Experimental Pressure Profiles Research Articles

A homogeneous relaxation model algorithm in density-based formulation with novel tabulated method for the modeling of CO2 flashing nozzles

Accurate prediction of the flow physics within nozzles and ejectors working with two-phase carbon dioxide remains particularly challenging. Indeed, the flashing phenomenon in the device often comes along with the formation of the metastable phase, which can severely affect both the flow physics, and the flow rate. Due to the particular challenges associated with building and operating two-phase carbon dioxide experimental setups, computational fluid dynamics constitutes a compelling alternative to study and predict nozzle and ejector flows. In this work, the metastability effects are modeled through a Homogeneous Relaxation Model for the first time expressed in density-based formulation, within the SU2 solver. The thermodynamic relations for the equation of state are tabulated using a novel quad-tree algorithm and directly coupled to the solver, ensuring fast and accurate predictions. The simulation tool is then validated against experimental nozzle pressure profiles and used to compare the commonly used Homogeneous Equilibrium Model to the Homogeneous Relaxation Model in terms of local flow topology and mass flow rates. Most notably, it was found that the Homogeneous Relaxation Model was able to better fit the experimental pressure profiles within the first part of the expansion.

Canonical and Experimental Plasma Pressure Profiles in Tokamaks

The statement that the so-called canonical plasma pressure profile is in good agreement with experimental data was the motivating basis for constructing the analytical model of plasma self-organization in tokamaks. The profiles of the normalized plasma electron pressure taken from the international database collecting the experimental data from different tokamaks are compared with the canonical profiles of two types. The comparison shows that the experimental pressure profiles considerably differ from these canonical profiles.

Mold filling behaviour of LPIM feedstocks using numerical simulations and real-scale injections

ABSTRACT This study aims to compare the flow patterns and in-cavity pressures obtained experimentally and numerically for different conditions. Four feedstocks based on 17-4PH stainless steel powder were fully characterised and implemented as material laws in an Autodesk Moldflow package before to obtain numerical simulations that were then validated using real-scale injections. The flow patterns obtained numerically for the different flat bar mold geometries were in good agreement with the experimental flow patterns, showing an almost perfect fit, whereas for the flow patterns of the complex mold geometry, there were some minor discrepancies. The simulated pressure profiles obtained for different mold geometries, feedstock temperatures, mold temperatures and solid loadings were in good agreement with the experimental pressure profiles in terms of trend and pressure values, with maximum relative differences varying from 30 to 64% depending on particular feedstocks and process parameters.

PIV mapping of pressure and velocity fields in the plane magnetohydrodynamic Couette flow

We present the first simultaneous mapping of two-dimensional, time-dependent velocity and pressure fields in a plane Couette flow pervaded by a transverse magnetic field. While electromagnetic forces are strongest in fluids of high electric conductivity such as liquid metals, their opacity excludes optical optical measurement methods. We circumvent this difficulty using a transparent electrolyte (Sulfuric acid), whose weaker conductivity is offset by higher magnetic fields. We describe an experimental rig based on this idea, where the Couette flow is entrained by a tape immersed in sulfuric acid and positioned flush onto the bore of large superconducting magnet, so that most of the flow is pervaded by a sufficiently homogeneous transverse magnetic field. Velocity and pressure fields are obtained by means of a bespoke PIV system, capable of recording the fluid's acceleration as well as its velocity. Both fields are then fed into a finite difference solver that extracts the pressure field from the magnetohydrodynamic governing equations. This method constitutes the first implementation of the pressure PIV technique to an MHD flow. Thanks to it, we obtain the first experimental velocity and pressure profiles in an MHD Couette flows and show that the transitional regime between laminar and turbulent states is dominated by near-wall, isolated, anisotropic perturbations.

