pressure drop are reported. The performance of existing predictive methods in predicting pressure drop, heat transfer and boiling incipience is also assessed. The study also evaluates the appropriateness of using singe phase correlations for predicting subcooled boiling pressure drop, a practice which is used in many flow boiling studies, and recommends that the approach be not used for low inlet subcooling.

Methodology for pressure drop of bubbly flow based on energy dissipation

Abstract Pressure drop of bubbly flow is a widely used parameter in petroleum industry. The energy dissipation rate is induced by three factors, including wall resistance, bubble breakup and coalescence, which is studied here from the perspective of the macroscopic flow and microscopic bubbles. This work details a model using the principle of energy conservation to clarify the mechanism of the pressure drop for turbulent bubbly flow in horizontal pipes. The model was validated via a comparison with experimental data of horizontal bubbly flow collected from nine previous studies with 200 points. Most of the errors are within ±20%. The proportions of pressure drop induced by wall resistance, bubble breakup and coalescence were calculated by the model. The results indicate that the largest proportion is from wall resistance, followed by bubble coalescence, with bubble breakup having the smallest proportion. In addition, the trends of proportion induced by the three factors above are analyzed by increasing gas volume fraction and mixture viscosity. The results show that the proportion induced by wall resistance decreases with the increasing volume fraction of the gas, and increases with the increasing mixture viscosity. The proportions induced by the bubble breakup and coalescence in the opposite case.

VALIDATION OF THE MOODY AND HENRY-FAUSKE CRITICAL FLOW MODELS IN APROS AGAINST MARVIKEN CRITICAL FLOW EXPERIMENTS

The Moody and Henry-Fauske critical flow models implemented in APROS have been validated against Marviken critical flow experiments and compared with other available simulations of the same experiments. Both models in combination with discharge coefficient 0.75 (suggested for best estimate calculations) produce results close to the experimental data for twophase flows, while one-phase flow of subcooled water is underpredicted. Using discharge coefficient 1.0 for subcooled water leads to a good match with the experimental results, while twophase flows become overpredicted.

Modelling soil water dynamics and root water uptake for apple trees under water storage pit irrigation

Water storage pit irrigation is a new method suitable for apple trees. It comes with advantages such as water saving, water retention and drought resistance. A precise study of soil water movement and root water uptake is essential to analyse and show the advantages of the method. In this study, a mathematical model (WSPI-WR model) for 3D soil water movement and root water uptake under water storage pit irrigation was established based on soil water dynamics and soil moisture and root distributions. Moreover, this model also considers the soil evaporation, pit wall evaporation and water level variation in the pit. The finite element method was used to solve the model, and the law of mass conservation was used to analyse the water level variation. The model was validated by experimental data of the sap flow of apple trees and soil moisture in the orchard. Results showed that the WSPI-WR model is highly accurate in simulating the root water uptake and soil water distributions. The WSPI-WR model can be used to simulate root water uptake and soil water movement under water storage pit irrigation. The simulation showed that orchard soil water content and root water uptake rate centers on the storage pit with an ellipsoid distribution. The maximum distribution region of soil water and root water uptake rate was near the bottom of the pit. Distribution can reduce soil evaporation in the orchard and improve the soil water use efficiency in the middle-deep soil. Keywords: root water uptake, soil water dynamics, numerical simulation, water storage pit irrigation, apple tree DOI: 10.25165/j.ijabe.20191205.4005 Citation: Guo X H, Lei T, Sun X H, Ma J J, Zheng L J, Zhang S W, et al. Modelling soil water dynamics and root water uptake for apple trees under water storage pit irrigation. Int J Agric & Biol Eng, 2019; 12(5): 126–134.

On the numerical simulation of sand transport in liquid and multiphase pipelines

Sand deposition in pipelines represents one of the problems that can arise in oil and natural gas production and transport. The main problems that sand can cause include the pipeline obstruction with the relative production loss, the increase of the lines erosion and corrosion and the compromising of the structural integrity. Moreover, there is a limit in the amount of sand that can be separated and removed. Therefore, methods and strategies to reduce the production of sand are key factors for safety and economic risks. In general sand deposition problems occur in different flow systems such as sand–multiphase mixtures of gas-oil-water or two-phase mixtures. In order to elaborate an effective method able to predict the amount of sand and to have a reliable prediction of sand transport velocity and entrainment processes, several factors requires to be considered, including sand characteristics, sand concentration, flow regimes, fluid properties and pipe properties.This paper presents the results of a detailed testing on the performance of a new sand transport model implemented in one-dimensional dynamic multiphase code, performed by comparing numerical results with experimental data. This study deals with both liquid-solid flow as well as gas-liquid-solid flow. The results demonstrate a good agreement between numerical and experimental data for the sand-liquid flow and sand transport in stratified gas-liquid flow, while show that for the sand transport in gas-liquid slug flow improvements are necessary.

