Alexandros Vouros

An Analytical Method for the Estimation of Radiation Heat Flux from Open Pool Fires and Pool Fires Impinging on Ceilings

This paper presents a new integral method for the estimation of the thermal radiation flux from open pool in air fires and pool fires having flames sometimes impinging under extensive ceilings. For open fires, a uniformly distributed emissive power to the cylinder that represents the flame envelop is used together with a radiant fraction that depends on the source diameter. Estimations and comparisons are produced using the mean as well as the continuous (stoichiometric) flame heights which are calculated and correlated numerically including flames impinging on the ceiling. The applicability of the method and comparison with previous analytical methods are validated for a range of heat release rates (1–300 kW) using experimental results of the literature. For fires under ceilings, the gas temperature distribution under the ceiling is used to estimate the thermal radiation from a disc that represents the flames if flames impinge on the ceiling as well as the hot gases in all the ceiling layer. Radiation flux from the ceiling jet is significant in this case, while the lower and higher values are estimated for the complicated view factor, assuming that the flame cylinder under the ceiling is opaque or transparent. Estimations are compared with experimental results of the literature, indicating that the adoption of a transparent flame cylinder produces conservative results for all the cases examined.

Turbulent free convection over a horizontal heated plate in an open top cavity

An experimental study of the thermal field established, over a horizontal heated plate (1000×500×12 mm3) in an open top cavity, of aspect ratio Γ = 2 is presented. The working fluid was air at atmospheric pressure and the imposed temperature conditions correspond to a Rayleigh number Ra = 4.1×108, based on the cavity height and the temperature difference across it. Schlieren visualization was used to identify characteristic structures developing over the heated plate. Local temperature measurements along the vertical axis over the plate centre were accomplished using a fine thermocouple (d = 0.025 mm). Distributions of mean and rms temperatures are presented along with the corresponding skewness and flatness distributions. The exponential form of the PDF temperature distributions observed in the present experiments, as in several experiments in hard turbulence, is compatible with the intermittent presence of fluid structures with different origin and past history. Temperature PDFs have been approximated by mixtures of weighed Gaussian distributions to illustrate this concept.