| 查看: 1082 | 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
生物医学材料前沿科普：低密度、高孔隙率的“多孔微球”核心技术与应用全景
已经有1人回复
-
湖南工业大学周贵寅组招生物医学工程（学硕07、08都行）、生物与医药（专硕08）硕士生
已经有0人回复
-
有机高分子材料论文润色/翻译怎么收费?
已经有131人回复
-
湖南工业大学周贵寅组招生物医学工程（学硕07、08都行）和生物与医药（专硕08）硕士生
已经有0人回复
-
考研求调剂
已经有0人回复
-
2026年中南民族大学化学与材料科学学院调剂公告
已经有40人回复
-
武汉纺织大学招生物材料、化学、高分子相关专业硕士生
已经有0人回复
-
武汉纺织大学招生物材料、化学、高分子相关专业硕士生-另有少量士兵计划可咨询
已经有0人回复
-
[武汉纺织大学]材料学院[姜伟团队名称]课题组-2026年硕士研究生调剂信息
已经有0人回复
-
中国科学院·过程工程研究所·招聘海内外高层次人才---过程所“百人计划”
已经有0人回复
-
中国科学院·过程工程研究所·招聘海内外高层次人才---过程所“百人计划”
已经有5人回复
5楼2009-08-29 12:50:08
 |
2楼2009-08-19 21:28:27
★ ★ ★ ★
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
