Showing papers on "Charring published in 1973"

Process for inlaying poured metal in wood

Abstract: A process for inlaying by pouring molten metal directly into a wood cavity without visibly charring or burning the outer wood surface. The process consisting essentially of the steps of routing out the desired design in a wood surface, providing a heat resistant and heat absorbent material in contact with the wood surface adjacent the design, pouring a liquid metal into the design formed in the wood so that metal fills the design to an elevation slightly above the final surface, removing the heat resistant and heat absorbent material, and sanding the wood surface and the raised metal until both metal and wood are at the same elevation.

Rate of charring combustion in a fire

Abstract: This paper deals with the rate and extent of charring of solid fuels, to forecast the intensityof a fire and the integrity of a structure. Literature review shows that most of the existing knowledge on wood charring is of empirical nature, and all the available theoretical work assumes Arrhenius-type pyrolysis kinetics, which invariably lead to numerical solutions. Hypothesizing that wood-pyrolysis kinetics, under realistic fire conditions, may be characterized by a “pyrolysis temperature,” at the attainment of which the solid pyrolyzes profusely, and a “char temperature,” at the attainment of which the solid is completely converted to char, this paper shows that the pyrolysis wave thickness is directly proportional to: (1) the solid thermal conductivity and (2) the temperature range in which the pyrolysis rate is measurable; and is inversely proportional to (3) the exposure heat flux and (4) the uncharred depth fraction. Neglecting the property variations, reactions in the char, moisture migration, internal convection, and fissure formation, the energy equation is solved with the assumption that the preheat temperature profile in the virgin zone is not significantly affected by the presence of the pyrolysis wave. The predicted trends are in excellent agreement with the available experimental data. Of special interest is the prediction that the pyrolysate mass flux at the surface is independent of the specimen thickness for thin solids, and is inversely proportional to the thickness for thick solids. By a passive technique suggested by the present analysis, data on the time to burn through 0.5-in.-thick planks of assorted species of wood are used to estimate the pyrolysis endothermicity to be 73–100 cal/g of volatiles. For α-cellulose and pine wood, it is determined respectively to be 73 and 78 cal/g volatiles. An expression for Spalding's masstransfer number B is obtained, incorporation of which in the stagnant-film hypothesis is shown to adequately describe the fire/fuel interaction, wherein the pyrolysis and boundary-layer phenomena adjust one another to bring about a stable combustion situation.

Laser damage in triglycine sulfate: Experimental results and thermal analysis

Abstract: An investigation of the effects of 10.6‐μm laser radiation on triglycine‐sulfate (TGS) crystals determined that the primary irreversible damage mechanisms in TGS pyroelectric detectors are cracking and thermal decomposition (charring). Irradiation thresholds for cracking and charring were determined for TGS crystals of typical detector dimensions as a function of laser power density and irradiation time. These energy density thresholds exhibit two distinct regions of behavior: For short irradiation times E0 is independent of τ while for long times E0 varies as τ1/2. The thresholds are given empirically by E0 (crack) = [0.65 + 22(τ)1/2] J/cm2 and E0(char) = [4.0 + 34 (τ)1/2] J/cm2. A theoretical model describing thermally induced damage in irradiated crystals is presented. The energy density damage thresholds obtained from this model are compared to the experimental results. These results on material damage are used to predict damage thresholds in operating TGS detectors. These predictions are in good agre...

An analysis of a charring ablator with thermal nonequilibrium, chemical kinetics, and mass transfer

Abstract: The differential equations governing the transient response of a one-dimensional ablative thermal protection system are presented for thermal nonequilibrium between the pyrolysis gases and the char layer and with finite rate chemical reactions occurring. The system consists of three layers (the char layer, the uncharred layer, and an optical insulation layer) with concentrated heat sinks at the back surface and between the second and third layers. The equations are solved numerically by using a modified implicit finite difference scheme to obtain solutions for the thickness of the charred and uncharred layers, surface recession and pyrolysis rates, solid temperatures, porosity profiles, and profiles of pyrolysis-gas temperature, pressure, composition, and flow rate. Good agreement is obtained between numerical results and exact solutions for a number of simplified cases. The complete numerical analysis is used to obtain solutions for an ablative system subjected to a constant heating environment. Effects of thermal, chemical, and mass transfer processes are shown.

Epoxy resin with metal salt of bisphenol or novolac as fire resistant composition

Abstract: Epoxy resin compositions having improved fire resistance are formed by the introduction into an epoxy resin composition of the type formed from epichlorohydrin and a dihydric phenol, of a small amount of a reactive hydroxy group containing polyvalent metal salt of either a dihydric phenol or a phenol-aldehyde resin of the novolac type. The resulting resins evidence increased charring of the surface when exposed to heating by a flame or undergoing combustion, the char acting as a barrier to heat transfer from the flame and retarding the flow of volatile gases from the pyrolyzing resin.

Heat shielding for Venus entry probes.

Abstract: Two contrasted approaches to ablative thermal protection of Venus entry probes are presented - a typical carbonaceous charring ablator and a dielectric reflective ablator. The interesting observation in this study is that mass loss is not the controlling variable in heat-shield sizing. A heat-soak problem determines the carbon phenolic sizing. For Teflon, the material thickness required to accomplish reflection is the sizing factor. The total heat-shield weight required to handle either steep or shallow entry is computed to be 13% less for a Teflon shield (if at least 3.2 mm are required for reflection) than for a charring ablator shield. If an efficient reflective backing is used with Teflon, the thickness can be reduced 1.0 mm and the computed weight is 31% less for Teflon than for the charring ablator. Such weight reductions may significantly increase the science payload weight of the miniprobes.

Modeling Sublimation of a Charring Ablator

Abstract: The Hertz-Knudsen analysis is shown to accurately predict the sublimation rate from a charring ablator. Porosity is shown to have a significant effect on the surface temperature. The predominant carbon species found in the vapor is C3, which agrees well with the results of previous investigations.

Fire resistant vinyl resin with metal salt of phenolic resin

Abstract: Vinyl halide resin compositions having improved fire resistance are formed by the introduction into said compositions of a small amount of a reactive hydroxy group-containing polyvalent metal salt of a phenol-aldehyde resin of the novolac type. The resulting vinyl halide resins evidence increase charring of the surface when exposed to heating by a flame or undergoing combustion, the surface char acting as a barrier to heat transfer from the flame and retarding the flow of volatile gases from the pyrolyzing resin.

Combustion characteristics of a solid propellant with a charring binder

Abstract: A brief investigation of the combustion characteristics of a solid propellant containing a binder which chars, as opposed to melting or volatizing, has been made. The burning rate of the propellant with the charring binder was significantly higher than similar propellants containing non-charring binders. High speed motion pictures of the burning propellant showed that the aluminum burned on the regressing surface, rather than a short distance from it as is typical with composite propellants.