Paolo Oresta

Heat transport in bubbling turbulent convection

Boiling is an extremely effective way to promote heat transfer from a hot surface to a liquid due to numerous mechanisms, many of which are not understood in quantitative detail. An important component of the overall process is that the buoyancy of the bubble compounds with that of the liquid to give rise to a much-enhanced natural convection. In this article, we focus specifically on this enhancement and present a numerical study of the resulting two-phase Rayleigh–Bénard convection process in a cylindrical cell with a diameter equal to its height. We make no attempt to model other aspects of the boiling process such as bubble nucleation and detachment. The cell base and top are held at temperatures above and below the boiling point of the liquid, respectively. By keeping this difference constant, we study the effect of the liquid superheat in a Rayleigh number range that, in the absence of boiling, would be between 2 × 106 and 5 × 109. We find a considerable enhancement of the heat transfer and study its dependence on the number of bubbles, the degree of superheat of the hot cell bottom, and the Rayleigh number. The increased buoyancy provided by the bubbles leads to more energetic hot plumes detaching from the cell bottom, and the strength of the circulation in the cell is significantly increased. Our results are in general agreement with recent experiments on boiling Rayleigh–Bénard convection.Rayleigh-Bénard convection Rajaram Lakkaraju ∗, Richard J. A. M. Stevens ∗ †, Paolo Oresta ‡ §, Roberto Verzicco ∗ ¶, Detlef Lohse ∗ , and Andrea Prosperetti ∗ † ∗Physics of Fluids, Faculty of Science and Technology, Mesa+ Institute and J. M. Burgers Center for Fluid Dynamics, University of Twente, 7500AE Enschede, The Netherlands,†Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218, USA,‡Department of Mathematics, Mechanics and Management, Polytechnic of Bari, Via Japigia 182, 70126, Bari, Italy.,§Department of Engineering for Innovation, University of Salento, Via per Arnesano, 73100 Lecce, Italy., and ¶Department of Mechanical Engineering, University of Rome ‘Tor Vergata’, Via del Politecnico 1, 00133 Rome, Italy

FLOW PATTERNS AND HEAT TRANSFER AROUND SIX IN-LINE CIRCULAR CYLINDERS AT LOW REYNOLDS NUMBER

The flow field and the heat transfer around six in-line iso-thermal circular cylinders has been studied by mean of numerical simulations. Two values of the center to center spacing (

Modification of turbulence in Rayleigh-Bénard convection by phase change

s=3.6d

Pair and multi-particle dispersion in numerical simulations of convective boundary layer turbulence

and

Buoyancy Effect on the Flow Pattern and the Thermal Performance of an Array of Circular Cylinders

4d

Influence of the Spool Velocity on The Performance of a Directional Hydraulic Valve

, where

Dispersion and Deposition of Particles in Rayleigh-Bénard Turbulent Flows

d

CFD analysis of melting process in a shell-and-tube latent heat storage for concentrated solar power plants

is the cylinder diameter) at Reynolds number of

Analysis of a directional hydraulic valve by a Direct Numerical Simulation using an immersed-boundary method

100

Effect of vapor bubbles on velocity fluctuations and dissipation rates in bubbly Rayleigh-Bénard convection

and Prandtl number of