1. The C.O.P for reverse Carnot refrigerator is 6. The ratio of lowest temperature to highest temperature will be _____
a) twice
b) three times
c) four times
d) seven times
Explanation: Reverse Carnot C.O.P. = \(\frac{t2-t1}{t1}\)
6 = \(\frac{X-Y}{Y}\)
6 = \(\frac{X}{Y}\) – 1
Thus, \(\frac{X}{Y}\) = 7 i.e. X=7Y i.e. Higher temperature = 7 times Lower temperature.
2. In general the ratio of lowest to highest temperature with respect to C.O.P. can be denoted by ________
a) C.O.P + 1 = Ratio of temperature
b) C.O.P/2 = Ratio of temperature
c) C.O.P + 4 = Ratio of temperature
d) C.O.P + 2 = Ratio of temperature
Explanation: In general, the ratio of lowest to highest temperature, say \(\frac{X-Y}{Y}\) = C.O.P. Hence, \(\frac{X}{Y}\) – 1 = C.O.P. i.e. \(\frac{X}{Y}\) = C.O.P + 1.
3. The C.O.P for reverse Carnot refrigerator is 2. The ratio of highest temperature to lowest temperature will be _____
a) 4 times
b) 3 times
c) 1/2 times
d) 1/3 times
Explanation: Reverse Carnot C.O.P. = \(\frac{t2-t1}{t1}\)
2 = \(\frac{X-Y}{Y}\)
2 = \(\frac{X}{Y}\) – 1
Thus, \(\frac{X}{Y}\) = 3 i.e. X=3Y i.e. Lowest temperature = \(\frac{1}{3}\) times Highest temperature..
4. The C.O.P of a reverse Carnot cycle doesn’t depend on which of the following?
a) Moisture
b) Evaporator temperature
c) Condenser temperature
d) Work done
Explanation: C.O.P for a reverse Carnot depends directly on the difference of Evaporator and Condenser temperature, and inversely on the Work done.
5. If a condenser and evaporator temperatures are ‘X’ K and 100 K respectively, and reverse Carnot C.O.P is 2.5 then find out the ‘X’.
a) 100 K
b) 150 K
c) 350 k
d) 200 k
Explanation: Reverse Carnot C.O.P. = \(\frac{t2-t1}{t1}\)
2.5 = \(\frac{X-100}{100}\)
X = 350 K.
6. Which of the following can be called as a refrigeration process?
a) Cooling of hot ingot from 1000 C to room temperature
b) Cooling of a pot of water by mixing it with a large block of ice
c) Cooling in rooms using a ceiling fan
d) Cooling of hot water by mixing it with tap water
Explanation: Refrigeration is the process of cooling the body with the help of evaporation during the contact with the other external surface, hence when Ice mixes with water, the water in pot will suddenly drop its temperature whereas the Ice will be converted liquid and evaporate (invisibly).
7. What is the main disadvantage of natural refrigeration methods?
a) They are expensive
b) They are poisonous
c) They are not environment friendly
d) They are dependent on local conditions
Explanation: Natural Refrigeration process is dependent on the local conditions like temperature of surrounding, pressure at which it occurs, and volume of the refrigerant etc. hence it cannot be predicted exactly.
8. For what condition, evaporative cooling system is ideal?
a) Hot and Dry
b) Hot and Humid
c) Cold and Humid
d) Moderate Hot but Humid
Explanation: As the humidity increases, it becomes difficult to produce refrigeration effect as there increases the need to set up a de-humidifier too.
9. Compared to natural refrigeration methods, artificial refrigeration methods are________
a) dis-continuous
b) not reliable
c) continuous
d) environment friendly
Explanation: As artificial refrigeration uses various refrigerants like R-12,R-14,R-150 etc. along with CFC it becomes harmful for environment, but it produces a constant cooling whenever required.
10. What is the main function of an expansion valve?
a) Reduce the refrigerant pressure
b) Maintain high and low side pressures
c) Protect evaporator
d) Control the velocity of flow of refrigerants
Explanation: Expansion valve mainly increases or decreases the flow of refrigerants, which directly affects the increase and decrease in the pressures.