CdSe-Based Quantum Dots as In Situ Pressure and Temperature Non-intrusive Sensors in Elastohydrodynamic Contacts

We present a new technique designed for in situ measurement of pressure and temperature in lubricating films. An innovative methodology has been developed, based on the photoluminescence properties of non-intrusive CdSe-based nanosize sensors (quantum dots). The sensitivity to pressure and temperature of these sensors dispersed in a carrier fluid was established through calibrations performed in diamond anvil cells. Elastohydrodynamic (EHD) contacts of different combinations of contacting solids (glass-steel, glass-Si3N4, sapphire-steel and sapphire-Si3N4) and submitted to various operating conditions were studied through in situ experiments and numerical simulations. Isothermal experiments were performed first: both experimental central pressures and pressure profiles were obtained, with a very good agreement with the values predicted by the numerical model. A series of non-isothermal experiments were then carried out to perform temperature measurements. Temperature rises in the central zone of EHD contacts involving various material pairs were measured and compared to predictions, leading to a very satisfying agreement. Overall, the deviation between measurements and predictions remained smaller than the uncertainty of the measurement method. Therefore, these findings proved the potential of the methodology to probe in situ pressure and temperature in EHD contacts. Comparative performance with competing techniques was examined in terms of intrusiveness, level of reliability, spatial resolution, accuracy and complexity. As this work is a pioneering development, the technique may be improved in the near future, opening an avenue for even more accurate or faster measurements for example, and eventually offering a better understanding of the mechanisms at work in this type of lubricated interface.

Experimental realization of incipient active failure in sand heap by seismic loading

Sand heaps avalanche when a static angle of repose is exceeded, and freeze at a dynamic angle of repose. The stress distribution in a planar sand heap stabilized at the angle of repose with an incipient active failure condition, by which the material is on the verge of failure everywhere, was examined. At the time of construction, the vertical pressure was initially not in the incipient failure. A slight amount of seismic loading using the sinusoidal motions of a shaking table was set up with just enough energy to rearrange the sand particles, to erase the formation history, and to fluctuate local density inside a sand heap without an excessive loss of mass. During the experiments, laser displacement sensors and pressure gauges were employed to monitor the vertical displacements above and the vertical pressures below the sand heap respectively. The non-linear differential equations, characterizing the stress distribution in an active sand heap, were formulated under the Mohr–Coulomb failure criterion and numerically solved by the Newton method. Bulk solids started flowing after the state of incipient failure; therefore, the experimental vertical pressure profiles were found to gradually conform to the theoretical vertical pressure profiles if the sand heap was subjected to sufficient excitation.

Spall Strength of Shock-Heated Zirconium and Phase Diagram of Its High-Pressure Polymorphic Modification

Spall strength of zirconium heated by a strong shock wave to thousand-degree temperatures and that underwent transformations into denser polymorphic modifications was determined. Pressure profiles at the sample–soft barrier boundary were measured in spall experiments under flat one-dimensional loading. The equations of state of three polymorphic modifications of zirconium were constructed in the pressure range up to 50 GPa. Thermodynamic states of zirconium, which were calculated under conditions of experiments, in combination with results of measurements of pressure profiles, made it possible to determine the spall strength of zirconium heated in the shock compression–unloading cycle. The spall strength of zirconium was –2.8(7) GPa at 1027(70) K. Experimental pressure profiles were analyzed using the results of mathematical modeling of the performed experiments.

Откольная прочность ударно-разогретого циркония и фазовая диаграмма в области существования его полиморфных модификаций высокого давления

Abstract Spall strength of zirconium heated by a strong shock wave to thousand-degree temperatures and that underwent transformations into denser polymorphic modifications was determined. Pressure profiles at the sample–soft barrier boundary were measured in spall experiments under flat one-dimensional loading. The equations of state of three polymorphic modifications of zirconium were constructed in the pressure range up to 50 GPa. Thermodynamic states of zirconium, which were calculated under conditions of experiments, in combination with results of measurements of pressure profiles, made it possible to determine the spall strength of zirconium heated in the shock compression–unloading cycle. The spall strength of zirconium was –2.8(7) GPa at 1027(70) K. Experimental pressure profiles were analyzed using the results of mathematical modeling of the performed experiments.

A Single Stroke Cylinder Rapid Compression Machine for Chemical Kinetic Study at Elevated Pressure and Temperatures

