Two Film Theory

[@pauloromero8894]

The best explanation about two film theory. Congratulation!

[@PLE_LU]

Thank you/Mattias

[@slstats7948]

Nice❤️🤗 From Sri Lanka 🇱🇰

[@saiakash707]

Excellent explanation sir... Thank you...

[@ccchen1013]

thank you so much. This helped me a lot with understanding Two Film Theory

[@PLE_LU]

You're welcome. I hope it helps my students as well :-)

[@ManishaSharma-br7yz]

thank you, sir !! The demonstrative way of teaching is very helpful in understanding the concept.

[@PLE_LU]

You're welcome, glad you liked it

[@ManishaSharma-br7yz]

Sir, I wanted to ask that will you be giving lectures on other topics too other than mass transfer ??

[@PLE_LU]

Currently two of us (Mattias Alveteg, i.e. me, and Per Warfvinge) at our department (www.chemeng.lth.se) are producing videos (for flipped classroom teaching) and we do that within the context of the courses we are responsible for, some of which are given in Swedish and others in English. A part from finishing up with 2-3 more short videos for our course "KETF40 Mass transfer in Environmental Engineering" (that also deals with some heat transfer) I have no immediate plans (or time currently) for more videos in English but plan to make some additional videos in Swedish for my course in Separation Processes (KETF10), on flow in porous media and membrane filtration to be more exact. So, the short answer for English videos is unfortunately: not apart from what we already have published on e.g. heat transfer.

[@ManishaSharma-br7yz]

ok sir !! Thanks for your contribution so far :)

[@saeedulhassan3655]

really interesting concept

[@anshumansinha5874]

Is bulk mass transfer different from the interfacial mass transfer? if yes, then how are they related?

[@PLE_LU]

Bulk usually refers to what happens in the main body of a fluid. Interfacial mass transfer, as I understand it, is the mass transfer between two phases. (Compare _inter_national trade, _inter_molecular forces and similar, which is about the relation _between_ different entities and _intra_molecular forces which is the forces between different parts of the same molecule) I'm _not_ an expert in interfacial mass transfer, so I extrapolate a bit here: As soon as you have two or more non-miscible fluids I would guess that you might need really complicated descriptions of the interaction between the phases, and hence really intricate models of interfacial mass transfer. Depending on the situation, I would tend to think that there are situations where it may be meaningful to talk about and model bulk mass transfer in the respective fluid and that there are situations that the term bulk transfer in the respective fluid is a rather useless concept. There might also be cases where it is useful to talk about bulk mass transfer as the combined transfer in the two fluids Consider e.g. your bloodstream. Some of the CO2 in your blood is dissolved in the liquid while some is adsorbed to hemoglobin. There is a bulk transfer of CO2 from your muscles to your lungs and in your lungs there is transport of CO2 from hemoglobin to the liquid and from the liquid to the air in your lungs. (Hopefully you don't have gas in your bloodstream though, but a flow with a gas, a liquid and a solid might happen in industrial applications)

[@anshumansinha5874]

@@PLE_LU yeah, two immiscible phases that are mechanically agitated. hence both phases are mowing as well! In such a case, how shall I approach the problem? Like, the transfer of species is occurring in the vicinity of the 2 phases, and then also there is a transfer of species from the bulk to the interface. Are these two species transfer related? or is the interfacial transfer independent on itself and bulk adjusts to the interface requirement? Thanks

[@PLE_LU]

@@anshumansinha5874 there is no single answer to your question. The degrees of freedom in your question is almost infinite even if we would limit ourselves to nicely behaved rheology. So, my advice to you is to look up the literature for the specific kind of problem you are looking at (and if nothing is published, to look for similar systems) or to seek advice from an expert in the precise field your looking into (whatever that field might be)

[@joanpinol3253]

Thank you very much for sharing! I’d like to ask you how can I find the VOC gas concentration at certain distance from interface (let’s say 1m) knowing only the VOC liquid concentration. This is for a real case. What I thought is to equal the mass transfer equation (Na=kg*(Ca,g-Ca,i), and Na=Dab*(Ca,g-Ca,i)/dz (where z is distance). I don’t really know if I can do that. Thank you!

[@PLE_LU]

Only if the film thickness is thicker than the distance you're interested in. What this means is that you have to be able to assume that there is no turbulence, i.e. that you can describe the instationary problem using the penetration theory or the steady-state problem using Stefan's equation. Note that Stefan's equation and the penetration theory describe slightly different situations. Penetration theory: ∂CA/∂t = D ∂^2 CA/∂z^2 Stefan's equation: nA = -D dCA/dt + CA*nA/ntot OR nA= -D*P/RT * dyA/dt + yA*nA where nA is the molar transport of A (mol/m2,s) In Penetration theory, there is no convection, but there is an accumulation In Stefan's equation there is no accumulation, but there is convection. You can derive Stefan's equation by integrating ∂CA/∂t + v_z * ∂CA/∂z= D ∂^2 CA/∂z^2 In Penetration theory C= C_eq - (C_eq - C_A2)*erf( z /(2 sqrt(D*t) ) where C_eq is the equilibrium concentration infinitely close to the surface boundary, C_A2 the conentration far away and erf the error function. In Stefan's equation, you get n_A=-D/delta *P/RT ln ( (1- yA∞) / (1 - yAeq) ). But since we are steady state, n_A is constant throughout the film and thus the molar fraction y* at a distance z from the surface boundary gives n_A=-D/z *P/RT ln ( (1- y*) / (1 - yAeq) ). Thus 1/delta * ln ( (1- yA∞) / (1 - yAeq) ) = 1/z * ln ( (1- y*) / (1 - yAeq) ) and this equation you can shuffle around to calculate y*

[@PLE_LU]

Sorry, typo. You can derive Stefan's equation by integrating v_z * ∂CA/∂z= D ∂^2 CA/∂z^2. The integration constant happens to be n_A. Integration constants typically have physical interpretations, see Stefan from 3D-equation: kzbin.info/www/bejne/aGmlp4l3nrGLmc0 Penetration theory: kzbin.info/www/bejne/rZmxXoubpdyLnck

[@ahmedtajir6688]

hello professor how can i contact you

[@PavanNayak7]

Thank you!

[@PLE_LU]

You're welcome