Change in temperature of air by friction is negligible as compared to heat transfer from pipe walls. Do a simple heat balance with initial air conditions and then heat exchanged in the pipes at your required conditions. If it is a pneumatic conveying system don’t forget the addition heat transferred due to the product addition in the system. ■

If you are looking at the problem from thermodynamics side then it will depend on what kind of expansion it is Isothermal / adiabatic expansion???? ■

Surely it's all down to the Gas Laws. If you know the numbers to put in, the answers fall out.

http://en.wikipedia.org/wiki/Gaslaws ■

dear usama,

As already explained by mr Mantoo and designer, you have to calculate the heat balance using the gas laws together with energy transfer with the environment,

First of all, gas cools down when expanding (external energy is delivered at cost of internal energy)

Due to friction losses at a certain speed, external energy is transferred into heat, which is flowing back into the gas, causing a temperature increase.

Which effect is the greatest determines whether the gas cools down or heats up.

Then there is heat exchange through the pipewall and between the gas and the eventual product that is carried.

This calculation needs to be executed for a pipe length dL and then integrated over the complete length.

A book, describing thermo dynamics of gases must supply the necessary theory.

success ■

I use a method for calculating the heat loss based on the attached document

Attachments

heat tranfer (DOC)

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Originally Posted by tathadream

I use a method for calculating the heat loss based on the attached document

Interesting paper; but rather elaborate for the topic. ■