•Defined local Froude number (Frl) to asses jet characteristics during calculations.•A model to dynamically prescribe turbulent Schmidt and Prandtl numbers is proposed.•Model identifies regions with ...possible occurrence of Kelvin-Helmholtz instability.•Improved results in case with occurrence of Kelvin-Helmholtz instability.
To theoretically investigate atmosphere mixing in an enclosure, three experiments of interaction of a vertical air jet with a helium-rich layer performed in SPARC, PANDA and MiniPanda experimental facilities, were simulated using the URANS approach. For the purposes of this work, firstly, a local Froude number is introduced, which can be directly used in computational fluid dynamics calculations to specify the regions with possible occurrence of Kelvin-Helmholtz instability. Namely, it is shown that in these regions, turbulent diffusion is underpredicted and turbulence model fails to replicate some phenomena. Secondly, a model for dynamically prescribe turbulent Schmidt and Prandtl numbers is proposed. The proposed model improves the results in isothermal case with possible occurrence of Kelvin-Helmholtz instability, while its effects are negligible in cases with higher temperature jets with lower local Froude number values, where the conditions for the Kelvin-Helmholtz instability are not established.
In this study, forced convection heat transfer of water/alumina Nano fluid in a rectangular microchannel with cross-flow injection is studied. The Nano fluid enters the microchannel with a ...temperature of 293 K and cools its walls. The upper wall of the microchannel is at constant temperature of 303 K. On the lower wall, there are two holes for injection of Nano fluid flow. Other parts of the microchannel wall are insulated. Slip velocity boundary condition is used for the walls of the microchannel. Simulations are performed for different injection velocities and the results are presented as velocity and temperature fields, and variation of the Nusselt number. The results show that the slip velocity on the channel wall and the Nusselt number increase by increasing the injection velocity. It is revealed that the Nusselt number is maximum at the channel entrance and decreases along the channel. After each injection, local Nusselt number increases due to the increase of the temperature gradient in the microchannel. Moreover, an optimal value for the ratio of the injection velocity to the inlet velocity is achieved using performance evaluation criteria (PEC). It is concluded that is an optimal value of the injection velocity, leading to maximum PEC.
•A fluid-dynamics model within an open-source CFD code was improved to simulate experiments on containment atmosphere mixing.•The model was validated against 10 experiments performed in PANDA and ...SPARC facilities.•Various possibilities to reduce the computational domain for practical reasons were considered.•Effects of reduced numerical domain is assessed and the suitability of the reductions is discussed.
Several experiments of interaction of air or steam jet with a horizontal helium rich layer in a closed vessel representing a NPP containment, which were performed in PANDA and SPARC experimental facilities, are simulated on the local instantaneous scale using the Unsteady Reynolds Averaged Navier Stokes approach. Axisymmetric two-dimensional and three-dimensional numerical models of cylindrical vessels are developed, and the effects of numerical domain reduction are studied. The mixing process is simulated as a single-phase flow with common momentum and energy equations. Consequently, an additional term accounting for enthalpy diffusion due to compositional changes is implemented into the energy equation. Included gas species mass fractions are considered as passive scalars and are calculated using the transport equation. However, the term describing the molecular diffusion cannot be neglected and had to be added to the diffusion equation implemented in the default OpenFOAM computational fluid dynamics code that was used. The k-ε turbulence model with additional turbulence generation and dissipation due to buoyancy is used for turbulence modelling. The comparison of simulation and experimental results shows that the improved physical model is able to successfully describe the phenomena in several experiments performed in different facilities with different initial and boundary conditions.
This paper presents an investigation into the reliability of substrate bonding between metal layers and gallium arsenide vertical-injection light-emitting diodes (GaAs VLEDs). In this study, ...molybdenum (Mo) acts as a buffer layer between the GaAs VLED and the aluminum-based metal core printed circuit board (MCPCB). The thermal expansion coefficient (CTE) value of GaAs is approximately equal to that of the Mo layer under the substrate. This is beneficial for slowing the decay of the adhesive bond due to temperature cycling from − 40°C to 125°C for 50 cycles. The experimental results show that the use of the Mo buffer layer greatly improved the electrical and optical performance of the LED packages. The average leakage current was reduced from 33.63 mA to 2.37 mA at the reversed voltage of − 3 V and the increase in light output power was 130% at an injection current of 0.7 A. The results also show that a Mo buffer layer can reduce the risk of cracking on bonding wires after the thermal shock test (TST). These results are useful for improving the aging of GaAs VLEDs.
In the present study, large eddy simulation methodology is applied to investigate the 3D non-premixed flameless oxidation in the IFRF furnace. In order to serve this purpose, to model the combustion ...and radiation, the partially stirred reactor and finite volume discrete ordinate model are used, respectively.Moreover, the detailed mechanism of GRI-2.11 is undertaken to represent chemistry reactions. The present simulations agree qualitatively well with published experimental data. Finally, the present study focusses on the assessment of the effects of variations in the fuel vertical injection by adding an inert gas as well as the fuel temperature on combustion behavior. The results revealed that important changes occur in the characteristics of the flameless oxidation process.
