Browsing by Author "Schmidt, Laura E."
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Item Effect of vapor bubbles on velocity fluctuations and dissipation rates in bubbly Rayleigh-B ?enard convection(Physical Review E, 9/19/2011) Lakkaraju, Rajaram; Schmidt, Laura E.; Oresta, Paolo; Toschi, Federico; Verzicco, Roberto; Lohse, Detlef; Prosperetti, AndreaNumerical results for kinetic and thermal energy dissipation rates in bubbly Rayleigh-Bénard convection are reported. Bubbles have a twofold effect on the flow: on the one hand, they absorb or release heat to the surrounding liquid phase, thus tending to decrease the temperature differences responsible for the convective motion; but on the other hand, the absorbed heat causes the bubbles to grow, thus increasing their buoyancy and enhancing turbulence (or, more properly, pseudoturbulence) by generating velocity fluctuations. This enhancement depends on the ratio of the sensible heat to the latent heat of the phase change, given by the Jakob number, which determines the dynamics of the bubble growth.Item Modification of turbulence in Rayleigh-B ?enard convection by phase change(New Journal of Physics, 2/3/2011) Schmidt, Laura E.; Oresta, Paolo; Toschi, Federico; Verzicco, Roberto; Lohse, Detlef; Prosperetti, AndreaHeavy or light particles introduced into a liquid trigger motion due to their buoyancy, with the potential to drive flow to a turbulent state. In the case of vapor bubbles present in a liquid near its boiling point, thermal coupling between the liquid and vapor can moderate this additional motion by reducing temperature gradients in the liquid. Whether the destabilizing mechanical feedback or stabilizing thermal feedback will dominate the system response depends on the number of bubbles present and the properties of the phase change. Here we study thermal convection with phase change in a cylindrical Rayleigh–Bénard cell to examine this competition. Using the Reynolds number of the flow as a signature of turbulence and the intensity of the flow, we show that in general the rising vapor bubbles destabilize the system and lead to higher velocities. The exception is a limited regime corresponding to phase change with a high latent heat of vaporization (corresponding to low Jakob number), where the vapor bubbles can eliminate the convective flow by smoothing temperature differences of the fluid.