The difference between screw compressors and scroll and falling film compressors
The following is a detailed comparison of screw, scroll and diaphragm compressors (note: falling film compressors are actually special types of diaphragm compressors):
1. Screw compressor
1. working principle
A pair of meshed male and female rotors are used to rotate in the cylinder to produce periodic volume changes to complete the suction, compression and discharge of gas. The rotors are sealed by oil injection to form an oil film, and are cooled and lubricated at the same time.
2. structural characteristics
- Simple structure, few wearing parts and reliable operation.
- The meshing gap between male and female rotors is small (5~10 wires) to ensure efficient sealing.
- It is divided into single screws and twin screws, with twin screws being more common.
3. performance advantages
- high thermal efficiency: The exhaust temperature is low and is insensitive to wet strokes.
- strong adaptability: Volume flow is almost unaffected by exhaust pressure and is suitable for a variety of working conditions.
- flexible adjustment: The exhaust volume can be adjusted through the slide valve, which has significant energy-saving effects.
4. application field
- Refrigeration equipment such as refrigeration, refrigeration, air conditioning and chemical technology.
- Heating and air conditioning (such as air heat source type, water heat pump type).
- Industrial fields (such as screw heat pumps for heat recovery).
2. Scroll compressor
1. working principle
The movable scroll disk and the fixed scroll disk are meshed with each other, and the movable disk is driven by the eccentric shaft to make a planar orbiting motion, forming multiple crescent-shaped compression chambers, in which the gas is gradually compressed and continuously discharged.
2. structural characteristics
- The end contact line of the movable and stationary scrolls is long and has good sealing performance.
- No suction/exhaust valve reduces resistance losses.
- High-precision processing equipment is needed to ensure the accuracy of scroll profile.
3. performance advantages
- high-efficiency energy-saving: Volume efficiency can reach 98%, low energy consumption.
- low noise: Smooth operation, small vibration and low noise.
- low maintenance cost: There are few main engine parts, few wearing parts, and long maintenance cycle.
4. application field
- Household and commercial air conditioning and heat pump systems.
- Refrigeration equipment (such as refrigerators, freezers).
- Small gas compression (such as car engine superchargers).
3. Diaphragm compressor
1. working principle
Relying on the diaphragm to reciprocate in the cylinder, the cylinder volume is changed through hydraulic drive to achieve gas compression and transportation. The diaphragm completely isolates the cylinder from the hydraulic chamber, ensuring that the gas is not contaminated.
2. structural characteristics
- The diaphragm is made of metallic or non-metallic material and the edges are clamped by limiting plates.
- Hydraulic drive, oil-free lubrication, ensuring gas purity.
- The structure is complex and requires precision machining and assembly.
3. performance advantages
- High purity compression: Gas does not come into contact with lubricating oil and is suitable for rare gases, toxic gases, etc.
- large compression ratio: The single-stage compression ratio can reach 25, and the multi-stage compression pressure exceeds 100MPa.
- good sealing: The cylinder has excellent sealing performance and small leakage.
4. application field
- Nuclear power, nuclear energy, food and medicine, petrochemicals.
- Electronics industry (such as semiconductor manufacturing).
- Defense and military industries (such as compressed radioactive gases).
4. Comparative summary of the three compressors
| characteristics | screw | scroll | diaphragm type |
|---|---|---|---|
| working principle | meshing compression of male and female rotors | Compression of scroll orbiting motion | The diaphragm reciprocates and compresses |
| structural complexity | simple | medium | complex |
| noise level | Higher (sound insulation measures required) | low | low |
| maintenance costs | medium | low | High (Diaphragm needs to be replaced regularly) |
| gas purity | Oil containing (requires post-treatment) | No oil (but scroll wear needs to be considered) | High (no oil and no pollution) |
| applicable scenarios | Large and medium-sized refrigeration/industrial systems | Household/commercial air conditioning, small refrigeration | High-purity gases, corrosive gases |
| cost | moderate | Higher (high machining accuracy) | Very high (high material/processing requirements) |
Selection suggestions
- Pursuing high efficiency, energy conservation and low noise: Choose scroll type (such as central air conditioning, household air conditioning).
- Requires large displacement or industrial applications: Choose screw type (such as cold storage, chemical process).
- Compression of high-purity/corrosive gases: Choose diaphragm type (such as semiconductors, pharmaceuticals).
Select the most suitable compressor type based on specific needs (such as gas purity, pressure, flow, cost).