A scroll compressor (also called spiral compressor , scroll pump and vacuum pump scroll ) is a device for compressing air or cooler. It is used in AC equipment, as a car supercharger (where it is known as a roll-type supercharger) and as a vacuum pump. Many residential central heat pumps and air conditioning systems and some automotive air conditioning systems use scroll compressors instead of traditional rotary, reciprocating, and wobble compressors.
The scroll compressor operating in reverse is known as scroll scroll , and can be used to generate mechanical work from expanding air, liquid or compressed gas.
Video Scroll compressor
Histori
LÃÆ' Â © on Creux first patented a scroll compressor in 1905 in France and the United States (Patent Number 801182). Creux created the compressor as a rotating steam engine concept, but the metal casting technology of that period was not advanced enough to build a working prototype, as the scroll compressor demands very strict tolerance to function effectively. The first practical scroll compressors did not appear on the market until after World War II, when high-precision machining equipment enabled their construction. They were not produced commercially for air conditioning until the early 1980s.
Maps Scroll compressor
Design
The scroll compressor uses two interleaving reels to pump, condense or press liquid such as liquids and gases. The propeller geometry may be tortuous, Archimedean arches, or hybrid curves.
Often, one of the scrolls remains, while the other orbits eccentrically without turning, thus trapping and pumping or pressing fluid pockets between rolls. Another method to produce compression movements is co-rotating coils, in synchronous motion, but with offset center offset. Movement is relatively the same as if one were orbiting.
Another variation is with a flexible pipe (layflat) in which the archimedean spiral acts as a peristaltic pump, operating on the same principle as a toothpaste tube. They have casing filled with lubricants to prevent outer abrasion of pump tubes and to assist heat dissipation, and use reinforced tubes, often called 'hoses'. This pump class is often called the 'oil well hose'. Because no moving parts come in contact with liquids, peristaltic pumps are inexpensive to produce. The lack of valves, seals, and glands makes them relatively cheap to treat, and hoses or tubes are low cost care items compared to other types of pumps.
Apps
- AC Compressor
- Vacuum pump
- Supercharger for car apps, e.g. Volkswagen G-Lader
Comparison of techniques to other pumps
These devices are known to operate more smoothly, quietly, and reliably than conventional compressors in some applications. Unlike pistons, the orbiting scroll mass can be perfectly balanced, with a simple mass, to minimize vibration. (An orbiting coil can not be offset if the use of the Oldham clutch is used.) The rolling gas processes are more continuous. In addition, the lack of dead space provides increased volumetric efficiency.
Pulse rotation and flow
The compression process occurs over 2 to 2 1/2 rotation of the crankshaft, compared with one turn for a rotating compressor, and one and a half rounds for a reciprocating compressor. The scroll discharge and suction process occur for full rotation, compared to less than half of the rotation for reciprocal suction process, and less than a quarter of rotation for the mutual discharge process. The reciprocating compressor has several cylinders (usually, anywhere from two to six), while the scroll compressor has only one compression element. The presence of several cylinders in the reciprocating compressor reduces suction and discharge pulsation. Therefore, it is difficult to state whether the scroll compressor has a lower pulsant rate than the reciprocating compressor as is often claimed by some scroll compressor suppliers. A more stable stream produces lower gas pulsation, lower noise and lower vibration than installed piping, while having no effect on the operating efficiency of the compressor.
Valves
The scroll compressor never has a suction valve, but depending on the application may or may not have a discharge valve. The use of dynamic release valves is more prominent in the application of high pressure ratio, typical of cooling. Typically, air conditioning rolls do not have a dynamic exhaust valve. The use of a dynamic release valve increases the efficiency of the scroll compressor through various operating conditions, when the operating pressure ratio is well above the compressor mounted pressure ratio. If the compressor is designed to operate near a single operating point, the scroll compressor can actually gain efficiency around this point if no existing dynamic discharge valve (since there is an additional discharge flow loss associated with the presence of the exhaust valve as well as the disposal port is likely smaller when discharge is present).
