Overall heat release

Enclosed fires may exhibit fire growth characteristics as shown in Figure 5-5. Unlike gaseous or liquid fuels, there may be a considerable fire growth period in which temperatures and overall heat release is low and the fire is localized. As the fire becomes fully developed, the entire room volume can become engulfed in flames, finally, as air is depleted or fuel is consumed, a decay period occurs. In many cases, an enclosure fire will be starved for air ("ventilation-limited"), and the available airflow becomes the limiting factor for the fuelburning rate. 

Since the burning surface becomes highly heterogeneous with increasing hmx the determination of values is no longer possible, which precludes the determination of the heat of reaction at the burning surface, Q. However, it is assumed that the decomposition of the HMX particles within the base matrix occurs relatively independently of the decomposition of the base matrix, i. e., the double-base propellant. The overall heat release at the burning surface of an HMX-CMDB propellant is thus represented by[i]... 

Figure 5 Illustration of the method used for the quantification of the individual contributions to the overall heat released during the polymerization process (a) and TMDSC traces (reversible curve first run) for the PCA powders obtained by the one-shot method (b)...

The heat release due to the decomposition of the HMX particles occurs relatively independently from the decomposition of the base matrix used. The overall heat release at the burning surface of HMX-CMDB propellant is represented by1251... 

When the reaction is started at a temperature near to reflux, the overall heat release of the reaction needs to be calculated from the sum of the individual heat release terms, that is ... 

In order to obtain the overall heat release profile for the reaction it is necessary to combine these two power output traces. The composite heat release curve is shown in Figure 4.23(c). The two dips in the trace, (G and H in Figure 4.23(c)), are due to a phase difference between the measurement of the heat flow and reflux data. 

The TMR can also be determined from isothermal DSC data - A test is initially carried out using scanning DSC to obtain the overall heat released, A//, and the specific heat, C. Several isothermal DSC experiments (Figure 4.30) are then carried out at different temperatures near to the exotherm onset temperature detected in the scanning DSC run. 

Reaction Calorimetry. The easiest way to follow a polymerization is to monitor the temperature of the reaction mixture or to use reaction calorimetry (cf above). Landau gives an excellent review on reaction calorimetry, its principles and application in chemical research in Reference 425. Table 23 summarizes papers dealing with reaction calorimetry of heterophase polymerizations. Reaction calorimetry gives on-line information with regard to the overall heat released during the reaction. This heat release is directly connected with the monomer conversion (eq. 49). 

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