Abstract
This study investigates the influence of gas jet angle on primary jet breakup and the resulting droplet size distribution for coaxial gas-assisted atomizers. In industrial applications, the gas jet of these atomizers are typically angled towards the liquid jet, whereas in most spray investigations in literature, parallel flow configurations are used. To enable a detailed analysis of the influence of the gas jet angle, three atomizers with angles of 0°, 15° and 30° were examined. Other geometric parameters, such as liquid jet diameter, gas gap width and wall thickness were kept constant. For each atomizer, two gas velocities at constant liquid mass flow were investigated i.e., two gas-to-liquid ratios (GLRs). An additional set of experiments was performed at increased system pressure using three atomizers with identical gas jet angles, but with an adapted gas orifice area in order to keep gas velocity, GLR and momentum flow ratio constant for all pressure levels. Water and a glycerol/water-mixture were applied in order to investigate the influence of liquid viscosity. The primary breakup process was monitored by a high-speed camera, whereas the resulting droplet size was detected using a phase-Doppler anemometer. For all system pressures and liquid viscosities under investigation, a distinct influence of gas jet angle on primary breakup as well as on resulting droplet size distribution was observed for low gas velocity.
Highlights
High-pressure entrained flow gasification (EFG) is a key technology in the realization of a future, carbon-neutral circular economy, as it is an enabling technology to close the carbon cycle through the conversion of biomass and waste-based feedstocks into syngas (CO + H2)
gas-to-liquid ratios (GLRs) 0.6 / 1.0 (i) Influence of the gas channel angle on the droplet size and primary breakup For the quantitative comparison of the resulting droplet size while utilizing different gas channel angles, radial phase Doppler analyzer (PDA) measurements were first performed for the higher liquid viscosity ηliq = 200 mPa∙s and angles α = 0 – 30°
As the gas velocity at the nozzle orifice remained constant at vgas = 60 m∙s-1 for every gas channel angle, a double-pulse Particle image velocimetry (PIV) was used to detect differences in the flow field of the exiting gas phase, which may be correlated to a change in the gas channel angle
Summary
High-pressure entrained flow gasification (EFG) is a key technology in the realization of a future, carbon-neutral circular economy, as it is an enabling technology to close the carbon cycle through the conversion of biomass and waste-based feedstocks into syngas (CO + H2). EFG typically uses oxygen as gasification agent, which serves as atomization agent; as a result gas-to-liquid ratios (GLRs) < 1 are applied [1]. Studies on the droplet size that resulted from this configuration applied Newtonian viscous liquids in a viscosity range of ηliq = 1 – 100 mPa∙s and GLR = 1 - 12, and were conducted by Lorenzetto [4], Jasuja [5], Rizk [6] and Walzel [7]. For GLR < 1 and 4 liquid viscosities, Sänger et al [8] detected 2 different primary instability modes (flapping and pulsating) that influenced the resulting drop size. High-velocity annular gas streams with a straight exit channel were typically utilized. Industrial applications typically use a converging exit (straight inner, angled outer wall) or an angled gas exit (inner and outer wall angled) [9,10,11,12,13]
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