This set of Refrigeration online quiz focuses on “Evaporators Types, Factors Affecting it and Defrosting Methods”.
1. Why is the evaporator used?
a) To improve C.O.P.
b) To decrease the refrigeration effect
c) To absorb heat
d) To reject heat
View Answer
Explanation: Evaporator is used to absorb the heat from the medium being cooled and get the refrigeration effect. Multiple evaporators are used to enhance the refrigeration effect and eventually the C.O.P. too.
2. What is the pressure side of a refrigerating system in which evaporator is used?
a) Low pressure
b) Zero pressure
c) Negative pressure
d) High pressure
View Answer
Explanation: Evaporator is used to convert liquid refrigerant into vapor refrigerant by absorbing heat. The liquid coming from the expansion valve is converted into vapor and forwarded to the compressor for compression. Evaporator gives the refrigeration effect. So, it is used on the lower pressure side to provide input for the compressor.
3. Evaporator is also called as Freezing, cooling or chilling coil.
a) False
b) True
View Answer
Explanation: Evaporator is used to convert liquid refrigerant into vapor refrigerant by absorbing heat. The liquid coming from the expansion valve is converted into vapor and forwarded to the compressor for compression. Evaporator gives the refrigeration effect. So, it is also called a Freezing, cooling, or chilling coil.
4. What evaporator does to the refrigerant coming from expansion valve in terms of state?
a) high-pressure liquid refrigerant
b) low-pressure liquid and vapor refrigerant
c) low-pressure vapor refrigerant
d) high-pressure vapor refrigerant
View Answer
Explanation: The liquid coming from the expansion valve is converted into vapor and forwarded to the compressor for compression. So, the evaporator absorbs the heat, and phase change occurs. There is a slight change in pressure but negligible. Thus, the state of refrigerant changes from low-pressure liquid to low-pressure vapor.
5. What is the formula for the capacity of evaporator?
a) Q = U A2 (T2 – T1)
b) Q = U A (T2 – T1)
c) Q = A (T2 – T1)
d) Q = U (T2 – T1)
View Answer
Explanation: Capacity of the evaporator is the amount of heat absorbed by it over a given period of time. So, the heat absorbed or capacity is the heat convection, can be given as,
Q = U A (T2 – T1), where U is overall heat transfer coefficient, A is the surface area of the evaporator and T1 & T2 are the saturation temperature of refrigerant and temperature of the medium to be cooled respectively.
6. Which of the following is not a factor affecting the capacity of evaporator?
a) Velocity of refrigerant
b) The thickness of the evaporator coil wall
c) Material
d) Evaporator pressure
View Answer
Explanation: Capacity of the evaporator is the amount of heat absorbed by it over a given period of time. Increase in the velocity can increase the heat transfer up to a certain extent. The thickness of the coil wall affects the convection, and hence capacity can be changed. The material should be a good conductor to get optimum heat transfer. Hence, evaporator pressure does not affect the capacity, but the temperature does have.
7. What is the value of the fluid side heat transfer coefficient when liquid flows through the evaporator shell?
a) C x m
b) C x (m)0.5
c) C x (m)2
d) C x (m)3
View Answer
Explanation: Fluid side heat transfer coefficient is denoted as hf and has a formula,
hf = [(CK / D) (V Dρ / μ)0.8 (Cp μ / K)0.4] W / m2 K
So, for liquid flowing through the shell, the value is hf = C x (m)0.5 = C x √m.
8. What is the value of fluid side heat transfer coefficient when air flows over finned coil by forced convection?
a) C x (m)0.1
b) C x (m)0.2
c) C x (m)0.3
d) C x (m)0.4
View Answer
Explanation: Fluid side heat transfer coefficient is denoted as hf and has a formula,
hf = [(CK / D) (V D ρ / μ)0.8 (Cp μ / K)0.4] W / m2 K
So, for air flowing over finned coil by forced convection, the value is hf = C x (m)0.4
9. What is the value of the fluid side heat transfer coefficient when air flows over cold pipes by natural convection?
a) 0.2 (Ta – Tm / D)1/4
b) 0.2 (Ta – Tm / D)
c) 0.2 (Ta – Tm / D)1/3
d) 0.2 (Ta – Tm / D)1/2
View Answer
Explanation: Fluid side heat transfer coefficient is denoted as hf and has a formula,
hf = [(CK / D) (V D ρ / μ)0.8 (Cp μ / K)0.4] W / m2 K
So, for air flowing over cold pipes by natural convection, the value is hf = 0.2 (Ta – Tm / D)1/4
10. The bare tube evaporators are called as _______ evaporators.
a) extended surface
b) bare surface
c) pipe surface
d) prime surface
View Answer
Explanation: The bare tube evaporators are also known as prime surface evaporators due to the simple construction of it. The bare tube coil is easy to clean and defrost; hence, it is called prime surface evaporator.
11. Which type of evaporator is generally used in home freezers, ice cream cabinets, etc?
a) Shell and coil evaporator
b) Finned evaporator
c) Shell and tube evaporator
d) Plate evaporator
View Answer
Explanation: Plate evaporators are generally used in home freezers, ice cream cabinets, beverage coolers, and locker plants, etc. In this type of evaporator, coils are either welded on one side of the plate or between two plates which are welded together at the edges.
12. Which type of evaporator is generally used for wine cooling and chilling oil in the petroleum industry?
a) Tube-in-tube evaporator
b) Finned evaporator
c) Shell and tube evaporator
d) Plate evaporator
View Answer
Explanation: Tube-in-tube evaporators are used for wine cooling and chilling oil in the petroleum industry. In this type of evaporator, one tube is inside another tube. It provides a high heat transfer rate.
13. Which type of evaporator is used in household refrigerators?
a) frosting evaporator
b) defrosting evaporator
c) non-frosting evaporator
d) non-corrosive evaporator
View Answer
Explanation: Evaporators used in household refrigerators, low-temperature evaporators, and bare pipe coils in storage boxes come under frosting type. These operate at temperature always below 0°C. Coils frost continuously and need to be defrosted at regular interval of time.
14. Which type of evaporator is generally used to cool drinking water?
a) Shell and tube evaporator
b) Finned evaporator
c) Shell and coil evaporator
d) Plate evaporator
View Answer
Explanation: The shell and coil evaporators are the dry expansion evaporators used to chill water. The shell may be sealed or open. If the shell is sealed, then it is used for cooling drinking water.
15. Finned evaporators are also known as prime surface evaporators.
a) False
b) True
View Answer
Explanation: Finned evaporators are the ones which use a number of fins to increase the contact surface for heat transfer. The specifications of fins depend on the required heat transfer rate. As fins are the extended material used for heat transfer enhancement so, finned evaporators are also called as extended surface evaporators whereas, bare tube coil evaporators are called as prime surface evaporators.
Sanfoundry Global Education & Learning Series – Refrigeration & Air Conditioning.
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