gas absorption in a falling liquid film we are studying hyrodynamics of the falling film (smooth interface or wavy at different flow conditions) and its effect on heat and mass transfer process.

Can Anybody help in the above topic

Anuj

I`m doing something what is conected with it. I mean a desorber - the second one impotrant part of thermal compressor of absorption device. This problems are very difficoult to simulate becouse of fenomona involved. A maragnoni convection is a standard process which you can find under Fluent. I`m sure you have to write UDFs for solution properties and for mass transfer. What kind of solution do you use?? What kind of absorber (tube in shell?? plate horizontal, vertical??) It will not be aesy to find someone who will help you. Not because people don`t want to help. It`s because it is difficoult and nat many people doing it. So far I know only one project (publicated) about absorption chillers or heat pumps done with FLUENT. Regards Grzesiek

Hello Grzesiek thanks for ur reply in this regard. I'm working on vertical falling film gas absorbers. Here i have used VOF for studying the hydrodynamics of the falling film. Now to check the enhancement of heat transfer due to these wavy film ,i'm using single phase CFD models(FLUENT). for reference, i have used Jayanti et al. paper, Int. J. of Heat and Mass Transfer, Vol. 40 ,page 179-190,year.1997. But in the same i'm not able to correlate the mean flow velocity for smooth films with that of simulations (as is mentioned in the paper). If u get to know anything in this regard ,kindly let me know. Also i have made a UDF to take into account the gas phase. Regards Akanksha

Is your fluid a solution or a single phase? Do you mean a velocity in you simulation isn`t like in real model ? What is you output data? concentration, mass flow of fluid? I wll try to help you but I`m not sure I will be able. Desorber is a little bit different greg

Hello Greg First of all thanks for an early reply. ya i'll explain u in detail. actually i'm using a solution(30% aqueous MEA)for which the viscosity and density are known. to start with i have taken constant density and viscosity. Now using VOF (for CO2-N2 mixture and 30% MEA sol) i have confirmed the formation of waves for very low reynolds number (for liquid). Also i have observed two types of waves , capillary (symmetrical sinusoidal )waves for REL < 20 and roll waves for REL>20 and REL<200. So to study the heat transfer effects, i have used both of these waves separately. Now as per the hydrodynamics study (VOF) an number of these waves were observed down the length of the reactor. So for studying the heat transfer effects and wall shear on velocity profiles, i have extracted only a portion of periodical wave as a test geometry. then using single phase model, the effect of gas mixture is taken by assuming a specified gas shear at the gas liquid interphase of known geometry. and the moving fluid is considered by assuming the reactor wall on the opposite side of the interface to me moving in a direction countercurrent to the liquid flow (called wavy velocity and its value is obtained using force balance on the wave i.e. gravity, interfacial shear and wall shear). the inlet of the liquid and the outlet of the liquid from that wave are assumed to be periodic (as a number of these waves were observed down the reactor length).After doing the simulations, the results were compared with jayanti's result (Int. J. Heat and Mass Transfer, page 179-190, year-1997). in his paper,a zero shear is assumed, so i also did the same, but i am not able to know how the mean flow velocity is calculated in his paper and how through simulations (where wave velocity is used) the mean velocity can be correlated to what is observed for smooth films. if u can kindly help me in this regard and give me some direction, it will be of great help to me. Also if u can tell me ur email id, i can send u my results along with that paper as an attachment. Thanks anyways for spending time on it.

I tried to look for something about absorption on film but I didn`t find anything conected with your problem. I`m sorry. I is too difficult for me. I wish you good luck. Regards Greg

I'm doing the same work now.I am using fluent,but some one said it can't deal with the place without air or fluid,such as the space without vapor,I have tried the mixture model,and now learning UDF,hope for more communion.

Hi Chanchan

Have u tried for single phase models. Elaborate ur work, so that i should also get to know bout ur problem. is it falling film reactors.

Thanks for you reply,my work is also about falling-flim absorption,the strong LiBr solution falls along a vertical plate at a reduced pressure space(such as a absorber),water-vapor was injected from top and absorbed by the film,my work is to model the heat and mass transfer process.There's not chemical reaction.Does one phase model can deal with the space without vapor.I will try.

It is interesting what u are doing. Are you going to introduce your own solution properties ora u are going to use internal lows prowided by Fluent (like volume weight mixing low for density (as I remember), mixing low for specific heat etc). I`m asking because there is no many (I never found) mathematic equations described thermal conductivity, diffusion coefficient etc. For desorber this is difficoult for me to establish that values (doesn`t mention about mass transfer )

Oh,I got to fluent several months before,much works are on the stage of plan,now I use the low within fluent,may be use UDF when needed,I don't find the heat transfer coefficient,may be it is not given,I want to calculate the value of the whole system with others I can get,sorry that I can't help you now,I will work on it and may be this paper can help( Fujita I, Hihara E. Heat and mass transfer coefficients of falling-film absorption process. Int. J. Heat and Mass Transfer, 2005, 48: 2779-2786),good luck!

So I wish you good luck too Thank you for paper. Greg

[shoushibo]

hi , Akanksha, have you succeeded in the simulation of gas absorption in falling liquid film? what i am doing is simular with you. can you give me some advice on mass transfer across the interface?

[mkt1363]

Dear all,

I am trying to simulate CO2 absorption through interface in an absorption column with a falling liquid film and countercurrent gas flow. I have problem to write udf for absorption, could anyone help me in this case ?

Thanks