simplifications: the heat of desorption is ignored 1 and the water in the fuel is 

 assumed to be completely vaporized at 100° C. A temperature- dependent dry fuel specific 

 heat (Dunlap 1912) , 



C d = C + C 1 T ' & 

 is used in place of the constant value used by Byram and coworkers (1952), where: 



C Q = 0.266 



C = 0.00116. 



Both members of the cell would absorb the same heat per unit mass if the unit cell 

 were uniformly heated. For example, the heat absorbed within the ' transverse member 

 would be: 



H A = V A p{fC w (100 - T a ) + fQ w ♦ [C Q + Cl (T. g + T a )/2](T. g - T ft ) } , (4) 

 where : 



V. = Volume of transverse member of unit cell 



A 



f = Fractional fuel moisture content relative to its ovendry mass 



C = Specific heat of water 



w r 



= Specific heat of ovendry fuel 



T\g = Ignition temperature 



= Ambient temperature 



Q = Heat of vaporization of water. 



w r 



Since H = pV Q and Q = Q = Q. for uniform heating, the heat of preignition 



r\ A. r\ A. D -L££ 



per unit ovendry mass of moist fuel rising from ambient to ignition temperature is: 



Q. = fC (100 - T ) + f Q + [C n + C, (T. + T )/2](T. - T ). (5) 

 < ig w a w L 1 ig a J ig a 



Q^g is made up of three products: the heat necessary to bring fuel moisture to 

 boiling temperature, the heat of vaporization of fuel moisture, and the heat necessary 

 to ignite ovendry fuel. 



The amount of heat nonuniformly absorbed by the unit cell is calculated stepwise 

 throughout the fuel member by using isotherms developed from the thermal gradient. 

 There are two equations for the heat absorbed by each member within the volume bounded 

 by consecutive isotherms: one for T Q _< 100° C. and one for T Q > 100° C, where T is 

 the minimum isotherm. Each equation consists of two parts: 



1. Heat absorbed by all area elements up to T Q ; 



Mleat of desorption should be included; however, the added refinement is not 

 justified when compared to the overall accuracy of these measurements. 



