# Thermal Engineering 21

Objective Questions and Answer: Thermal Engineering 21

Subject: Thermal Engineering 21

Part 21: Objective questions and answers of Thermal Engineering

Q1. Free air is the air at

a) Atmospheric conditions at any specific location

b) 20°C and 1 kg/cm^2 and relative humidity of 36%

c) 0°C and standard atmospheric conditions

d) 15°C and 1 kg/cm^2

Q2. Isothermal compression though most efficient, but is not -practicable because

a) It requires very big cylinder

b) It does not increase pressure much

c) It is impossible in practice

d) Compressor has to run at very slow speed to achieve it

Q3. Standard air is the air at

a) Atmospheric conditions at any specific location

b) 20#176; C and 1 kg/cm^2 and relative humidity 36%

c) 0°C and standard atmospheric conditions

d) 15°C and 1 kg/cm^2

Q4. 1 m of air at atmospheric condition weighs approximately

a) 0.5 kg

b) 1.0 kg

c) 1.3 kg

d) 2.2 kg

Q5. Adiabatic compression is one in which

a) Temperature during compression remains constant

b) No heat leaves or enters the compressor cylinder during compression

c) Temperature rise follows a linear relationship

d) Work done is maximum

Q6. The capacity of a compressor is 5 m /min. 5 m /min refers to

a) Standard air

b) Free air

c) Compressed air

d) Compressed air at delivery pressure

Q7. The overall isothermal efficiency of compressor is defined as the ratio of

a) Isothermal h.p. To the BHP of motor

b) Isothermal h.p. To adiabatic h.p.

c) Power to drive compressor to isothermal h.p.

d) Work to compress air isothermally to work for actual compression

Q8. The- most efficient method of compressing air is to compress it

a) Isothermally

c) Isentropically

d) Isochronically

Q9. Maximum work is done in compressing air when the compression is

a) Isothermal

c) Polytropic

d) Any one of the above

Q10. The pressure and temperature conditions of air at the suction of compressor are

a) Atmospheric

b) Slightly more than atmospheric

c) Pressure slightly less than atmospheric and temperature slightly more than atmospheric.

d) Pressure slightly more than atmospheric and temperature slightly less than atmospheric

Q11. Isothermal compression efficiency can be attained by running the compressor

a) At very high speed

b) At very slow speed

c) At average speed

d) At zero speed

Q12. The compressor capacity with decrease in suction temperature

a) Increases

b) Decreases

c) Remains unaffected

d) May increase or decrease depending on compressor capacity

Q13. Isothermal compression efficiency, even when running at high speed, can be approached by using

a) Multi-stage compression

b) Cold water spray

c) Both (a) and (b) above

d) Fully insulating the cylinder

Q14. Compression efficiency is compared against

a) Ideal compression

c) Botii isothermal and adiabatic compression

d) Isothermal compression.

Q15. Aero planes employ following type of compressor

b) Axial flow

c) Centrifugal

d) Combination of above

Q16. Inter cooling in compressors

a) Cools the delivered air

b) Results in saving of power in compressing a given volume to given pressure

c) Is the standard practice for big compressors

d) Enables compression in two stages

Q17. An ideal air compressor cycle without clearance on p-v diagram can be represented by following processes

a) One adiabatic, two isobaric, and one constant volume

b) Two adiabatic and two isobaric

c) Two adiabatic, one isobaric and one constant volume

d) One adiabatic, one isobaric and two constant volume

Q18. An ideal air compressor cycle with clearance on p-v diagram can be represented by following processes

a) One adiabatic, two isobaric, and one constant volume

b) Two adiabatic and two isobaric

c) Two adiabatic, one isobaric and one constant volume,

d) One adiabatic, one isobaric and two constant volume

Q19. What will be the volume of air at 327°C if its volume at 27°C is 1.5 m^3/mt

a) 3 m^3/mt

b) 1.5 m^3/mt

c) 18 m^3/mt

d) 6 m^3/mt

Q20. The work done per unit mass of air in compression will be least when n is equal to

a) 1

b) 1.2

c) 1.3

d) 1.4

Part 21: Objective questions and answers of Thermal Engineering