Quick Comparison between Gas Refrigeration Cycle and Vapor Refrigeration Cycle

air refrigeration vapour refrigeration

Gas Refrigeration Cycle
Vapor Refrigeration Cycle
Gases used as refrigerant
Liquids like Freon is used as refrigerant

No phase change in gas throughout the process (gaseous state only).
Phase change of refrigerant involved at heat exchangers (liquid – vapor)

Large volume of refrigerant required
Volume of referent required per ton of refrigeration is low

It has sensible heat only
Both sensible heat and latent heat involved in the refrigeration cycle.

High running cost
Low running cost

Low COP
High COP

Application: Air craft air-conditioning, not applicable for domestic and industrial purpose due to its size

Application: Domestic and industrial

- Advantages and Disadvantages of Vapor Compression Refrigeration Cycle over Air Refrigeration System
- Open and Closed Type of Refrigeration System – Advantages and Application
- Comparison Between COP of Heat Engine, Refrigerator, And Heat Pump

Advantages and Disadvantages of Vapor Compression Refrigeration Cycle over Air Refrigeration System

pour compresssion system

Advantages

  1. Size is small when compared to an air refrigeration system for a given capacity of refrigeration.
  2. Volume of refrigerant circulated is low. Hence the running cost is low.
  3. High coefficient of performance.
  4. The operating temperature range is huge.
  5. The temperature at the evaporator can be easily controlled by regulating expansion valve.
  6. Latent heat involved in Phase change ensures high value of heat removal, while air refrigeration system has sensible heat only. 
  7. It requires smaller evaporator.
- Advantages and Disadvantages of Air Refrigeration System
- Comparison Between Heat Engine, Refrigerator, And Heat Pump

Disadvantages

  1. High initial cost, costly refrigerant.
  2. Environmental hazardous refrigerant involved.
  3. Must ensure the prevention of leakage of refrigerant..

Advantages and Disadvantages of Air/ Bell Coleman Refrigeration System

advantages and disavantages of Air refrigeration

Advantages and application of air refrigeration system

  1. Cheap and abundant refrigerant, highly reliable: Air is used as refrigerant, which is easily available and inexpensive.
  2. Charging of refrigerant is very easy.
  3. Design and construction is simple, No complicated parts and its maintenance cost is low
  4. Refrigerant (Air) is non-toxic, non-flammable, non-corrosive. There is no danger of any kind of leakage
  5. There is no phase change (liquid- gas) during the operation of system
  6. The cold air can be directly used for refrigeration; it is useful in aircraft refrigeration at high altitude.
  7. There would be no significant change in the performance of air refrigeration if it is operated much away from its design conditions.
  8. It can produce very high temperature differences between hot and cold region. So the same system can be used for both cooling and heating effects. It also helps to achieve very low temperature.
  9. Air refrigeration is used in aircraft due to availability cold air at high altitude and it can can achieve both air-conditioning, as well as the pressurization of the cabin.
- Advantages and Disadvantages of Vapor Compression Refrigeration Cycle over Air Refrigeration System

Disadvantages of air refrigeration system

  1. Lower C.O.P. compared to other refrigeration cycle.
  2. Running cost is high.
  3. The mass of air required to circulate in the system is very high when compared to other type of refrigeration cycle due to low specific heat capacity.
  4. System components are bulky, large space per ton of refrigeration.
  5. The chance of frosting at expander is more due to moisture content in the air.
  6. Air contains pollutant particle, so do regular cleaning of air filter in open system.

Open and Closed Type of Refrigeration System – Advantages and Application

oper_air_refrigeration_closed_air_refrigeration

Air cycle refrigeration is one of the earliest methods used for cooling. The key features of this method is that, the refrigerant air remain gaseous state throughout the refrigeration cycle. Based on the operation, the air refrigeration system can be classified into
  1. Open air refrigeration cycle
  2. Closed refrigeration cycle

Open air refrigeration cycle

In an open refrigeration system, the air is directly passed over the space is to be cooled, and allowed to circulate through the cooler. The pressure of open refrigeration cycle is limited to the atmospheric pressure.  A simple diagram of the open-air Refrigeration system is given below.

