Experimental Pressure Data Research Articles

An Alternative Parameterization of Relative Permeability and Capillary Pressure Curves

SummaryThis paper presents a theoretically rigorous correlation of the performance of capillary pressure and relative permeability of naturally fractured sandstone and carbonate reservoirs involving saturation shocks and loading/unloading hysteresis under various stress and thermal conditions. The proposed modeling approach accounts for the combined effects of the porous-rock alteration by various processes, including deformation, transformation, deterioration, and collapse of pore structure, under prevailing temperature and stress conditions during loading and unloading processes, and their effect on the capillary pressure and relative permeability of naturally fractured reservoirs. A saturation shock causing a slope discontinuity in the capillary pressure and relative permeability is shown to occur during saturation change in some sandstone- and carbonate-reservoir formations at a critical saturation condition. This phenomenon can be triggered by alteration of fluid-percolation pathways as a result of the transition from open to closed natural or induced fractures and the deformation of pore structure. The effect of the saturation shock and loading/unloading hysteresis on the capillary pressure and relative permeability of reservoir-rock formations is formulated by means of a phenomenological kinetics model and its applicability is demonstrated by analyzing and correlating the available experimental data.In this paper, the proven comprehensive model developed from a kinetics equation is shown to lead to a theoretically meaningful, universal, and practical constitutive equation in the form of a modified power law. This kinetics equation expresses the probability of dependence of a petrophysical property of porous rocks on a variable, such as saturation for capillary pressure and relative permeability, based on the value of the property relative to its low- and high-end limit values. The applicability of the modified power-law equation is validated by means of the experimental data of the capillary pressure and relative permeability gathered by testing of representative samples from various sandstone and carbonate reservoirs. The phenomenological parameters of the core samples obtained from sandstone and carbonate reservoirs are determined for best match of the experimental data with the modified power-law equation. The value of the critical fluid saturation is determined by the observance of a slope discontinuity occurring in the measured experimental data of the variation of the capillary pressure and relative permeability with saturation. The scenarios presented in this study indicate that loading/unloading hysteresis and saturation shock have significant effects on the stress- and temperature-dependent capillary pressure and relative permeability of the porous reservoir-rock formations. The data-inferred physics-based model presented in this paper is proved to describe the stress- and temperature-dependent capillary pressure and relative permeability of sandstone and carbonate rocks with high accuracy while meeting the endpoint-limit conditions satisfactorily.

Thermodynamic properties of trifluoroethene (R1123): (p, ρ, T) behavior and fundamental equation of state

Abstract The (p, ρ, T) behavior of trifluoroethene (R1123) was investigated with the isochoric method. A total of 87 (p, ρ, T) data were measured along nine isochores (42, 98, 151, 197, 296, 493, 691, 790, and 888 kg · m − 3 ) at temperatures from 300 K to 430 K and pressures up to 6.9 MPa. The uncertainties in temperature are estimated to be within 10 mK below 380 K and 20 mK at higher temperatures, and the uncertainties in pressure are estimated to be within 1 kPa below 380 K and 2 kPa at higher temperatures. The estimated relative uncertainties in the density measurements are 0.15 % or less. A new Helmholtz energy equation of state was formulated based on the (p, ρ, T) data and recently published experimental data for the vapor pressure, liquid and vapor densities including those at saturation, vapor-phase sound speed, and ideal-gas isobaric heat capacity. The equation is applicable at temperatures from the triple-point temperature (195.15 K) to 480 K and pressures up to 20 MPa. Typical uncertainties in calculated properties are 0.1 % for vapor pressures, 0.1 % for liquid densities, and 0.2 % for vapor densities, except in the critical region where larger deviations up to about 1.5 % are sometimes observed in densities. The uncertainties in calculated vapor-phase sound speeds and ideal-gas isobaric heat capacities are 0.03 % and 1 %, respectively. The equation shows reasonable extrapolation behavior at extremely low and high temperatures, and at high pressures.

