Centrifugal Compressor are generally used for the refrigerants that requires low condensing pressure, such as R-11 and R-113. It uses Centrifugal force to increase the low-pressure vapour refrigerant to high pressure.
A Centrifugal Compressor consists of an impeller to which symmetrical vanes are fitted. The impeller rotates in airtight casing with inlet and outlet points.
The impeller takes the low-pressure refrigerant from the evaporator through inlet. When the refrigerant rotates, it pushes the vapor refrigerant from the center to the periphery. The vapour refrigerant gains the high velocity at the tip of the vanes of the impeller. the kinetic energy is thus converted into the pressure energy when the refrigerant vapour passes over the diffuser. The volute casing collects the refrigerant from the diffuser. It further converts the kinetic energy into the pressure energy before it leaves.
Advantages and disadvantages of Centrifugal Compressor
- The working life of these compressors is more as they don’t have valves, pistons, cylinders, or connecting rods.
- There are no unbalanced masses so these compressors operate with little or no vibration.
- The efficiency of these compressors is generally high.
- Centrifugal Compressors require less floor areas than reciprocating compressors.
- They can directly be connected to electric motors or steam engines as they can run with more than 3000 R.P.M
- These Compressors can handle large volume of vapour refrigerant because of its high speed.
- They can work with the temperature range between -90°C and +10°C
- The increase in pressure is less.
- Centrifugal compressors are not practical below 50 tonnes capacity load.
- Refrigerant used with these compressor should have a high specific volume.
- The main disadvantage of the centrifugal compressor is surging.
Surging occurs when the refrigeration load decreases below 35% of rated capacity.