傳熱傳質(zhì)基本的理論

1、 傳熱傳質(zhì)基本的理論 （Heat and Mass Transfer Theory）第三章 傳質(zhì)理論3-1 概述 在材料加工、化工、冶金、低溫工程、空間技術等領域中，質(zhì)量傳輸是很重要的過程。 許多加工工藝的單元操作，如加熱、溶解、焊接、表面熱處理等，也都涉及傳質(zhì)過程。345(1) 濃度梯度引起的分子擴散(2) 溫度梯度引起的熱擴散(3) 壓力梯度引起的壓力擴散(4) 除重力外的其它外力引起的強迫擴散(5) 強迫對流傳質(zhì)(6) 自然對流傳質(zhì)(7) 紊流傳質(zhì)(8) 相際傳質(zhì)6傳質(zhì)現(xiàn)象的八種形式:R.B. Bird, Theory of Diffusion, Adv. Chem. Eng., 195

2、6 (1) 170.73-2 質(zhì)量傳輸方式、濃度、物質(zhì)流89101112131415163-3 Fick第一定律1718192021223-4 Fick第二定律23243-5 固體中的擴散和擴散系數(shù)2526272829303132（4） 化學勢驅(qū)動下的擴散系數(shù)33343536（5） 溫度對擴散系數(shù)的影響37383-6 流體和多孔介質(zhì)中的擴散和擴散系數(shù)394041424344The origin of dispersion（彌散）Physically, a non-constant advecting velocity occurs in porous media with disturbanc

3、e near pore wall. Parts of the material are carried faster than others, so that the distribution gets stretched and distorted. This results in sharp gradients perpendicular to the flow, which diffusion can then iron out. The combination of a shearing advection velocity with weak diffusion can lead t

4、o quite effective mixing.多孔介質(zhì)中的彌散傳質(zhì)45Theoretical analysesVolume averageIntrinsic averageMicroscopic governing equationsSchematic of a porous media46Volume-averaged macroscopic GEs 47Subtracting the volume-averaged equations from the microscopic equations reads the spatial deviation: where48Note the

5、relationship(*)49Thus the last equation can be simplified as:Equation (*) now can be written as:can be written as a function of Ddiswhere Ddis can be determined.503-7 對流傳質(zhì)5152533-8 相際傳質(zhì)54The solubility of gas in the liquid 55自由度 F 是當系統(tǒng)為平衡狀態(tài)時，在不改變相的數(shù)目情況下，可獨立改變的因素（如溫度和壓力）。56575859606162638.1. 平衡溶解度6465這三個表達式的本質(zhì)是一致的6667亨利定律的適用范圍：(4) 溶質(zhì)遵守亨利定律；而溶劑遵守 拉烏爾定律。688.2. 相平衡與吸收過程的關系698.2. 相平衡與吸收過程的關系708.2. 相平衡與吸收過程的關系