A25 mm diameter high voltage power line has an electrical resistance of 10-4 ohm/m, and is transmitting current of 1000 a.

if ambient air at temperature tinfinity =10 degreec and wind freestream velocity is uinfinity = 10 m/s is in cross-flow over the power line (assume it to be a long copper cylinder), what is its surface temperature?

[assume a temperature of 300k while looking for properties of copper and air in heat transfer property tables]

Explanation:

For this case we need to make some assumptions. For example the properties not change in the time. steady conditions and that we just have conduction on the cylinder creating radial conduction.

The next step would be calculate the properties for each element at 300K using th table A.4

Air

Copper

, k=400 W/mK[/tex]

Solution to problem

Now in order to solve the problem we can use conservation of energy assuming a control volume of unit length, and we have the following equation:

And we have this :

From the correlation of Churchill we can find like this:

And if we replace we got:

Then we can find the value for

And finally we can calculate the surface temperature with this formula:

And replacing we have:

answer:

put more,