The fabrication of a rapid compression machine (RCM) is in its early phase of design. The machine is designed to enhance the study of ignition delay and validation of detailed kinetics models of fuels. The machine compresses fuel/air mixtures isentropically within 25 to 52 ms with a varying stroke. The combustion chamber design is not fixed and can be adjusted through the threaded shaft lock and within chamber slots. The originality of the facility is the inclusion of a pneumatic piston release mechanism (PPRM), which is pneumatically operated. The current test facility has been characterised by conducting a nonreactive and reactive experiment, the result showed that an obtainable compressed pressure of 21 bar and end gas temperature of approximately 1000 K was achievable within the present facility. The fidelity of the facility was performed with a non-reactive experiment, which experimental pressure profile was seen to follow each other closely showing that the data are highly repeatable within the test condition, the result was free from any form of rebound or disturbance, which would have adversely distort the result. The experiment data was simulated implementing the effective volume approach and was seen to perfectly match with the experiment at both stages of compression. The reactive experiment was demonstrated with heptane/air mixture at stoichiometric condition, TC = 625 ⩽ 689 K. The results show that the experimental pressure traces overlay each other thus signifying a repeatable pressure trace and this demonstrates that the Shef-RCM is operable and ready at its first stage of design for studying the ignition delay time of liquid fuels operating within an engine like conditions and for validating chemical kinetics models.

Model Guided Application for Investigating Particle Number (PN) Emissions in GDI Spark Ignition Engines

<div class="section abstract"><div class="htmlview paragraph">Model guided application (MGA) combining physico-chemical internal combustion engine simulation with advanced analytics offers a robust framework to develop and test particle number (PN) emissions reduction strategies. The digital engineering workflow presented in this paper integrates the <i>k</i>inetics & SRM Engine Suite with parameter estimation techniques applicable to the simulation of particle formation and dynamics in gasoline direct injection (GDI) spark ignition (SI) engines. The evolution of the particle population characteristics at engine-out and through the sampling system is investigated. The particle population balance model is extended beyond soot to include sulphates and soluble organic fractions (SOF). This particle model is coupled with the gas phase chemistry precursors and is solved using a sectional method. The combustion chamber is divided into a wall zone and a bulk zone and the fuel impingement on the cylinder wall is simulated. The wall zone is responsible for resolving the distribution of equivalence ratios near the wall, a factor that is essential to account for the formation of soot in GDI SI engines. In this work, a stochastic reactor model (SRM) is calibrated to a single-cylinder test engine operated at 12 steady state load-speed operating points. First, the flame propagation model is calibrated using the experimental in-cylinder pressure profiles. Then, the population balance model parameters are calibrated based on the experimental data for particle size distributions from the same operating conditions. Good agreement was obtained for the in-cylinder pressure profiles and gas phase emissions such as NO<sub>x</sub>. The MGA also employs a reactor network approach to align with the particle sampling measurements procedure, and the influence of dilution ratios and temperature on the PN measurement is investigated. Lastly, the MGA and the measurements procedure are applied to size-resolved chemical characterisation of the emitted particles.</div></div>

Numerical study on convective mass transfer enhancement by lateral sweep vortex generators

Passive mass transfer enhancement from the surface of a liquefying substance using Lateral Sweep Vortex Generators (LSVG) placed in high-speed flow is presented. Numerical simulation of three-dimensional turbulent compressible flowfield involving species transport has been carried out using Advection Upstream Splitting Method (AUSM) scheme based Finite Volume solver. A temperature dependent mass efflux boundary condition has been developed and implemented in the computational procedure for updating the boundary mass flux. Computational procedure has been validated using the experimental wall pressure profile reported for a similar vortex generator placed in high speed flow and could capture the complex flow features resulted by the vortex-boundary layer interactions. Convective mass transfer of species is found to get improved in wake region of the LSVG by the horseshoe vortex and further get transported downstream by the counter-rotating vortex pair. Extensive numerical simulations have been carried out with several lateral sweep angles of LSVG to explore the role of vortices in promotion of the convective mass transfer. It has been observed that the mass efflux enhances with increase in sweep angle of the vortex generator due to the vorticity augmentation. Analysis of the vortex trajectories could figure out the influence of vortex interactions leading to the peak mass efflux. Further, an exponential-power law based correlation between relative Sherwood number and relative streamwise vorticity has been developed.

