Thermodynamics? number crunching thermal conductivity

[fastline]

I am working on some basic calcs for heat transfer from polyethylene pipe. My numbers are not working out right so I need a little refresher.

The PE pipe would have a TC of about .46 W/(m.*C). to get to BTU/(hr.ft.*F), I mult by .5779 to get .266.

Assuming 10sf of PE pipe, and let's say a dT of 10*F, how do I arrive at my BTU/hr? Wall thickness of piping is .120" but I am told that does not matter. IIRC, the unit is actualy per sf PER ft so I might actually divide by my thickness which gets me closer at around 2.22 BTU/hr/sf*F of pipe?

 

[Chestermiller]

I am working on some basic calcs for heat transfer from polyethylene pipe. My numbers are not working out right so I need a little refresher.

The PE pipe would have a TC of about .46 W/(m.*C). to get to BTU/(hr.ft.*F), I mult by .5779 to get .266.

Assuming 10sf of PE pipe, and let's say a dT of 10*F, how do I arrive at my BTU/hr? Wall thickness of piping is .120" but I am told that does not matter. IIRC, the unit is actualy per sf PER ft so I might actually divide by my thickness which gets me closer at around 2.22 BTU/hr/sf*F of pipe?

The formula for the heat load Q (BTU/hr) is:
$$Q=\frac{k}{d}ΔTA$$
where d is the wall thickness.

 

[fastline]

I guess I am second guessing the units here. Would you mind applying the math to my above figures? Would this indeed be

k=.266
d=.120

k/d = 2.22BTU?

 

[Chestermiller]

I guess I am second guessing the units here. Would you mind applying the math to my above figures? Would this indeed be

k=.266
d=.120

k/d = 2.22BTU?

You need to use d expressed in feet. How many inches are there in 1 ft?

 

[sardar]

Thermodynamics is the study of energy and its transformations, specifically in relation to heat and work. In your case, you are using thermodynamic principles to calculate the heat transfer from polyethylene pipe. It is important to note that thermal conductivity is a property that describes the ability of a material to conduct heat, and it is typically measured in units of W/(m*K) or BTU/(hr*ft*F). In order to convert from W/(m*K) to BTU/(hr*ft*F), you need to multiply by 0.5779, as you correctly noted.

To calculate the heat transfer in BTU/hr, you need to consider the surface area of the pipe and the temperature difference between the inside and outside of the pipe. In your example, assuming a surface area of 10 square feet and a temperature difference of 10*F, you would need to multiply by the surface area and temperature difference to get the total heat transfer in BTU/hr.

It is also important to consider the thickness of the pipe, as this can affect the heat transfer rate. In your case, you can divide by the thickness of the pipe to get the heat transfer per unit thickness, which is closer to the expected value of 2.22 BTU/hr/sf*F.

In summary, to accurately calculate the heat transfer from polyethylene pipe, you need to consider the thermal conductivity, surface area, and temperature difference, as well as the thickness of the pipe. I would suggest double-checking your calculations and considering any other factors that may be affecting the heat transfer rate. If you are still having trouble, it may be helpful to consult with a thermodynamics expert or reference a thermodynamics textbook for further guidance.