Heat flux for ignition

Experimentally, time to ignition is measured at various heat flux values and critical heat flux for ignition and TRP are quantified using techniques such as the one used in the FMRC Small-Scale Flammability Apparatus ( 4,6). 

Sample No. Material Critical Heat Flux for Ignition (kW/m 2) Ignition Temperature °C (°F) Thermal Response (kWs2/nr) Heat of Gasification (kJ/g) Flame Heat Flux (kW/m2)... 

For long heating times, eventually at t —> oo, the temperature just reaches Tig. Thus for any heat flux below this critical heat flux for ignition, gig crit, no ignition is possible by the conduction model. The critical flux is given by the steady state condition for Equation... 

The minimum heat flux for ignition, c/mm, is closely related to 7 g. This heat flux is just sufficient... 

The gas flow to the radiant panel is set to obtain a heat flux at the 50 mm location that is 5-10kW/m2 above the critical heat flux for ignition (Section 14.3.2.3.2). The heat flux is verified with a heat flux meter inserted into a calcium silicate dummy specimen. The heat flux profile is shown in Figure 14.6 and can be used to determine the incident radiant heat flux at any location along the specimen center-line. The flux invariant may vary slightly and is usually determined for each apparatus during the initial calibration. 

Ignitability (time to ignition (tig), critical mass loss (ML) rate or heat flux for ignition, ignition temperature (7,), etc.)... 

Calculate the time to ignite (piloted) for the materials listed below if the irradiance is 30 kW/ m2 and the initial temperature is 25 °C. The materials are thick and the convective heat transfer coefficient is 15 W/m2 K. Compute the critical flux for ignition as well. 

The methodology [21] that has been used to the PA6 nanocomposite to deduce the thermal properties and critical heat flux was applied to the EVA and PBT nanocomposites (Section 19.7.1.1). The corrected ignition times as a function of the external heat flux for both EVA and PBT nanocomposites are shown in Figure 19.33. The final deduced thermal properties and critical heat flux are summarized in Table 19.7, along with the values reported for pure EVA and PBT in [22],... 

Figure 11.4. Reiationship between the time to ignition measured in the ASTM E2058 Apparatus and external heat flux for 100-mm square and 25-mm thick siab of PMMA. The surface was coated biack in the experiments. Data are taken from Ref. [39].

This test method determines the material properties related to piloted ignition of a vertically oriented sample under a constant and uniform heat flnx and to lateral flame spread on a vertical snrface dne to an externally applied radiant-heat flux. For the ignition test, a 155-nun (6-inch) square sample is exposed to a... 

FIGURE 53.2. Time to ignition versus external heat flux for a 100x100 mmxlO mm thick silicone based polymer. Data were measured in the ASTM E 2058 FPA. Data satisfy the thermally-thick behavior away from the critical heat flux value. 

Fig. 12. Critical heat flux versus ignition temperature. Symbols are measurements at sustained ignition. Lines are calculated from abscissa for incipient ignition (solid) and incipient burning (dashed).

Price (P9) has also investigated the ignition characteristics of JPN, a double-base propellant, in an arc-imaging furnace. Price s data show agreement with the predictions of Eq. (8b) for heat fluxes below 1.5 cal/cm2-sec. Above this flux level, the data deviated from the theoretical predictions. 

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