Analysis of thermodynamic scope engine simulation model empirical coefficients: Suitability assessment and tuning of conventional hydrocarbon fuel coefficients for bio syngas

The sensitivity of empirical correlations and coefficients of thermodynamic quasi and zero dimensional SI engine models to mixture thermo-chemistry and engine thermo-kinematic response variations is addressed. Mixture thermo-chemistry alterations, as in case engine operation with non-regular alternatives, and accompanying in-cylinder fluid flow and combustion dynamics perturbations induce variations in full cycle thermodynamic and process thermo-kinematic response with potential influence on empirical coefficients. As an example, producer gas and natural gas thermo-physical properties differ significantly, extending to thermo-kinematic response over a range of operating conditions. Literature indicates monotonous adoptions of conventional fuel coefficients for simulation studies with non-regular fuels and tuning efforts are directed at initial and boundary conditions, which are many times thermodynamically untenable. The current work evaluates the suitability of empirical correlations and coefficients tuned for conventional hydrocarbon fuels, for numerical simulation of producer gas fuelled operation. Producer gas specific coefficients are evolved, following a generic approach, wherever necessary.Assessment of producer gas thermo-physical properties indicates four times higher thermal conductivity of producer gas (40.0 mW/mK) compared to gasoline (11.2 mW/mK), attributed to the presence of hydrogen. The influence is on convective cooling which is reflected in about 32% cooling load as against 25% for spark ignited engines. In response, the Reynolds number power coefficient of convective heat transfer correlation nearly doubles from 0.35 to 0.76. Analysing laminar flame speed coefficients, the inability of CHEMKIN-III to accurately predict laminar flame speed of hydrogen containing gases requiring adoption of CHEMKIN-II is a key observation. Substantial deviations are also observed for apparent heat release profiles with extended terminal stage combustion duration for producer gas, attributed to enhanced convective cooling. Curve fit analysis evolves producer gas specific shape and efficiency coefficients of 0.71 and 2.23 as against 2.0 and 5.0 for conventional fuels. The terminal combustion duration also changes from 1.22 to 2.12 ms. Using tuned coefficients permits near concurrent evolution of simulation and experimental pressure and heat release profiles establishing the need for fuel specific coefficients.

Experimental and numerical studies on the explosion severities of coal dust/air mixtures in a 20-L spherical vessel

Severity parameters are critical for safety management and risk assessment of coal dust explosions. We evaluated explosion severity parameters using a 20-L spherical vessel and numerical simulation by the program FLUENT to reveal the explosion mechanism of coal dusts. The explosion pressure and the rate of explosion pressure increased with coal dust concentration and the ignition delay up to a concentration of 250g/m3 coal dust and an ignition delay of 60ms for a maximum explosion pressure of 0.67MPa and a rate of explosion pressure rise of 68.89MPa/s. Comparison of the numerical and experimental explosion pressure profiles showed reasonable quantitative and qualitative agreement. Additionally, the numerical simulation was used to address the technical difficulties of understanding the mechanisms of dust explosion, it suggested that the airflow of the dust explosion played a more important role in the secondary explosion of dusts in a closed chamber than in a half-closed one.

Modeling of a Piezoelectric MEMS Micropump Dedicated to Insulin Delivery and Experimental Validation Using Integrated Pressure Sensors: Application to Partial Occlusion Management

A numerical model based on equivalent electrical networks has been built to simulate the dynamic behavior of a positive-displacement MEMS micropump dedicated to insulin delivery. This device comprises a reservoir in direct communication with the inlet check valve, a pumping membrane actuated by a piezo actuator, two integrated piezoresistive pressure sensors, an anti-free-flow check valve at the outlet, and finally a fluidic pathway up to the patient cannula. The pressure profiles delivered by the sensors are continuously analyzed during the therapy in order to detect failures like occlusion. The numerical modeling is a reliable way to better understand the behavior of the micropump in case of failure. The experimental pressure profiles measured during the actuation phase have been used to validate the numerical modeling. The effect of partial occlusion on the pressure profiles has been also simulated. Based on this analysis, a new management of partial occlusion for MEMS micropump is finally proposed.

Features of shock-wave and vortex processes simulation at depressurization of circuits with superheated water coolant

Formation and evolution of pressure waves on the barrier were numerically simulated at non-staionary outflow of the superheated vapor from the vessel. The simulation conditions were fully consistent with the experimental conditions (1982) [1]. The calculated pressure fields were calculated both at the initial stage of non-stationary vapor outflow and at the quasistationary flow of superheated vapor on the barrier. The dynamics of interaction between shock waves and vortex structures on the barrier was studied at quasi-stationary outflow of the superheated vapor, and the experimental pressure profile on the target was compared with the calculated pressure profile. Comparison of the experimental data and the calculation results has showed acceptable agreement between the pressure profiles on the target up to a distance from the target to the nozzle approximately X/D = 6.

