Prediction of LI-SF6 wick combustion

Abstract

A theoretical and experimental investigation was conducted to study the wick combustion of lithium (Li) and sulfur hexafluoride (SF6). The wick combustion experiments were conducted in a vacuum chamber at a pressure of 0.01 MPa. At this condition, the wick combustion of Li and SF6 yields a bright luminous flame. During the combustion, the lithium bath temperature was maintained near its saturation temperature at the system pressure. A prediction model based on the conserved-scalar approach is presented along with an interface analysis. The predicted interface temperature was in agreement with the experimental liquid bath temperature. The model prediction yields a reasonable flame stand off distance as compared to the experiments reported elsewhere. The flowfleld analysis shows self-similar solutions for planar wick combustion of Li and SF6 and nonsimilar solutions for the cylindrical wick combustion. Property variations and wick curvature are found important to the flowfleld prediction of the Li-SF6 wick diffusion flame. Nomenclature A - parameter, Eq. (15) c - parameter, Eq. (8) D - binary diffusion coefficient DK - species parameter, Eq. (28) / = dimensionless stream function, Eq. (7) Gr = Grashof number, Eq. (15) g - acceleration of gravity H = plate or cylinder height h = enthalpy k - thermal conductivity L = enthalpy of gasification NK - species parameter, Eq. (28) Pr = Prandtl number T - temperature u - streamwise velocity v = cross-stream velocity x = streamwise direction y, = mass fraction of species / y = cross-stream direction y0 = radius of cylindrical wick Z = mixture fraction 17 = similarity variable, Eq. (10) jti = dynamic viscosity v — kinematic viscosity f = similarity variable, Eq. (10) p - density ^ = stream function, Eq. (9) a) = source term to account for the polymerization of gas species, Eq. (21)