×
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

Wall temperature

Wall temperature

Wall temperature

(OP)
Hello all!
I am intrested to know how to calculate a wall temperature in a heat exchanger. Both temperatures on the different sides of the wall are known. Is it the mean temperature?

Thanks,
Mask

RE: Wall temperature

You need to calculate the film coefficients (including the fouling coefficients as applicable) in the exchanger either on an overall basis or for a specific location(s) in the exchanger. Given the amount of heat being transferred either on an overall basis or a specific location, you then can calculate the tube temperature.  Basically, you have the overall bulk temperature difference and overall heat transfer rate.  Then, you calculate the required dT across each 'resistance' layer (either film, fouling or tube wall though the latter is typically very small) to achieve the same heat transfer as that is constant for each layer.

If the heat transfer coefficient on one side is much larger than the other and is clean (eg. condensing steam inside a coil in a water bath), then the metal temperature would be pretty close to the saturation steam temperature since the condensing steam heat transfer coefficient is much larger than the natural convective heat transfer coefficient from the coil to the water bath.

If you have a copy of the TEMA standards, I believe they go through this calculation.

RE: Wall temperature

In fact, there is a temperature profile within the wall, which you can characterized by both wall surface temperature. Being the heat flux constant across the fluid and wall, one can derive  (plane geometry)

 h1.A.(T1-Tw1) = k.A/e.(Tw1-Tw2)= h2.A.(Tw2-T2)

Notation seems to be typical....

hence, being

Tw2= h1/h2*(T1-Tw1) + T2,

the expression for Tw1 can be found:

            (e/k+1/h2).T1 + T2/h1
 Tw1  = ---------------------------
               1/h1 + 1/h2 + e/k
So, the wall temperature is higly dependent upon the relative heat transfer coefficient. Here, if the heat transfer coefficient for Side 2 is 100 (water) and 10 for Side 1 (Oil), the wall temperature will be closer to the side 2 Bulk temperature.
Regards    


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