Browsing by Subject "Atomization"
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Item Atomization of Non-Newtonian Fluids by Counterflow Atomizer(2022-05) Band, ChinmayiThe effects of shear-thinning non-Newtonian liquid on droplet diameter distributionsgenerated using a Counterflow atomizer were studied. Aqueous solutions of Sodium Carboxymethyl cellulose (SCMC) salt of 0.5%, 1%, 1.5% and 2% by weight were considered for experiments, with corresponding zero shear viscosity values of 13.8 mPas, 28.2 mPas, 508 mPas and 1280 mPas. Droplet diameters were measured using a Particle Digital Image Analysis technique combined with diffuse back illuminated shadowgraphs. Flow visualization in the near-field of the nozzle exit was used to gain insight into the flow patterns inside the nozzle near the exit plane, and to explain far-field droplet distribution statistics. Tree-like spray structure similar to effervescent atomization was observed for test solutions with higher weight concentrations. During secondary atomization, droplets connected with thin filaments were observed, indicating a probable existence of extensional stresses in the fluid. At lower concentrations of solutions, the spray emerged as a plume of droplets that are shed from a liquid film on the inner wall of the nozzle discharge tube, accompanied by a gas core. The variation of the Sauter Mean Diameter in the axial and radial directions indicated that the filaments in the near field are sheared by the gas flow, and undergo secondary atomization, leading to small droplet diameters and a more uniform distribution as we proceed downstream.Item Atomization of viscous fluids using counterflow nozzle(2020-08) Rangarajan, RoshanIn the present work, we study the enhanced atomization of viscous liquids by using a novel twin-fluid atomizer. A two-phase mixing region is developed within the nozzle using counterflow configuration by supplying air and liquid streams in opposite directions. Detailed qualitative and quantitative measurements for droplet size were conducted using shadowgraph technique. Near-field spray images from the nozzle exit suggest that the spray emerges out as a fine droplets with little scope for further atomization. The performance of this nozzle is compared to that of ‘flow-blurring’ nozzle. Three test liquids (Water, Propylene Glycol & Glycerol 85% soln) are used to vary the liquid viscosity in the range from 1 to 133.5 mPa.s. The counterflow nozzle produces a spray whose characteristics are relatively insensitive to fluid viscosity over the range of gas-liquid mass flow ratios between 0.25 and 1.Item Bubble size effect on effervescent atomization.(2011-07) Shepard, Thomas G.This paper presents the results from a number of studies conducted in an effort to gain insight into how to control bubble size during gas injection through a porous media into a liquid cross-flow, what effect bubble size has on the spray characteristics from an effervescent atomizer, and to provide input for future effervescent atomizer designs and studies. Experiments were performed in a specially designed atomizer which allowed for manipulation of the air injector geometry in order to vary bubble size from sizes much smaller than the nozzle exit diameter to much larger than the exit diameter. A parametric study was conducted to examine how three different bubble control mechanisms affect the average bubble size, bubble size standard deviation, and gas to liquid mass flow ratio (GLR) at the transition point between bubbly flow and slug flow. It was found that changing the channel hydraulic diameter at the air injection site had the largest effect while pore size and electrolyte concentration had smaller, though still significant, effects. A dimensional analysis was performed which arrived at a similarity parameter which correlates to bubble size for air injected through a porous media into a cross-flow. Bubble size was seen to have an effect on the stability, spray half cone angle, and Sauter mean diameter of the liquid droplets produced by an effervescent atomizer. The effect of bubble size on improving spray characteristics was shown to be optimal for bubble sizes on the order of the exit diameter. The mechanism by which bubble size has an affect is suggested to be due to liquid velocity fluctuations at the exit of the nozzle as opposed to the often cited mechanism of causing the flow to choke thus allowing gas to expand beyond the exit. A comparison of bubbly and annular flows at identical conditions further suggests that effervescent atomizer design and operation may benefit from trying to produce annular flow conditions at low GLRs rather than bubbly flow conditions at high GLRs.Item A Parametric Study of Counterflow Atomization(2021-05) Buchanan, ColeNovel atomizers using counterflow gas injection have shown the potential to produce water sprays comparable to commercial air-assist internal-mixing atomizers at up to 50% energy savings, with even larger savings possible for higher viscosity liquids [22]. Furthermore, counterflow atomization was shown to produce sprays with centerline Sauter mean diameters (SMD or d32) that are weakly sensitive over two magnitudes to liquid viscosity [23]. A preliminary model was posed by Johnson and colleagues [21] relating the observed effects of annulus thickness (tN), gas molar mass, and gas-to-liquid mass ratio (GLR) on the centerline SMD produced by counterflow atomizers. In their study, the effects of injection gas molar mass were determined that, in contrast to effervescent or co-flow atomizers, gasses with lighter molar masses produce sprays of significantly smaller SMD [21] [27]. This study investigates the effects of liquid volumetric flow rate, GLR, and counterflow atomizer exit orifice diameter, D0 and annulus thickness, tN on the atomizer’s performance in terms of the resultant sprays’ centerline SMD and relative span factor (RSF). In doing so, a modified model is proposed relating flow conditions to atomizer performance leading to a further understanding of the physical mechanisms of counterflow atomization.