PVC vs Copper Pipe Thermal Conductivity

AI Thread Summary
The discussion centers on comparing the thermal conductivity of 100 feet of 4-inch PVC pipe to an equivalent length of copper pipe, considering the surrounding medium of earth or water. The thermal conductivities are significantly different, with copper at 400 and PVC at 0.19, leading to complex calculations involving conduction, convection, and turbulence effects. Turbulence in the air inside the pipe could increase heat transfer by approximately 40%, while water transfers heat four times faster than earth. The conversation highlights the need for specific temperature conditions and additional details about the setup to provide accurate calculations. Overall, the inquiry seeks to determine the equivalent length of copper pipe necessary to match the heat transfer characteristics of the specified PVC length.
Flyfisherman
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Question#1 I would like to compare a 100' length of 4" PVC pipe with air in it surrounded by Earth and/or water. What length of 4" copper pipe would equal a 100' length of PVC?
Question#2 If the inside of the pipe had turbulence what length of non-turbulent 100' PVC 4" pipe would it equal?

I do not know the equations that is why I am on this site. The EngineeringToolBox website states that copper is 400, PVC is .19, Earth is 1.5 and water is .58 thermal conductivity (k). The Earth and/or water surrounding the tube is 65°F Turbulence creates a ballpark of a 40% increase in heat transfer. I also read that water surrounding a tube is 4x times faster at transferring heat than the earth.

I appreciate any help as I am not an engineer.
 
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It is a relatively complex answer to this question. You have 3 modes of heat transfer occurring. Natural convection on the outisde of the pipe due to no motion of the earth/water. This could be ignored if it is assumed that the rate of heat transfer is such that the outer surface of the pipe is kept constant at the given temperature. Secondly you have conduction through the pipes. Thirdly the internal forced convection of the air inside the pipes.

When you ask for the same length do you mean what length of pipe would result in the same net heat transfer to the internal fluid flow?

The rates of heat transfer are going greatly different due to the factor of 1000 difference in thermal conductivities. An initial temperature for the air would be required in order to get the air properties.

Internal forced convection: Q=hAs(Ts-Tair)
Conduction Q=kAs(dt/dx)
 
Yes, what length of copper pipe would equal 100' of PVC pipe?
We will assume the air temperature in the pipe is starting at 90°F.
 
Any others out there that can help on this?
 
Too open ended a question to answer in a few lines . Can you tell us more about the actual set up and what you are trying to achieve with this project ?
 
The air can be stagnate or flow through depending on what is easier to calculate. I am trying to figure out what length of copper pipe will equal x length of PVC pipe. I set 100' of 4" PVC pipe as an example.
 
.115 wall thickness for copper and .237 wall thickness for PVC
 

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