Showing papers by "Mahesh V. Panchagnula published in 2006"

Eulerian multi-fluid model of air blast atomization

Abstract: A fully Eulerian “multi-fluid” model of air blast atomization is discussed. The model envisions the system as consisting one carrier fluid phase and N drop phases, each having a discrete diameter. Discretization of the drop size distribution is often employed as part of numerical solutions. In the current approach, discretization is made part of the model itself in order to both take advantage of the large body of existing knowledge related to multiphase continuum mechanics and to make the resulting formulation consistent with the structures of the Eulerian multi-fluid solvers contained in contemporary commercial CFD packages. A complete formulation involving balances of mass, linear momentum, and energy for N+1 fluid-like continua (fluid phase plus N drop phases) is discussed. Some preliminary results are presented for a model problem allowing closed form solution. These are interpreted to illustrate the drop breakup concepts.

Development of CFD Model for a Swirl Stabilized Spray Combustor

Abstract: Swirling jet characteristics in a commercial burner are studied computationally. The analysis includes a 2D axisymmetric model of the burner which is extended to three dimensions with some preliminary results. In the current study, k-e and RSM turbulence models were used to simulate the flow field. Specific computational strategies that were adopted to model the swirling flow are also discussed. It was found that the swirl component in the flow caused a flow reversal along the axis resulting in the formation of centretoroidal zone. Case studies ranging from low swirl number of 1.28 to swirl number 3.75 are presented. The vortex size seems to exhibit two types of behavior. For low swirl numbers, the vortex size takes discrete sizes depending on various ranges of swirl numbers. For large swirl numbers, the vortex size seems to demonstrate a continuous increase.Copyright © 2006 by ASME

Flow Regimes of Newtonian Fluids in Vertical Co-Axial Flows

Abstract: This paper presents experimental and numerical results of the interfacial dynamics of liquid-liquid flows when a dispersed phase liquid introduced in a continuous phase liquid flow with an arbitrary inlet velocity profile. The flow dynamics are studied as a function of the individual phase Reynolds and Capillary numbers, viscosity ratio, flow rate ratio, and Bond number. Fully-developed (or self-similar solution) model predicted multiple (one to three) solutions of jet diameter for a range of dimensionless numbers. The critical bifurcation parameters are identified in order to study the jet instability. The fully developed jet diameter solutions are plotted in terms of flow ratio of liquid phases and indicate three solution branches. Experiments have been carried out using Poly Ethylene Glycol (PEG)-Canola oil to investigate the three possible solutions predicted by fully developed theory. The measured values of inner fluid radius agree very well with the lower branch of the three branched solution and the deviation of the experimental results for the rest of the branches is observed to be more than 50 percent. Numerical simulations also have been performed to compare the self-similar solution results of liquid jet radius using FLUENT® software. The results predicted by numerical simulations agree very well with both the lower and upper branches of solution predicted by fully developed theory.Copyright © 2006 by ASME

Non-intrusive technique for measuring instability wave amplitudes at simplex swirl atomizer exit

Abstract: An optical method for non-intrusive wave amplitude measurement is examined. An experimental setup was constructed to produce sprays of various fluids including Canola oil and glycerin-water mixtures, such that precise control of pressure up to 140 psi was possible. A spray was produced by a 20 Gallon per hour oil burner nozzle at varying pressures. Initially, a smooth laminar conical sheet was noticed which eventually was found to break up into droplets. A laser was passed through the laminar conical sheet and was projected onto a surface on the other side and resulted in a vertical linear projection. This projection is postulated to be formed due to the scanning motion of the laser beam as instability waves pass through the laser. The angle of this scan was found to be a function of pressure, cone angle, and distance of laser from nozzle. High resolution images were taken of the film profile as well as the projected image and image analysis software was used to calculate cone angles and angular scan of the laser. Tests were performed with Canola Oil as well as a mixture of glycerin and water in order to evaluate the effect of viscosity and surface tension on the measurements. The resulting data was used to illustrate a principle for determining the instability wave amplitude using this technique.Copyright © 2006 by ASME

Laser induced fluorometry and velocimetry: implementation of quantum dots as fluorophores

Abstract: The characteristics of fuel atomizers have been studied by using a fluorescence optical patternator via establishing a laser sheet illumination of the spray and an image capturing system. Line laser Mie-scattering and fluorescence imaging technique is used to study the fuel mass distribution, geometrical properties, angle and symmetry in sprays. The proposed experimental setup employs Rhodamine 6G as the fluorophore. A set of filters have been used to reduce the signature from the combustion fire while being able to image the nanoparticles. Experimental results are obtained under the conditions of the fuel with and without being seeded with quantum dots and under both non-combusting and combusting spray conditions. The results from the study are validated against existing volume flux distribution measurements by conventional techniques. Owing to the high luminescence properties of quantum dots, the liquid volume distribution can accurately be determined in an evaporating as well as a non-evaporating spray using this technique. Quantum dots are semiconductor nanoparticles whose emission wavelength can be tuned by the choice of their size. Also their, high luminescence properties are advantageous in a spectrally “noisy” combustion environment.

Surface Topography Induced Ultrahydrophobic Behavior: Effect of Three-Phase Contact Line Topology

Abstract: The wettability of silicon surface hydrophobized using silanization reagents was studied. The advancing and receding contact angles were measured with the captive needle approach. In this approach, a drop under study was held on the hydrophobized surface with a fine needle immersed in it. The asymptotic advancing and receding angles were obtained by incrementally increasing the volume added and removed, respectively, until no change in angles was observed. The values were compared with the previously published results. Further, the wetting behavior of water droplets on periodically structured hydrophobic surfaces was investigated. The surfaces were prepared with the wet etching process and contain posts and holes of different sizes and void fractions. The surface geometry brought up a scope to study the Wenzel (filling of surface grooves) and Cassie (non filling of the surface grooves) theories and effects of surface geometry and roughness on the contact angle. Experimental data point to an anomalous behavior where the data does not obey either Wenzel or Cassie type phenomenology. This behavior is explained by an understanding of the contact line topography. The effect of contact line topography on the contact angle was thus parametrically studied. It was also inferred that, the contact angle increased with the increase in void fraction. The observations may serve as guidelines in designing surfaces with the desired wetting behavior.Copyright © 2006 by ASME

Laser Induced Fluorometry and Velocimetry

Abstract: The characteristics of fuel atomizers have been studied by using a fluorescence optical patternator via establishing a laser sheet illumination of the spray and an image capturing system. Line laser Mie-scattering and fluorescence imaging technique is used to study the fuel mass distribution, geometrical properties, angle and symmetry in sprays. The proposed experimental setup employs Rhodamine 6G as the fluorophore. A set of filters have been used to reduce the signature from the combustion fire while being able to image the nanoparticles. Experimental results are obtained under the conditions of the fuel with and without being seeded with quantum dots and under both non-combusting and combusting spray conditions. The results from the study are validated against existing volume flux distribution measurements by conventional techniques. Owing to the high luminescence properties of quantum dots, the liquid volume distribution can accurately be determined in an evaporating as well as a non-evaporating spray using this technique. Quantum dots are semiconductor nanoparticles whose emission wavelength can be tuned by the choice of their size. Also their, high luminescence properties are advantageous in a spectrally "noisy" combustion environment.Copyright © 2006 by ASME