Departamento de Ingeniería Mecánica y Minera
URI permanente para esta comunidadhttps://hdl.handle.net/10953/41
En esta Comunidad se recogen los documentos generados por el Departamento de Ingeniería Mecánica y Minera y que cumplen los requisitos de Copyright para su difusión en acceso abierto.
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Examinando Departamento de Ingeniería Mecánica y Minera por Autor "Bolaños-Jiménez, Rocío"
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Ítem Bubble pressure requirements to control the bubbling process in forced co-axial air-water jets(Elsevier, 2020-12-01) Ruiz-Rus, Javier; Bolaños-Jiménez, Rocío; Sevilla-Santiago, Alejandro; Martínez-Bazán, CarlosWe analyse the controlled generation of bubbles of a given size at a determined bubbling rate in a co-flowing water stream forcing the gas flow. The temporal evolution of the bubble size, R(t), the air flow rate, Qa(t), and the pressure evolution inside the bubble, pb(t), during the bubbling process are reported. To that aim, the temporal evolution of the bubble shape and the pressure inside the air feeding chamber, pc(t), where a harmonic perturbation is induced using a loudspeaker, are obtained from high-speed images synchronized with pressure measurements. A model is developed to describe the unsteady motion of the gas stream along the injection needle, coupled with the Rayleigh-Plesset equation for the growing bubble, allowing us to obtain pb(t). Thus, the minimum pressure amplitudes required inside the forming bubble to control their size and bubbling frequency are provided as a function of the gas flow rate, the liquid velocity, uw, and the forcing frequency, ff. Two different behaviors have been observed, depending on the liquid-to-gas velocity ratio, Λ. For small enough values of Λ, the critical pressure amplitude is given by p_s ∼ ρ_a c u_a St_f3, associated to a rapid pressure increase taking place during an interval of time of the order of the acoustic time. However, for larger values of Λ, ps ∼ ρ u_w^2 St_f^3 Λ^{−1/5} We^{−1/4}. Here ρ and ρa are the liquid and gas densities respectively, c the speed of sound in air and St_f = f_f r_o/u_w and We = ρ u_w^2 r_o/σ the Strouhal and Weber numbers, where r_o denotes the outer radius of the injector.Ítem Controlled formation of bubbles in a planar co-flow configuration(Elsevier, 2017-03-01) Ruiz-Rus, Javier; Bolaños-Jiménez, Rocío; Gutiérrez-Montes, Cándido; Sevilla-Santiago, Alejandro; Martínez-Bazán, CarlosWe present a new method that allows to control the bubble size and formation frequency in a planar air-water co-flow configuration by modulating the Water velocity at the nozzle exit. The forcing process has been experimentally characterized determining the amplitude of the water velocity fluctuations from measurements of the pressure variations in the water stream. The effect of the forcing on the bubbling process has been described by analyzing the pressute signals in the air stream in combinatiOn with visualizations performed with a high-speed camera. We show that, when the forcing amplitude is sufficiently large, the bubbles can be generated at a rate different from the natural bubbling frequency, f(n), which depends on the water-to-air velocity ratio, Lambda u(n)/u(q), and the Weber number, We rho(w)u(n)(2)H(0)/sigma, where H(0) is the half-thickness of the air stream at the exit slit, rho(w), the water density and a the surface tension coefficient. Consequently, when the forcing is effective, monodisperse bubbles, of sizes smaller than those generated without stimulation, are produced at the prescribed frequency, f(f) > f(n). The effect of the forcing process on the bubble size is also characterized by measuring the resulting intact length, l, i.e. the length of the air stem that remains attached to the injector when a bubble is released. In addition, the physics behind the forcing procedure is explained as a purely kinematic mechanism that is added to the effect of the pressure evolution inside the air stream that would take place in the unforced case. Finally, the downstream position of the maximum perturbation amplitude has been determined by a one-dimensional model, exhibiting a good agreement with both experiments and numerical simulations performed with OpenFOAM.