OCR Text |
Show 2.1.9 The term Eh•p• that accounts for the energy of chemical reactions and the vaporization of liquid water becomes N dR Eh p * - E p i 6(r-R ) --^± (18) 1 1 k=K gK K k dt where K denotes the moving core (or isotherm) closest to the center plane, line, or point, and N denotes the moving core closest to the particle surface. The heat storage term in the equation (10) can also be approximated as a phase change process.When the temperature of a point inside the particle changes from Tk_- to Tk, the process can be understood as a phase change that requires the heat of phase change Pk-1c, -(Tk~Tk_1), which is endothermic for heating and exothermic for cooling. Thus, N dR, pc H - - .\ {Vick-i(VTk-i» 6(r-V 7? 19) k=K dt This approximation simply means that the heat capacity of the material between the moving cores R^.* and R, is concentrated on the moving core R, . THE PROPAGATION OF THE ISOTHERMS INSIDE THE PARTICLE Fig.3. The vaporization of the liquid water, the pyrolysis and the heat storage are all treated as phase change processes. NEW ISOTHERM IS GENERATED ON THE SURFACE WHEN TS>TN+, ISOTHERMS DISAPPEAR IN THE CENTER POINT, LINE OR PLANE ISOTHERMS SWEEP THROUGH THE PARTICLE, VOLATILES ARE ASSUMED TO BE GENERATED ON THE ISOTHERMS HEAT CAPACITIES ARE CONCENTRATED ON THE ISOTHERMS WATER STEAM IS GENERATED ON THE ISOTHERM 373 K |