Engineering Thermodynamics
A closed system is one in which

Mass crosses the boundary but not the energy
Neither mass nor energy crosses the boundaries of the system
Both energy and mass cross the boundaries of the system
Mass does not cross boundaries of the system, though energy may do so

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Engineering Thermodynamics
The work ratio of a gas turbine plant is given by

(Actual temperature drop)/(Isentropic temperature drop)
(Isentropic increase in temperature)/(Actual increase in temperature)
(Net work output)/(Heat supplied)
(Net work output)/(Work-done by the turbine)

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