Typical heat flux levels

Minimum for pain to skin (relative short exposure)[4] 1 

The highest possible heat flux from the sun is not possible of igniting common solids. However, magnification of the sun s rays through a fish bowl was found to have ignited thin draperies in an accidental fire. 

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Table 7.1 lists heat flux levels commonly encountered in fire and contrasts them with perceptible levels. It is typically found for common materials that the lowest heat fluxes to cause piloted ignition are about 10 kW/m2 for thin materials and 20 kW/m2 for thick materials. The time for ignition at these critical fluxes is theoretically infinite, but practically can be (9(1 min) (order of magnitude of a minute). Hashover, or more precisely the onset to a fully involved compartment fire, is sometimes associated with a heat flux of 20 kW/m2 to the floor. This flow heat flux can be associated with typical... 

Typically, for any given pressure, industrial packaged boilers operate at higher heat-flux rates than field-erected boilers, This requires that the package boiler FW quality should be substantially better (i.e., lower overall TDS and lower levels of silica and sodium). Appropriate MU water pretreatment may, for example, necessitate the use of twin bed and mixed bed demineralization ion exchange, or RO and mixed bed (in addition to mechanical deaeration and other processes). 

Using factorial analysis, samples of the mohair/silk (MS) fabric were variously treated with a selection of flame retardants, back-coating formulations and adhesive, mounted on a typical aramid honeycomb board specimen, and each composite was tested using cone calorimetry at the preferred heat flux of 50 kW (shown to be equivalent to the 35 kW m flux used in the OSU calorimeter). 1 An optimum combination of flame retardant, back-coating and adhesive at specific application levels was found to yield the lowest heat release values, and this system was applied to each of the above six fabrics. Testing in both the OSU at 35 kW m heat flux and at 50 kW m" in the cone calorimeter gave the results for peak heat release in Table 4.5 below. From this it is seen that all fabrics have PHRR values < 65 kW m" and that OSU and cone calorimeter results are equivalent. 

For LPG, the level of heat flux through typical insulation of 5 W/m is too small again by several orders of magnitude, compared with the minimum local heat flux of 10 kW/m, required to produce nucleate boiling. 

In most, if not all, storage situations, the heat flow through the insulation and tank walls into the liquid is a much more gentle process with a heat flux of typically less than 100 W/m for LNG. This level of heat flux is some two orders of magnitude less than the minimum of 10,000 W/m required for heterogeneous nucleate boiling. It can only be released from the liquid by surface evaporation, with no boiling at all. 

The AG molecule is converted to a strong acid (AH) upon absorption of a photon and the rate of this reaction is fast, with the extent of reaction being governed by the quantum effeciency of the particular acid generator and flux. The acid proton affects the desired deprotection reaction (4) with a finite rate constant. This rate is a function of the acid concentration, [H4-], the temperature and most importantly, the diffusion rate of the acid in the polymer matrix. The diffusion rate in turn, depends on the temperature and the polarity of the polymer matirx. At room temperature, the rate of this reaction is typically slow and it is generally necessary to heat the film to well above room temperature to increase reaction rates and/or diffusion to acceptable levels. The acid (H+) is regenerated (reaction 4) and continues to be available for subsequent reaction, hence the amplification nature of the system. 

It is estimated that in a large LOCA a discrete amount of water remains in the reactor vessel, typically up to the level of the lower core support plate. This is equivalent to the possibility of cooling one half of the molten core in a PWR and even more in a BWR. If it is supposed that all the core collects on the bottom as debris, it would be necessary to dissipate about 2 MW of heat, which is possible at high pressure but not at low pressure because the dryout flux would need to be overcome. 

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