Gas Cycle Refrigeration | Mechanical Engineering SSC JE (Technical) PDF Download

GAS CYCLE REFRIGERATION

DRAW BACK IN CARNOT CYCLE WHEN GAS IS USED AS REFRIGERANT

  •   Due to isentropic compression, very high pressure and due to isothermal heat rejection very high volume of gas is developed.
  •   Isothermal heat transfer with a gas is not possible practically due to very small specific heat of the gas.
  •   Small irreversibilities in a gas cycle causes much increase in work due to narrowness of the cycle.

REVERSED BRAYTON OR JOULE OR BELL COLEMAN CYCLE

  •  In this cycle, the two isothermal process of carnot cycle is replaced by is two isobaric process.
  •   These changes decrease the refrigerating effect and increase the work done.
  •  This cycle is used for aircraft refrigeration.
  •   Its COP is less than that or vapour compression cycle.

Gas Cycle Refrigeration | Mechanical Engineering SSC JE (Technical)
Gas Cycle Refrigeration | Mechanical Engineering SSC JE (Technical)
Gas Cycle Refrigeration | Mechanical Engineering SSC JE (Technical)
Refrigeration effect 
q0 =Cp (T1 - T4 )
Heat rejected
Gas Cycle Refrigeration | Mechanical Engineering SSC JE (Technical)
Isentropic compressor work
Gas Cycle Refrigeration | Mechanical Engineering SSC JE (Technical)
Isentropic expander work
Gas Cycle Refrigeration | Mechanical Engineering SSC JE (Technical)
Net work =
Gas Cycle Refrigeration | Mechanical Engineering SSC JE (Technical)
r = Pressure Ratio =
Gas Cycle Refrigeration | Mechanical Engineering SSC JE (Technical)

  •  If Pk increases or P0 decreases pressure ratio (r) increases and so COP of the cycle decreases
  •  Minimum pressure is generally fixed as being atmospheric pressure.
  •  It the maximum pressure increases, refrigerating effect and work done both increases but COP decreases, as increase in work done is more than that of refrigerating effect.

Application to Aircraft Refrigeration

  •  The gas cycle is exclusively used in aircraft refrigeration systems of military and commercial aircraft.
  •  Only air is used as working substance in this application. Hence it's called Air

Refrigeratin Cycle.

  •  Power per tonner of refrigeration is more compared to vapor compression system.

TYPE OF AIR REFRIGERATION CYCLE
Closed Cycle

  •  It can work at suction pressure higher than atmospheric pressure.
  •  It has more COP as pressure ratio is reduced.
  •   It needs heat exchanger for refrigeration process.
  •  Its weight & cost are more.

Open Cycle

  •   It can work at atmospheric pressure as suction pressure.
  •   Its COP is less
  •   It does not require heat exchanger for refrigeration process as fresh air is directly led to conditional space.
  •   Its weight & cost is less.

ADVANTAGE OF AIR REFRIGERATION CYCLE OVER VAPOUR COMPRESSION CYCLE

  •   Leakage of refrigerant is tolerable.
  •  In open type system no heat exchanger is required.
  •  Refrigerant being air is available in mid atmosphere.
  •  Cabin pressurization and air conditioning can be done simultaneously.
  •  Initial compression of the air is obtained by ram effect.

Ram Effect

  •  Conversion of high kinetic energy of the ambient air into enthalpy and pressue rise in an air craft is called ram effect.

Gas Cycle Refrigeration | Mechanical Engineering SSC JE (Technical)

Ram Efficiency = 
Gas Cycle Refrigeration | Mechanical Engineering SSC JE (Technical)

The document Gas Cycle Refrigeration | Mechanical Engineering SSC JE (Technical) is a part of the Mechanical Engineering Course Mechanical Engineering SSC JE (Technical).
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FAQs on Gas Cycle Refrigeration - Mechanical Engineering SSC JE (Technical)

1. What is gas cycle refrigeration?
Ans. Gas cycle refrigeration is a type of refrigeration system that uses a gas as the refrigerant to transfer heat from a low-temperature region to a high-temperature region. It operates on the principle of the gas cycle, which involves compression, condensation, expansion, and evaporation of the refrigerant gas.
2. How does gas cycle refrigeration work?
Ans. Gas cycle refrigeration works by compressing the refrigerant gas using a compressor, which increases its pressure and temperature. The high-pressure gas then enters a condenser, where it is cooled and condensed into a liquid state by releasing heat to the surroundings. The liquid refrigerant then passes through an expansion valve, where it undergoes a pressure drop, leading to a decrease in temperature. This low-temperature liquid then enters an evaporator, where it absorbs heat from the surroundings and evaporates back into a gas. The cycle then repeats.
3. What are the advantages of gas cycle refrigeration?
Ans. Gas cycle refrigeration offers several advantages, such as high cooling capacity, compact size, and the ability to work with a wide range of temperatures. It also provides better efficiency compared to other refrigeration systems and can be used in various applications, including air conditioning, industrial refrigeration, and transportation cooling.
4. What are the limitations of gas cycle refrigeration?
Ans. Gas cycle refrigeration has some limitations, including the release of greenhouse gases if the refrigerant used is not environmentally friendly. It also requires a power source to operate the compressor, which can increase energy consumption. Additionally, gas cycle refrigeration systems may require regular maintenance and can be more complex to design and install compared to other refrigeration systems.
5. What are some common refrigerants used in gas cycle refrigeration?
Ans. Some common refrigerants used in gas cycle refrigeration include hydrofluorocarbons (HFCs) such as R134a and R410a, hydrochlorofluorocarbons (HCFCs) such as R22, and natural refrigerants such as ammonia (NH3) and carbon dioxide (CO2). The choice of refrigerant depends on factors such as environmental impact, thermodynamic properties, safety considerations, and application requirements.
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