×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Determine Glycol Outlet Temperature

Determine Glycol Outlet Temperature

Determine Glycol Outlet Temperature

(OP)
I am trying to find out what the outlet temperature of a 30% propylene glycol solution after it exchanges heat with air through a finned coil.  Here goes the knowns I have:

Glycol Solution Mass/Volumetric Flow Rate (using minimal hydraulic flow of the pump)
Glycol entering temperature (set point on chiller)
Heat capacity of 30% propylene glycol
U Value for the Heat Exchange Coil
Air Mass/Volumetric Flow Rate (design)
Air Entering Temperature (design)

What I'm trying to calculate:
Air Exiting Temperature
Glycol Exiting Temperature

Haven't done a heat transfer calculation like this in a while.  Can I these 2 equations equal:

(m)(Cp)(deltaT) = UA(deltaT log mean)

And solve using excel to get the 2 outlet temperatures (air and glycol)?  Or is there another method for this type of heat transfer calculation?

Thanks in advance.
 

RE: Determine Glycol Outlet Temperature

If I'm reading your post right you know the glycol flow rate and the air flow rate as well as the air inlet temperature and glycol inlet temperature.

Your glycol exiting temperature is linked to the air exit temperature due to the conservation of energy.  I've used Excel as you mentioned, vary the glycol outlet temperature, calculate the air outlet temperature (based on the amount of energy given up by the glycol) and then see if my UAdTlm equation gives me the same amount of energy transferred.

Are you calculating the individual heat transfer coefficients to come up with the overall U or do you have some other way of estimating the U overall?

RE: Determine Glycol Outlet Temperature

On the left side of the equation there is a delt T so you must know the inlet and outlet temperatures of the glycol. Then it is not necessary to use a trial and error procedure to calculate the outlet temperature of the air. You can use one of the thermal effectiveness charts to calculate P, the ratio of the glycol dela T to (glycol inlet temperature -air inlet temperature)     

RE: Determine Glycol Outlet Temperature

(OP)
TD2K - I got the U value from the coil vendor.

Srfish - Can you show me on the internet where one of these charts are?  I have the Process HEat Transfer Book from Donald Kern but can't find a chart in there.

Thanks.

RE: Determine Glycol Outlet Temperature

To use the internet, try using the search term; e-NTU. One site is www,mak.etu but you need to enlarge the charts. TEMA has the charts for counterflow and two shell-and-tube configerations. Process Heat Transfer by Hewitt, etal and Heat Exchanger Design Handbook have the charts.

RE: Determine Glycol Outlet Temperature

If you know the inlet and outlet temperatures of glycol, you can just calculate the outlet temperature of air from the equation (or vice versa).

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources