Moisture transfer by turbulent natural convection

We present an experimental and numerical study of natural convection with moist air as convecting fluid. By simplifying the system as two-component convection, an experimental method is proposed for indirectly measuring the moisture transfer rates in buoyancy-driven flows. We verify the results using direct numerical simulations. It is found that the non-dimensionalized transfer rates for both sensible heat (Nu(T)) and water vapour (Nu(e)) are essentially determined by a generalized Grashof number Gr (the ratio of combined buoyancy generated by the imposed temperature and vapour pressure gradients to viscous force), and are only weakly dependent on the buoyancy ratio Lambda (the ratio of buoyancy induced by temperature variation to that due to vapour pressure variation). Moreover, we show that the full set of control parameters {Gr, Lambda, Pr, Sc} is more suitable than other choices for characterizing the two-component system under investigation. As a special case, the Schmidt number dependence for passive scalar transport rates in buoyancy-driven flows is also deduced.