Caveats of using fractal analysis for clay rich pore systems

The conventional techniques cannot accurately predict the multiphase flow behaviour in clay rich low permeability rocks. This is particularly important in applications such as hydraulic fracturing where fluid uptake into low permeability rocks is of interest. This inability has given rise to the use of fractal-based estimation of petrophysical properties of such rocks. The concept of fractal theory revolves around the fractal dimension (Df) representing the entire pore structure which is often estimated using the mercury-intrusion capillary pressure (MICP) data among other techniques. However, rocks containing high clay content often exhibit higher capillary pressures than those based on MICP. This is due to interaction of clay minerals with external fluids such as hydraulic fracturing fluid and subsequent transient change in pore structure. This also in turn causes the Df value to vary thus leading to errors and uncertainties in fractal-estimated petrophysical properties of clay rich rocks. This transient aspect of clay rich rocks’ pore network is not yet fully understood nor systematically investigated or incorporated in current fractal methods. We have therefore conducted a comprehensive study to narrate a cautionary tale on the use of MICP-based fractal methods in clay rich tight rocks analyses. We first highlighted the uncertainty in the MICP-based Df value by comparing experimental and simulated oil recoveries from three clay-rich low permeability sandstone samples. We then developed, for the first time, a new set of physical equations to describe the transient pore network based on MICP-based fractal theory in order to partially overcome these uncertainties. We next compared the new theoretical model with experimental oil-water capillary pressure data. Through such rigorous analyses, it was concluded that MICP-based fractal theory relying on an unchanging pore structure is not accurate in its current form. Although our new approach can address the issue with the transient nature of clay rich pore network, there is yet immense space for improvement to overcome the limitations associated with fractal based petrophysical property estimation.

Improved Parameterization of Protein-DNA Interactions for Molecular Dynamics Simulations of PCNA Diffusion on DNA.

As the field of molecular dynamics simulation utilizing the force fields is moving toward more complex systems, the accuracy of intermolecular interactions has become a central issue of the field. Here, we quantitatively evaluate the accuracy of the protein-DNA interactions in AMBER and CHARMM force fields by comparing experimental and simulated diffusion coefficients of proliferating cell nuclear antigen. We find that both force fields underestimate diffusion coefficients by at least an order of magnitude because the interactions between basic amino acids and DNA phosphate groups are too attractive. Then, we propose Lennard-Jones parameters optimized using the experimental osmotic pressure data of model chemicals, by using which one can reproduce the experimental diffusion coefficients. Newly optimized parameters will have a broad impact on general protein-DNA interactions.

Comparison of Artificial Neural Network and Fuzzy Logic Approaches for the Prediction of In-Cylinder Pressure in a Spark Ignition Engine

Abstract In first stage, a machine learning (ML) was performed to predict in-cylinder pressure using both fuzzy logic (FL) and artificial neural networks (ANN) depending on the results of experimental studies in a spark ignition (SI) engine. In the ML phase, the experimental in-cylinder pressure data of SI engine was used. SI engine was operated at stoichiometric air–fuel mixture (φ = 1.0) at 1200, 1400, and 1600 rpm engine speeds. Six different ignition timings, ranging from 15 to 45 °CA, were used for each engine speed. Correlations (R2) between data from in-cylinder pressure obtained via FL and ANN models and data form experimental in-cylinder pressure were determined. R2 values over 0.995 were obtained at an ML stage of ANN model for all test conditions of the engine. However, R2 values were remained between range of 0.820–0.949 with the FL model for different engine speeds and ignition timings. In the second stage, in-cylinder pressure prediction was performed by using an ANN model for engine operating conditions where no experimental results were obtained. Furthermore, indicated mean effective pressure (IMEP) values were calculated by predicting in-cylinder pressure data for different engine operation conditions, and then compared with experimental IMEP values. The results show that the in-cylinder pressure and IMEP results estimated with the trained ANN model are fairly close to the experimental results. Moreover, it was found that using the trained ANN model, the ignition timing corresponding to the maximum brake torque (MBT) used in the engine management systems and engine studies could be determined with high accuracy.

