Thermodynamics? number crunching thermal conductivity

In summary, the conversation is about calculating heat transfer from polyethylene pipe, with the speaker seeking clarification on the formula and units to use. The speaker is working with a TC of .46 W/(m.*C) and a wall thickness of .120 inches, and is questioning whether the units are correct. They are looking for confirmation that the calculation of k/d results in 2.22 BTU.
  • #1
fastline
25
0
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?
 
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  • #2
fastline said:
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:
[tex]Q=\frac{k}{d}ΔTA[/tex]
where d is the wall thickness.
 
  • #3
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?
 
  • #4
fastline said:
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?
 
  • #5


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.
 

1. What is thermodynamics?

Thermodynamics is a branch of physics that deals with the study of heat and its relationship with other forms of energy, such as work and temperature. It also encompasses the laws governing the behavior of these systems and the processes that occur within them.

2. How is thermodynamics related to number crunching?

Thermodynamics involves a lot of calculations and mathematical models to analyze the behavior of different systems. This includes using number crunching techniques to solve equations and determine properties such as temperature, pressure, and energy.

3. What is thermal conductivity?

Thermal conductivity is a measure of a material's ability to conduct heat. It is defined as the amount of heat that is transferred through a material of unit thickness and unit area in a unit time when there is a unit temperature difference between the two sides of the material.

4. How is thermal conductivity important in thermodynamics?

Thermal conductivity plays a crucial role in thermodynamics as it helps determine the rate of heat transfer in a system. This is essential in understanding and predicting how a system will respond to changes in temperature and other factors.

5. Can thermodynamics be applied to real-world situations?

Yes, thermodynamics has numerous practical applications in various fields such as engineering, chemistry, and biology. It is used to design and optimize systems and processes, such as power plants, refrigeration systems, and chemical reactions, to name a few.

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