Characterization of Injection Nozzles for Gas-Solid Flow Applications

1991 ◽  
Vol 113 (3) ◽  
pp. 469-474 ◽  
Author(s):  
F. T. Dodge ◽  
S. T. Green ◽  
J. E. Johnson
Keyword(s):  
Pressure Drop ◽  
Single Phase ◽  
Cone Angle ◽  
Stokes Number ◽  
Velocity Profiles ◽  
Particle Mass ◽  
Straight Tube ◽  
Turbulence Level ◽  
Free Jet ◽  
Combustion Systems

Laser phase-doppler velocimetry measurements have been used to characterize the particle-gas sprays produced by straight-tube nozzles that simulate idealized fuel injectors for solid fuel combustion systems. Tests were conducted on two nozzle sizes, for two particle sizes, two loading ratios, and two gas velocities. The Reynolds numbers was varied from 9500 to 19000, and the Stokes number from 1.9 to 61.4. It was found that the velocities of the particles in the spray decelerate more slowly, and the velocity profiles are generally more narrow, than for a single-phase free-jet. The turbulence level of the particles in the sprays was found to be less than half the turbulence level of a single-phase free-jet, and the turbulent velocity profiles were not yet fully developed at X = 40D. The hydrodynamic characteristics of the nozzles that are the most important for combustion systems were found to be: (a) the particle spray expands radially at a cone angle of 2° (measured at the radius corresponding to the peak of the particle mass flux distribution); and (b) the nozzle pressure drop and particle mass flow can be related by a correlation that depends on loading ratio, Reynolds number, Stokes number, and the pressure drop coefficient of the nozzle for a single phase flow.

LIQUID–LIQUID MIXTURES FLOW IN MICROCHANNELS

2013 ◽  
Vol 37 (3) ◽  
pp. 631-640 ◽  
Author(s):  
Ben-Ran Fu
Keyword(s):  
Pressure Drop ◽  
Single Phase ◽  
Cfd Simulation ◽  
Liquid Mixtures ◽  
Velocity Profiles ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Theoretical Predictions ◽  
Simulation Results ◽  
Good Agreement

This study constitutes an experimental and numerical investigation into the single-phase flow of liquid–liquid mixtures and of water in uniform, converging and diverging microchannels. The experimental results for the pressure drop in three microchannels show good agreement with both theoretical predictions and CFD simulation results. The numerical velocity profiles in microchannels are also presented and show excellent agreement with the analytical velocity profiles. In addition, the pressure distribution prediction for the converging and diverging microchannels is also consistent with that obtained through the CFD results.

Comparing selected parameters of a two-dimensional turbulent free jet on the basis of experimental results, digital simulations, and theoretical analyses

2016 ◽  
Vol 1 (20) ◽  
pp. 31-48
Author(s):  
Aldona Skotnicka-Siepsiak
Keyword(s):  
Linear Function ◽  
Analytical Methods ◽  
Relative Length ◽  
Wall Layer ◽  
Turbulence Level ◽  
Two Dimensional ◽  
Free Jet ◽  
Theoretical Assumptions ◽  
Digital Simulations ◽  
Theoretical Analyses

The presented experimental and digital examinations of a two-dimensional turbulent free jet are a first phase of in the study of the Coandă effect and its hysteresis. Additionally, basing on theoretical analyses, selected results for a turbulent jest have been also mentioned, considering theoretical assumptions for the wall layer. As the result, on the basis of experimental, digital, and analytical methods, a review of characteristic jet properties has been prepared, which includes a jet spreading ratio, its cross and longitudinal sections, and turbulence level. The jet spreading radio has been expressed as a non-linear function of the x : b relative length.

Measurements of the nearly isotropic turbulence behind a uniform jet grid

1974 ◽  
Vol 62 (1) ◽  
pp. 115-143 ◽  
Author(s):  
Mohamed Gad-El-Hak ◽  
Stanley Corrsin
Keyword(s):  
Pressure Drop ◽  
Kinetic Energy ◽  
Static Pressure ◽  
Isotropic Turbulence ◽  
Decay Rates ◽  
Turbulence Energy ◽  
Turbulence Level ◽  
Average Force ◽  
General Behaviour ◽  
Decay Behaviour

Wind-tunnel turbulence behind a parallel-rod grid with jets evenly distributed along each rod is nearly isotropic. Homogeneity improvement over prior related experiments was attained by the use of controllable nozzles. Compared with the ‘passive’ case, the downwind-jet ‘active’ grid has a smaller static pressure drop across it and gives a smaller turbulence level at a prescribed distance from it, while the upwind-jet grid gives a larger static pressure drop and larger turbulence level. ‘Counterflow injection’ generates larger turbulence energy and larger scales, both events being evidently associated with instability of the jet system. This behaviour is much like that commonly observed behind passive grids of higher solidities.If the turbulent kinetic energy is approximated as an inverse power law in distance, the (positive) exponent decreases with increasing (downwind or upwind) jet strength, corresponding to slower absolute decay rates. No peculiar decay behaviour occurs when the jet grid is ‘self-propelled’ (zero net average force), or when the static pressure drop across it is zero.The injection does not change the general behaviour of the energy spectra, although the absolute spectra change inasmuch as the turbulence kinetic energy changes.

