Laminar Viscous Model Research Articles

Effect of Magnetic Baffles and Magnetic Nanofluid on Thermo-Hydraulic Characteristics of Dimple Mini Channel for Thermal Energy Applications

The combined effect of a magnetic baffle and a dimple turbulator on the heat transfer and pressure drop is investigated computationally in a mini channel. Fe3O4 magnetic nanofluid is used as a working fluid. The Reynolds number (Re) is varied from 150 to 210 and the magnetic field intensities range from 1200 G to 2000 G. Finite-volume based commercial computational fluid dynamics (CFD) solver ANSYS-Fluent 18.1 was used for the numerical simulations. A laminar viscous model is used with pressure-velocity coupling along with second-order upwind discretization and QUICK scheme for discretizing the momentum and energy equations. The results show that there is an increase of 3.53%, 10.77%, and 25.39% in the Nusselt numbers when the magnetic fields of 1200 G, 1500 G and 2000 G, respectively, are applied at x = 15 mm, as compared to the flow without a magnetic field when the pitch = 10 mm. These values change to 1.51%, 6.14% and 18.47% for a pitch = 5 mm and 0.85%, 4.33%, and 15.25% for a pitch = 2.5 mm, when compared to the flow without a magnetic field in the respective geometries. When the two sources are placed at x = 7.5 mm and 15 mm, there is an increase of 4.52%, 13.93%, and 33.08% in the Nusselt numbers when magnetic fields of 1200 G, 1500 G, and 2000 G are applied when the pitch = 10 mm. The increment changed to 1.82%, 8.16%, and 22.31% for a pitch = 5 mm and 1.01%, 5.96%, and 21.38% for a pitch = 2.5 mm. This clearly shows that the two sources at the front have a higher increment in the Nusselt numbers compared to one source, due to higher turbulence. In addition, there is a decrease in the pressure drop of 10.82%, 16.778%, and 26.75% when magnetic fields of 1200 G, 1500 G, and 2000 G, respectively, are applied at x = 15 mm, as compared to flow without magnetic field when the pitch = 10 mm. These values change to 2.46%, 4.98%, and 8.54% for a pitch = 5 mm and 1.62%, 3.52%, and 4.78% for a pitch = 2.5 mm, when compared to flow without magnetic field in the respective geometries. When two sources are placed at x = 7.5 mm and 15 mm, there is an decrease of 19.02%, 31.3%, and 50.34% in the pressure drop when the magnetic fields of 1200 G, 1500 G and 2000 G are applied when the pitch = 10 mm. These values change to 4.18%, 9.52%, and 16.52% for a pitch = 5 mm and 3.08%, 6.88%, and 14.88% for a pitch = 2.5 mm. Hence, with the increase in the magnetic field, there is a decrease in pressure drop for both the cases and the pitches. This trend is valid only at lower magnetic field strength, because the decrease in the pressure drop dominates over the increase in pressure drop due to turbulence.

Effect of turbulence modeling on hydrodynamics of a turbulent contact absorber

A computational fluid dynamics (CFD) study is conducted to find a suitable two equation turbulence model for accurate prediction of hydrodynamics of an inhouse turbulence contact absorber (TCA) at high gas and liquid velocities. Based on the multi-fluid Eulerian approach, hydrodynamics of TCA is simulated by incorporating three turbulence models i.e. standard k–ε model, RNG k–ε model and SST k–ω model in ANSYS Fluent®. The solid phase stresses were closed by using the kinetic theory of granular flows (KTGF). TCA hydrodynamics parameters; expanded bed height and bed pressure drop were used to compare the results of this study with experimental data and also with earlier numerical study published with laminar viscous model. It was found that the RNG k–ε model predicted the bed height and pressure drop better than its counterparts. To accurately find the effects of secondary phase turbulence, two RNG k–ε model options i-e. per phase and dispersed were also evaluated. The results show that the “per phase” option of RNG k–ε model produced the expanded bed height and pressure drop in close agreement with available experimental data at similar operating conditions.

Numerical analysis of the flow pathlines in thermo-acoustic couples

Abstract Thermo-acoustic systems use a high amplitude sound-wave for refrigeration or electricity generation without the drawbacks of expensive construction, adverse environmental impact or high maintenance cost. The effective conversion of energy occurs within the “stack” considered as the heart of the system. The time-averaged rate of heat transfer across the edges of the stack is a good indicator of an effective performance. Hence, studying the effect of the geometry of the stack edges together with their locations is useful. Furthermore, current manufacturing practices make it possible to develop diverse stack edges, resulting in an improved efficiency of the heat transfer. For effective modelling of the heat transfer rate, a second-order, double-precision discretization of state variables and a laminar viscous model was used. A numerical model was developed using the commercial code FLUENT. The evolution of the flow vortices at different drive ratio was analyzed. Two edges shapes were considered namely rectangular and rounded edges. Using numerical analysis, this study has pointed out that stack edge profiles has a significant effect on the overall performance of thermo-acoustic systems. Rounding the stack edge profile appears to be beneficial for the system performance. This study points out the link between the non-linearity observed in thermo-acoustic systems, the flow streaming and the mean vorticity at the stack edges.

