Contact US

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!

*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

Time to heat up material in a pipe

Time to heat up material in a pipe

Time to heat up material in a pipe

Hello All,

We have a water line that we are looking to bleed down every time it gets up to a temperature set point from the ambient temperature of the room. I am trying to calculate how long it will take to reach that temperature so I can estimate how much water we would bleed off in a day.

The line is 100 ft of 0.5" NPS Sch 40 carbon steel piping, uninsulated. In the summer, the water is typically 80-90 F and the room temp is 125. The temperature set point for bleeding is 120F.

Thanks for any help you can provide.

RE: Time to heat up material in a pipe

You have a pipe full of water in a hot room.

When the water gets warm you "bleed" it. To where? The drain?

Then fill it up again.



Just empty it and leave it empty. Save you time, save some water.

RE: Time to heat up material in a pipe

This souds very similar to this recent post https://www.eng-tips.com/viewthread.cfm?qid=442968

At an end difference of only 5F, I think it will take a loooooong time / never to get to your set point as heat flux is governed in part by delta T

It is though still a variable heat flow so you need to do this in steps of proabably 5F to get total time.

I also wonder why though....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Time to heat up material in a pipe

How about a P + I thermostatically controlled continuous bleed @ 120°F or ~49°C? Once calibrated, the time constant would be factored out.


"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: Time to heat up material in a pipe

It will bleed to the cooling tower. The reason we are bleeding it is it is for a safety shower, so the water has a max temp for safety reasons.

RE: Time to heat up material in a pipe

You'll have to do a time step analysis on a spread sheet. So the water is stagnant within a small pipe which are heated in a hot room. The analysis will take on the form of energy entering the pipe equal to the increase of internal energy of the water and pipe. Only consider an incremental length of 1' 5' or 10' since 100' of the pipe is being heated. Also discount the effects of convection within the water as you have a small diameter pipe(Dp). Also discount conduction thru the pipe and the water as both will be assumed at the same temperature which is increasing with time (no temperature gradient). Assuming no forced air movement, therefore, the estimated coefficient of convective heat transfer(Hc) equation was developed as follows: Hc=[0.27 *(Tr-To(t))/ Dp]^0.25 which is referenced in Kent "Power" 12th ed.;pg3-18; To(t) is the temperature of water/ pipe and is time dependent. The general equation is : Hc*A*(Tr-To(t))= ((M*Cv)pipe+(M*Cv)water)*(To(t+dt)-To(t))/dt; The result is T(t+dt)= {[(0.27*pie*Dp*Lp)/ Dp^0.25]/[(M*Cvc)pipe+(M*Cv)water]}*(Tr-To(t))^1.25+T(t))]. Tr room temp; M and Cv are mass and specific heat at constant volume; A is pipe surface area; Lp is the incremental pipe length; dt is the incremental time. BE CAREFUL ABOUT UNITS. I work with English units but you may decide to use Metric. The procedure lends nicely to the use of a spread sheet with the first column as being time and the last being T(t+dt).

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! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close