Engineering Thermodynamics
A closed system is one in which

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

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Engineering Thermodynamics
According to Clausius statement of second law of thermodynamics

Heat can be transferred from low temperature to high temperature source if COP of process is more than unity
Heat can
Heat can be transferred for low temperature to high temperature source by using refrigeration cycle
Heat can

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