2. Discussion ① Application: given t,D→C(x,0) x/2√D x→2=x/2√D→ookp→erf(2)→C(x,) 2 C-x curve (concentration penetration curve) x=0→5=0→erf()=0 与时间无关 at x=0. the concentration is invariable
2. Discussion: ① Application: ② C－x curve. (concentration penetration curve) given t, D C(x,t) x = 0 = 0 erf() = 0 2 1 2 0 C C C + = x = x / 2 Dt lookup erf() C(x,t) = x / 2 Dt 与时间无关 at x = 0, the concentration is invariable
+∞ ac dc as Ox ds a 2 C+O C-x curve is symmetrical.(x=0, C 2 0
1 1 : C C x C C = = = + + 2 2 1 d 2 d 2 2 1 − = − = − Dt e C C x C x C C－x curve is symmetrical. ( ) 2 0, C1 C2 x C + = = 0 t 1 t 2 t C1 C2 C 0 x 2 C1 +C2