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# Heat transfer to/from burried oil pipleline

## Heat transfer to/from burried oil pipleline

(OP)
Hello

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 Re0.8 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/hi+ ri/k ln(ro/ri)+(ri/ro·1/ho)-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?

Thanks alot
Roy

### RE: Heat transfer to/from burried oil pipleline

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

### RE: Heat transfer to/from burried oil pipleline

AVOID WASTING OUR TIME
DO NOT DOUBLE POST

I have pretty much given you the same story here,

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?

### RE: Heat transfer to/from burried oil pipleline

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

### RE: Heat transfer to/from burried oil pipleline

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

### RE: Heat transfer to/from burried oil pipleline

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.

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