Thermal Engineering II Set 5

Mechanical Engineering

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This set of Thermal Engineering 2 Multiple Choice Questions & Answers (MCQs) focuses on Thermal Engineering II Set 5

Q1 | The expansion process is
  • isentropic
  • reversible
  • adiabatic
  • all of the mentioned
Answer: adiabatic
Explaination:
the expansion process is adiabatic but not isentropic and is irreversible.
Q2 | The evaporation process is a
  • constant volume reversible process
  • constant pressure reversible process
  • adiabatic throttling process
  • reversible adiabatic process
Answer: constant pressure reversible process
Explaination:
this is the last process and it completes the cycle.
Q3 | The evaporator produces the cooling or refrigerating effect.
  • true
  • false
Answer: true
Explaination:
it absorbs heat from the surroundings by evaporation.
Q4 | In the expansion process, which of the following remains constant?
  • work done
  • heat supplied
  • internal energy
  • enthalpy
Answer: enthalpy
Explaination:
the expansion is an adiabatic throttling process in which enthalpy remains unchanged.
Q5 | The COP of cycle is given by(Q2=heat absorbed by evaporator and Wc=work done by compressor)
  • 1- (q2/wc)
  • 1- (wc/q2)
  • q2/wc
  • wc/q2
Answer: q2/wc
Explaination:
this is the cop of vapour refrigeration cycle.
Q6 | One tonne of refrigeration is given as the rate of heat removal from surroundings equivalent to heat required for melting one tonne of ice in a day.
  • true
  • false
Answer: true
Explaination:
this is the definition of “one
Q7 | Which of the following is recommended in a refrigeration cycle?
  • superheating of vapour
  • subcooling of liquid
  • both of the mentioned
  • none of the mentioned
Answer: both of the mentioned
Explaination:
the superheating of vapour is done at evaporator outlet and subcooling of liquid occurs at condenser outlet.
Q8 | A condenser must and then the compressed refrigerant.
  • superheat, evaporate
  • desuperheat, evaporate
  • superheat, condense
  • desuperheat, condense
Answer: desuperheat, condense
Explaination:
this is the function of a condenser.
Q9 | In absorption refrigeration cycle, which of the following is used?
  • refrigerant
  • absorbent
  • both of the mentioned
  • none of the mentioned
Answer: both of the mentioned
Explaination:
both refrigerant and absorbent are used in absorption refrigeration cycle.
Q10 | In absorption system, compressor in vapour compression cycle is replaced by absorber- generator assembly.
  • true
  • false
Answer: true
Explaination:
the absorber-generator assembly involves less mechanical work.
Q11 | In the aqua-ammonia absorption system,
  • water is the refrigerant and ammonia is the absorbent
  • ammonia is the refrigerant and water is the absorbent
  • both ammonia and water can be used as refrigerant or absorbent
  • none of the mentioned
Answer: ammonia is the refrigerant and water is the absorbent
Explaination:
this is the basic absorption refrigeration cycle.
Q12 | Which of the following statement is true?
  • ammonia vapour is absorbed in water
  • boiling point of ammonia is more than that of water
  • both of the mentioned
  • none of the mentioned
Answer: ammonia vapour is absorbed in water
Explaination:
the boiling point of ammonia is less than that of water.
Q13 | Which of the following condenses first?
  • ammonia vapour
  • water vapour
  • both condense at same temperature
  • none of the mentioned
Answer: water vapour
Explaination:
the saturation temperature of water is higher than ammonia at any given pressure.
Q14 | The vapour going to condenser is in temperature and in ammonia.
  • higher, less
  • higher, richer
  • lower, less
  • lower, richer
Answer: lower, richer
Explaination:
when passing through analyser, the vapour is cooled and enriched by ammonia.
Q15 | Lithium bromide-water vapour is another absorption refrigeration system.
  • true
  • false
Answer: true
Explaination:
in this, water is the refrigerant and solution of lithium bromide in water is the absorbent.
Q16 | Water is used as a in air conditioning units.
  • absorbent
  • refrigerant
  • absorbent and refrigerant
  • none of the mentioned
Answer: refrigerant
Explaination:
the reason is that water cannot be cooled below 0 degree celsius.
Q17 | Room air conditioners and packaged units are examples of                    
  • direct expansion systems
  • indirect expansion systems
  • chilled water systems
  • indirect contraction systems
Answer: direct expansion systems
Explaination:
air conditioning systems are classified into two categories. these are direct expansion systems and chilled water
Q18 | Which of the following is not a component of packaged air conditioners?
  • compressor
  • condenser
  • chiller
  • evaporator
Answer: chiller
Explaination:
packaged air conditioners consist of a compressor, condenser, evaporator and a fan. unlike packaged air
Q19 | In a chilled water system, the refrigerant is used to cool the air directly while in the direct expansion system, a secondary medium like water is used to cool the air.
  • true
  • false
Answer: false
Explaination:
in the direct expansion system, the refrigerant is used to cool the air directly while in the chilled water system, a secondary medium like water is used to cool the air. in the chilled water system, the refrigerant first cools the water and then the water cools the air.
Q20 | In which component of the chilled water system, the return air and the fresh air mixture is filtered?
  • fan coil unit
  • ducting grill
  • compressor
  • evaporator
Answer: fan coil unit
Explaination:
in the chilled water system, the return air and the fresh air mixture is filtered in the fan coil unit. here, in addition to filtration, the mixture is cooled and dehumidified. after this, it is distributed to the conditioned space through ducting and grills.
Q21 | Which of the following qualities is not possessed by the filters in the air conditioning system?
  • they should be capable of removing dust particles from the incoming air
  • they should afford easy cleaning
  • they should offer low frictional resistance to the airflow
  • they should offer high frictional resistance to the airflow
Answer: they should offer high frictional resistance to the airflow
Explaination:
the filters in the air conditioning system should be capable of removing dust particles from the incoming air. they should afford easy cleaning and should offer low frictional resistance to the airflow.
Q22 | Viscous type filters are made of screens of spilt wire and coated with non-drying viscous oil in order to catch and remove the dust particles from the incoming air.
  • true
  • false
Answer: true
Explaination:
viscous type filters are made of screens of spilt wire and coated with non- drying viscous oil in order to catch and remove the dust particles from the incoming air. they can be of two types – unit type or automatic type.
Q23 | Which of the following statements about electric precipitators is false?
  • they are used to remove dust by providing a strong electric field
  • their initial installation cost is high
  • their operational cost is low
  • dust particles get attached to the positive electrode
Answer: dust particles get attached to the positive electrode
Explaination:
electric precipitators are used to remove dust by providing a strong electric field. in an electric precipitator, the dust particles get attached to the negative
Q24 | The process of extraction of the certain required amount of water from air is known as                        
  • heating
  • cooling
  • humidification
  • dehumidification
Answer: dehumidification
Explaination:
the process of extraction of a certain required amount of water from air is known as dehumidification. this can be achieved by condensation or desiccation.
Q25 | Which of the following is capable of absorbing excess moisture from the air?
  • silica gel
  • charcoal
  • salts of calcium or ammonia
  • activated alumina
Answer: salts of calcium or ammonia
Explaination:
absorbents like salts of calcium or ammonia are capable of absorbing excess moisture from the air. however, the adsorbents like silica gel and activated alumina allow moisture to stay only at the surface.
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