A numerical study of the combustion of lean methane/air
mixtures in a porous media burner is performed using a novelty
geometry, cylindrical annular space. The combustion process
takes place in the porous annular space located between two
pipes, which are filled with alumina beads of 5.6 mm diameter
(Al2O3) forming a porosity of 0.4. The outer tube diameter of
3.82 cm is isolated; meanwhile the inner tube of 2 cm in
diameter is covered by a continuous set of thermoelectric
elements (TEE) for transforming heat energy into electricity. To
achieve and maintain the proper temperature gradient on TEE,
convective heat losses are considered from the TEE. The
respective heat transfer coefficient is variable and is in the
range 800 < h < 1500 [W / m2]. The 2D mathematical model
includes the energy equations for solid and gas phases, the
momentum equations, the continuity equation, the fuel mass
conservation, the perfect gas law and it is solved by Means of
computational simulations in COMSOL Multiphysics.
Computer simulations focus on the two-dimensional
temperature analysis and displacement dynamics of the
combustion front inside the reactor, depending on the values of
the filtration velocity (0.1 < ug0 < 1.0, m/s) and the fuel
equivalence ratio (0.06 < Φ < 0.5). The conditions that
maximized the overall performance of the process of energy
conversion are ug0 = 0.7 [m / s], Φ = 0.363 and h = 1500
[W/m2K], to obtain 2.05 [V] electrical potential, 21 [W] of
electrical power and an overall efficiency of process η = 5.64%.
The study shows that the cylindrical annular geometry can be
used for converting the energy of combustion from lean gas
mixtures into electricity, with a performance similar to the
specified by manufacturers of TEEs.
Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016.