Evaluation of dynamic behavior of a falling porous magnesium particle over the ignition and combustion processes
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Evaluation of dynamic behavior of a falling porous magnesium particle over the ignition and combustion processes Peyman Maghsoudi1 · Mehdi Bidabadi1 Received: 4 January 2020 / Accepted: 27 April 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract In this research study, combustion of micron-sized porous magnesium particle which freely falls into an infinite hot oxidizer medium is investigated. To examine the particle behavior during the process, acceleration and all forces acting on it including mass, buoyancy and drag forces are considered. The effects of produced magnesium oxide and both types of porosity consisting of surface and volume porosities are applied in mathematical modeling. The governing equations including magnesium particle mass continuity, linear momentum balance and energy conservation are numerically solved. Afterward, the impacts of important parameters on combustion characteristics are studied. Results show that by considering both types of surface and volume porosities, combustion time decreases compared to the cases in which one of these parameters is employed. With increasing the particle diameter and its porosity factor, velocity and acceleration enhance. Moreover, during the combustion process, mass and drag forces of magnesium oxide and its radius variations have the most effective contributions in total acceleration with the shares of 39.8%, 30.07% and 12.8%, respectively. Also, contribution of magnesium oxide in total acceleration is 4.8 times greater than that of magnesium. Keywords Magnesium · Surface porosity · Combustion · Acceleration List of symbols Aeff Effective surface area (m2) a Particle acceleration (m s−2) Bi Biot number Cox Weight fraction of oxygen in air CP Specific heat of particle (J K−1 kg−1) Ea Activation energy (J kg−1) FB Buoyant force (kg m s−2) FD Drag force (kg m s−2) hconv Average of convective heat transfer coefficient (W m−2 K−1) k Thermal conductivity (W m−1 K−1) K Permeability (m2) m Mass (kg) Mw Molecular weight (kg mol−1) Nu Nusselt number Pe Peclet number Pr Prandtl number * Mehdi Bidabadi [email protected] 1
School of Engineering, Mechanical Engineering Department, Iran University of Science and Technology, Narmak, Tehran, Iran
QComb Specific heat of magnesium combustion (J kg−1) r Radius (m) R Pore radius (m) rMg,0 Magnesium initial radius (m) Re Reynolds number RMg Gas constant for magnesium (J K−1 kg−1) rP Particle radius (m) t Time (s) T Temperature (K) T Initial temperature (K) Tsurr Temperature of surrounding (K) T∞ Temperature of oxidizer medium (K) V Volume (m3) v Velocity (m s−1) W Mass force (kg m s−2) x Location (m) Greek symbols ε Emissivity ε𝜄 Defined in Eq. 20 μ Dynamic viscosity (m kg−1 s−1) ρ Density (kg m−3) σ Stefan–Boltzmann constant (W m−2 K−4) τ Magnesium burning time (ms)
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Vol.:(0123456789)
φ Porosity factor ω Reaction rate (kg s−1 m−2) Subscripts in Input out Output Mg Magnesium MgO Magnesium oxide com Combustion sys System ∞ Oxidizer medium
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