Combined heat and mass transfer in laminar flow diffusion nucleation chambers

The effect of mass transfer on heat transfer in laminar flow diffusion chambers (LFDCs) is modelled as two coupled convective diffusion problems in Poiseuille flow. The energy flux due to mass diffusion is considered as the major coupling mechanism. Latent heat release and particle growth via condensation are neglected. A dimensionless parameter γ is introduced to measure the strength of the coupling effect. Exact analytical solutions are derived in two limiting cases and an approximate solution is proposed for the general case. The approximate ansatz is valid over the range −6 γ 1, as determined by comparing it with accurate numerical solutions. The effect of the coupling on the saturation ratio is illustrated by considering relevant examples of LFDC systems compiled from the literature. It is found significant for systems containing some organic vapours like propanol, as well as for air–water mixtures, implying that the coupling term should be incorporated in theoretical analyses of such experiments. It is found negligible for n-pentanol and for low vapour pressure species like dibutyl phthalate (DBP). A perturbative expansion is used to understand the numerical observation that the gas temperature increases for positive γ, causing a significant decrease in the saturation ratio and a corresponding suppression of calculated homogeneous nucleation rates, whereas the opposite effect is noted for negative γ values.