Steam Boilers, Engines, Nozzles and Turbines
In regenerative air preheaters, the heat is transferred

Heat is transferred by bleeding some gas from furnace
From heating an intermediate material and then heating the air from this material
From a metal wall from one medium to another
By direct mixing

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Steam Boilers, Engines, Nozzles and Turbines
The efficiency of a boiler is defined as

None of these
Ratio of heat actually used in producing steam to the heat liberated in the furnace
Ratio of the heat liberated in the furnace to the heat actually used in producing steam
Ratio of the mass of steam produced to the mass of total water supplied in a given time

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