Leading-edge bluntness effects in hypervelocity flat plate flow

The combined effects of leading-edge bluntness and high enthalpy are examined for hypersonic flat plate flow. Experimental pressure and heat transfer data are presented for both sharp and blunt leading-edge flat plates. For the sharp leading-edge flows, the data are in agreement with perfect gas theory. For the blunt leading-edge flows, the low and high enthalpy pressure data approach the perfect gas blast wave theory as the flow proceeds downstream, consistent with earlier studies at low enthalpy. Toward the front of the plate, the heat transfer data lie above the corresponding values obtained with the sharp leading-edge configuration. The difference between sharp and blunt leading-edge heat transfer levels appears to be smaller at high enthalpy. This seems to be due to dissociation which occurs in the nose region, thus reducing the shock stand-off distance and increasing the chemical potential enthalpy of the flow. When the presence of dissociated species in the flow is accounted for, the data close to the leading-edge are seen to compare well with perfect gas bluntness–viscous similitudes. Farther downstream, the measured heat transfer values are greater than the perfect gas theoretical predictions for blunt leading-edge flow, and closer to both the corresponding predictions at chemical equilibrium, and sharp leading-edge theory for perfect gas flow.

Modified PC-SAFT characterization technique for modeling asphaltenic crude oil phase behavior

The perturbed-chain version of Statistical Association Fluid Theory (PC-SAFT) emerged as a powerful tool to study the phase behavior of complex fluids such as polymers and asphaltene. In spite of this, it has not gained widespread acceptance in the industry because of its sophisticated oil characterization procedure. In fact, the predictive performance of the current characterization methods is limited and not all-inclusive as they use a large number of fitting parameters and/or a non-integrated procedure. In this study, a convenient and easy-to-use procedure for crude oil characterization is proposed, assuming asphaltene as a combination of poly-nuclear aromatics, benzene derivatives, and saturates.To achieve the best match between measured and model predictions, a simple and robust Trust-Region based optimization method is used. A set of weighting factors is also used based on uncertainties in experimental data. Additionally, it is showed that the poor agreement between the measured amounts of precipitated asphaltene (from filtration test) and thermodynamic model predictions —tuned toward experimental asphaltene onset pressure data— is because of the inherent difference between the accuracy of the experimental methods.The performance of the proposed method is evaluated against reliable literature data of three frequently used crude oils which have been previously characterized over wide range of temperature, pressure, and compositions, and a reservoir fluid sample taken from a southwestern Iranian reservoir. The results are encouraging if compared to the available characterization procedures in the literature.

Thermal performance and flow characteristics of two-phase loop thermosyphons

A detailed 2-D computational fluid dynamics (CFD) model simulating two-phase flow and heat transfer in a two-phase loop thermosyphon (TPLTS) is presented. The CFD simulation was built to represent two-phase flow and heat transfer phenomena during the transient and steady-state operation analysis of a TPLTS under various operating conditions. The two-phase flow was modeled using the volume of fluid (VOF) model, and the Lee model was utilized for evaporation and condensation. Simulation results were compared with experimental temperature, pressure, and flow visualization data.

Phase Behavior of Hydrocarbon Mixtures for the Low Concentration of Heavy Hydrocarbon Components

The present work shows the accurate calorimetric measurements of phase equilibria of hydrocarbon mixtures for the low concentration of heavy hydrocarbon components in particular the system methane + propane + decane with special emphasis on the concentration of decane below one mole percentage. Heat capacity, internal energy, pressure, and temperature derivative of pressure at constant volume for the ternary system have been measured in the range of 100–370 K and 0.1–40 MPa. To show a procedure of the phase diagram plotting by a precision adiabatic calorimetry, the typical phase diagram for a hydrocarbon mixture has been plotted in detail. A phase diagram has been plotted based on the experimental data of heat capacity, internal energy, pressure, and temperature derivative of pressure at constant volume. A phase transition is localized by a finite discontinuity in a temperature derivative of the thermodynamic potential. A closed area surrounded by the typical phase envelope for a pressure–temperature diagram is the two-phase region. Our particular attention is paid to the ternary system methane + propane + heavy hydrocarbon component for the low concentration of heavy hydrocarbon, in particular, of decane, due to the fact the conventional PVT approach does not guarantee the efficiency and accuracy of the phase diagram plotting for this system. Our investigations show the phase behavior of a hydrocarbon mixture for the low concentration of decane is drastically transformed compared to the customary concept. The hydrocarbon mixture splits into two phases, a macrophase enriched by methane and propane (a decane-poor phase) and a decane-rich microphase. To prove that all phases are equilibrium phases, a cooling mode of measurements is used. At the cooling mode of measurements, the same phase transitions as at the heating mode occur. These phase transitions correspond to the formation of a decane-rich microphase and a macrophase enriched by methane and propane.

