Abstract
In this article, entropy generation due to natural convection in entrapped trapezoidal cavities filled with nanofluid under the influence of magnetic field was numerically investigated. The upper (lower) enclosure is filled with CuO-water (Al2O3-water) nanofluid. The top and bottom horizontal walls of the trapezoidal enclosures are maintained at constant hot temperature while other inclined walls of the enclosures are at constant cold temperature. Different combinations of Hartmann numbers are imposed on the upper and lower trapezoidal cavities. Numerical simulations are conducted for different values of Rayleigh numbers, Hartmann number and solid volume fraction of the nanofluid by using the finite element method. In the upper and lower trapezoidal cavities magnetic fields with different combinations of Hartmann numbers are imposed. It is observed that the averaged heat transfer reduction with magnetic field is more pronounced at the highest value of the Rayleigh number. When there is no magnetic field in the lower cavity, the averaged Nusselt number enhances as the value of the Hartmann number of the upper cavity increases. The heat transfer enhancement rates with nanofluids which are in the range of 10% and 12% are not affected by the presence of the magnetic field. Second law analysis of the system for various values of Hartmann number and nanoparticle volume fractions of upper and lower trapezoidal domains is performed.
Highlights
Natural convection in cavities is encountered in various applications including chemical reactors, heat exchangers, cooling of electronic devices, room ventilation and solar collectors due to its simplicity and low cost
The numerical investigation was performed for various values of Rayleigh numbers, Hartmann number and solid volume fraction of the nanofluid
Al2 O3 -water nanofluid under the influence of horizontally aligned magnetic fields (γ = 0o )
Summary
Natural convection in cavities is encountered in various applications including chemical reactors, heat exchangers, cooling of electronic devices, room ventilation and solar collectors due to its simplicity and low cost. Silva et al [8] numerically investigated the natural convection in trapezoidal cavities with two internal baffles They studied the effects of inclination angles of the upper surface as well as the effect of the Rayleigh number, the Prandtl number, and the baffle height on the fluid flow and heat transfer. Varol [9] performed a numerical study of natural convection in divided trapezoidal enclosures filled with fluid saturated porous media. He has noted that that the conduction mode of heat transfer became dominant for higher thickness of the partition, low thermal conductivity ratio and low Rayleigh numbers
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