Refrigeration and Air Conditioning important question and answer

Question 1 : 
Heat removing capacity of a one-ton refrigerator is 
Option A: 25 Kcal / sec
Option B: 50 Kcal / min
Option C: 50 Kcal / hour
Option D: 100 Kcal / hour 
Explaination: 50 Kcal/min

Question 2 : 
In SI units, one tonne of refrigeration is equivalent to  
Option A: 1.5 kW
Option B: 2.5 kW
Option C: 3.5 kW
Option D: 5 kW
Explanation: In SI units, one tonne of refrigeration is equivalent to 3.5 kW and 210 kJ/min. 

Question 3 : 
In a refrigeration system, the moisture is removed by 
Option A: Driers
Option B: Desiccants
Option C: Filter driers
Option D: All of the above
Explanation: Moisture is removed by driers, filter driers and desiccants too. 

Question 4 :
Subcooling occurs when the vapour
Option A: Has high latent heat
Option B: Has low latent heat
Option C: Removes sensible heat from the refrigerant
Option D: Has high thermal conductivity
Explanation: Subcooling occurs when the vapour removes sensible heat from the refrigerant.

Question 5: 
In the sensible cooling process, specific humidity
Option A: Increases
Option B: Decreases
Option C: Remain constant
Option D: NONE
Explanation: In a sensible cooling process, specific humidity remains constant and relative humidity increases.  

Question 6: 
The dew point temperature as compared to wet bulb temperature for unsaturated air is
Option A: Equal
Option B: Less
Option C: More 
Option D: Unpredictable
Explanation: DPT is less than WBT for unsaturated air.

Question 7:
Air conditioning means?
Option A: Cooling and Heating
Option B: Removal of air impurities
Option C: Dehumidifying
Option D: All of the above
Explanation: A system for controlling the humidity, ventilation, and temperature in a building or vehicle, typically to maintain a cool atmosphere in warm conditions. 

Question 8: 
The main parts of a vapour compression refrigeration system in a sequence are
Option A: Compressor, Condensor, Evaporator and Throttle valve
Option B: Compressor, Throttle valve, Condensor, and Evaporator
Option C: Compressor, Evaporator, Condensor, and Throttle valve
Option D: Compressor, Condensor, Throttle valve, and Evaporator
Explanation: First compressor then condenser, throttle valve and last evaporator. 

Question 9: 
If a refrigerant is having low specific heat, then co-efficient of performance will be
Option A: Lower
Option B: Higher
Option C: Same
Option D: NONE
Explanation: Higher

Question 10: 
The ratio for sensible heat factor is 
Option A: Latent heat to Sensible heat
Option B: Sensible heat to Latent heat
Option C: Latent heat to Total heat
Option D: Sensible heat to Total heat
Explanation: SHF = Sensible heat / Total Heat 
Sensible heat is the heat which increases or decreases the temperature of the body.

Question 11: 
The subcooling in the refrigeration cycle, 
Option A: Increases COP
Option B: Reduce cooling
Option C: Increases work of compression
Option D: Reduce condenser size
Explanation: The subcooling process increases the COP of the refrigeration cycle. 
The coefficient of performance or COP of a heat pump, refrigerator or air conditioning system is a ratio of useful heating or cooling provided to work required. Higher COPs equate to lower operating costs. 

Question 12: 
The phenomenon of emf developed between two dissimilar metals in contact is which of the following effect
Option A: Seeback effect
Option B: Thomson effect
Option C: Peltier effect
Option D: Thermocouple effect

Explanation: A temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage difference is called as seeback effect. 

Question 13: 
In a refrigeration cycle, the heat is absorbed by a refrigerant in a and heat is rejected by a refrigerant in a
Option A: Evaporator, Condensor 
Option B: Evaporator, Compressor
Option C: Condensor, Evaporator
Option D: Evaporator, Expansion valve 
Explanation: The heat is absorbed by an evaporator and rejected by the condenser. 

Question 14: 
Mass of the water vapour present in 1 kg of dry air is called, 
Option A: Relative humidity
Option B: Absolute humidity
Option C: Humidity ratio
Option D: Percentage humidity
Explanation: Humidity ratio, it is also known as specific humidity. 

Question 15: 
Mass of the water vapour present in 1 m³ of dry air is called, 
Option A: Relative humidity
Option B: Absolute humidity
Option C: Percentage of humidity
Option D: Humidity ratio
Explanation: Absolute humidity

Question 16: 
Dew point is the temperature at which, 
Option A: Ice starts melting in the presence of air without external aid
Option B: Condensation of water vapour in air starts
Option C: Vapourisation of water vapour in air starts
Option D: NONE
Explanation: The dew point is the temperature to which air must be cooled to become saturated with water vapour. Dew point temperature indicates dryness of the air, moisture content of air, condition of air. 

