Can anyone give me some guidance on approximately how much water temperature could increase through an 8-inch metalic pipe (above ground) if the water is coming out of a bore well over a distance of say 4Klm. Outside temperature would be a maximum of 50c (water coming out of bore well would be apprx 30c).
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Water Tempature through Pipe
- Thread starter AWT78
- Start date
LittleInch
Petroleum
Flow rate?
Lying on the surface or on supports with free flow all around the pipe?
Solar radiation or just air somehow?
Any insulation?
Any painting? Colour?
Wind speed assumed ?( increases the heat input into the pipe if above ground )
If the flow is at least 1-2 m/sec, my best estimate without Solar radiation would be 35 to 40C at the end.
If you're getting Solar radiation as well, then it could be higher than 50C.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
Lying on the surface or on supports with free flow all around the pipe?
Solar radiation or just air somehow?
Any insulation?
Any painting? Colour?
Wind speed assumed ?( increases the heat input into the pipe if above ground )
If the flow is at least 1-2 m/sec, my best estimate without Solar radiation would be 35 to 40C at the end.
If you're getting Solar radiation as well, then it could be higher than 50C.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
Hi,
To support effectively provide technical information about the piping /insulation/ wind and of course flow rate.
We cannot read your mind.
Steel pipe, DN 8", water Velocity 1.5 m/s, 30 C, air velocity 3m/s,50 C, emissivity pipe 0.8, no insulation > temperature outlet about 36 C
Pierre
To support effectively provide technical information about the piping /insulation/ wind and of course flow rate.
We cannot read your mind.
Steel pipe, DN 8", water Velocity 1.5 m/s, 30 C, air velocity 3m/s,50 C, emissivity pipe 0.8, no insulation > temperature outlet about 36 C
Pierre
georgeverghese
Chemical
Total exposed surface 2760m2, of which say 70% may be used as effective surface for incident solar radiation. Total Solar radiation S is 900w/m2 max in the infra red. Assume pipe surface absorptivity = 0.8, and water velocity = v.
Over an incremental length dL of pipe traversed, heat absorbed per sec dQ = S x 0.8 x .7 x pi x D x dL
Heat absorbed by Mass of water traversing through pipe per sec, dQ = dL/dt . pi. (D2/4). rho. Cp. dT
Equating the 2 expressions and simplifying, D/4 . rho . Cp. dT/dt = S . 0.56, which can be integrated easily for the total traversal time. So for 4000m at 1.5m/sec, t = 4000/1.5 = 2670secs, and T-30 = 5.8degC, for Cp = 4180J/kg/degC. So T = 36degC. You can adjust the traversal time t if your water velocity is not 1.5m/sec.
Natural or forced convection from hot air to pipe is small at low wind velocity in comparison and neglected.
Over an incremental length dL of pipe traversed, heat absorbed per sec dQ = S x 0.8 x .7 x pi x D x dL
Heat absorbed by Mass of water traversing through pipe per sec, dQ = dL/dt . pi. (D2/4). rho. Cp. dT
Equating the 2 expressions and simplifying, D/4 . rho . Cp. dT/dt = S . 0.56, which can be integrated easily for the total traversal time. So for 4000m at 1.5m/sec, t = 4000/1.5 = 2670secs, and T-30 = 5.8degC, for Cp = 4180J/kg/degC. So T = 36degC. You can adjust the traversal time t if your water velocity is not 1.5m/sec.
Natural or forced convection from hot air to pipe is small at low wind velocity in comparison and neglected.
LittleInch
Petroleum
If this was the opposite way round, 50C inside, 30C outside, I would have estimated in 4 km you would lose a few degrees C. It's a fairly large area to volume ratio.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
LittleInch
Petroleum
Thought it wouldn't be insignificant alright.
So combined should be somewhere between 40 to 45C. Less at night time of course....
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
So combined should be somewhere between 40 to 45C. Less at night time of course....
