The properties at film temperature will be taken into the consideration during the phenomena of either boiling or condensation. Film temperature is the average temperaure, at which properties of fluid likedesitty, dynamic viscosity, thermal conductivity, temperature coefficient, latent heat of evaporation, are evaluated

For condensation phenomena, generally McAdams equation is used      

Hello guys,

ANSYS Fluent have those capabilities, here some info that may be of your help. The first two links are the theory guide and some overview of the model used and the last one is a tutorial I found online.

http://www.arc.vt.edu/ansys_help/flu_th/flu_th_sec_mp_evap_cond.html

http://www.tandfonline.com/doi/abs/10.1080/10407790.2014.915681#.VFIXyPnF8wA

http://www.cae-club.ru/sites/default/files/users/files/2053/02-boil.pdf

Yes it can

For phase change model either you can use evaporation model, already available in FLUENT or write your own UDF for phase change simulation. Most probably available evaporation of FLUENT is not going to give you satisfactory result due to its limitations. So its better to go for UDF, you may get lot of ideas from UDF manual of fluent. One more option is boiling model available in FLUENT 14.0, that you may also try.

Thanks so much guys, currently, I'm writing my own UDF to do this simulation. I can simulate the evaporation easily. But I didn't see any condensation even after 200s transient calculation. Should I change the water vapor density to "ideal gas"? Or check my UDF?

Hello! How your progress on this issue?

I too can simulate the evaporation easily. But I did not see any condensation. :(

Hello Somnath

Please can you tell me what is the meaning of the  (LAT_HT 2455e3 )?

which equation is this:

m_dot_v = 0.1*C_VOF(cell, sec_th)*C_R(cell, sec_th)*fabs(C_T(cell, sec_th) - T_SAT)/T_SAT;

can you tell me each part of it please?

Dear Hayder, LAT_HT is that the latent heat of evaporation and condensation in related problem. Here value of latent heat is 2455000 J/Kg.

The equation that you have written here is  the mass source in a phase change problem which is based on "LEE evaporation and condensation model" . Meaning of terms are:

C_VOF(cell,sec_th)  :     volume fraction of secondary phase in a cell which is denoted by alpha in fluent.

C_R(cell, sec_th)   :     density of secondary phase in a cell

C_T(cell, sec_th)     :      temperature of secondary phase in a cell

I suggest you to go through fluent udf manual and fluent theory guide for get more details. Search about evaporation condensation model in fluent.

Thanks & Regards

R K Pal

NIT Rourkela, India 

thanks Ram for your answer.

if I use another solution rather than water. what should I change in this UDF?

Hiii, You have to change value of latent heat according to fluid used by you in simulation. In your udf code pri_th and sec_th refers primary phase and secondary phase material defined by you in fluent setting during simulation like:

C_R(cell, pri_th)   : density of primary phase

C_R(cell, sec_th)  : density of secondary phase

You have to define primary and secondary phase in fluent setting according to your code.

I suggest you to go through fluent udf manual. No need to read entire manual. You have to just see some specific terms:

1. DEFINE_SOURCE

2. Multi-phase macro 

See page numbers 104, 228, 229, 230 and 265 in fluent 15.0 udf manual. I have attached here udf manual.

Thanks & Regards

R K Pal

NIT Rourkela, India 

many thanks Ram

that's helpful. But I have another question, please.

I did CFD modeling of a condensation of water via fluent. why I not get a completely liquid phase adjacent the wall.? I get a low percentage of the liquid there. if you look to the labels of the figures attached, the red color have concentration of the liquid phase for 4.53e-04, which is very low.

regarding to the mesh, I did a very thin layer adjacent the wall

thanks in advance

Hayder

Hi

Yes it is possible, perhaps you have already handle.

https://youtu.be/DTYqKxYLE20

Fluent 14.5 can simulate evaporation and condensation in a closed thermosyphon without programming any UDF ( you should only define your primary and secondery phase than you active evaporation and condensation). You Will find attached an important article in which the author validated VOF + some UDFSs for mass and heat transfer model with the experimentale results.

In this numerical study, and when I use the model in fluent pricising two mass transfer : one from liquid to vapor and the other one from vapor to liquid. The liquid film in the condenser section is not appearing ( I think that Iam doing something wrong ).

Here is my email adress to exchange. Cas files for those who are interested in this work. 

Email: [email protected] 

Sayf din.

@Reza Haghani... You don't need to specify additional energy source term udf. Fluent will take care of the heating and cooling effect by itself. But you need to give the correct latent heat value for your liquid and vapor phase in the materials section. Heat removed = mass evaporated * Latent heat of vaporization 

hi sir will you please give me your udf code?

i am also trying to create code for condensation problame .

@San deep sir, I want to simulate an evaporation model in a horizontal smooth tube.

Currently I m using r22 as primary n secondary phase and I put the properties from REFPROP for saturation temp 278 deg K.

My problems are...where should I put the corresponding saturation pressure ...inlet or outlet or operating pressure?

I am using inlet velocity, outlet pressure and wall temperature (283k plus) as boundary conditions. 

Which multiphase model do u prefer for that?...now I m using mixture model.

Thnx in advance

@Sachin Shinde See attached code , may be beneficial for you. 

Hi

I'm trying to simulate thermosyphon. But when the UDF will read, and I want to run, the following error was printed!

please help

Hi Mehrdad

Remove the gap between the folder name like you did in New folder. It should be Newfolder. It may help.

Best wishes

Mahesh

Dear friend,

I made a UDF of Define source for species.

I first calculate the species and store it in a C_UDMI(when i plot this in fluent it look oke). when i store the C_UDMI to my source and hook it in for species source panel. it doesnot do anuthing. I give a Mesaage statement in the DEFINE_SCOURCE and it dosnot print it. I look like that fluent do not go into the fuction.

do You know maybe why this happen

Dear friends,

I am using the sample udf code ( in the manual) for mass transfer based on saturation temperature for bubble growth, but I am getting the same error as "Mehrdad Zakizadeh" when I initialize. can anyone help me fix this problem?

Thank you in advance.

@ronnie, Dear I am doing problem of evaporation with reacting species. I want to know about your udf. May be i can solve my problem

I am doing the same type of problem i am trying to simulate the micro heat pipe in fluent, basically it is a heat pipe with condensation occurring at one end evaporation at other end and capillary forces due to change in curvature of vapour-liquid interface moves the fluid at corners from condenser section to evaporator and vapour move in central region

I have taken a 1000 micrometer pipe with 300mm of both evaporation and condenser section from both end and leaving 400 in between as adiabatic section

Problem I am facing while simulation is that the liquid is evaporating in evaporation section but not condensing in condenser section i am using the VOF model

I am new into all this any type of help is deeply appreciated, if any one can share the fluent case of evaporation/condensation process it will be of great help

[email protected]

I completed a thesis on ANSYS FLUENT 18 on condensation inside a wickless thermosyphon. The (built-in) Lee model is enough to do the job.

*REMEMBER: Water should be the primary phase! vapor secondary.

I compared completely new UDFs against Lee, also switching between water vapor for primary phases (because calculations are performed in more detail for the secondary phase in VOF, so for condensation you want water to be simulated in more detail, i.e 2ndary = water-liquid). Even so, Lee was proven way better, even when a new UDF completely mimicked the Lee model but structured to fit water as 2ndary!

+However, based on the judgement of Fadhl et al. + Alammar et al. you could add a water density(ρ) and surface tension(σ) UDFs (which are really simple Temp-based equations). For more accurate results.

++For fast results you could do Implicit simulation. The VOF contours will be a mess but it will finish way faster than Explicit. Temp results will be adequate.