Investigating the explosion of ethyl acetate in the presence of hydrogen

The explosion characteristics of ethyl acetate/hydrogen-air (EA/H2/air) mixtures have been investigated in this document using a constant volume combustion vessel. The experiments were executed using the initial pressure (1, 2, and 3 bar) and temperature (358 K) over a wide range of equivalence ratios. Hydrogen was mixed with compressed air in the volumetric proportion of 0%, 4%, 8%, and 12% and added to EA. The experimental pressure data were refined to determine the explosion characteristics. The explosion characteristics of EA/H2/air using different H2 fractions were compared. The study indicated that there was a slight difference between the peak explosion pressures of 4%, 8%, and 12% H2 fraction, however, the explosion with H2 of 12% had the maximum pressure rise rate and deflagration index when the explosion was evaluated in terms of the pressure rise rate and deflagration index. The explosion time at 8% and 12% hydrogen was relatively shorter than that of 4%.

Simulation of a Scaled down 250 MWe CFB Boiler Using Computational Particle Fluid Dynamics Numerical Model

Abstract Eulerian-Eulerian approach and conventional Eulerian-Lagrangian model are computationally exhaustive for modelling circulating fluidized bed (CFB) riser which has wide particle size distribution and billions of particles Alternatively, the relatively recent Eulerian- Lagrangian computational particle fluid dynamics (CPFD) model enables simulation of the CFB system with lesser computational resources. Most of the published studies on CPFD simulations of CFB risers deal with single grate system. The present study aimed to investigate the performance of the CPFD model for predicting solids distribution in a CFB riser with pant-leg structure (dual grate) and characteristics similar to a commercial boiler. Experiments conducted in a scaled down 250 MWe CFB facility according to Glicksman’s simplified similarity laws for fluidized beds were simulated using commercial code Barracuda. The bottom dense bed, upper lean solid phase, increase in bottom bed voidage with increasing fluidizing velocity and reducing solids inventory, decrease in bottom bed solids concentration with decrease in particle size and exchange of solids between the legs typically occurring in a CFB with pant-leg structure were successfully captured by the CPFD calculations. Simulation results showed that the upper solids concentration is hardly influenced by the solids inventory level in line with the experimental observation, therefore the amount of solids inventory can be optimized during actual operation. The predicted pressures varied from the average experimental pressure data within the range –10 to 39 %.

Chlorine and felsic magma evolution: Modeling the behavior of an under-appreciated volatile component