Updating the Conceptual Model for Fine Particle Mass Emissions from Combustion Systems Allen L. Robinson

2010 ◽  
Vol 60 (10) ◽  
pp. 1204-1222 ◽  
Author(s):  
Allen L. Robinson ◽  
Andrew P. Grieshop ◽  
Neil M. Donahue ◽  
Sherri W. Hunt
Keyword(s):  
Conceptual Model ◽  
Fine Particle ◽  
Particle Mass ◽  
Combustion Systems

Numerical Prediction of Particulate Flow Over a Backward-Facing Step Followed by a Filter Medium

2012 ◽  
Author(s):  
A. K. Dange ◽  
K. C. Ravi ◽  
F. W. Chambers
Keyword(s):  
Porous Medium ◽  
Recirculation Zone ◽  
Stokes Number ◽  
Velocity Profiles ◽  
Experimental Results ◽  
Phase Model ◽  
Discrete Phase Model ◽  
Backward Facing Step ◽  
Zone Length ◽  
Discrete Phase

Flow in air filter housings often is characterized by separation upstream of the filter. The effect of the separation on the motion of particles and their distribution at the filter is important to filter performance. The current research investigates these effects by applying CFD modeling to turbulent particulate flows over a backward-facing step followed by a porous medium representing a filter. The two-dimensional step flow was selected as it is an archetype for separated flow with many studies in the literature. The flow examined has a step expansion ratio of 1:2, with an entrance length of 30 step heights to the step followed by a length of 60 step heights. Computations were performed at step Reynolds numbers of 6550 and 10,000 for the step without a porous medium and with the medium placed 4.25 and 6.75 step heights downstream of the step. The mesh was developed in ICEM CFD and modeling was done using the Fluent commercial CFD package. The carrier phase turbulence was modeled using the RNG k-epsilon model. The particles were modeled using the discrete phase model with dispersion modeled using stochastic tracking. The boundary conditions are uniform velocity at the inlet, no-slip at the walls, porous jump at the porous medium, and outflow at the outlet. The particle boundary condition is “reflect” at the walls and “trap” at the filter. The numerical results for the no filter case matched experimental results for recirculation zone length and velocity profiles at 3.75 and 6.25 step heights well. The computed velocity profiles at 3.75 step heights do not match experimental profiles for the filter at 4.25 step heights so well, though the results show a profound effect on the recirculation zone length, matching the experiments. Differences are attributed to different velocity profiles at the step. With the medium 6.75 step heights downstream, the effect on the recirculation zone is negligible, again matching experimental results. The discrete phase model tracks injected particles and provides results which are qualitatively similar to the literature. It is observed that particles with lower Stokes number, and thus lower momentum, tend to follow the flow and enter the recirculation zone while particles with higher Stokes number tend to move directly to the porous medium. When the filter is moved downstream to 6.75 step heights, the increased length of the recirculation zone results in more particles entering the recirculation zone. Results for monodispersed and polydispersed particles agree.

Hydrodynamic and Thermal Performance of a Vapor-Venting Microchannel Copper Heat Exchanger

2008 ◽  
Author(s):  
Milnes P. David ◽  
Amy Marconnet ◽  
Kenneth E. Goodson
Keyword(s):  
Heat Exchanger ◽  
Carbon Fiber ◽  
Pressure Drop ◽  
Thermal Resistance ◽  
Heat Exchangers ◽  
Single Phase ◽  
Two Phase ◽  
Microchannel Heat Exchanger ◽  
Large Pressure ◽  
Dry Out

Two-phase microfluidic cooling has the potential to achieve low thermal resistances with relatively small pumping power requirements compared to single-phase heat exchanger technology. Two-phase cooling systems face practical challenges however, due to the instabilities, large pressure drop, and dry-out potential associated with the vapor phase. Our past work demonstrated that a novel vapor-venting membrane attached to a silicon microchannel heat exchanger can reduce the pressure drop for two-phase convection. This work develops two different types of vapor-venting copper heat exchangers with integrated hydrophobic PTFE membranes and attached thermocouples to quantify the thermal resistance and pressure-drop improvement over a non-venting control. The first type of heat exchanger, consisting of a PTFE phase separation membrane and a 170 micron thick carbon-fiber support membrane, shows no improvement in the thermal resistance and pressure drop. The results suggest that condensation and leakage into the carbon-fiber membrane suppresses venting and results in poor device performance. The second type of heat exchanger, which evacuates any liquid water on the vapor side of the PTFE membrane using 200 ml/min of air, reduces the thermal resistance by almost 35% in the single-phase regime in comparison. This work shows that water management, mechanical and surface properties of the membrane as well as its attachment and support within the heat exchanger are all key elements of the design of vapor-venting heat exchangers.

scholarly journals Experimental Investigation of Embedded Micropin-Fins for Single-Phase Heat Transfer and Pressure Drop

