Heat of gasification

In the study, five FRC samples, about 3 to 5 mm in thickness, were examined. The results from the study show that FRC materials have high resistance to ignition, high heat of gasification and high resistance to self-sustained fire propagation. These results suggest that a composite combat vehicle, by virtue of its construction, does not present an unusual fire hazard. 

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)... 

Figure 8. Ratio of the Chemical Heat of Combustion to Heat of Gasification for Fiber Reinforced Composite and Non-Composite Materials...

In this form, the energy needed to break the original polymer bonds to cause unzipping or volatilization with char is closer to values representative of noncharring solid polymers. Table 9.1 gives some representative values found for the heats of gasification. 

We shall formalize our use of L by considering analyses for the steady burning of liquid fuels where the heat of gasification is a true fuel property. 

The final result for the burning rate can be expressed in terms of the heat of gasification of the virgin solid, L0 ... 

This equation along with Equation (9.97) allows us to eliminate the convective flame heat flux to develop an equation for the flame temperature. This equation will still contain the burning rate in terms of the effective heat of gasification, Lm. From Equation (9.97), we define Lm as the modified heat of gasification by the following ... 

This shows that this modified heat of gasification includes all effects that augment or reduce the mass loss rate. Recall that the term in the [ ] becomes zero if the solid is thermally thick and the virgin solid equilibrates to the steady state. Equating Equations (9.107) and (9.108) gives an equation for the flame temperature ... 

The properties needed are taken from Reference [28] for consistency and are given in Table 9.4. The heat of gasification of wood is approximated since it is unsteady and charring. 

Heat of combustion = 12.0 kJ/g Heat of gasification = 6.0 kJ/g Effective vaporization temperature = 380 °C Radiative loss fraction = 0.35 Conversion constants ... 

Table 3 Surface re-radiation loss q"r and heat of gasification (L) of polymers...

Austin, P.J., Buch, R.R., and Kashiwagi, T., Gasification of silicone fluids under external thermal radiation part I. Gasification rate and global heat of gasification, Fire Mater. 1998, 22, 221. 

There are two intrinsic material characteristics that are related to heat release rate. These two properties are the effective heat of combustion, AHc (MJ/kg), and the heat of gasification, L (MJ/kg). The effective heat of combustion is the ratio of heat release rate to mass loss rate measured in a bench-scale calorimeter ... 

The second material property is heat of gasification, L, defined as the net heat flow into the material required to convert one unit mass of solid material to volatiles. The net heat flux into the material can be obtained from an energy balance at the surface of the specimen. Typically, a sample exposed in a bench-scale calorimeter is heated by external heaters and by its own flame. Heat is lost from the surface in the form of radiation. Owing to the small sample size, the flame flux is primarily convective, and flame absorption of external heater and specimen surface radiation can be neglected. Hence, L can be defined as... 

Stoliarov, S. I. and Walters R. N. (2008) Determination of the heats of gasification of polymers using differential scanning calorimetry, Polymer Degradation and Stability 93(2)422-427. 

Of the several approaches that have been used to calculate fuel generation rates from solid materials in CFD-based fire growth calculations, the simplest are empirical models. Instead of attempting to model the physical processes that lead to gaseous fuel production inside decomposing solids, empirical data that can be measured (transient heat release or mass loss rate) or inferred (heat of gasification) from common bench-scale fire tests such as the Cone Calorimeter are used to characterize fuel generation processes. 

With empirical pyrolysis models, a material s burning rate is zero until its surface is heated to its ignition temperature (Tig), at which time ignition occurs. After ignition, the mass loss rate of a fuel element is estimated from the net heat flux to the fuel s surface (q"a) divided by the effective heat of gasification (A7/g) ... 

The effective heat of gasification in Equation 20.17 is a material fire property that is the quantity of heat required to generate unit mass of volatiles at temperature 7, from unit mass of solid initially at T0. 

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