In this article I am going to start one new subject that is refrigeration and air conditioning, its part is Refrigeration System- Definition, Main Function, Unit of Refrigeration.
Short Answers of Each Topic-
What is refrigeration system?– It is a system which decrease temperature of system than surrounding.
Main Function- Decreasing temperature of system than surrounding.
Unit of Refrigeration- TR(Means Ton of Refrigeration)
1 TR = 3.5 KW
So, let’s start.
What is Refrigeration System?
Engineers design refrigeration systems to transfer heat from one location to another by using the principles of thermodynamics.
The primary purpose of a refrigeration system is to create and maintain a low temperature within a specific area or application. A wide range of industries, including food preservation, medical storage, and industrial manufacturing, use these systems.
The basic components of a refrigeration system include a compressor, a condenser, an evaporator, and an expansion valve. The compressor is responsible for compressing the refrigerant, which increases its temperature and pressure.
The system sends this high-pressure gas to the condenser, where it loses heat to the surrounding environment and condenses into a liquid.
The liquid refrigerant then flows through an expansion valve, which reduces its pressure and temperature, causing it to evaporate into a gas.
The system sends this low-pressure gas to the evaporator, where it absorbs heat from the surrounding area, causing the temperature of the area to decrease.
One of the most important considerations when designing a refrigeration system is the choice of refrigerant.
Different refrigerants have different properties and are suitable for different applications. Some common refrigerants include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs).
In addition to the basic components, refrigeration systems may also include other components, such as filters, oil separators, and control systems. The system uses filters to remove impurities from the refrigerant and oil separators to remove oil from the refrigerant.
Control systems are used to regulate the temperature and pressure of the refrigerant and ensure that the system operates efficiently.
Overall, refrigeration systems are an essential technology that enables a wide range of applications, from preserving food to storing medical supplies. By understanding the basic principles of refrigeration and the components of a refrigeration system, it is possible to design and operate these systems effectively and efficiently.
Main Function of Refrigeration System-
Refrigeration systems are essential in maintaining low temperatures in a specific area or application. The primary function of a refrigeration system is to transfer heat from a low-temperature area to a high-temperature area.
The system compresses and circulates a refrigerant through a series of components that work together to remove heat from the environment and transfer it to a different location, achieving this goal.
The main components of a refrigeration system include a compressor, a condenser, an evaporator, and an expansion valve.
The compressor is responsible for compressing the refrigerant, which raises its temperature and pressure. The high-pressure gas then flows to the condenser, where it loses heat to the environment and condenses into a liquid.
The liquid refrigerant then passes through an expansion valve, which reduces its pressure and temperature, causing it to evaporate into a gas.
This low-pressure gas then flows into the evaporator, where it absorbs heat from the surrounding area, causing the temperature of the area to decrease.
The refrigeration system’s main function is to remove heat from a specific area and transfer it to another location, typically the environment.
The refrigerant circulating through the components of the refrigeration system achieves this by removing heat from the surrounding environment.
The refrigeration system’s efficiency is critical to its function, and various factors affect its efficiency, including the choice of refrigerant, the design of the components, and the control systems’ operation.
The refrigeration system’s overall function and performance depend on these factors, and it is essential to consider them when designing and operating a refrigeration system.
In summary, the main function of a refrigeration system is to remove heat from a specific area and transfer it to another location.
The system’s components work together to compress, condense, expand, and evaporate the refrigerant to achieve this function. The efficiency and performance of the system depend on various factors, including the choice of refrigerant, component design, and control systems operation.
What is the Unit of Refrigeration System-
The unit of measurement for refrigeration systems is typically expressed in tons of refrigeration (TR) or British Thermal Units per hour (BTU/h).
1 Ton of Refrigeration(TR) = 3.5 KW = 210 KJ/min = 50 Kcal/min
One ton of refrigeration is defined as the amount of heat required to melt one ton of ice (2,000 pounds) in 24 hours, or approximately 12,000 BTU/h.
Therefore, if a refrigeration system has a cooling capacity of 2 TR, it can remove 24,000 BTU of heat per hour.
Kilowatts (kW), which is the electrical power input required to run the system, and pounds per hour (lb/hr), which is the amount of refrigerant flow rate, are other common units of measurement for refrigeration systems.
The specific unit used depends on the type of refrigeration system and the application it is used for.
