Temperature rise when chilling stops

[pterridactyl]

Hi! Heat Transfer has never been my strong suit, so I need some help calculating how long it will take cooling water to rise to a certain temperature once all chilling ability is lost.

I have a closed loop water system that is cooled via a set of chillers. If all chillers are turned off at once, but water is still flowing, I need to figure out (in simple terms) how long will it take the water in the circuit to rise to a certain temperature.

I know:
- Flow rate: 15 kg/s
- Temperature starting points
Chiller outlet temp: 5degC
Water temp entering process: 6degC
Water temp exiting process: 10degC
Chiller inlet temp: 11degC
(Basically, water warms 1degC for each trip to/from the chillers)

Need to know:
Once chillers are turned off, how long until cooling water temp rises to 45degC

Other:
Ignore thermodynamics of passing through water pumps
Ambient air temperature will be hotter than comfortable room temperature
Make any other simplifying assumptions necessary

Any bright ideas?

Thanks in advance for your help!

Best,
Terri

 

[Latexman]

Sounds like homework Terri. We don't do homework for you. That's against site policy.

It looks like there is some missing information. Do you have the mass or volume of the cooling water?

Good luck,
Latexman

 

[pterridactyl]

Thanks, Latexman.

This is not a homework assignment. I have been out of college longer than I'd like to admit publicly

I am currently working for a large contracting company and have recently been put on a contract that deals with conducting risk assessments on chemical facilities. Right now, we are looking at the consequences of losing a portion of HVAC functionality, including a certain bank of chillers. The goal is to come up with an SOP for how much time the operators should wait until they initiate a controlled shutdown of the process.

Sorry to have omitted mass/volume from my first post! The cooling water system is about 630 kg total.

 

[IRstuff]

So 42s per round trip, assuming there's no reservoir. 6°rise per trip, assume everything's at 11° --> 34°rise to 45°, so 6 trips --> 252 s --> about 4 minutes. Probably a bit longer than that, since it's unclear what the chiller does to the temperature when it's just been turned off.

YMMV


TTFN
faq731-376

 

[pterridactyl]

Thanks much, IRstuff! This is exactly the simplified calculation I needed. Will have to dig out my Heat & Mass Transfer text tonight and brush up.

Terri