Question 17:
Dry bulb, wet bulb and dew point temperature are the same for, 
Option A: Dry air
Option B: Saturated air
Option C: Wet air
Option D: NONE
Explanation: Saturated air 

Question 18: 
The difference between the dry bulb and wet bulb temperature is called
Option A: Dry bulb temperature
Option B: Wet-bulb temperature
Option C: Dew point temperature
Option D: NONE
Explanation: WBT = DBT - WBT 

Question 19: 
The moisture content of air is indicated by, 
Option A: Dry bulb temperature
Option B: Wet-bulb temperature
Option C: Dew point temperature
Option D: Both A and B
Explanation: Moisture content of air is indicated by the dry bulb and wet bulb temperature. 

Question 20: 
If wet-bulb depression is zero, it indicates
Option A: Relative humidity is zero
Option B: Relative humidity is 100%
Option C: Rain is likely to occur
Option D: NONE
Explanation: If the wet-bulb depression is zero relative humidity is 100% as wet-bulb depression indicates relative humidity. 

Thermodynamics important questions

Question No 1 :

The following are examples of some intensive and extensive properties :

1. Pressure
2. Temperature
3. Volume
4. Velocity
5. Electronic charge
6. Magnetisation
7. Viscosity
8. Potential energy

Which one of the following sets gives the correct combinations of Intensive and Extensive properties?

Option A : Intensive - 1 2 3 4 Extensive - 5 6 7 8

Option B : Intensive - 1 3 5 7 Extensive - 2 4 6 8

Option C : Intensive - 1 2 4 7 Extensive - 3 5 6 8

Option D : Intensive - 2 3 6 8 Extensive - 1 4 5 7

Explanation : 

Intensive properties : Independent of mass 

Extensive properties : Dependent of mass 

Question No 2 :

In an isothermal process, internal energy?

Option A: Increases

Option B: Decreases 

Option C: Remain constant

Option D: Gradually increases

Explanation: Decreases

Question No 3 : 

A reversible process?

Option A: Must pass through a continuous series of equilibrium states

Option B: Leaves no history of the events in surroundings 

Option C: Must pass through the same states on the reversed path as on the forward path 

Option D: All of these

Explanation: All of the above

Question No 4 : 

The specific heat of water with rising of temperature?

Option A: Increases

Option B: Decreases 

Option C: First decreases to a minimum then increases

Option D: Remain constant 

Explanation: Decrease to a minimum first then increase 

Question No 5 : 

When two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. This statement is :

Option A: Zeroth law of thermodynamics 

Option B: First law of thermodynamics 

Option C: Second law of thermodynamics 

Option D: None of the above 

Explanation: This is the statement of the zeroth law of thermodynamics 

Question No 6 : 

Kelvin-Plank's law deals with?

Option A: Conversion of work into heat

Option B: Conversion of heat into work 

Option C: Conversion of work 

Option D: Conversion of heat 

Explanation: Conversion of heat into work 

Question No 7 : 

According to the kinetic theory of gases, at absolute zero?

Option A: Specific heat of molecules reduces to zero 

Option B: Volume of gas reduce to zero

Option C: Kinetic energy of molecules reduces to zero 

Option D: Pressure of gas reduces to zero 

Explanation: Kinetic energy of molecules reduces to zero 

Question No 8 :

In a throttling process?

Option A : W = 0 

Option B : H = 0 

Option C : E = 0 

Option D : All of the above 

Explanation : At throttling all W, H, E = 0 

Question No 9 : 

In all reversible process, the entropy of the universe?

Option A: Increases 

Option B: Decreases 

Option C: Remains the same 

Option D: None of the above 

Explanation: Increases

Question No 10 : 

Efficiency of Carnot cycle is given by :

Option A : T1 + T2 / T1 

Option B : T1 - T2 / T1 

Option C : T1 / T1 + T2

Option D : T1 / T1 - T2 

Explanation : T1 - T2 / T1 

Question No 11 : 

The Carnot cycle consists of two reversible adiabatic processes and 

Option A: Two reversible isothermal processes 

Option B: Two reversible constant pressure processes 

Option C: Two reversible constant volume processes 

Option D: One reversible constant pressure processes

Explanation: Two reversible isothermal processes

Question No 12 : 

Carnot cycle has maximum efficiency for?

Option A : Petrol engine 

Option B : Diesel engine 

Option C : Reversible engine 

Option D : Irreversible engine 

Explanation : Reversible engine 

Question No 13 :

In the Carnot cycle, the algebraic sum of the entropy changes for the cycle is?