Numerical Investigation of Convective Heat Transfer of Refined Kerosene-Alumina Nanofluid Under Laminar and Turbulent Regime

The study reports Computational Fluid Dynamics (CFD) investigations of the convective heat transfer coefficient of Al2O3/refined kerosene nanofluids. The study was carried out under laminar and turbulent regime in a circular tube under uniform and constant heat flux on the wall. The study was carried out for Re 500 to 5500 for base refined kerosene and with alumina added with 0.01% and 0.05% volume concentration in the base refined kerosene. The size of the alumina nanoparticle was 35 nm. Different computational models of Ansys-Fluent were used for the study. For laminar flows, laminar viscous models and K-Epsilon model for turbulence modelling was used. Energy model was used to define convective heat transfer and a discrete phase model to study particle behaviour and flow pattern in the tube. Multi-phase model with two phase refined kerosene suspended with alumina nano particles were used for the study. Experimental and simulation results showed that as the Reynolds number and the particle concentration increased there was an enhancement in the thermal performance of nanofluids which was found to be higher than that of the base fluid. The convective heat transfer increased by 14% for volume concentration of 0.05% and Reynolds number of 5500.

To Investigate the Effect of Oil Film Thickness at the Entrance of the Infinitely Long Slider Bearing Using CFD Analysis

The oil film thickness between slider and shoe is a significant parameter and has a strong influence on the bearings performance. A CFD analysis has been carried out to find the effect of oil film thickness at the entrance of the slider using ANSYS workbench. Laminar viscous model with SIMPLE pressure-velocity coupling are used for the analysis. 2-D steady state, Navier-Stoke equations are discretized with finite volume approximations using structured grids. First the analysis has been carried out for the maximum load carrying capacity (i.e. m = 1.1889). For validation, CFD values are compared with the available analytical solution of Reynolds equation. CFD results showed good concord with the analytical values with a maximum error of 1%. After validation, the analysis has extended to four more 1m1 values such as 0.5, 1, 1.5 and 2. If bearing operate at below maximum load carrying capacity, the result shows that low load carrying capacity and high frictional losses. But for above, frictional forces reduces and blunt of the pressure profile at peak also decreases which will influence the action of extremely high load on a very small area of the shoe.

An investigation of the flow field within patient-specific models of an abdominal aortic aneurysm under steady inflow conditions

The flow fields within three patient-specific models of an abdominal aortic aneurysm (AAA) were investigated under steady laminar inflow conditions over a range of Reynolds numbers. Each model extended from the renal arteries to downstream of the iliac bifurcation. The aneurysms (referred to as models A, B, and C) are mature, with D/d ratios of 1.83, 1.57, and 1.95 respectively. The mass flowrates in each of the iliac arteries were equal. Using flow visualization it was observed that the flow proximally in the aneurysm was characterized by a primary jet that separated from either the posterior wall or the lateral wall or both, producing large recirculating zones. The primary jet impinged either normally or obliquely upon the anterior or right lateral wall in the distal half of the aneurysm, the flow distally in the aneurysm having been greatly disturbed. Measurements of the turbulence intensity along the median lumen centre-line showed that in each model the onset of transition and full turbulence occurred at Reynolds numbers much lower than those previously measured in idealized models. Computational fluid dynamics showed substantial differences in the velocity and stress fields when using the shear stress transport turbulence model as opposed to a laminar viscous model. It was also observed that turbulence was largely produced along the shear layers surrounding the primary jet and, in particular, at interfaces between the jet and the recirculating zones. In conclusion, turbulence may be expected to exist at Reynolds numbers typically encountered within an AAA, and it must be taken account of in an analysis of the flow field.

Dynamics of droplet transport induced by electrowetting actuation

This study reports on the dynamics of droplets in the capillary regime induced by electrowetting-on-dielectric actuation. The configuration investigated allows for comparing the experimental results with respect to the predictions of Brochard’s theoretical model (Brochard in Langmuir 5:432–438, 1989). Firstly, side-view observations using stroboscopic recording techniques were used to measure and analyse droplet deformations as well as the front and rear apparent contact angles during motion. Secondly, the influence of viscosity on the droplet velocity as a function of the applied voltage was studied. This has revealed that low Reynolds number droplet motion can be described by the simple laminar viscous model of Brochard. Finally, the influence of the dielectric thickness on the droplet dynamics was studied. It is shown that droplet velocity is limited by a saturation effect of the driving electrostatic force and that this phenomenon is very similar to that occurring in static experiments.

Deposition efficiency of dust particles on a single, falling and charged water droplet

A numerical algorithm for simulating dust particle deposition on a charged spherical collector is presented in this paper. Trajectories of the charged dust particles are traced in three-dimensional space by solving the Newton equation, taking into account inertial, air drag, gravitational and electrostatic forces. The collector (charged droplet) falls down freely and its trajectory is also determined. A laminar viscous model is assumed for the airflow in the vicinity of the collector and modeled using the finite-element method in two-dimensional cylindrical coordinates. The deposition efficiency is defined in terms of the volume of space, from which all particles are deposited on the collector. The calculation results for different Stokes, Coulomb, and Reynolds numbers are given.