Mechanical Engineering Quiz # 8

The capacity of a compressor is expressed in

M3/min

Kg/m2

M3/kg

Kg/m3

The stagnation pressure rise in a centrifugal compressor takes place

In the impeller only

In the inlet guide vanes only

In the diffuser and impeller

In the diffuser only

The compression ratio in a gas turbine is

9

4

12

1

The total heat rejected in a reciprocating air compressor is equal to the sum of the heat rejected during polytropic compression per kg of air and heat rejected in the intercooler per kg of air.

False

True

The type of rotary compressor used in gas turbines, is of

Axial flow type

Radial flow type

Centrifugal type

None of these

Which of the following statement is wrong?

The ratio of the volume of free air delivery per stroke to the swept volume of the piston is called volumetric efficiency.

The minimum work required for a two stage reciprocating air compressor is double the work required for each stage.

In a two stage reciprocating air compressor with complete intercooling, maximum work is saved.

None of these

The rotary compressors are suitable for large discharge of air at low pressure.

False

True

When the temperature of air leaving the intercooler, in a two stage compression with intercooler, is __________ the original atmospheric air temperature, then the intercooling is known as perfect or complete intercooling.

More than

Equal to

Less than

Gas turbine as compared to steam turbine

Requires less space for installation

Has less efficiency

Has compressor and combustion chamber

All of these

In a reciprocating air compressor, the compression work per kg of air

Increases as clearance volume increases

Is independent of clearance volume

Increases as clearance volume decreases

Decreases as clearance volume increases

An open cycle gas turbine works on the same cycle as that of a closed cycle gas turbine.

No

Yes

Rotary compressors are used for delivering

Small quantities of air at high pressures

Small quantities of air at low pressures

Large quantities of air at high pressures

Large quantities of air at low pressures

Which of the following statement is correct?

The ratio of the discharge pressure to the inlet pressure of air is called compressor efficiency.

The compression ratio for the compressor is always greater than unity.

The compressor capacity is the ratio of workdone per cycle to the stroke volume.

During isothermal compression of air, the workdone in a compressor is maximum.

The maximum temperature in a gas turbine is

500°C

200°C

700°C

1000°C

Intercooling in gas turbines

Decreases net output and thermal efficiency both

Increases net output and thermal efficiency both

Increases net output but decreases thermal efficiency

Decreases net output but increases thermal efficiency

A rocket works with maximum overall efficiency when air-craft velocity is __________ the jet velocity.

Equal to

One-half

Double

The optimum effective temperature for human comfort is

Same in winter and summer

Higher in winter than in summer

Lower in winter than in summer

Not dependent on season

The highest thermal diffusivity is of

Concrete

Iron

Lead

Wood

The temperature of ammonia after compression in a vapour compression system is

50 to 70° C

None of these

20 to 50° C

70 to 110° C

The wet bulb temperature during sensible heating of air

Remains constant

Decreases

Increases

An electrolux refrigerator is called a __________ absorption system.

Single fluid

Two fluids

Three fluids

Degree of saturation or percentage humidity is

The mass of water vapour present in 1 m3 of dry air

The ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure

The mass of water vapour present in 1 kg of dry air

The ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure.

In case of solids, the heat transfer takes place according to radiation.

Incorrect

Correct

The subcooling in a refrigeration cycle

Increases C.O.P.

None of these

Does not alter C.O.P.

Decreases C.O.P.

In a refrigerating machine, heat rejected is __________ heat absorbed.

Equal to

Greater than

Less than

The water, alcohol and ammonia have same refrigerating effect at different altitudes.

Yes

No

During sensible cooling of air __________ decreases.

Specific humidity

Wet bulb temperature

Dry bulb temperature

Relative humidity

According to Dalton's law of partial pressures, (where pb = Barometric pressure, pa = Partial pressure of dry air, and pv = Partial pressure of water vapour)

Pb = pa/pv

Pb = pa + pv

Pb = pa - pv

Pb = pa x pv

In aqua-ammonia and Lithium-bromide water absorption refrigeration systems, the refrigerants are respectively

Ammonia and water

Water and lithium bromide

Water and water

Ammonia and lithium bromide

The centrifugal compressors are generally used for refrigerants that require

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

Quiz:	Mechanical Engineering Quiz # 8
Subject:	Compressors Gas Dynamics And Gas Turbines
Total Questions:	1465 MCQs
Time:	1465 Minutes