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"ocr_t":"2.1.16 The transient mass flow rates from the particle are easily obtained from the expressions for the transient masses by derivating. For the dimensionless transient mass flow rate, when the initial wet mass is chosen as the reference, we get 1 jm N P^u r dxi (1+1u)_m 0ddmF_o ,z _ , „g k_, (1+r)xr k_ _k {37) k=K (1+u)p0 dFo or in the units 1/s 1 Xm n N PrrV r dXl <1+u)m0 ddmt (1-+mu )m0 = aRo' kz= K (1+guJ)ip_o (1+r)x£k _d_FkQ (38) The mass flow rate of the water is obtained correspondingly. It could also be possible to estimate the concentrations of the gas flowing out from the particle as a function of time, if it is assumed that the concentration of different species depends only on the temperature they are generated, and the secondary char reactions (reactions between the char and the volatiles flowing through the char layer) are neglected. The off-gas concentrations for the whole particle as a function of time obtained by summing up the gas concentrations generated on different temperature cores. The gas concentrations that are generated on different temperatures and needed for the calculations can be measured , when a small powder sample is gradually heated, and the temperature is slowly increased. The efflux of steam and volatiles from the particle reduces the convective heat transfer coefficient. According to /13/ hc _ 1/st h exp(1/St)-1 CO for plates, cylinders and spheres. The Stanton number on the particle surface is St=h /C\". The heat capacity flow rate on r CO s the particle surface is obtained from the equation (23) with k=N and r=R or Cg=-A f (Fo)/R, and the Biot number becomes Bi= -f (Fo)/(exp(-X f (Fo)/h 0R)-1) . T h e heat transfer coefficient h may also depend on time, if the velocity of the atmosphere CO changes. The Nusselt number or h is calculated by applying a proper correlation depending on the situation (a single particle",
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