Engineering Thermodynamics
A closed system is one in which

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

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

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

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