Effect of double-diffusive convection with cross gradients on heat and mass transfer in a cubical enclosure with adiabatic cylindrical obstacles

https://doi.org/10.1016/j.ijheatfluidflow.2020.108574Get rights and content
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Highlights

  • The combined effect of cross gradients results in enhancement in heat transfer at lower thermal Rayleigh numbers.

  • Relative location of obstacles w.r.t the boundary layer influences its role on heat transfer.

  • Obstacles results in higher heat and mass transfer even though the average flow velocity decreases.

  • At lower buoyancy ratio, the mass transfer at the horizontal walls are highly enhanced with the increase in Lewis number.

Abstract

We investigate natural convection driven by a horizontal temperature gradient and a vertical concentration gradient in fluid-filled enclosures with obstructions inside it. Within the domain, nine adiabatic and impermeable cylinders are placed, occupying 30% of the domain volume. The Boussinesq approximation is used to account for density variations within the fluid and the flow is fully resolved. The solutal Rayleigh number has been fixed at RaC=106 and the Prandtl number at Pr=5.4. The Lewis number has been varied in the range of 1 ≤ Le ≤ 100 and the buoyancy ratio in the range of 0.1 ≤ |N| ≤ 10. The rate of heat and mass transfer are compared to those found in single-scalar natural convection, i.e solely thermal or concentration driven convection. Besides, the obtained heat and mass transfer rate in the cylinder-packed enclosure have been compared to those found in a fluid-only domain. We observe that the addition of a destabilizing concentration gradient to a side-heated enclosure results in heat transfer enhancement, which decreases with Lewis number and thermal Rayleigh number. Similarly, the temperature gradient increases the mass transfer, especially at high Lewis numbers and lower concentration buoyancy force over its thermal counterpart. Although the presence of the cylindrical obstacles reduced the flow velocity, the mass transfer was enhanced at lower buoyancy ratio.

Keywords

Natural convection
Double-diffusive convection
Temperature gradient
Concentration gradient
Obstacles
Quasi-steady flow
Laminar flow

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1

M. Chakkingal and R. Voigt contributed equally to this manuscript.