SYSTEM COMPONENTS
Topics:1.Compressors -general classification -comparison -Advantages and Disadvantages.
Compressors -general classification -comparison -Advantages and Disadvantages.
Refrigerant Compressors : A refrigerant compressor, as the name indicates, is a machine used to compress the vapourrefrigerant from the evaporator and to raise its pressure so that the corresponding saturation temperature is higher than that of the cooling medium.
1.Reciprocating Compressors: the Compressors in which the vapourrefrigerant is compressed by the reciprocating (back and forth) motion of the piston, are called Reciprocating Compressors.
A. Single acting vertical compressors
B. Double acting horizontal compressors
A. Single acting vertical compressors:
B. Double acting horizontal compressors Working:
2. Rotary Compressors: In Rotary Compressors, the vapourrefrigerant from the evaporator is compressed due to the movement of blades.
Classification:
A. RollingPiston type (single stationary blade type or Fixed vane Type)
B. Multiple vane type
C. Screw type and
D. Scroll type.
A. Rolling Piston type
(single stationary blade type
or Fixed vane Type): Working
•Don’t Required Inlet valve
•Leakage is VERY HIGH.
•Fine surface finish is required
B. Multiple vane type : Working
•It Consists Of a 4 slots and 4 vans.
•Don’t required suction pot and discharge pot.
C. Screw type : Working
•It consist of two helical-grooved rotors, (i) male rotor, (ii) female Rotor.
•male rotor drives the female rotor.
•The male rotor has lobes, the female rotor has flutes or gullies.
3. Centrifugal compressor or turbo compressor: working
•Low pressure refrigerant enters the compressor through the eye of the impeller. Eye of the impeller is nothing but the inlet of the impeller from the eye the refrigerant enters the flow passages formed by the impeller blades which
rotate at very high speed.
•That means the impeller will be rotating at very high speed. As the refrigerant flows through the passages towards the tip of the impeller its angular momentum and static pressure increase from the tip of the impeller the refrigerant flows into a stationary diffuser.
Centrifugal Compressors vs Reciprocating Compressors
Advantages :
1.High reliability, eliminating the need for multiple compressors and installed standby capacity.
2. For the same operating conditions, machine prices are lower for high volume flow rates.
3.Less plot area for installation for a given flow rate.
4. Machine is small and light weight with respect to its flow rate capacity.
Disadvantages :
1.Lower efficiency than most positive displacement types for the same flow rate and pressure ratio, especially for pressure ratios over 2.
2. Due to recycle not efficient below the surge point.
3. Very sensitive to changes in gas properties, especially molecular weight
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