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

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

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

Ratio of the mass of steam produced to the mass of total water supplied in a given time
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

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Steam Boilers, Engines, Nozzles and Turbines
In forced circulation type boiler

Feed pump is employed to supplement natural circulation in water wall type furnace
Heating takes place at bottom and the water supplied at bottom gets converted into the mixture of steam bubbles and hot water which rise to drum
Water is converted into steam in one pass without any recirculation
Water is supplied in drum and through down comers located in atmospheric condition it passes to the water wall and rises to drum in the form of mixture of water and steam

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