. A long 10-cm-diameter steam pipe whose external surface temperature is 110oC passes through some open area that is not protected against the winds. Determine the rate of heat loss from the pipe per unit of its length when the air is at 1 atm pressure and 10oC and the wind is blowing across the pipe at a velocity of 8 m/s. Use the following relation to calculate the Nusselt number.

Explanation:

Let consider that pipe is a horizontal cylinder. The Nusselt number is equal to:

, for .

Where is the Rayleigh number associated with the cylinder.

The Rayleigh number is:

By assuming that air behaves ideally, the coefficient of volume expansion is:

The cinematic and dynamic viscosities, thermal conductivity and isobaric specific heat of air at 10 °C and 1 atm are:

The Prandtl number is:

Likewise, the Rayleigh number is:

Finally, the Nusselt number is:

this could be newton#'s law of cooling. the cooling curve is exponential