Heat transfer from copper coil

In summary, the conversation discusses a project involving a copper pipe coil placed inside an acrylic box to pump water and achieve a desired temperature. The goal is to develop a transfer function for the coil's temperature transfer when subjected to different flow rates and water temperatures. The conversation also includes suggestions for estimating the external convection of the coil in different orientations and the recommendation to run tests and develop a correlation for the entire system. There is also a discussion about the difficulties of accounting for variable temperatures along the surface of the coil.
  • #1
vincent28
2
0
Hi,

I am currently doing my final year project in college. I am using a copper pipe which is 8m long with 8.5mm ID and 10mm OD. The pipe is bent into a coil which will be placed inside a acrylic box. The aim is to pump water through the coil to get the box to a desired temperature. At the moment I am trying to characterise the coil. For testing, the coil is left out of the box and is subject to ambient air temperature of ~20 degrees. I need to know the relationship between temperature transfer from the coil i.e. power output from the coil when different flow rates and water temperatures are applied. Any help would much be appreciated. I need to develop a transfer function that can be implemented into a Simulink model.
 
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  • #2
Hmmmm, well, as for the internal convection, you can kind of cheat and find the pressure difference at the inlet and outlet of the pipes for a given flow rate. This can be translated into a Nusselt number.

friction factor = (P_inlet-P_outlet)*(D/L)/(0.5*density*V_average^2)

V_average can be calculated if the flow rate is known:

volumetric flow rate = density*cross sectional area of pipe*V_average

Chilton-Colburn analogy then gives us:

friction factor/8 = Nu/( Re*Pr^(1/3) )

As for solving for the external convection while suspended in either the air or a water tank or whatever, it kind of depends on how the coil is oriented. There are some good correlations for cylinders you could probably apply to the shape of the coil without too much error, but they would not accurately describe the flow inside the coil.

If the cylinder is oriented vertically, you can estimate with vertical plate correlations, use:

Nu = 0.59*Ra^(1/4) for 10^4 < Ra < 10^9
Nu = 0.10*Ra^(1/3) for 10^9 < Ra < 10^13

If the axis of the coil is oriented horizontally, use:

Nu = {0.60 + (0.387*Ra^(1/6))/[ {1+[0.559/Pr]^(9/16)}^(8/27) ] }^2 for Ra < 10^12

These are just a starting point. You'll probably want to run some tests and develop a correction for the whole system under a given flow rate and input temperature (or temperature difference between inlet and ambient). It's a complex system, I'd have to think about how to best treat it, but that's a start anyway.
 
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  • #3
Hi,

Thanks for the reply. What i essentially need for the model is a transfer function that relates input water temperature and flow rate to the coil to heat transfer from the coil per degree difference in input water temperature and surrounding air temperature?

Kind regards
 
  • #4
With variable temperature along the surface, that becomes quite difficult. That's why my final recommendation was to run some tests and come up with your own correlation. Using averaged temperatures you can at least get an idea of the order of magnitude. Especially in the air, isothermal tubing probably becomes reasonable. Submerged in water, that assumption probably won't hold.

If there are major changes to the average tube temperature along the length of the tube, you can assume a variable average temperature along the axis of the wound cylinder.
 

1. How does heat transfer occur in a copper coil?

Heat transfer in a copper coil occurs through conduction, where heat energy is transferred from one molecule to another through direct contact.

2. What factors affect the rate of heat transfer in a copper coil?

The rate of heat transfer in a copper coil is affected by the temperature difference between the coil and its surroundings, the material and thickness of the coil, and the surface area of the coil.

3. Can heat transfer be controlled in a copper coil?

Yes, heat transfer in a copper coil can be controlled by adjusting the temperature difference, using insulation to reduce heat loss, or altering the surface area of the coil.

4. How is heat transfer measured in a copper coil?

Heat transfer in a copper coil can be measured using a thermometer to monitor the temperature change in the coil over time, or by measuring the amount of heat energy transferred per unit time (in watts) using specialized equipment.

5. What are the practical applications of heat transfer from a copper coil?

Heat transfer from a copper coil has many practical applications, including heating and cooling systems, electrical components, and cooking appliances. It is also used in industries such as power generation, refrigeration, and automotive engineering.

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