Soot Layer Research Articles

The reflection of slow electrons from a soot-covered surface

The traditional way of reducing electron reflection at metal surfaces is by the deposition of a layer of soot. The reflection coefficient for incident electron energies of less than 24 eV on such soot-covered surfaces has been measured and compared with surfaces coated with colloidal graphite. For electrons of <10 eV the reflection on graphite is about five times larger than on soot. The reflection of visible light on these surfaces suggests that the micro-geometry of covered surfaces is a controlling factor in the reflection of slow electrons.

Surface processes in carburizing

In calculating carburizing processes in furnaces with a fluidized bed one can disregard the limiting effect of mass transfer on the surface; the efficiency of the general process of carburizing is fairly accurately described in this case by solving the diffusion equation with first-order boundary conditions. The rate of carburizing in convection furnaces operating with a liquid or gaseous carburizer is slowed down by surface processes. An increase of the carbon diffusion coefficient in the steel as the result of raising the carburizing temperature and increasing the thickness of the layer of soot increases the retarding effect of surface processes.

On temperature distribution over the external surface of screen tubes

An equation is presented which describes the temperature distribution over the external surface of a smooth tube of a single-row screen at different values of radiant flux from the furnace, thermal resistance of the soot layer, temperature of the heated medium and relative tube spacing. This equation also accounts for intrinsic radiation of the soot deposits and absorption of reflected heat fluxes, radiation of the lining being uniform. The integro-differential equation is solved by the finite-difference method on an electronic computer. Uniformity of the temperature distribution is shown to increase with the relative spacing, temperature of the heated medium, incident heat flux and with decreasing thermal resistance of the soot layer on the tubes. The predicted values are compared with experimental data.

The emissivity of luminous flames

The results of previous experimental work on extinction coefficients have been expressed in the form Kλ=k·λ−α, where k is indenpendent of the wavelength (λ) of the incident radiation. This paper describes the results of an experimental investigation into the values of α corresponding to soot layers deposited from a small laminar diffusion flame, on optically ground rock salt discs. The fuels used in the flame included amyl acetate, gas oil, petrotherm, towns gas, and some hydrocarbon gases. Extinction curves were obtained for each soot layer by means of an infrared spectrometer. The results are: (i) The variation of α with λ may be approximated by a+blnλ in some cases, and by a parabola in λ in others; (ii) The “mean” α for any soot [obtained as the slope of the best-fit straight line to the results plotted in the form of graphs of ln·ln (I0/IL) against lnλ] appears to be independent of the mean soot particle size; (iii) α appears to be definitely correlated with the carbon to hydrogen ratio of the soot.

Stenalderhuse på Knardrup Galgebakke

Stenalderhuse på Knardrup Galgebakke

A New Method of Light Microscopy

WITHOUT criticizing the vector treatment of amplitude and phase-contrast microscopy kindly given by Dr. Barer in his comment on my letter1, I would like to make the following comments: (1) Using my second method, phase-advancing objects appear darker than the background. The soot layer appears to cause a considerable phase retardation in addition to the absorption. (2) If the absorbing annulus is made substantially darker, the resulting image becomes peculiarly glossy and too unsharp to be of any value. Thus the “central dark-ground illumination” does not seem to be very promising in this connexion. (3) According to Oettlé2, as well as from my own observations, ordinary negative phase-contrast methods do not produce images comparable with those of positive phase-contrast in clarity. The inherent haziness and glare of the negative phase-contrast picture may be due entirely to the light reflected from the phase plate and converged back to the area under observation. Due to the reflectivity of absorbing annuli evaporated by ordinary means, this additional surface illumination may reach higher values than the light passing the objective annulus. My method does not suffer from this in the same degree since the reflectivity of soot is small.

A new method of light microscopy.

WITHOUT criticizing the vector treatment of amplitude and phase-contrast microscopy kindly given by Dr. Barer in his comment on my letter1, I would like to make the following comments: (1) Using my second method, phase-advancing objects appear darker than the background. The soot layer appears to cause a considerable phase retardation in addition to the absorption. (2) If the absorbing annulus is made substantially darker, the resulting image becomes peculiarly glossy and too unsharp to be of any value. Thus the “central dark-ground illumination” does not seem to be very promising in this connexion. (3) According to Oettle2, as well as from my own observations, ordinary negative phase-contrast methods do not produce images comparable with those of positive phase-contrast in clarity. The inherent haziness and glare of the negative phase-contrast picture may be due entirely to the light reflected from the phase plate and converged back to the area under observation. Due to the reflectivity of absorbing annuli evaporated by ordinary means, this additional surface illumination may reach higher values than the light passing the objective annulus. My method does not suffer from this in the same degree since the reflectivity of soot is small.