Chemistry
Chemistry
Problem
A gas turbine operates at steady state. Hot compressed air enters the turbine, cooler expanded air leaves, and the turbine casing is well insulated so that any heat transfer with the surroundings is negligible. Classify the turbine as an open, closed, or isolated system and state whether the entropy within the turbine (control volume) is guaranteed to increase, decrease, remain constant, or cannot be predicted without additional information during steady operation. Briefly justify your answer.Intuitive explanation
A turbine is an open system because mass flows in and out across its boundaries. For entropy within the control volume at steady state, you need to distinguish between the entropy generation (which is always positive for an irreversible process) and the net entropy change of the gas inside the turbine itself. Since the turbine operates at steady state, the amount and properties of gas within the control volume don't change over time—so the entropy stored there remains constant, even though entropy is generated by irreversibilities like friction and turbulence.
Intuitive explanation
A turbine is an open system because mass flows in and out across its boundaries. For entropy within the control volume at steady state, you need to distinguish between the entropy generation (which is always positive for an irreversible process) and the net entropy change of the gas inside the turbine itself. Since the turbine operates at steady state, the amount and properties of gas within the control volume don't change over time—so the entropy stored there remains constant, even though entropy is generated by irreversibilities like friction and turbulence.