Condensation with Fluent 19.1
 

Hi Dear CFDonline members,

I want to simulate condensation over tubes/plates in plate-fin exchanger.

My case is:

Inlet Air : 318.15 K DB - %92 RH - 1.837 m/s (homogeneous multiphase flow, same velocity for whole mixture)

Known experimental values for outlet : 314.5 K - %100 RH

From psychrometrics : Dew point : 316.5 K
Volume Fraction : water vapor : 0.0871 and air : 0.9129 (i found)

My Humid air components are;

Primary Ph : Water Vapor (density : ideal gas)
Secondary Ph.1 : Water Liquid (density : constant)
Secondary Ph.2 : Air (density : ideal gas)
Other properties constant.

My setup is :

Steady State

Eulerian Multiphase
Evaporation-Condensation
Heat Tr. Relation : all of them ranz-marshall
Mass Tr. From Ph : water liquid To Phase : water vapor
Lee Model
Implicit

Flow
Viscous - K-Epsion - Enhanced Wall Treatment

BC's:

Velocity Inlet : Gauge pressure : 0
Velocity for air&vapor : 1.837 m/s
Vol. Fr for vapor : 0.0871
Vol. Fr for air : 0.9129
Velocity for water : 0 m/s
Vol. Fr for water : 0

Cold Wall : Temperature : 303.15 K

The other walls adiabatic : convection : 0

Pressure Outlet : Gauge pressure : 0
From neighboring cell

I have 2 problem :

1. As we know, after saturation temp. density of water vapor must decrease with decreasing temperature. Outlet density of water vapor must be lesser than inlet density.

But it is not in my model.

2. According to ideal gas relations at 101325 Pa pressure, 318.15 K - %92RH water vapor has density of 0,06 kg/m3 but fluent calculates 0,69 kg/m3!!

how can i solve these problems?

Please help friends..

is there anyone who can give ideas?

I'm not sure if I can help you but I am working on the simulation of humid air in counterflow heat exchanger.

I'm using the VOF model, my primary phase is water and my secondary phase is a mixture of air with water vapor, using species transport.

I've written an UDF that computes the saturation temperature for each cell in function of the cell water vapor content. It is needed for the Lee model to work the saturation temperature is not constant over the domain.

I hope this helps.

thank you for your reply alex2293.

do you have trouble with density of district phases?

which combination of phases (primary-secondary) im giving volume fraction for vapor and dry air.. when the calculation started, my water vapor density calculated wrong..

i think if i can solve this, i can handle this simulation..

what is your setup can you write detailed?

i would like to compare with mine to find any wrong choice..

Did you find solution of the problem? :confused: :confused: :confused:

Hi, can u share your UDF? I trying to simulate condesation of water from wet air in heat exchanger.