| OCR Text |
Show 2.1.7 Fig.1. Measured equilibrium curves for wood and peat, measured with the heating rate 5K/min. e(T) 0.5 WILLOW FIR PEAT «-» * LOW MOOR PEAT X MEDIUM MOOR PEAT 200 473 300 400 573 673 TEMPERATURE 500 773 600 873 700 <°C> 973 T (K) In the present model the rate equation (14) is applied instead of the usual Arrhenius type rate equation. The curves in Fig.1. have been measured by using the heating rate 5K/minr the exact equilibrium curves could be achieved by using infite small heating rate. Increasing the heating rate shifts the curves slightly towards higher temperatures according to the measurements made in C.N.R.S /9/ for cellulose. The validity of the rate equation or its basis, the relation (13), could be tested by the simultaneous measurements of local temperatures and local densities inside a large particle in a transient state. Measured simultaneous temperature and density profiles at fire level surface heat fluxes have been reported /10/,/11/ for wood samples. The transient density profiles can be calculated by using the reported temperature profiles and the relation (13). The comparison between the calculated and the measured transient density profiles, when the effect of shrinkage is taken into account, shows a good agreement. For small particles in fire environment the heating rates become usually so fast that the kinetics become the limiting step and the rate equation (14) is not recommended. |
