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External natural convection is rarely studied by numerical simulation in the literature due to the fact that flow of interest takes place in an unbounded domain and that if a limited computational domain is used the corresponding outer boundary conditions are unknown. In this study, we propose outer boundary conditions for a limited computational domain and make the corresponding numerical implementation in the scope of a projection method combining spectral methods and domain decomposition techniques. Numerical simulations are performed for both steady natural convection about an isothermal cylinder and transient natural convection around a line‐source. An experiment is also realized in water using particle image velocimetry and thermocouples to make a comparison during transients of external natural convection around a platinum wire heated by Joule effect. Good agreement, observed between numerical simulations and experiments, validated the outer boundary conditions proposed and their numerical implementation. It is also shown that, if one tolerates prediction error, numerical results obtained remain at least reasonable in a region near the line‐source during the entire transients. We thus paved the way for numerical simulation of external natural convection although further studies remain to be done for higher heating power (higher Rayleigh number).

The purpose of this paper is to study a gas bubble flowing in a micro-channel filled with liquid and to quantify the compressibility effects induced in the bubble by a heat supply at the walls of the channel.

The paper presents a model and its numerical implementation. A hybrid method combining front-tracking techniques and a Heaviside step function is introduced to ensure an accurate satisfaction of the mass and energy conservation laws.

Compressibility effects in the bubble are quantified. Test cases for numerical simulations of two-phase flows involving heat transfer are proposed.

The authors present original test cases in which expansion or compression of a gas bubble flowing in a liquid are induced by heat transfer at the wall.