CFD modeling of riser with Group B particles

A series of tests were conducted in a large cold flow CFB unit (18m long riser and 30cm in diameter) with two different Group B powders. The impact of particle nature on the riser hydrodynamics was investigated at similar operating conditions through pressure taps and extraction probes. To study the impact of particle size and sphericity, sand and glass beads were used. Resulting axial pressure profiles are very different in both the acceleration and in the fully developed region. These differences can most probably be explained by the difference in shape between the solids. Higher sphericity seems to generate smaller pressure drop. Through extraction probe measurements, the core-annulus regime was found on the developed zone of the riser. An assessment of a commercial CFD code to predict riser flow was carried out. For glass beads, simulation results agree reasonably well with experimental pressure profiles, but the core annulus structure is underpredicted. However, pressure drop along the riser is strongly underestimated in sand simulations.

Interpretation of tokamak self-consistent pressure profiles

The phenomenon of a pressure profiles self-consistency in tokamak plasmas is interpreted in the framework of a ‘thermodynamic’ approach, used successfully in complex non-equilibrium systems studies. The solutions for the self-consistent pressure profiles are in accordance with experimental pressure profiles. The heat transport features in the vicinity of the minimum of the free energy are analysed. The deduced energy confinement scaling law is in qualitative agreement with the empirical so-called IPB98(y,2) scaling law.

Effect of Exhaust Gas Recirculation in NOx Control for Compression Ignition and Homogeneous Charge Compression Ignition Engines

Abstract Exhaust Gas Recirculation (EGR) is a potential option for controlling in-cylinder NOx in automobiles. This paper aims to study the effect of EGR on NOx emissions and in Compression Ignition (CI) engines at various conditions. To this end, low dimensional models are developed using a first principles approach without recourse to empirics. Fuel oxidation represented by a three-step global kinetic model coupled with the Zeldovich mechanism for NOx formation is used to predict the composition of the entire spectrum of engine-out gases. Solution of the conservation equations using MATLAB provides the in-cylinder variation of parameters like volume, pressure, torque, speed and work done and species (Fuel, CO, CO 2 , NO X , etc.) with respect to Crank Angle Displacement (CAD). The inlet conditions are the fuel-air equivalence ratio, engine specifications and the inlet air temperature. The simulations are validated against experimental pressure profiles from the literature. External EGR is then implemented to study its effect on engine-out emissions under cold start conditions. The effect of EGR at various combinations of engine operating conditions is examined in detail.

Supercritical CO2 generator using bubble collapse by water hammer

We have developed a new apparatus to dynamically generate supercritical CO2 (scCO2) bubbles in water using a water hammer facility by efficiently concentrating water energy. We measured the internal and external pressures of a CO2 bubble covered with a rubber membrane using pressure transducers, and observed the bubble's oscillations by a high-speed video camera. We evaluated the maximum duration of the scCO2 for conditions 60μs in experiments. We performed numerical simulations using the Rayleigh–Plesset equation by substituting the experimental external pressure profiles of the bubble and confirmed that numerical results agreed with the experimental internal pressure. Moreover, in the minimum external pressure condition where we experimentally achieved the condition of scCO2 in the bubble for 16μs by water hammer, we obtained the maximum duration of scCO2 conditions up to 55μs by numerical simulations assuming isotropic compression.

An approach to evaluate Venturi-device effects on gas wells production

Abstract This paper presents a theoretical analysis of the effect produced by Venturi devices in gas wells. The first part of our methodology consists of performing steady-state simulations to fit experimental and theoretical pressure profiles. These simulations were carried out in Aspen Plus® to reproduce gas production in wells. The results in our case study have indicated that the flow pattern corresponds to a mist type. Then CFD simulations have been used to reproduce the gas–liquid flow through a Venturi device based on ANSYS CFX®. It has been observed that the Venturi increases the gas volume fraction and easy formation of smaller bubbles, which tend to flow in the center of the well. CFD simulations were carried out assuming an Eulerian–Eulerian approach for the bubbles dispersion through the Venturi device. The RNG k–e model and the homogeneous MUSIG model are used to include the turbulence effect and to represent the bubbles population balance, respectively. Thus the numerical evidence indicates that Venturi-devices promote a flow pattern where the pressure drop decreases and hence it can increase the gas production in certain types of gas wells.