Option A: Positive

Option B: Negative 

Option C: Zero 

Option D: None of the above 

Explanation: Zero 

Question No 14 : 
In the Carnot cycle, the process carried at extremely slow speed is 
Option A: Isothermal compression 
Option B: Adiabatic compression 
Option C: Adiabatic expansion 
Option D: All of these 
Explanation: All are extremely slow speed processes

Question No 15 :
Control volume refers to a 
Option A: Specific mass
Option B: Fixed region in the space
Option C: Closed system 
Option D: NONE 
Explanation: Fixed region in the space

Question No 16 : 
The internal energy of a perfect gas depends upon
Option A: Temperature only
Option B: Temperature and pressure 
Option C: Temperature, pressure and specific heats
Option D: NONE
Explanation: Temperature only

Question No 17 :
Joule Thomson coefficient for an ideal gas having equation pV=RT is 
Option A: Zero
Option B: 0.5
Option C: Unity
Option D: Infinite 
Explanation: Zero

Question No 18 :
The temperature of a gas is a measure of 
Option A: Average distance between gas molecules 
Option B: Average kinetic energy of gas molecules
Option C: Average potential energy of gas molecules
Option D: NONE
Explanation: Average kinetic energy of gas molecules

Question No 19 :
A gas, which obeys kinetic theory perfectly is 
Option A: Pure gas
Option B: Real gas
Option C: Perfect gas
Option D: All of these
Explanation: Real gas

Question No 20 : 
The temperature at which, the volume of a gas becomes zero, is called
Option A: Absolute temperature
Option B: Absolute zero temperature
Option C: Absolute scale of temperature
Option D: NONE of these
Explanation: Absolute zero temperature

Question No 21 :
The absolute zero pressure exists 
Option A: At sea level
Option B: At -273 K
Option C: At vacuum condition 
Option D: When the molecular momentum of the system becomes zero 
Explanation: When the molecular momentum of the system becomes zero 

Question No 22 :
Specific heat of gas, Cp = Cv, at
Option A: Absolute zero
Option B: Critical temperature
Option C: Triple point
Option D: All temperatures
Explanation: Absolute zero

Question No 23 : 
The gas constant R is equal to the
Option A: Sum of two specific heats
Option B: Difference of two specific heats
Option C: Product of two specific heats
Option D: Ratio of two specific heat 
Explanation: Difference of two specific heats

Question No 24 : 
Triple point 
Option A: Occurs in a mixture of two or more gases
Option B: In the point, where three phases exist together
Option C: Occurs in sublimation
Option D: None of the above
Explanation: In the point, where three phases exist together

Question No 25 : 
For a pure substance at its triple point, the number of degrees of freedom is 
Option A: 0
Option B: 1
Option C: 2
Option D: None of these
Explanation: Zero 
Consider a system consisting of pure gas, say A. It is, evidently, a one-component, one phase system. The two variable required to be specified will be temperature and pressure. The composition will remain invariable A. The degree of freedom will be 2 if the system will be bivariant. One component system having two phases called mono variant and three phases coexist defines the system completely, therefore, is said to be non-variant or invariant or degree of freedom is zero.  

Question No 26 : 
The efficiency of a Rankine cycle 
Option A: Increases with decreasing temperature of heat rejection
Option B: Decreases with decreasing temperature of heat rejection 
Option C: Decreases with increasing temperature of heat rejection
Option D: None of the above
Explanation: Increase with decreasing temperature and decrease with increasing temperature of heat rejection.

Question No 27 : 
Rankine cycle efficiency for a power plant is 29%. The Carnot cycle efficiency will be
Option A: Less
Option B: More 
Option C: Equal 
Option D: NONE of the above
Explanation: Carnot cycle efficiency is more than the Rankine cycle for the power plant. 

Question No 28 : 
The ideal efficiency of a simple gas turbine cycle depends upon
Option A: Pressure ratio
Option B: Cut-off ratio
Option C: Both A & B
Option D: None of the above
Explanation: Pressure ratio

Question No 29 : 
A system is said to be consisting of a pure substance when 
Option A: It is homogeneous in composition
Option B: It is homogeneous and invariable in chemical aggregation
Option C: It has only one phase
Option D: It has more than one phase
Explanation: It is homogeneous and invariable in chemical aggregation
A pure substance is one which is
Homogeneous in composition 
Homogeneous in chemical aggregation
Invariable in chemical aggregation

Question No 30 :

At its critical point, any substance will 

Option A: Exist all the three phases simultaneously

Option B: Change directly from solid to vapour

Option C: Lose phase distinction between liquid and vapour

Option D: Behave as an ideal gas

Explanation: Lose phase distinction between liquid and vapour