Research on magmatic Cl has proven useful for understanding melt evolution, degassing, and other igneous processes. Magmatic Cl behavior varies strongly with its solubility in melt, and Cl solubility and its partitioning between melts and fluids vary with the Cl content of the system, melt composition, pressure, and the abundance of oxidized magmatic sulfur. Given these relationships and given that they differ from other magmatic volatiles, Cl can provide unique insights on magma evolution. We present a new method of interpreting melt Cl concentrations that are normalized to their calculated Cl solubilities, and the most accurate results apply to solubilities computed at 200 MPa due to insufficient experimental data for other pressures. We apply the new method to compositional data for more than 3500 dacitic to rhyolitic melt inclusions and matrix glasses, representing 64 felsic igneous systems, to demonstrate how the behavior of Cl during magmatic, magmatic-hydrothermal, and degassing processes can be more accurately interpreted.Variations in Cl for most of the 64 systems agree with modeled Cl behavior indicative of melt evolution dominated by fractional crystallization of fluid(s)-saturated melts, and the majority of these systems were apparently saturated in fluid(s) well before melt inclusion entrapment. Comparison of Cl solubility-normalized Cl concentrations of these glasses with modeled results identifies magmas saturated in hydrosaline liquid ± vapor at pressures as high as 600 MPa. Modeling of pressure reductions from 600 down to 20 MPa distinguishes other magmas that exsolved hydrosaline liquid as magmas ascend to shallower depths. This new approach also supports computation of Cl concentrations of magmatic fluids at 200 MPa, for each of the >3500 glasses, and shows how the Cl contents of fluids vary with the (fluid/melt) mass ratio. For example, Cl contents of magmatic fluids range from 0.3 to nearly 70 wt.% at fluid/melt mass ratios of 2 × 10−3, and from 0.3 to a maximum of only 11 wt.% Cl for fluid/melt mass ratios of 4.2 × 10−2.Compositional trends in the glass data show either increasing Cl contents of residual melt, essentially no change of Cl in melt, or decreasing Cl contents of aliquots of residual melt with progressive melt evolution. This method identifies melts that have assimilated magmatic or externally sourced hydrosaline liquids. Plots of (measured Cl in melt/modeled solubility of Cl in melt; Cl[Me/Mo]) versus the Larsen melt differentiation index show minimal dispersion for the least-evolved dacitic melts and increasing dispersion with melt evolution to rhyolitic compositions. Increased dispersion may be a consequence and indication of equilibrium or non-equilibrium degassing and/or assimilation of hydrosaline liquid.

Establishment of an initial water production evaluation chart for the gas province in the East China Sea

In order to reveal the reasons for the differences in initial water production characteristics of gas wells in different regions of the East China Sea Basin and to screen favorable targets for low-permeability reservoir reconstruction, a calculation method of initial production water–gas ratios at different gas column heights was established by combining gas-water two-phase capillary pressure with J function definition, power function relative permeability model and fractional flow equation. Then based on the experimental data of standard capillary pressure and standard relative permeability in the gas province of the East China Sea, an evaluation chart on initial production water–gas ratio of the East China Sea at different gas column heights was calculated and established. Finally, the evaluation chart was validated by using the data of the tested or commissioned gas wells in the gas reservoirs of the East China Sea, and the physical property conditions suitable for reservoir reconstruction of low-permeability gas reservoirs in the East China Sea were determined according to the evaluation chart. The following research results were obtained. First, the evaluation chart established in this paper reflects that the correlation between the parameters is similar to the actual production law and matches well with the actual data, which verifies the correctness and reliability of the chart establishment method and the key parameter calculation method. Second, with the production water–gas ratio less than 1 m3/104 m3 as the screening condition, for the permeability of the low-permeability gas reservoirs (with gas column height of about 50 m) in the west sub-sag, the central uplift belt and the periphery suitable for reservoir reconstruction shall be greater than 0.65 mD, and that of the large low-permeability gas reservoirs (with a gas column height of more than 100 m) in the north of central uplift belt shall be greater than 0.26 mD. Third, there is no gas–water contact in gas reservoirs under the hydrocarbon accumulation conditions of in-situ reservoirs, so the method and the evaluation chart proposed in this paper are not applicable. It is concluded that the method of establishing the initial water production evaluation chart and the method of calculating the key parameters proposed in this paper can provide meaningful reference for the development and evaluation of other gas fields in China.

Parameter estimation to study the immediate impact of aortic cross-clamping using reduced order models.

Aortic cross-clamping is a common strategy during vascular surgery, however, its instantaneous impact on hemodynamics is unknown. We, therefore, developed two numerical models to estimate the immediate impact of aortic clamping on the vascular properties. To assess the validity of the models, we recorded continuous invasive pressure signals during abdominal aneurysm repair surgery, immediately before and after clamping. The first model is a zero-dimensional (0D) three-element Windkessel model, which we coupled to a gradient-based parameter estimation algorithm to identify patient-specific parameters such as vascular resistance and compliance. We found a 10% increase in the total resistance and a 20% decrease in the total compliance after clamping. The second model is a nine-artery network corresponding to an average human body in which we solved the one-dimensional (1D) blood flow equations. With a similar parameter estimation method and using the results from the 0D model, we identified the resistance boundary conditions of the 1D network. Determining the patient-specific total resistance and the distribution of peripheral resistances through the parameter estimation process was sufficient for the 1D model to accurately reproduce the impact of clamping on the pressure waveform. Both models gave an accurate description of the pressure wave and had a high correlation (R2 > .95) with experimental blood pressure data.