Refrigeration System Questions with Solutions-
SSC JE Previous Year Questions with Solution-
Question 1: The working fluid used in a domestic refrigerator is __________.
Solution:
The working fluid used in a domestic refrigerator is a type of halocarbon refrigerant, such as R-134a or R-12 (which has been phased out due to environmental concerns).
Hence, the answer is halocarbon refrigerant.
Question 2: A refrigerator operates between 260 K and 310 K. If the COP of the refrigerator is 4, then the heat rejected to the surrounding per hour, if 3 kW of work is done on the system, will be __________.
Solution:
The heat absorbed by the refrigerant per hour is given by:
Qh = W / COP
where W is the work done on the system and COP is the coefficient of performance of the refrigerator.
In this case, Qh = 3 / 4 = 0.75 kW. The heat rejected to the surroundings is given by:
Qc = Qh – W
Hence, the heat rejected to the surroundings per hour is 0.75 kW – 3 kW = -2.25 kW.
Note: The negative sign indicates that heat is being rejected from the system to the surroundings.
Question 3: The coefficient of performance of a Carnot refrigeration cycle operating between -23°C and 27°C is __________.
Solution:
The coefficient of performance of a Carnot refrigeration cycle is given by:
COP = Tc / (Th – Tc)
where Tc is the temperature of the refrigerated space and Th is the temperature of the surroundings.
In this case, Tc = -23°C = 250 K and Th = 27°C = 300 K. Therefore, the COP is:
COP = 250 / (300 – 250) = 5
Hence, the coefficient of performance of a Carnot refrigeration cycle operating between -23°C and 27°C is 5.
Question 4: The cooling capacity of a refrigerator is 4 TR. If the temperature difference between the evaporator and the surrounding is 25°C, the rate of heat transfer will be __________.
Solution:
The cooling capacity of a refrigerator is given by:
Qe = TR × 12,000 BTU/hr
where TR is the tonnage of the refrigerator.
In this case, TR = 4.
Therefore, the cooling capacity of the refrigerator is:
Qe = 4 × 12,000 = 48,000 BTU/hr
The rate of heat transfer is given by:
Qdot = Qe / (Th – Tc)
where Th is the temperature of the surroundings, Tc is the temperature of the evaporator, and Qe is the cooling capacity of the refrigerator.
In this case, Th – Tc = 25°C. Therefore, the rate of heat transfer is:
Qdot = 48,000 / (25 + 273) = 153.85 W
Hence, the rate of heat transfer is 153.85 W.
Question 5: The refrigerant used in a vapour compression refrigeration system should have __________.
Solution:
The refrigerant used in a vapour compression refrigeration system should have the following properties:
- Low boiling point
- High latent heat of vaporization
- High specific heat
- Low toxicity
- Low flammability
- Good thermodynamic properties
These properties are essential for the efficient operation of the refrigeration system and the safety of the users.
Hence, the answer is low boiling point, high latent heat of vaporization, high specific heat.
GATE Previous Year Question with Solution-
Question 1: A refrigerator operates at a steady state between the temperature limits of 5°C and 25°C. The coefficient of performance of the refrigerator is 5. The power input required to operate the refrigerator is __________ kW per ton of refrigeration.
Solution:
The refrigeration effect is given by:
Qe = COP x W
where Qe is the refrigeration effect, COP is the coefficient of performance, and W is the power input.
The refrigeration effect per ton of refrigeration is given by:
Qe/TR = 210 kJ/kg
where TR is the ton of refrigeration.
Substituting COP = 5 and Qe/TR = 210 kJ/kg, we get:
W/TR = Qe/TR / COP = 42 kJ/kg
Converting kJ/kg to kW/TR, we get:
W/TR = 42 / 3600 = 0.0117 kW/TR
Hence, the power input required to operate the refrigerator is 0.0117 kW per ton of refrigeration.
Question 2: The COP of a refrigerator is 3.5. If the evaporator temperature is -10°C, the condenser temperature is __________.
Solution:
The COP of a refrigerator is given by:
COP = Qe / W
where Qe is the refrigeration effect and W is the power input.
The refrigeration effect per ton of refrigeration is given by:
Qe/TR = 210 kJ/kg
where TR is the ton of refrigeration.
Substituting COP = 3.5 and Qe/TR = 210 kJ/kg, we get:
W/TR = Qe/TR / COP = 60 kJ/kg
The temperature difference between the evaporator and condenser is given by:
ΔT = Tc – Te
where Tc is the condenser temperature and Te is the evaporator temperature.
