Char Depth Research Articles

Correlation of Theoretical Analysis With Experimental Data on The Performance of Charring Ablators

Experimental data are obtained for surface recession, char depth, and temperatures in silica phenolic and carbon phenolic ablators from static test conducted on rocket nozzles. In an attempt to correlate the theoretical analysis with the experimental observations, it is found that the effective thermal conductivity of char is strongly dependent on the wall heat flux. An hypothesis is postulated that the char conductivity can best be correlated by cold wall heat flux treated as a generalized variable that includes the effects of other factors like temperature and chemical composition of the char. Exponential dependence of char conductivity on the cold wall heat flux is observed for both the ablators, and has offered excellent comparison between the theoretical and the experimental system response.

Thermal degradation of polymers. VII. Ablation studies on a series of composite specimens containing asbestos fiber with various high‐temperature resin binders

AbstractThe use of a laboratory ablation test ring for the assessment of tubular asbestos‐reinforced composites is described. Ablation resistance, char depth, smoke, and flash measurements have been made on a series of composites produced using asbestos fiber with a variety of commercially available high‐temperature resin binders. The results have been compared with those obtained from a standard asbestos/phenolic composite and are discussed in terms of the properties of the composite and its components.

Thermal degradation of polymers. VIII. Ablation studies on a series of fiber‐reinforced phenolic resin composites

AbstractThe use of a laboratory ablation test rig for the assessment of tubular fiber‐reinforced composites is described. Ablation resistance, char depth, smoke, and flash measurements have been made on a series of composites based on a standard phenol–formaldehyde resin incorporating various fibrous reinforcing agents. The results have been compared with those obtained from a standard asbestos‐reinforced composite prepared from the same resin. Results are discussed in terms of the properties of the composite and of the fibrous reinforcing agent.

Effect of additives on ablation of phenolic-silica composites.

The behavior of three additives, Cr2O3, Fe, and Fe2O3, incorporated into the resin phase of a typical phenolic-silica charring-ablatiye material, was investigated. The performance, as indicated by the over-all char depth, of additive-cont aining ablators relative to that of identically fabricated control material was evaluated during exposure to two different environments, provided by an arc-imaging furnace and by a small hybrid rocket motor employing polymethylmethacrylate/oxygen propellants. Important improvements in ablator performance were observed, particularly in the more extreme hybrid-rocket-motor tests. Char samples were examined by means of scanning-electron microscopy. Composites containing Cr2O3 exhibited the least reduction in char depth. The Cr2O3 particles did not appear to interact appreciably with either carbon or silica during exposure in the rocket motor. The effect of Fe was an over-all char-depth reduction of about 10%. Microscopically observed interactions between the Fe phase and silica were highly supportive of a mechanism of silica reduction by carbon dissolved in iron, as postulated. The largest reduction in the char depth, ranging up to 30%, was observed in composites containing Fe2O3. Results of microscopic examinations were consistent with the hypothesis that the decrease in char depth was due mainly to heat absorption by endothermic reduction of iron oxides. Nomenclature Kp = chemical equilibrium constant based on partial pressures N = mole fraction p = partial pressure a = activity y = activity coefficient AH = heat of reaction

Selecting cooling techniques for liquid rockets for spacecraft

A* = nozzle throat area, in. AC = combustion chamber cross-sectional area, in. Ae = nozzle exit plane area, in. F = thrust, Ib h = heat-transfer coefficient, Btu/hr-ft-°R /sp = specific impulse, Ibf/(Ibm/sec) // = total impulse, Ib-sec k = thermal conductivity, Btu/hr-ft-°F L* = characteristic length, in. Pc = chamber pressure, psia P i nj = propellant injection pressure, psia q/A = heat flux, Btu/hr-ft TI = inside radius, in., ft Tg = gas recovery temperature, °R Tw = wall temperature, °R T co = effective heat sink temperature, °R t — wall thickness, in. AT = temperature difference between gas and wall V = velocity, fps WfC — coolant flow WT = propellant plus coolant flow, Ib/sec 6 = time, sec e = exterior wall emissivity a = effective thermal diffusivity, in./sec 5 = char depth, in. a= Stefan-Boltzmann constant, Btu/ft-°R-hr