Effects of pressure and impingement angle in flaming processes

Abstract

urbulent jets impinging on plane surfaces are used extensively in the process industries to achieve intense heating, cooling or T drying rates. Examples can be drawn from the drying and blasting processes, from glass melting, from metal cutting and forming, from fire testing of building materials, from oxy-flame and bonding applications, etc.The isothermal velocity field and the overall heat and mass transfer performance of jet impingement flows have been experimentally and computationally examined by several researchers (e.g., Jambunathan et al., 1992; Baugh and Shimizu, 1989; Cooper et a1.,1993;Craft et al., 1993). The flame impingement heat transfer effects, thermal conduction, non-luminous gaseous radiation, forced convection and thermochemical heat release have been studied by Hoogendoorm e t al. (1 978), Baukal et al. (1996), and Cebhart (1997) Mathematical FormulationA finite volume approach for the solution of the elliptic momentum, energy and turbulent transport equations has been adopted. The resulting system of partial differential equations has been solved, along with the boundary and inlet conditions, in their two-dimensional form using Cartesian coordinates and an iterative procedure is employed, based on a staggered grid arrangement, using the SIMPLEST algorithm, the second order upwind differencing discretization scheme and the Tri-Diagonal Matrix Algorithm.'Author to whom correspondence niay be addressed. E-mail address: N.Markatos@ tihra.gr 834This work investigates the effects of varying the pressure of the mixture reactants and the angle of impingement on the performance characteristics of a turbulent premixed jet flame impinging on a solid surface. These effects are important for the design of torches and flaming machines used for material and metal cutting and forming. The combustion and flow characteristics are modelled using a finite volume computational approach. Based on the simulation results, it is shown that, by increasing the pressure of the mixture reactants, the flame-surface interaction mechanisms are modified. Changing the impingement angle increases the role of chemical kinetics and reduces maximum temperature values due to increased local flame extinction. The heat released and temperature predictions are compared to experimental data and the agreement is satisfactory.

Numerical Study of Thermal Radiation Effect on Confined Turbulent Free Triangular Jets

“…Therefore, it is expected that the -RNG model gives better results in the regions of the flow where the mean strain rates are high. The performance of the -RNG model of turbulence has been investigated by Knowles and Saddington [11], Gordeev et al [12], Sharif and Mothe [13], Fernández et al [14], Chen [15], Liakos et al [16,17] and Sharif and Mothe [18] in jet flows and all confirmed that the -RNG model can be successfully used to model this type of flows. The -RNG model is numerically robust and faster than the triple transport model and has minimum turn-over time requirements for the calculations [17].…”

Impinging jet cooling on concave surfaces

“…They can therefore be applied in this flow where no previous computational experience exists. In general, details of turbulence characteristics can be captured only after careful selection and implementation of an appropriate turbulence model (Liakos et al, 2000a, b). Modified turbulence models (such as modified k –ε models; nonlinear k –ε models; low‐Reynolds number models; algebraic models of two, three, or more equations) show their numerical superiority over the standard k –ε, only in specific geometries, and should be implemented on a case‐to‐case basis.…”