The Carnot COP is given by:
COPc = Th / (Th – Tc)
where Th is the temperature of the high-temperature reservoir.
Substituting Te = -10°C and COPc = 3.5, we get:
Th = Tc / (1 – 1 / COPc) + Te = 39.3°C
Substituting Th = 39.3°C and Te = -10°C, we get:
Tc = 25.2°C
Hence, the condenser temperature is 25.2°C.
Question 3: The refrigeration capacity of a plant producing ice at -10°C from water at 20°C is 500 kW. The rate of heat rejection to the surroundings at 30°C is __________.
Solution:
The rate of heat rejection to the surroundings is given by:
Qr = Qe + Qa
where Qe is the refrigeration effect and Qa is the amount of heat absorbed by the compressor.
In this case, Qe = 500 kW. The amount of heat absorbed by the compressor is negligible compared to Qe. Therefore, Qr ≈ Qe.
The rate of heat rejection to the surroundings is:
Qr = Qe / COP
where COP is the coefficient of performance.
Here,
COP = Qe / Qa = Qe / (Qe – Qc),
The system rejects a certain amount of heat to the surroundings, and this amount is represented by Qc.
Substituting COP = 5 and Qe = 500 kW, we get:
500 = 5(Qe – Qc)
Qc = 400 kW
Hence, the rate of heat rejection to the surroundings is 400 kW.
Basic MCQ’s with Solution for Competition Exams-
1. What is the purpose of a refrigeration system?
a) To increase the temperature of a space
b) To maintain a constant temperature in a space
c) To remove heat from a space d) To generate heat in a space
Solution: c) To remove heat from a space
2. What is the function of an evaporator in a refrigeration system?
a) To compress the refrigerant
b) To remove oil from the refrigerant
c) To remove impurities from the refrigerant
d) To absorb heat from the surrounding environment
Solution: d) To absorb heat from the surrounding environment
3. Which of the following is a common refrigerant used in refrigeration systems?
a) Carbon dioxide
b) Nitrogen
c) Oxygen
d) Water vapor
Solution: a) Carbon dioxide
4. What is the purpose of a condenser in a refrigeration system?
a) To compress the refrigerant
b) To remove oil from the refrigerant
c) To remove impurities from the refrigerant
d) To release heat to the surrounding environment
Solution: d) To release heat to the surrounding environment
5. What is the main function of a refrigeration system control system?
a) To regulate the temperature and pressure of the refrigerant
b) To compress the refrigerant
c) To remove oil from the refrigerant
d) To remove impurities from the refrigerant
Solution: a) To regulate the temperature and pressure of the refrigerant
Basic Questions with Solution-
1. What is a refrigerant and what are its desirable properties for use in a refrigeration system?
Solution: A refrigerant is a substance that is used in a refrigeration system to transfer heat from one location to another. Desirable properties for a refrigerant include low toxicity, low flammability, high stability, and a high boiling point. Some commonly used refrigerants are ammonia, carbon dioxide, and hydrofluorocarbons (HFCs).
2. What is the purpose of the evaporator in a refrigeration system?
Solution: The purpose of the evaporator in a refrigeration system is to absorb heat from the surrounding environment, causing the temperature of the area to decrease. The refrigerant, which is in a low-pressure gas state, flows through the evaporator, and as it absorbs heat, it becomes a high-pressure gas.
3. What is the purpose of the condenser in a refrigeration system?
Solution: The purpose of the condenser in a refrigeration system is to release heat to the surrounding environment, causing the temperature of the area to increase. The refrigerant, which is in a high-pressure gas state, flows through the condenser, and as it releases heat, it becomes a high-pressure liquid.
4. What is the role of the compressor in a refrigeration system?
Solution: The role of the compressor in a refrigeration system is to increase the pressure of the refrigerant, which increases its temperature and enables it to release heat to the surrounding environment in the condenser. The compressor also circulates the refrigerant through the system.
5. What is the purpose of the expansion valve in a refrigeration system?
Solution: The purpose of the expansion valve in a refrigeration system is to reduce the pressure of the refrigerant, which causes its temperature to decrease and enables it to absorb heat from the surrounding environment in the evaporator. The expansion valve controls the flow rate of the refrigerant into the evaporator.