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
- Thread starter
- #8
georgeverghese
Chemical
HDPE in the Middle East ought to be UV stabilised - carbon black impregnated HDPE. The carbon would have some effect on the assumed solar radiation absorptivity value of 0.8 used in these calcs - adjust parameters in the calc as required.
- Thread starter
- #10
LittleInch
Petroleum
Yes it would reduce the temp, but only d/s the chiller.
If this is HDPE, watch for both thermal expansion - PE is 10 times that of steel and more importantly the allowable design pressure goes down and shouldn't exceed 50C surface temp.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
If this is HDPE, watch for both thermal expansion - PE is 10 times that of steel and more importantly the allowable design pressure goes down and shouldn't exceed 50C surface temp.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
georgeverghese
Chemical
Error in my calc.
"Total Solar radiation S is 900w/m2 max in the infra red."
Of the total, only 50% is in the infrared and capable of heating. Remaining is UV and visible light. So, including a 0.5 multiplier on the RHS to S, temp rise would be 2.9degC and not 5.8degC. Exit temp = 33degC. Note the influence of water flowrate on the exit temp ( lower flowrate = higher traversal time = higher exit temp). So the highest temp you'd get is when water flow is at its minimum. Read the calc carefully and adjust where required to suit your conditions.
"Total Solar radiation S is 900w/m2 max in the infra red."
Of the total, only 50% is in the infrared and capable of heating. Remaining is UV and visible light. So, including a 0.5 multiplier on the RHS to S, temp rise would be 2.9degC and not 5.8degC. Exit temp = 33degC. Note the influence of water flowrate on the exit temp ( lower flowrate = higher traversal time = higher exit temp). So the highest temp you'd get is when water flow is at its minimum. Read the calc carefully and adjust where required to suit your conditions.
Compositepro
Chemical
The entire spectrum is converted to heat, not just IR.
That makes for a long tedious calculation, assuming you can find the spectral absorption
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georgeverghese
Chemical
@Compositepro From what I've read, only IR enables heating when absorbing solar radiation. See the following in the section on infrared light. UV and visible can cause chemical reactions for photosensitive chemicals, but not heating.
From your graph, since reflectance is the complement of emissivity for opaque materials (where transmissivity = 0), we can say, for UV stabilised black HDPE, e = 1-0.1 = 0.9 over the IR wavelength range ( assuming r remains at 0.1 in the far infrared also). And absorptivity is more or less = emissivity for most materials (Kirchoff's Law approximation). And 0.9 inferred from this graph is close enough to the 0.8 value used previously in the calcs.
From your graph, since reflectance is the complement of emissivity for opaque materials (where transmissivity = 0), we can say, for UV stabilised black HDPE, e = 1-0.1 = 0.9 over the IR wavelength range ( assuming r remains at 0.1 in the far infrared also). And absorptivity is more or less = emissivity for most materials (Kirchoff's Law approximation). And 0.9 inferred from this graph is close enough to the 0.8 value used previously in the calcs.
If the visible reflectance is less than 100%, then visible light is absorbed, and that equates to heat; even white PVC is not 100% reflective in the visible, so it will get heat from visible light
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georgeverghese
Chemical
@IR, thanks for that - agreed, something must happen within the opaque material for any light not reflected.
In the chapter on radiation in Perry, it says for polished metals, emittance in the infra red results from free electron excitation, while bound electron excitation dominates at emission in the shorter wavelengths, including within the visible range of 0.4micron to 0.7micron. And the converse must also be true for absorptance I guess.
So temp rise is 5.8degC at 1.5m/sec water velocity even for UV stabilised HDPE pipe.
In the chapter on radiation in Perry, it says for polished metals, emittance in the infra red results from free electron excitation, while bound electron excitation dominates at emission in the shorter wavelengths, including within the visible range of 0.4micron to 0.7micron. And the converse must also be true for absorptance I guess.
So temp rise is 5.8degC at 1.5m/sec water velocity even for UV stabilised HDPE pipe.
Scanning the responses above I did not see any adjustment to the slight increase in internal energy of the water due to friction from the flow in the pipe. The increase in internal energy wont be much but could account for an additional degree or fraction thereof.
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