Advantages and application

  • It eliminates the need of a heat exchanger.
  • It is used in aircraft because it helps to achieve cabin pressurization and air conditioning at once

Disadvantages

One of the disadvantages of this system is that its large size. The air supplied to the refrigeration system is at atmospheric pressure, so the volume of air handled by the system is large. Thus the size of compressor and expander also should be large. Another disadvantage of the open cycle system is that the moisture is regularly carried away by the circulating air, this leads to the formation of frost at the end of the expansion process and clogs the line, and hence a use of dryer is preferable to the open air refrigeration system.

- Comparison between COP of Heat Engine, Refrigerator, And Heat Pump
- Quick Comparison between Gas Refrigeration Cycle and Vapor Refrigeration Cycle

Closed refrigeration system / Dense air refrigeration cycle

In closed or dense air refrigeration cycle, air refrigerant is contained within pipes and component part of the system at all time. The circulated air does not have to direct contact with the space to be cooled. The air is used to cool another fluid (brine), and this fluid is circulated into the space to be cooled. So the disadvantages listed in open air refrigeration can be eliminated.  The advantages of closed air refrigeration system are

Advantages

  • The suction to the compressor may be at high pressure, therefore the volume of air handled by the compressor and expander is low when compared to an open system. Hence the size of compressor and expander is small compared to the open air system.
  • The chance of freezing of moister and choke the valve is eliminated.
  • In this system, higher coefficient of performance can be achieved by reducing operating pressure ratio.

Comparison Between Heat Engine, Refrigerator, And Heat Pump

heat flow in heat engine, refrigerator, heat pump
The coefficient of performance or C.O.P. is defined as the ratio of useful heating or cooling effect to work required. C.O.P. of heat engine, refrigerator, and heat pump is discussed below

Heat engine

Fig a shows a schematic diagram of the heat engine. The C.O.P. of an engine is express as its efficiency. Heat engine took Q2 amount of heat from the hot body and did work equivalent to WE. The heat supplied to sink is equal to Q1. Here the useful effect is Work done, WE., it is equal to Q2 – Q1
The C.O.P of heat engine, engine efficiency η= Work done/ Heat applied
η = WE/Q2
engine efficiency equation

Refrigerator

Fig b shows a diagram of refrigeration. Q1 amount of heat is extracted from the cold body and deliver Q2 amount of heat to the hot body with the help of input work WR. Here Q2 = Q1 + WR. In refrigeration system the useful effect is the extraction of heat Q1, then the C.O.P of refrigeration is
COP refrigerator
- Coefficient of Performance and Relative Coefficient of Performance of Refrigeration Cycle
- Open and Closed Type of Refrigeration System – Advantages and Application

Heat pump

Fig c shows a schematic diagram of the heat pump. The heat flow is similar to the refrigerator; but in this case, the desired effect is the heat delivered Q2
Then the coefficient of performance of a heat pump is
COP heat pump
The relation between the COP of refrigerant and COP of heat pump
relation between COP of refrigeration and COP of heat pump

From the above equation we see that the C.O.P of heat pump is always greater than the unity
[ Prove the Coefficient of performance of heat pump always greater than one? ]

Coefficient of Performance and Relative Coefficient of Performance of Refrigeration Cycle

coefficient_of_performance_refrigerator_heat_flow

Coefficient of performance of refrigeration

The refrigerator is a device that extracts heat from colder part/ reservoir of the system and delivered it to the hotter sink/ environment. According to the second law of thermodynamics, the heat flow from a cold body to a hot body occur only by doing some outside work. The coefficient of performance of a refrigerator is defined as the ratio of useful cooling effect provided by the refrigerator to the work required.

Mathematically theoretical coefficient of performance of refrigeration is denoted as follows
Theoretical C.O.P. = Q/W
Where, Q = the total heat extracted in refrigeration (amount of cooling effect)
W = amount of work done by the refrigeration system

Relative coefficient of performance

A cooling system usually has heat loss during the operation. So its C.O.P is always slightly different from its theoretical C.O.P., the new C.O.P. is known as Actual C.O.P. Relative coefficient of performance defined as the ratio of actual C.O.P. to the theoretical C.O.P.

Relative C.O.P. = Actual C.O.P./Theoretical C.O.P.

- Comparison between COP of Heat Engine, Refrigerator, and Heat Pump
- Open and Closed Type of Refrigeration System – Advantages and Application