A new model of emulsion flow in porous media for conformance control

Emulsion flow in porous media is of paramount importance to the use of emulsions in the conformance control and enhanced oil recovery processes. In this paper, a new theoretical model, incorporating physical properties of porous media, physicochemical properties of the emulsion system, injection strategy, and the interactions between porous media and emulsion, was developed to quantitatively describe flow behaviors of emulsions in porous media. The resistance factor of an emulsion when transported in porous media was first derived through a-two phase flow method. The strong interaction between emulsion droplets and porous media was characterized by the capillary resistance force in the model. A non-uniform capillary model which considers size differences of the pore-body and pore-throat in porous media was proposed to represent the complicated real porous media. By analyzing the adsorption and plugging properties of different emulsion droplets in the non-uniform capillary model, the capillary resistance force was finally determined. To describe emulsion flow in the subsequent water flooding process after emulsion injection, an emulsion dilution factor was introduced into the model. A set of experimental data of emulsion flow in sandpacks was used to validate the reliability of the newly proposed model. The validation results show that by appropriately choosing coefficients, the simulated results are in good agreement with experimental values, with a maximum average absolute error less than 10%, and the developed theoretical flow model can be used to describe emulsion flow behavior in porous media.

Application and adaption of Dynamic Mode Decomposition to experimental and numerical data of turbomachinery flow

AbstractUnsteady turbomachinery flows are challenging in terms of resolving turbulent characteristics and instability mechanisms like rotating stall, rotor‐stator interaction and von Karmán vortex streets. Furthermore, in part load conditions these flow phenoma can induce vibrations leading to resonance problems and high cycle fatigue. Flowfield measurements of a centrifugal fan were taken by high‐speed particle image velocimetry (PIV). CFD results, calculated as unsteady Reynolds averaged Navier Stokes (URANS) and based on Menter's shear‐stress transport (SST) model, are the source of numerical data. In former examinations discrepancies between experiment and simulation in time‐averaged velocity profil data for part load conditions have been stated. The source of theses discrepancies is still unknown. Hence, a new approach is needed for further examination of measured and calculated flowfields. The Dynamic Mode Decomosition is employed in order to compare experimental and numerical datasets. Information about coherent structures and the dynamical behaviour are contained in the eigenvalues and their associated eigenvectors offered by DMD. While the eigenvectors are describing the coherent structures, the associated eigenvalues describe the dynamic behaviour of the structure. The eigenvectors are denoted as DMD‐Modes. The results acquired by DMD based on experimental and numerical data are compared to investigate congruent behaviour and therefore if it is possible to obtain reliable information about dynamic behaviour of a system even with URANS simulations. Comparisons between singular value and eigenvalues are presented and discussed.

The stochastic theory of the turbulence

The general results of new stochastic theory of turbulence for isothermal flows are presented. Stochastic equations for laws of conservation and for equivalence of measures between deterministic process and random process, the review of results of an analytical expressions are presented for the isothermal turbulent flow in the tube and for the flow on the flat plate depending on initial fluctuation in medium. An important result of a new theory is the fact that even if the fluctuation has an initial spectrum in the form of a delta-function, the modular fractal equation obtained in theory determines both the fractal equation for the diffusion process of energy transfer and the fractal generation equation of Landau type described the subsequent expansion of the spectrum. Derived formulas for critical Reynolds numbers and critical point, the velocity profile, the second-order correlation, and friction coefficients give the satisfactory agreement with the experimental data for both flows.

Modeling non-Darcian flow and solute transport in porous media with the Caputo–Fabrizio derivative

• Caputo–Fabrizio fractional derivative model for non-Darcian flow is established. • Caputo–Fabrizio fractional derivative model for diffusive transport is presented. • All proposed models are in good agreements with experimental results. In this study, the non-Darcian flow and solute transport in porous media are modeled with a revised Caputo derivative called the Caputo–Fabrizio fractional derivative. The fractional Swartzendruber model is proposed for the non-Darcian flow in porous media. Furthermore, the normal diffusion equation is converted into a fractional diffusion equation in order to describe the diffusive transport in porous media. The proposed Caputo–Fabrizio fractional derivative models are addressed analytically by applying the Laplace transform method . Sensitivity analyses were performed for the proposed models according to the fractional derivative order . The fractional Swartzendruber model was validated based on experimental data for water flows in soil–rock mixtures. In addition , the fractional diffusion model was illustrated by fitting experimental data obtained for fluid flows and chloride transport in porous media. Both of the proposed fractional derivative models were highly consistent with the experimental results.

