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Chapter 27

輸 送 現 象. Chapter 27. 不穩定質傳 Unsteady-state Mass Transfer. 輸 送 現 象. Unsteady-state Mass Transfer. 切一塊 ( Δ x* Δ y* Δ z ) 下來討論 若時間 t 濃度為 C A ，經過 dt 後 時間 t+dt 濃度為 C A +dC A 則此區塊累積量 = Δ x* Δ y* Δ z = ( N A in - N A out )* Δ y* Δ z. Fick 第二定律. A.

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Chapter 27

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  1. 輸送現象 Chapter 27 不穩定質傳 Unsteady-state Mass Transfer

  2. 輸送現象 Unsteady-state Mass Transfer • 切一塊(Δx*Δy*Δz)下來討論 若時間 t 濃度為CA，經過 dt 後 時間 t+dt濃度為CA+dCA 則此區塊累積量 = Δx*Δy*Δz = (NAin-NAout)* Δy*Δz Fick第二定律 A =NA|x NAin =NA|x+Δx NAout Δy Δz Δx

  3. 輸送現象 Unsteady-state Transfer in a flat plate with negligible surface resistance c • 無限大平板之不穩定質傳 • t=0,x=x,c=c0 初始條件 • t=t,x=0,c=c1 邊界條件 • t=t,x=2x1,c=c1 邊界條件 • 經過t後，x=x,c=？ C0 At t=0 NA c C1 C1 x1 2x1 x dx X=D*t/x12

  4. 輸送現象 Error function

  5. 輸送現象 Unsteady-state Transfer in a flat plate with surface resistance NA1 NA2 c cLi NA2＝ky（yA－yAi） NA1＝kx（xAi－xA） =kcx(cAi－cA） 分析V，L兩相 =kcx (cLi－cL） =kcy (c－ ci） steady-state unsteady-state cLi=K ci K Equilibrium Distribution Coefficient 討論在V相中之質傳，就L相中 Kcx K 不同情況說明如右 ci cL1 ci cL1 cLi NA1≠NA2 K=1 K>1 ci ci cLi cLi cL1 cL1 K<1 K<1

  6. 輸送現象 Unsteady-state Transfer& Equilibrium Distribution Coefficient K (平衡分配係數)

  7. 輸送現象 透過介面在某相中，傳向無限遠之不穩定質傳與熱傳（Fig 5.3-3） 無限大

  8. 輸送現象 透過距離2x1兩介面在某相中，傳向中心之不穩定質傳與熱傳（Appendix F）p.662 2x1 F.4

  9. 輸送現象 Example -1 Diffusion in a slab of Agar Gel • A slab of 5.15wt% agar gel is 10.16mm(2x1) thick and contains urea (0.1kgmole/m3) • a) t=10h, x=5.08mm&x=2.54mm,find c=? • b) 2x1=5.08, t=10h, x=2.54mm,find c=?

  10. 輸送現象 Example -2 Diffusion in a Semi-infinite slab • A very thick slab contains A (c0= 0.01kgmole A/m3). The front face is exposed to a flowing fluid (c1= 0. 1kgmole A/m3, kc= 2*10-7m/s .K=2.0) • a) t=3*104s, x=0mm & x=0.01m,find c=?

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