53) During peak load periods, the best method of controlling compressors is

start-stop motor

constant speed unloader

relief valve

variable speed

Answer is:

constant speed unloader

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54) A centrifugal compressor works on the principle of

conversion of pressure energy into kinetic energy

conversion of kinetic energy into pressure energy

centripetal action

generating pressure directly

Answer is:

conversion of kinetic energy into pressure energy

55) For a compressor, least work will be done if the compression is

isentropic

isothermal

polytropic

somewhere in between isentropic and isothermal

Answer is:

isothermal

56) In a compressor, free air delivered is the actual volume delivered at the stated pressure reduced to

N.T.P. conditions

intake temperature and pressure conditions

0°C and 1 kg/cm2

20°C and 1 kg/cm2

Answer is:

intake temperature and pressure conditions

Explanation:

Free air delivery is the actual volume delivered by a compressor when reduced to the normal temperature and pressure conditions. The capacity of a compressor is generally given in terms of free air delivery.

57) The volumetirc efficiency of a compressor is calculated on the basis of

volume of air inhaled at working conditions

volume of air inhaled at N.T.P. conditions

volume at 0°C and 1 kg/cm2

volume at 20°C and 1 kg/cm2

Answer is:

volume of air inhaled at N.T.P. conditions

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