Steam Boilers, Engines, Nozzles and Turbines
The object of producing draught in a boiler is

To discharge the gases of combustion to the atmosphere through the chimney
All of the listed here
To exhaust the gases of combustion from the combustion chamber
To provide an adequate supply of air for the fuel combustion

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Steam Boilers, Engines, Nozzles and Turbines
The relative efficiency is defined as the

Product of thermal efficiency and Rankine efficiency
Ratio of thermal efficiency to Rankine efficiency
Ratio of heat equivalent to indicated power to the energy supplied in steam
Ratio of brake power to the indicated power

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