Flow Through Ducts
Friction is present in all real flow passages. There are many practical flow situations where the effect of wall friction is small compared to the effect produced due to other driving potential like area, transfer of heat and addition of mass. In such situations, the result of analysis with assumption of frictionless flow does not make much deviation from the real situation. Nevertheless; there are many practical cases where the effect of friction cannot be neglected in the analysis in such cases the assumption of frictionless flow leads to unrealistic influence the flow. In high speed flow through pipe lines for long distances of power plants, gas turbines and air compressors, the effect of friction on working fluid is more than the effect of heat transfer ,it cannot be neglected An adiabatic flow with friction through a constant area duct is called fanno flow when shown in h-s diagram, curves ,obtained are fanno lines. Friction induces irreversibility resulting in entropy increase. The flow is adiabatic since no transfer of heat is assumed.
A steady one-dimensional flow in a constant area duct with friction in the absence of Work and heat transfer is known as “fanno flow”.
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