2018 ◽  
Vol 140 (2) ◽  
Author(s):  
Chirag R. Kharangate ◽  
Ki Wook Jung ◽  
Sangwoo Jung ◽  
Daeyoung Kong ◽  
Joseph Schaadt ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Friction Factor ◽  
Integrated Circuit ◽  
Single Phase ◽  
Absolute Error ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Working Fluid ◽  
Pin Fin

Three-dimensional (3D) stacked integrated circuit (IC) chips offer significant performance improvement, but offer important challenges for thermal management including, for the case of microfluidic cooling, constraints on channel dimensions, and pressure drop. Here, we investigate heat transfer and pressure drop characteristics of a microfluidic cooling device with staggered pin-fin array arrangement with dimensions as follows: diameter D = 46.5 μm; spacing, S ∼ 100 μm; and height, H ∼ 110 μm. Deionized single-phase water with mass flow rates of m˙ = 15.1–64.1 g/min was used as the working fluid, corresponding to values of Re (based on pin fin diameter) from 23 to 135, where heat fluxes up to 141 W/cm2 are removed. The measurements yield local Nusselt numbers that vary little along the heated channel length and values for both the Nu and the friction factor do not agree well with most data for pin fin geometries in the literature. Two new correlations for the average Nusselt number (∼Re1.04) and Fanning friction factor (∼Re−0.52) are proposed that capture the heat transfer and pressure drop behavior for the geometric and operating conditions tested in this study with mean absolute error (MAE) of 4.9% and 1.7%, respectively. The work shows that a more comprehensive investigation is required on thermofluidic characterization of pin fin arrays with channel heights Hf < 150 μm and fin spacing S = 50–500 μm, respectively, with the Reynolds number, Re < 300.

Two-Phase Flow Behavior in Channels With Sudden Area Change Using Experimental and Computational Approach

2017 ◽  
Author(s):  
Ashish Kotwal ◽  
Che-Hao Yang ◽  
Clement Tang
Keyword(s):  
Experimental Data ◽  
Pressure Drop ◽  
Experimental Analysis ◽  
Single Phase ◽  
Computational Analysis ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase ◽  
Flow Rates ◽  
Area Change

The current study shows computational and experimental analysis of multiphase flows (gas-liquid two-phase flow) in channels with sudden area change. Four test sections used for sudden contraction and expansion of area in experiments and computational analysis. These are 0.5–0.375, 0.5–0.315, 0.5–0.19, 0.5–0.14, inversely true for expansion channels. Liquid Flow rates ranging from 0.005 kg/s to 0.03 kg/s employed, while gas flow rates ranging from 0.00049 kg/s to 0.029 kg/s implemented. First, single-phase flow consists of only water, and second two-phase Nitrogen-Water mixture flow analyzed experimentally and computationally. For Single-phase flow, two mathematical models used for comparison: the two transport equations k-epsilon turbulence model (K-Epsilon), and the five transport equations Reynolds stress turbulence interaction model (RSM). A Eulerian-Eulerian multiphase approach and the RSM mathematical model developed for two-phase gas-liquid flows based on current experimental data. As area changes, the pressure drop observed, which is directly proportional to the Reynolds number. The computational analysis can show precise prediction and a good agreement with experimental data when area ratio and pressure differences are smaller for laminar and turbulent flows in circular geometries. During two-phase flows, the pressure drop generated shows reasonable dependence on void fraction parameter, regardless of numerical analysis and experimental analysis.

Pressure Drop, Air Entrainment and Moments of the Axial Velocity in the Laminar-Turbulent Transition Jet Flow in Domestic Gas Injectors

2021 ◽  
Author(s):  
William Alexander Carrillo Ibañez ◽  
Márcio Demétrio ◽  
Amir Oliveira ◽  
Fernando Pereira
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Axial Velocity ◽  
Energy Flow ◽  
Discharge Coefficient ◽  
Mixing Layer ◽  
Air Entrainment ◽  
Flow Rates ◽  
Free Jet ◽  
Internal Mixing

Abstract This works aims at characterizing the flow in the outlet of three gas injectors used in atmospheric burners and developing correlations for the discharge coefficient, air entrainment, momentum and energy flow rates. These devices have millimeter sized orifices, a cup-like region at the injector outlet and the flow occurs in the transition from the laminar to the fully turbulent regimes. The pressure drop was measured and correlated as a function of the orifice Reynolds number for the three injectors. The correlations are able to predict the discharge coefficient within ± 5% deviation from the measurements in the range 90 &lt; Re &lt; 4400. The axial velocity and turbulent intensity were measured at the outlet of the injectors using a hot-wire anemometer at the orifice Reynolds number of 3060, which is typical of the applications. The measurements were compared to CFD solutions using the gamma - Re-theta RANS transition model in the STAR-CCM+ commercial package. The results indicate the strong influence of the shape of the outlet cup-like region of the injectors in the development of an internal mixing layer and the external mixing layer in the free jet. The momentum and energy flow rates for the injector model with the largest cup are reduced to 50% and 21%, respectively, of the simplest gas injector. However, the gas jet in this injector carries 28% of the stoichiometric air before leaving the cup. These aspects must be taken into account in the preliminary design of atmospheric burners.

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