Numerical modeling of the horizontal flow and concentration distribution of nitrogen within a stored-paddy bulk in a large warehouse: Poster

The insect population in grain stores can be kept under control by maintaining a high concentration of N2 gas throughout the grain bed. The development of controlled atmosphere storage technology for insect control requires an accurate prediction of the distribution of introduced gases in bulk grain. In this paper, based on the convective-diffusion model, the horizontal flow of N2, which was introduced into the paddy bulk in a large warehouse by means of the horizontal ventilation system, are modeled as fluid flow in a porous medium. The experimental data for N2 transfer and flow through ducts and bulk paddy were used to validate the model. The equations were solved using the finite difference method, and the predictions from the proposed model were in good agreement with the experimental results. The concentration distribution and flow uniformity of nitrogen in stored paddy were also analyzed during the nitrogen-filling procedure for CA storage. It was shown that it is feasible and practical to introduce nitrogen into stored bulk grain in a large warehouse by means of the horizontal ventilation system.

CFD analysis of flow distributor designs for numbering-up of biodiesel synthesis

Micro-chemical plants increased production by the parallelization of microdevices. The uniform distribution of flow through the microdevices are made by the flow distributor. Inadequate distributor design reduces the micro-chemical plant performance. The present research aims to perform a numerical analysis of distributor designs. Three designs were evaluated varying the distributor height and the presence or absence of internal obstacle. Analyses of flow rate and phase distribution uniformity and the prediction of biodiesel synthesis occurrence inside the distributors were performed. Different numerical approaches were used for the specific systems, including single-phase flow, multi-component flow and Volume of Fluid (VOF) simulations. The VOF-based model provided good agreement with experimental data of water flow. The viscous dominated oil flow, presented good distribution in all proposed designs. Water and ethanol presented bulk recirculation inside the distributor, depreciating the flow uniformity. The ethanol-oil mixture flow resulted in high flow nonuniformity and in the occurrence of biodiesel synthesis for all operating conditions. Based on the numerical predictions, the micro-chemical plants require two distributors in order to perform the transesterification reaction only inside the microdevices. The simulations were employed as a design tool providing flow details and substantiating the project optimization for further development of micro-chemical plants.

Laboratory investigation of chemical mechanisms driving oil recovery from oil-wet carbonate rocks

The purpose of this work is twofold; to improve current understanding of the oil recovery mechanism behind chemically tuned waterflooding in oil-wet carbonate rocks, and to propose a set of governing chemical reactions consistent with this mechanism. For this, a series of waterflood experiments were conducted at 90 °C with synthetic seawater type brine solutions with varying compositions of potential determining ions (Ca2+, Mg2+, and SO42−). Characterization techniques like zeta potential, contact angle, and trace element analysis were implemented to account for the ionic interactions taking place among the rock, the brine solution, and the crude oil. Additionally, relative permeabilities were estimated using the Brooks and Corey model where the wettability exponents were tuned against the experimental fractional flow data. Zeta potential measurements highlight the affinity of Mg2+, Ca2+, and SO42− ions toward the rock surface in chemically tuned brines where an increase in the magnitude of zeta potential was observed corresponding to the increase in the concentration of each of these ions in the suspension. Oil recovery measurements show an increase for all chemically tuned brines when compared to plain seawater injection. Relative permeability estimations and contact angle measurements show corresponding trends of increasing water–wetness, suggesting the alteration of wettability. Maximum recovery of ∼76% original oil in place (OOIP) was observed for the brine with increased Mg2+ ion concentration due to higher activity of Mg2+ ions and their ability to replace Ca2+ ions from the rock surface. A lower recovery of ∼64% OOIP was seen for the brine with increased Ca2+ ion concentration due to lower activity of Ca2+ ions as opposed to Mg2+ ions. Further lower recovery of ∼59% OOIP was seen for the brine with increased SO42− ion concentration due to the increased precipitation of these ions on the rock surface. These chemical reactions including salt precipitation, crude oil desorption/solubilization, and mineral dissolution were confirmed through ionic analysis of the effluent brine during each waterflooding experiment. The presented experimental results and the proposed sequence of chemical reactions can be used for the development of an appropriate reaction model for predicting oil recovery via wettability alteration.