Solubility of Water in Hydrogen at High Pressures: A Molecular Simulation Study

Hydrogen is one of the most popular alternatives for energy storage. Because of its low volumetric energy density, hydrogen should be compressed for practical storage and transportation purposes. Recently, electrochemical hydrogen compressors (EHCs) have been developed that are capable of compressing hydrogen up to P = 1000 bar, and have the potential of reducing compression costs to 3 kWh/kg. As EHC compressed hydrogen is saturated with water, the maximum water content in gaseous hydrogen should meet the fuel requirements issued by the International Organization for Standardization (ISO) when refuelling fuel cell electric vehicles. The ISO 14687-2:2012 standard has limited the water concentration in hydrogen gas to 5 μmol water per mol hydrogen fuel mixture. Knowledge on the vapor liquid equilibrium of H2O-H2 mixtures is crucial for designing a method to remove H2O from compressed H2. To the best of our knowledge, the only experimental high pressure data (P > 300 bar) for the H2O-H2 phase coexistence is from 1927 [J. Am. Chem. Soc., 1927, 49, 65-78]. In this paper, we have used molecular simulation and thermodynamic modeling to study the phase coexistence of the H2O-H2 system for temperatures between T = 283 K and T = 423 K and pressures between P = 10 bar and P = 1000 bar. It is shown that the Peng-Robinson equation of state and the Soave Redlich-Kwong equation of state with van der Waals mixing rules fail to accurately predict the equilibrium coexistence compositions of the liquid and gas phase, with or without fitted binary interaction parameters. We have shown that the solubility of water in compressed hydrogen is adequately predicted using force-field-based molecular simulations. The modeling of phase coexistence of H2O-H2 mixtures will be improved by using polarizable models for water. In the Supporting Information, we present a detailed overview of available experimental vapor-liquid equilibrium and solubility data for the H2O-H2 system at high pressures.

Functional-Segment Activity Coefficient Equation of State: F-SAC-Phi

COSMO-RS refinements and applications have been the focus of numerous works, mainly due to their great predictive capacity. However, these models do not directly include pressure effects. In this work, a methodology for the inclusion of pressure effects in the functional-segment activity coefficient model, F-SAC (a COSMO-based group-contribution method), is proposed. This is accomplished by the combination of F-SAC and lattice-fluid ideas by the inclusion of free volume in the form of holes, generating the F-SAC-Phi model. The computational cost when computing the pressure (given temperature, volume, and molar volume) with the proposed model is similar to the cost for computing activity coefficients with any COSMO-type implementation. For a given pressure, the computational cost increases since an iterative method is needed. The concept is tested for representative substances and mixtures, ranging from light gases to molecules with up to 10 carbons. The proposed model is able to correlate experimental data of saturation pressure and saturated liquid volume of pure substances with deviations of 1.7 and 1.1%, respectively. In the prediction of mixture vapor–liquid equilibria, the resulting model is superior to COSMO-SAC-Phi, SRK-MC (Soave–Redlich–Kwong with the Mathias–Copeman α-function) with the classic van der Waals mixing rule, and PSRK in almost all tested cases, from low pressures to over 100 bar.

