OCR Text |
Show 2.1.15 iterative calculation is needed during the actual computation - the transient location of the drying front is obtained directly, since instead of calculating the temperature distribution, the locations of the isotherms to be followed are calculated. The isotherms are chosen in advance for example with distance 30 K - the calculation proceeds explicitly in time, however, the time step AFo may be larger and the accuracy still remain good. In the usual methods Fo<0.5(Ax)2 with a fixed Ax. Now Ax is the distance between the two successive moving isotherms,and AFo becomes larger when the temperature gradients are small, and AFo is small (increasing the accuracy), when the gradients are large. The transient dimensionless mass (momentary mass/initial mass) at different times can be calculated by using the momentary locations of the isotherms. The transient mass/initial (wet) mass 1S TT-V-=1" " ~^- + S -^-xf + 1 (34) (1+u)m„ k=1 (1+u)Po k=K ( i + u ) P o k It may be better to use the dry initial mass as the reference, when particles having different initial moisture content are compared. The transient mass/dry initial mass is 2 = i+u - E ^1S + S !£!S Xr + 1 (35) m° k=1 p0 k=K p0 K The transient mass of the water/initial wet mass is -- = ^- x£ + 1 , T =373 K, when K<k<N (1+u)m0 (1+u)p0 m , when N<k, T, =3 7 3 K and (36) (1+u)m0 m w 1+u ' " ~' k 0 , when k<K, T =373 K (1+u)m0 k The volatiles generated on different cores are obtained from Fig.2 (which is based on the measured curve Fig.1) by using the equation (15). |