Unsteady double diffusive convection inside a partial porous building enclosure subjected to time-periodic temperature boundary condition

Abstract

Unsteady double diffusive convection under the influence of time-periodic sidewall temperature inside a rectangular enclosure with a porous wall is performed using numerical simulation and analytical prediction. The ranges of investigated physical parameters are listed as Darcy number (10−10 ≤ Da ≤ 101), thickness of porous wall (0 ≤ d ≤ 1), thermal Rayleigh number (103 ≤ Ra ≤ 107), buoyancy ratio (−1 ≤ N ≤ 1) and oscillating frequency of time-periodic sidewall temperature (0.01 ≤ ω ≤ 10). Results indicate that rates of heat and moisture transfer are impacted by time-periodic temperature and have a sinusoidal variation with time. The heat and moisture resonance phenomenon occurs when the convection effect is sufficiently stronger. Scale analysis has been performed to obtain the correlations of overall heat and moisture transfer rates in basic steady state and the resonant frequency, where the fluctuations of heat and moisture transfer are increased. A good agreement is observed from the analytical and numerical results. Present work could be applied to determine the heat and moisture transfer rates and resonant frequency in a thermal storage system, where the sidewall temperature is varying periodically with time due to the weather condition (solar radiation) and ambient temperature during a typical day.