Heat transfer to/from burried oil pipleline

[friedmanroy]

Hello
Please, your help:

I have real problem of heat tranfer of oil line, I have to solve:
Gasoline flows through a steel pipe line that is burried in the ground. I need to know the exit temp of gasoline in the exit from the pipe.
I know:
Properties of Gasoline
Cp = 2.22 Kj/Kg K
Density = 740 kg/m³
k : 0.15 W/mK
Viscosity= 0.88 cSt (0.88X 10^-6 m²/sec)
µ = 6.512·10^-4 kg/m s
Flowrate = 500 m³/hour=100 kg/sec
V (velocity)=0.76 m/Sec
T inlet of the Gasoline to the pipe = 13 deg C
T of ground= 16 deg C

Pipe properties:
Material : Carbon Steel
Outside Diameter: 20 inch= 0.508 m
Inside Diameter: 19 inch=0.4826 m
k=54 W/mK
Density=7833 kg/m³ (of the carbon steel)
Length of pipeline=2730 meter

How do I solve this?
1) Find Pr number for gasoline:
Pr=µ Cp/k
Pr=(6.512·10^-4·2220/0.15)=9.63
Re= (0.76 ·0.4826/0.88·10^-6)=416,790
Nu=0.029 Re^0.8 Pr ^0.43=2406
Nu=h·D/k
h=Nu k/D = 2400 ·0.15 /0.4826 = 750 W/m²K ( is that for the Gasoline only?)

Now, I think I have to use the follwing, but I am not sure how:
U=(1/h_i+ r_i/k ln(r_o/r_i)+(r_i/r_o·1/h_o)^-1

How do I calculate the the conduction of the ground/soil ? (lets assume that k= 0.5 W/mK for the soil)
Is the method diffrent if the soil(ground) is hotter or colder than the inlet temp of Gasoline?
Please help me find the outlet temp of Gasoline...

Thanks alot
Roy

 

[LittleInch]

Roy,

You seem to be taking this to an extreme for a 3 degree C difference??

You miss out the very important impact of the pipeline coating (I assume it is not bare steel). It is very surprising what a 3mm 3 layer protection has on thermal conductivity. Also I think you need to look at heat transfer and not whatever calculation you propose which I confess I didn't follow.

Years of doing this tells me that for a 2.7 km line, especially for one this size, assuming that there is some sort of anti corrosion coating, your temperature "rise" will be 0.5 to 1 degrees or less.

there are two effects going on here.

You can model this as a steady state heat transfer assuming a constant ground temperature at, say 1m from the pipe. This heat travels through the ground - 1W/m/K is a more realistic figure - This will give you a heat flux per metre of pipe which you can total for the entire length, then work out how much the temperature rise is for you total volume of fluid - it won't be very big.

For larger differences in temperature, in reality there is a transient effect also where the ground gradually heats up or cools down over a period of around 5-10 days of constant flow. A temperature gradient then starts to exist between the outside of the pipe and the "general" ground" I know from readings I've taken that this is a curve which drops off about 1.5m t0 2m from the pipe. However in your case I suspect it will be much smaller.

I have no idea why you are so interested in such a minute change in temperature, given the short line, the variability of soil properties and the variability of soil temperature - there is no such thing as constant ground temperature over a full year. it might not change too much, but change it does.

hope this helps.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BigInch]

AVOID WASTING OUR TIME
DO NOT DOUBLE POST

I have pretty much given you the same story here,

http://www.eng-tips.com/viewthread.cfm?qid=380169

I ALSO ASKED WHY YOU CARE ABOUT A POTENTIAL 3 DEGREE RISE IN TEMP.
Now I can say, Unless you like to waste your own time as well?
Why is it?

 

[LittleInch]

didn't see the second one....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BigInch]

I didn't see the first one.
There is a third as well.

 

[MortenA]

There is a lot of software out there that will do the calculation for much faster. Getting a consult to do the calculation using this software will most likely be cheaper than doing it yourself if you dont have a license/experience for this software.