×
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

Heat Loss from uninsulated sch 80 CPVC

Heat Loss from uninsulated sch 80 CPVC

Heat Loss from uninsulated sch 80 CPVC

(OP)
I am trying to determine the heat loss from a 2-1/2" schedule 80 CPVC pipe that is carrying a 27 deg F solution of 30% propylene glycol. The pipe is inside a 70 deg F plant.

I found a similar thread (thread391-289057: Heat loss from underground pipe (insulated versus non insulated)) but it's focus was on buried pipe and no mention of glycol. I have seen the formulas where the heat loss is calculated based on pipe surface temperature, ambient temperature, wind speed, etc

In my case I don't know the surface temp, just the fluid temp inside. It's probably fair to assume zero wind, since we are inside the plant.

Can anyone point me to a reference or provide a formula?

RE: Heat Loss from uninsulated sch 80 CPVC

It's actually heat gain, right, since your fluid temperature is less than the ambient temperature?

This is still essentially a convection and possibly radiation HT problem. The surface temperature is not a priori required. In the most expanded case, there are at least 3 simultaneous equations using T.fluid, T.insidewall, T.outsidewall, T.ambient. Since energy is conserved, there is only one set of temperatures that satisfies the three equations:

Convective/conductive transfer from innerwall to fluid
Conduction from outerwall to innerwall
Convection/radiation from ambient to outerwall

You may need to throw in something to deal with the temperature increase as the fluid flows along the pipe, i.e., some sort of temperature differencing. Length of piping and flowrate will directly affect the solution. You could assume a worst-case heat gain by keeping the fluid temperature constant.

TTFN
FAQ731-376: Eng-Tips.com Forum Policies

RE: Heat Loss from uninsulated sch 80 CPVC

It is an "insulation" style calculation ([link Pipe Insulation]http://www.raeng.org.uk/education/diploma/maths/pd...[/link]). Once you know the layer temperatures, you need to apply the glycol mixture specific heat to get a temperature rise. Basic thermodynamics

RE: Heat Loss from uninsulated sch 80 CPVC

If the glycol is flowing , then the inside temperature is close to 27 degrees. Now the problem is to first find the temperature at the surface which can be done iteratively. First assume the temperature is 27, get the radiation and natural convection coefficients like
hr=.173[(T0/100)^4-(Ts/100)^4]/(T0-Ts) for radiation
A good estimate of convective coefficient is
hc=0.27[(T-Ts)/D]^.25
D=2.87/12 for 2.5 schedule 80
Now the conductance across the cpvc wall is
k/l=0.11/lw
lw=wall thickness in feet
I got
k/lw=4
and
hr =0.66
and
hc =.988

hr+hc=1.65
k/l=4=4
From this first iteration get the surface temperature
(T0-Ts)/(T0-Ti)=(70-Ts)/(70-27)=(1/(hr+hc)/[1/(hr+hc)+l/k]
This gives the new Ts from which you get the new hc,hr .
You probably need one more iteration to get an accurate Ts


Your final overall coefficient of conductance would be the
reciprocal of 1/(hr+hc)+k/lw

Note: strictly speaking l/k is only an estimate of the resistance through the wall but is accurate for lw/D small, the case here

RE: Heat Loss from uninsulated sch 80 CPVC

Correction

Should read

Your final overall coefficient of conductance would be the
reciprocal of 1/(hr+hc)+lw/k

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