ANALYSIS OF DOUBLE-DIFFUSIVE CONVECTION WITH TEMPERATURE MODULATIONS AT THE BOUNDARIES

The stability of a double-diffusive system modulated at both the boundaries is investigated. The modulations are found to cause mean flow, microconvection, at the edges of the diffusive core such that its amplitude dies off exponentially away from the boundaries. The mean heat and mass transfer values associated with microconvection are found to be several orders of magnitude less than those associated with diffusion, indicating the marginal influence of boundary modulations on scalar transport across the diffusive core. Linear stability analysis reveals that instability due to direct modes sets in earlier than predicted for nonperiodic boundaries. The critical thermal Rayleigh number correction factor associated with boundary modulations is found to be dependent on their amplitudes and the phase difference between them. This dependence is such that the convective currents have the largest amplitude when upper and lower modulations are in phase, resulting in the largest magnitude of the correction in critical thermal Rayleigh number.