Fuel injection location studies on pylon-cavity aided jet in supersonic crossflow

The current study numerically investigates the effect of fuel injection locations within a pylon-cavity aided Supersonic Combustion Ramjet (SCRAMJET) combustor on mixing enhancement, flame holding, fuel jet penetration and total pressure loss. RANS equations for compressed real gas are solved by coupled, implicit, second-order upwind solver. Two-equation SST model is used for turbulence modelling. The computational model is validated using experimental steady wall pressure data and 2D velocity field. The study uses seven distinct sonic fuel injection location cases of hydrogen fuel through a 1 mm diameter hole along the axis of the test section floor. All cases maintain crossflow of Mach number 2.2. The simulations show that the counter rotating vortex pair within the cavity plays a vital role in fuel dispersion and fuel jet penetration capability. The presence of pylon resulted in an increase of pressure loss by 7%, whereas the influence on total pressure loss due to transverse fuel injection is found to be insignificant. The injection locations within the cavity give around 55% (max) increase in fuel dispersion compared to location upstream of the pylon. Also the cavity floor locations give about 55% - 90% more flammable plume area than the injection from other locations.

Gas–liquid slug flow in a horizontal concentric annulus, a comparison of numerical simulations and experimental data

Multiphase flow simulations were run in OpenFOAM utilizing InterFoam, a volume of fluid type solver. A concentric annulus geometry was constructed and periodic boundary conditions were applied to alleviate the requirement for a longer domain. The simulations were run in 3, 5 and 7 m long domains with the annulus dimensioned such that the outer and inner cylinder diameter were 0.1 and 0.05 m respectively. The 4 individual mesh designs were constructed such that the coarsest mesh consists of 102k cells/m while the finest mesh was generated with 400k cells/m. Each mesh was significantly refined within 0.005 m of both the inner and outer cylinder wall. The simulation data was compared with experimental pressure and holdup data collected at Institute for Energy Technology in Norway. The 3 and 7 m domains reproduced slug frequencies to within 9% of the experiment results of 1.43 Hz for all mesh densities. Comparatively, the 5 m domain has larger errors with respect to slugging frequency (22–27%). The 5 m case performs poorly, probably due to an artificial restraint introduced by the limitation of available liquid which is set as αoil=0.53 for all cases. The αoil restriction combined with the domain length determines the amount of liquid in the system. This interaction of factors means that the domain length is an important parameter when preparing the simulation. The pressure data display a stronger dependence on the mesh quality in comparison to the slug frequency analysis. The 3 m domain with a 400k cells/m mesh resulted in a maximum and minimum pressure gradient of 1783.5 and 803.9 Pa/m, compared to the experiment values of 1785 and 822 Pa/m, which are within 3% of the expected results.

Numerical study of the flow dynamics at no-load operation for a high head Francis turbine at model scale

No-load operation is among the most damaging operating conditions. Since no energy is extracted by the turbine during this operation, the fluid energy is dissipated by highly energetic and turbulent flow phenomena causing high pressure and strain fluctuations on the turbine components. These highly turbulent flows are complex and, until now, poorly understood. This paper presents preliminary three-dimensional simulations of no-load turbulent flow within a high head Francis turbine at model scale using Computational Fluid Dynamics and the SAS-SST turbulence model. The numerical results are compared with unsteady experimental pressure data acquired on the runner blades of a model turbine. A preliminary study of the numerical results reveals some specific flow behaviors present at no-load operation.

Thermodynamically Consistent Force Field for Coarse-Grained Modeling of Aqueous Electrolyte Solution.

We propose a thermodynamically consistent methodology to parameterize interactions between charged particles inside the dissipative particle dynamics (DPD) formalism. We used osmotic pressure experimental data as a function of the salinity in order to optimize the interaction parameters. Results for NaCl aqueous solution show that both mean osmotic and activity coefficients of individual ions allowed the determination of Na+-water, Cl--water, and Na+-Cl- DPD repulsion parameters. A simple linear relationship between the hydration-free energies of ions and the ion-water repulsion parameters that allows the parameterization of the complete series of halide and alkaline ions is proposed. Two strategies have been used to obtain the anion-cation interaction parameters for halide and alkaline ions. In the first one, the parameters are obtained based on the numerical optimization of the anion-cation repulsion parameter with respect to the experimental osmotic pressure data (with mean average deviations <4%). Second, we propose a predictive approach based on the free-energy difference of hydration energies of anions and cations in the spirit of the law of matching water affinities [with a mean absolute relative deviation of about 13%, better than 6% if small ions (Li+ and F-) are removed].