A method for forming a current blocking layer (CBL) by ion implantation in GaN-based vertical-injection light-emitting diodes (VI-LEDs) was proposed. It was found that the use of CBL in VI-LEDs can ...effectively reduce the current crowding effect and enhance the light output power. The uniform emission intensity distribution of VI-LEDs with CBL was demonstrated by electroluminescence measurements. Experimental results show that the wall-plug efficiency was enhanced by 12.3% at an injection current of 20 mA, compared to that of VI-LEDs without CBL, and by 56.2% compared to that of conventional LEDs. The device simulation results reveal that the current path can be blocked by CBL, resulting in high light extraction efficiencies and large current densities within the effective emission region of active layers.
Introduction. In this article, the problem of temperature distribution in an oil-bearing formation with a hydraulic fracture and a vertical injection well is numerically modeled.
Materials and ...Methods. To describe the process of temperature distribution in the formation under the action of the fluid injected into the formation, the Fourier-Kirchhoff equation of convective heat transfer is used. To solve this equation, the discontinuous Galerkin method on staggered unstructured grids is used. To describe the process of pressure change in the formation under the action of the injection well, an equation is used that is obtained based on the continuity equation and Darcy’s law. To solve it, the discontinuous Galerkin method on an unstructured triangular grid is used. To parallelize the numerical algorithm, the MPI library is used.
Results. The article presents a numerical algorithm and the results of modeling the dynamics of the temperature fields in an oil reservoir with a hydraulic fracture and a vertical injection well.
Discussion and Conclusion. A numerical algorithm based on the discontinuous Galerkin method for math modeling of the temperature and pressure fields in a oil-bearing formation with a hydraulic fracture and injection well was developed and implemented. The results obtained for the distribution of temperature and pressure in the fracture are adequate and in good agreement with the specified initial-boundary conditions. Further work in this direction involves modeling on tetrahedral unstructured meshes for a more accurate study of the ongoing processes.
In this study, novel thin-GaN-based ultraviolet light-emitting diodes (NTG-LEDs) were fabricated using wafer bonding, laser lift-off, dry etching, textured surface, and interconnection techniques. ...Placing PN electrodes on the same side minimized the absorption caused by electrodes in conventional vertical injection light-emitting diodes (V-LEDs) and the current spreading was improved. The light output power (700 mA) of the NTG-LEDs was enhanced by 18.3% compared with that of the V-LEDs, and the external quantum efficiency (EQE) of the NTG-LEDs was also relatively enhanced by 20.0% compared with that of a reference device. When the current operations were 1,500 mA, the enhancements of the light output power and EQE were 27.4% and 27.2%, respectively. Additionally, the efficiency droop was improved by more than 15% at the same current level.
The enhanced light extraction and collimated output beam profile from GaN-InGaN vertical-injection light-emitting diodes (VI-LEDs) are demonstrated utilizing high-aspect-ratio nanorod arrays. The ...nanorod arrays are patterned by self-assembled silica spheres, followed by inductively coupled-plasma reactive ion etching. The fabricated nanorod arrays not only provide an omnidirectional escaping zone for photons, but also serve as waveguiding channels for the emitted light, resulting in a relatively collimated beam profile. The light output power of the VI-LED with nanorod arrays is enhanced by 40%, compared to a conventional VI-LED. The measured far-field profiles indicate that the enhancement is mainly along the surface normal direction, within a view angle of 20deg.
Over the past few decades, foam flooding has emerged as a decent option for diverting flow from high permeable layers toward dense layers. Here, a visualization study of the conventional foam and ...polymer enhanced foam (PEF) behavior in the heterogeneous porous media is presented and the PEF performance in horizontal and vertical injection modes is evaluated. A heterogeneous porous medium made of transparent plexiglass packed with two different layers of glass beads to attain a heterogeneity ratio of 4:1 was used in various flooding experiments. The results of dynamic tests in the absence of oil showed that the presence of polymer in the foaming solution increases the flow resistance of foam in the porous medium and prevents foam fingering in the low-permeable layers. Horizontal oil displacement experiments showed that PEF flooding has an excellent plugging capacity and oil recovery increased by 72.5% of water flooded residual oil (S*or), which was 19.1% more than that of conventional foam injection. Comparison between vertical and horizontal PEF flooding proved that due to the positive gravity effect, the performance of PEF in vertical mode was better than that in horizontal mode, and the recovery factor increased to 78.3% water-flooded residual oil.
•Combination of CTAB surfactant and PVA polymer performs well as foam stabilizer.•The proposed polymer enhanced foam (PEF) sweeps more oil at the tertiary mode.•The flow behaviour of PEF and conventional foam in heterogeneous media is compared.•PVA compensates the destructive effect of gravitational force on EOR performance of foam.
PDF
