| 查看: 1020 | 回复: 4 | |||
| 当前主题已经存档。 | |||
| 当前只显示满足指定条件的回帖，点击这里查看本话题的所有回帖 | |||
[交流]
【求助】Fick扩散定律的公式
|
|||
|
各位虫友，我在看一篇外文文献中看到其对Fick定律的公式书写如下： J=-ρD(dw/dx) 其中，w是vapor fraction？？ 谁能解释一下w的含义，这个公式和传热学书的公式：J=-D(dρ/dy) 是不是一回事啊？ |
回复此楼» 猜你喜欢
生物医用材料分类与典型应用介绍
已经有0人回复
-
二苯甲酮亚胺的合成
已经有1人回复
-
有机高分子材料论文润色/翻译怎么收费?
已经有128人回复
-
聚左旋乳酸的作用与机制：从胶原再生到组织修复
已经有0人回复
-
可生物降解聚酯聚己内酯的性能分析与发展趋势
已经有0人回复
-
带膜支架的膜和支架之间的结合力如何测试
已经有2人回复
-
西交利物浦大学奖学金博士招生（生物传感或机器学习方向）
已经有1人回复
-
南方科技大学招收金属材料方向博士生
已经有23人回复
-
可降解聚酯材料在医疗器械中的应用趋势与创新方向
已经有0人回复
-
可降解微球如何提升药物精准治疗效果
已经有0人回复
-
静电纺丝膜分层问题
已经有0人回复
leiws
至尊木虫 (职业作家)
木虫浪子
- 应助: 327 (大学生)
- 金币: 20371.5
- 散金: 1872
- 红花: 62
- 帖子: 3920
- 在线: 2134.6小时
- 虫号: 832300
- 注册: 2009-08-22
- 性别: GG
- 专业: 催化化学
5楼2009-08-29 12:50:08
 |
2楼2009-08-19 21:28:27
星竹石
铁杆木虫 (著名写手)
- 应助: 4 (幼儿园)
- 金币: 6658.2
- 散金: 19
- 红花: 12
- 帖子: 1515
- 在线: 304.1小时
- 虫号: 91692
- 注册: 2005-09-06
- 性别: GG
- 专业: 矿物工程与物质分离科学
★ ★ ★ ★
小木虫(金币+0.5):给个红包，谢谢回帖交流
dnp(金币+3,VIP+0):谢谢应助~~ 8-20 13:39
小木虫(金币+0.5):给个红包，谢谢回帖交流
dnp(金币+3,VIP+0):谢谢应助~~ 8-20 13:39
|
Consider a binary mixture of ideal gases 1 and 2 at constant T and P. From a momentum balance describing collisions between molecules of species1 and molecules of species 2, we can obtain ▽p1= - f12 y1 y2 (v1 - v2), (yi - mole fraction) where f12 is an empirical parameter like a friction factor or drag coefficient. For convience, we just define an inverse drag coefficient D12 = P/f12, hence we can rewrite the above equation as d1=▽p1/P=- y1 y2 (v1 - v2) / D12 [VERY IMPORTANT STEP] Here d1=▽p1/P=(1/P)▽p1 is the driving force for diffusion of species 1 in a ideal gas mixture at constant T and P. This is the so called Maxwell-Stefan equation(MS equation), D12 is the MS-diffusivity. , when the systme pressure is constant across the diffusion path, the equation can be simplified to ▽y1 = - y1 y2(v1 - v2)/D12. furthermore, with some simple deduction given in many textbooks, we can get, for a binary mixture of ideal gas where the driving force for diffusion is the mole fraction gradient, the flux will be J1=-c D12 d1 = - c D12 ▽y1 At about the same time when Maxwell and Stefan were developing their ideas of diffusion in multicomponent mixtures , Fick and others uncovered the basic diffusion equations through a large amoutnt of experimental studies , the result of his work is the first Fick's law: for a binary mixture in a isothermal , isobaric system, the rate equation is J1=-c D12 ▽x1 (xi - mass fraction) where D12 is Fick diffusivity D12=D12 Γ where Γ is a thermodynamic factor which has some relationship with activity coefficients. you can find the details about it in phsical chemistry or thermodynamics text books, but for the ideal system Γ = 1 [ Last edited by 星竹石 on 2009-8-20 at 09:14 ] |
3楼2009-08-20 09:12:29
4楼2009-08-22 12:28:35