Experimental study on growth and spread of dispersed particle-laden plume in a linearly stratified environment

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We present results of laboratory experiments conducted to study the evolution, growth, and spreading rate of a dispersed particle-laden plume produced by a constant inflow into a density varying environment. Particles having mean size, \(d_p=100\ \upmu \)m, density \(\rho _p=2500 \ {\text{ kg/m}}^3\), volume fraction, \(\phi _v =\) 0–0.7 % , were injected along with the lighter buoyant fluid into a linearly stratified medium. It was observed that a particle-laden plume intruding at the neutral density layer is characterized by four spreading regimes: (i) radial momentum flux balanced by the inertia force; (ii) inertia buoyancy regime; (iii) fluid-particle inertia regime, and (iv) viscous buoyancy regime. Regimes (i), (ii), and (iv) are similar to that of a single-phase plume, for which \(\phi _v = 0\,\%\). The maximum height, \(Z_m\), for \(\phi _v > 0\,\%\) was observed to be consistently lower than the single-phase case. An empirical parameterization was developed for the maximum height for particle-laden case, and was found to be in very good agreement with the experimental data. In the inertia buoyancy regime, the radial spread of the plume, \(R_f\), for \(\phi _v > 0\,\%\), advanced in time as \(R_f \propto t^{0.68 \pm 0.02}\) which is slower compared to the single-phase plume that propagates at \(R_f \propto t^{0.74 \pm 0.02}\). Due to the presence of particles, ‘particle fall out’ effect occurs, which along with the formation of a secondary umbrella region inhibits the spreading rate and results in slower propagation of the particle-laden plume. The effect of particles on spreading height of plume, \(Z_s\), and thickness of the plume, \(h_p\), were also studied, and these results were compared with the single-phase case. Overall from these experiments, it was found that the evolution, growth, and spread of dispersed particle-laden plume is very different from that of the single-phase plume, and presence of low concentration of particles (\( \phi _v < 1\,\%\)) could have significant effects on the plume dynamics.