In single phase, steady, turbulent axisymmetric jets, the time-averaged velocity field can be characterised by the decay in centreline velocity and increased spread with increasing distance from the jet orifice. In a two-phase or ‘particle-laden’ jet, the particles will modulate the jet turbulence and exchange momentum with the gas phase. Consequently, these effects reduce both the centreline velocity decay and spreading rates with respect to the single-phase jet. Empirical exponential scaling factors were found by previous authors to describe the reduced centreline decay and spreading rates well for low Stokes numbers. In this thesis, power-law scaling factors are found to scale well a wide range of centreline velocity decay and spreading rate data published over the past 40 years, for a wide range of Stokes numbers. The power-law scaling is composed of three different regimes. For low Stokes numbers St₀ ≲20, it is found that the gas phase centreline velocity, u₀/uc collapses if plotted as a function of x/D(1 + Ø₀)⁻¹, and the velocity profile half widths r₁/ ₂ collapse if plotted as a function of x/D(1+Ø₀)⁻¹. Here, u₀ is the exit velocity, Ø₀ is the exit mass loading, x is the axial coordinate and D is the pipe diameter. For intermediate Stokes numbers, u₀/uc collapses if plotted as a function of x/D(1 + Ø₀)⁻¹ and r₁/ ₂ collapses if plotted as a function of x/D(1 + Ø₀)⁻¹/². For high Stokes numbers St₀ ≳ 200, u₀/uc collapses if plotted as a function of x/D(1 + Ø₀)⁻¹/² and the half width is approximately independent of Ø₀. In addition to the velocity of the gas phase, other aspects of particle- laden jets are found to be amenable to scaling by power-law functions. It is found that reported solid phase mass flux data scales similarly to gas phase measurements. Limited solid phase concentration and entrainment measurements reported in the literature are also found to scale by power-law functions. Whereas that limited data was obtained from the literature, measurements of the distribution of particles in particle-laden jets were conducted to further assess the validity of the scaling regimes to the solid phase. A planar light scattering technique is conducted to measure the distribution of particles in an axisymmetric jet and their subsequent scaling (or lack thereof) are reported for a variation in Ø₀, Stokes number and gas phase jet exit density. For Stokes numbers based on the pipe friction velocity St* ₀ ∼ 1, half widths of particle distributions were found to scale with x/D(1+Ø₀)⁻¹/² . The apparent centreline concentration was found to be independent of Ø₀ at this same St* ₀ . For Stokes numbers based on the pipe friction velocity St*₀ < 1, half widths are independent of Ø₀. The effect of the other parameters, i.e. Stokes number and density ratio, on centreline distributions and half widths are also investigated. Measurements of particle distributions, delivered via an annular channel, in a triangular oscillating jet (OJ) flow are also reported for a variation in momentum ratio, the ratio of OJ momentum to channel momentum and mass loading. The results of the variation in momentum ratio on particle distributions are compared with an existing precessing jet (PJ) study. It is the aim of this study to determine the experimental conditions for which the OJ nozzle is superior to the PJ nozzle. The use of an OJ nozzle is preferable at an industrial scale by virtue of its lower driving pressure compared with a PJ nozzle. It is found that particle distributions in a PJ flow spread at a greater rate with increasing momentum ratio compared with the spread of particles in an OJ flow. However, at momentum ratios approximately less than unity, the absolute spread from an OJ is greater. This also corresponds to nozzle driving pressure less than approximately 10kPA. For an increase in mass loading, the spread of particle distribution in the OJ decreases and recirculation increases. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1337352 / Thesis (M.Eng.Sc.) -- University of Adelaide, School of Mechanical Engineering, 2008
| Identifer | oai:union.ndltd.org:ADTP/282717 |
| Date | January 2008 |
| Creators | Foreman, Richard J. |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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