CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > FLUENT > Fluent Multiphase

Why a different enthalpy of water is used in the tutorials?

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree1Likes
  • 1 Post By yun_cn

LinkBack Thread Tools Search this Thread Display Modes
Old   November 2, 2017, 04:35
Default Why a different enthalpy of water is used in the tutorials?
New Member
Yun MO
Join Date: Aug 2016
Posts: 5
Rep Power: 9
yun_cn is on a distinguished road
Hi, Fluenters,

When I mimic the Fluent Tutorial: Modeling Nucleate Boiling Using Ansys Fluent and the Tutorial : Heat and Mass Transfer with Mixture Model and Evaporation-Condensation model, I found that I could not find a reason why the latent heat (= enthalpy of saturated vapor - enthalpy of saturated liquid)  of water is different to that in the thermal property tables of saturated water what we are using.

In the Fluent Tutorials, saturated water and vapor are set as follows.

Reference temperature:298.15K
For saturated water: h = 0 J/kg.mol
For saturated vapor: h_g = 2.992325e7 J/kg.mol

However, I found they are as follow from the handbook, for an example, 2001 ASHRAE Fundamentals Handbook (SI),

h_f = 104.83 kJ/kg, 9
h_g=2546.5 kJ/kg
Latent =h_g h_f = 2526.5 104.83 = 2441.67 kJ/kg = 2441.67 * 18.015(water molecular weight, kg/kmol) =43986KJ/kmol = 4.399e7 J/kmol.

If we set h_f= 0 J/kmol, h_g = h_f + L = 0 + 4.399e7 J/kmol = 4.399e7 J/kmol.

It can see that it totally differs to that in the tutorials.

On the other hand, the saturated properties of water and vapor can be directly obtained from the library in Fluent as follows:
M= 18.015 Kg/kmol
T= 298 K
h_f= -2.858412E+08 j/kmol
h_g= -2.418379E+08 j/kmol

Latent heat =h_g h_f=4.400330E+07j/kmol
Latent hat =4.400e7 J/kmol / 18.015kg/kmol = 2.442592E+06 j/kg

It agrees to the one that I can find in the handbook.

And then why the latent heat of water at 298.15K in the tutorials is 2.992325e7J/kg.mol (that is, 1661KJ/kg, but not 2443KJ/kg)?

And since there is a water library in Fluent, why the tutorials intently set h_f = 0 j/kmol, h_g = 2.992325e7 j/kg.mol?

Why? Where the latent heat (or enthalpy) of water in the tutorials was got?

I asked the support of Ansys Japan but they could not tell the reason.

Could anyone explain why the latent heat in the tutorials is different to the one in the handbook?
Yolanda likes this.
yun_cn is offline   Reply With Quote


enthalpy, latent heat, saturated water, tutorial

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Setting the height of the stream in the free channel kevinmccartin CFX 12 October 13, 2022 21:43
Ricardo Wave Water Injection Simulation randomspeedfreak Main CFD Forum 0 April 2, 2015 12:20
How to model Salinity, density, fresh water & sea water grayback87 FLUENT 3 December 30, 2014 02:00
Constant velocity of the material Sas CFX 15 July 13, 2010 08:56
Liquid water, gaseous water and another gas Andy FLUENT 1 May 22, 2006 08:51

All times are GMT -4. The time now is 21:14.