Howard W. Emmons

Fire induced flow through an opening

Abstract The buoyantly driven flow of fire gases out through a window or door of a burning room is calculated for a constant density hot gas layer. An experimental model employing kerosene and water is developed to test the validity of the theory. The results indicate that the theory, with flow coefficients determined from the experiment can adequately predict the behavior. While the theory discussed fails to predict the room layer depth at low inflow rates by a large factor, the absolute error of only a few inches is of no practical consequence. Fire safety implications for doorway and window design are noted. Flow formulas useful for practical calculations are presented.

The fire whirl

A fire whirl from a liquid-fuel pool (acetone) is formed at the center of a rotating screen which imparts a controlled angular momentum to the ambient air. Measurements show that outside of the core the fluid motion is that of a free vortex. A hot-wire method of measurement of the radial temperature distribution is developed. The temperature distribution shows that the fire whirl consists of a rotating cylinder, fuel rich inside, lean outside. The turbulent plume theory is extended to include combustion and angular momentum. This theory checks the experimental results and provides: o 1. The turbulent mixing coefficient decreases with increasing angular momentum, as is to be expected. 2. The turbulent mixing coefficient increases with elevation above the ground. This effect was not expected. Its cause remains unknown, although it may be in some way related to the vertex-jump (vortex breakdown) phenomena which may be required if the whirl is to satisfy both ground-level and “high”-altitude boundary conditions.

Arc Measurement of High‐Temperature Gas Transport Properties

A confined electric arc for the determination of gas transport properties is developed to the point that the resultant properties are found within a few percent. The measurements include the arc electrical gradient characteristic, the flow pressure drop, the radiative heat transfer, the spectral temperature distribution, and microwave resonance characteristics. Values of the electrical and thermal conductivity of equilibrium argon are tabulated for the temperature range from 7500 to 13 750°K. Helium in the confined arc at atmospheric pressure up to 400 A is shown not to be in thermodynamic equilibrium and hence its equilibrium properties cannot be determined by use of this experimental arrangement.

Stability of Laminar Flames

Markstein theory of stability of laminar flames is shown to be supported by experimental results on oscillated laminar propane‐air flames. Disturbances in appropriate wavelength ranges grow and distort while for other ranges disturbances are damped. These facts imply important restrictions on the nature of a turbulent flame and its interaction with the surrounding flow field.

Combustion of wood charcoal

The dynamics of burning of wood charcoal in an air stream is examined both experimentally and theoretically. To simplify the theory, an experimental arrangement approximating a one dimensional phenomenon was adopted. The theory includes conduction in the solid, chemical reactions and heat release at the surface, and heat and mass transfer in the gas boundary layer above the surface. The molar CO/CO2 ratio is measured. The theory predicts surface temperature, solid temperature distribution and burning rate within experimental error. An effective reaction rate formula is developed.

The prediction of fires in buildings

A building fire viewed as the interaction of many components; pyrolysis, flames plumes, hot layers, radiative and conductive heat transfers, and flows can be predicted with presently available fundamental and/or empirical knowledge. The method is presented and the degree of success is shown by some comparisons between predicted and measured full-scale room fire results. The development of the prediction program shows the need for new research efforts on many of the component phenomena.

Poiseuille Plasma Experiment

The flow of gas and electric current simultaneously through a tube provides an experimental arrangement for the study of the flow of high‐temperature gases capable of precision measurements and a precise mathematical theory. The precision experimental technique and some initial experimental results together with a simplified theory are presented in this paper. Mean electrical conductivities and kinematic viscosities are given for a number of gases. The arc performance is shown to be predictable with fair precision by a very simple discontinuous model of the plasma properties which is capable of wide exploitation in magnetohydrodynamics.

Thermal degradation and spontaneous ignition of paper sheets in air by irradiation

The temperature and surface-density histories of a radiantly heated thermally thin filter-paper sheet held freely in air were measured in order to study the dynamics of the ignition of paper. Analyses of these histories indicate that the chemically complex degradation reactions can be approximately represented for fire dynamics purposes by two competitive first-order reactions with Arrhenius kinetics as observed by Tang [3]. One of these reactions with a preexponential factor 5.9 × 10 6 sec −1 and an activation energy 26 kcal/gm-mole is dominant at less than about 655°K. At higher temperatures, the other reaction with a preexponential factor 1.9 × 10 16 sec −1 and an activation cnergy 54 kcal/gm-mole is dominant. The heat-transfer rates to and from the test sheet were measured in order to estimate the energetics of the reactions. The data were insensitive to the small heat of the low-temperature reaction. Assuming this heat to be −88 cal/g (endothermic), based on DTA measurements of Tang and Neill [8], the heat of the high-temperature reaction is estimated to be about 444 cal/g (exothermic). An approximate formula is developed to predict the spontaneous ignition of a thermally thin sheet under known heating and cooling conditions, provided the Arrhenius kinetics and the heat of a first-order reaction in the sheet are known. Using the measured kinetics and heat of the high-temperature reaction in this formula, the results are compared with the measured data as well as with Martins [9] ignition data.

Fire spread in paper arrays

Measurements have been made of the rate of fire spread in a solid fuel array consisting of horizontal paper strips standing on edge, separated by various amounts of space. It is found that ignition transients show evidence of several burning modes and in some cases the steady burning can also occur in two different ways, at different speeds. The steady spread rate correlates with the height spacing ratio for both low and high values, but not for intermediate values. The available fire-spread theories are shown to be self consistent in the sense that the predicted relationship between various measured quantities is verified. However, the absence of the possibility of prediction of burning-zone properties, prevents the prediction of fire-spread rate from first principles.

Fire research abroad

During the latter part of 1966, the author visited 42 organizations in 11 nations of Europe and Asia. These organizations are engaged in all phases of the fire problem. Here, he summarizes his findings and discusses the strengths and weaknesses of the fire effort abroad.