Engineering Thermodynamics
A closed system is one in which

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
Mass crosses the boundary but not the energy

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Engineering Thermodynamics
Mond gas is obtained by

Passing air and a large amount of steam over waste coal at about 650°C
Carbonisation of bituminous coal
Partial combustion of coal, coke, anthracite coal or charcoal in a mixed air steam blast
Passing steam over incandescent coke

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