Efficiency
The isentropic efficiency of the scroll compressor is slightly higher than that of a typical reciprocating compressor when the compressor is designed to operate near a selected rating point. Scroll compressors are more efficient in this case because they do not have a dynamic release valve that introduces additional throttling losses. However, the efficiency of a scroll compressor that does not have a discharge valve starts to decline compared to the reciprocating compressor at higher pressure ratio operations. This is the result of lower compression losses occurring at the high-pressure operation ratio of a positive displacement compressor that does not have a dynamic exhaust valve.
The scroll compression process is almost 100% volumetric efficient in pumping trapped fluid. The suction process creates its own volume, apart from the process of compression and further discharging inside. In comparison, the reciprocating compressor leaves a small amount of compressed gas in the cylinder, as it is impractical for the piston to touch the head or the valve plate. The residual gas from the last cycle then occupies the space intended for suction gas. Capacity reduction (ie volumetric efficiency) depends on suction pressure and discharge with larger reductions occurring at higher discharge ratios of suction pressure.
Reliability
The scroll compressor has fewer moving parts than the reciprocating compressor which, theoretically, should increase reliability. According to Emerson Climate Technologies, a scroll compressor manufacturer Copeland, the scroll compressor has 70 percent fewer moving parts than a conventional reciprocating compressor.
In 2006, a major food service manufacturer, Stoelting, chose to change the design of one of the soft serve ice cream machines from reciprocating to scroll compressors. They found through testing that the scroll compressor design provides better reliability and energy efficiency in operation.
Size
The scroll compressor tends to be very compact and runs smoothly so it does not require spring suspension. This allows them to have a very small shell enclosure that reduces overall costs but also results in a smaller free volume. This is a weakness in terms of handling fluids. Their corresponding strength is in the lack of a suction valve that drives the most likely point of failure to a propulsion system that might be made somewhat stronger. Thus the scroll mechanism itself is more tolerant of fluid consumption but at the same time easier to experience in operation. The small size and quiet operation of the scroll compressor allows the unit to be built into computers with high power density, such as the IBM mainframe. The scroll compressor also simplifies the pipeline design, as it does not require an external connection for the primary cooler.
Partial load
Until now, the compressor powered rolls can only operate at full capacity. Capacity modulation is performed outside the scroll pool. To achieve a partial load, engineers will cut the refrigerant from the compression pocket between returning to suction, varying the speed of the motor, or providing some compressors and installing and discharging them sequentially. Each of these methods has disadvantages:
- Bypass short circuits are normal cooling cycles and allow some partially compressed gases to return to compressor suction without doing any useful work. This practice reduces overall system efficiency.
- Two-speed motor requires more electrical connections and switches, increases costs, and may have to stop to switch.
- Variable speed motors require enhancements to supply electrical power throughout the desired frequency range. Also variable frequency drivers associated with variable speed compressors have their own electrical losses, and are a significant additional source of cost and often an additional reliability problem.
- The compressor cycle requires more compressors and can be expensive. In addition, some compressors in the system may have to be very small to accurately control the process temperature.
Recently, scroll compressors have been manufactured that provide partial load capacity in one compressor. This compressor changes the current capacity.
Reciprocating compressors often have better unloading capabilities than scroll compressors. Reciprocating compressors operate efficiently in unloaded mode when the flow to some cylinders is completely disconnected by the internal solenoid valve. The two-stage reciprocating compressor is also suitable for steam injection (or so-called operational savings when the partially expanded flow is injected between the first and second compression stages for capacity building and efficiency improvements. While scroll compressors can also rely on steam injection to vary the capacity, their steam injection operations are not as efficient as the case of reciprocating compressors. This inefficiency is caused by the constantly changing volume of compressor scroll compression compresses during the steam injection process. As the volume continues to change, the pressure in the compression pouch is also constantly changing which adds to the inefficiency of the steam injection process. In the case of a two-stage reciprocating compressor, a steam injection occurs between two stages, in which no volume is changed. Scroll and reciprocating compressors can be derived from middle-stage compression, but reciprocating compressors are also more efficient for unloading modes than scroll compressors, since the port dimensions that are not loaded in terms of scroll are limited by the size of the internal port, which would not be the case for reciprocating compressors where disassembly again occurs from between two stages.
Emerson manufactures scroll compressors capable of varying the flow of refrigerants as needed. Instead of repairing the scrolls together, the scrolls are allowed to move separately. When the windings move apart, the motor continues to spin but the coil loses the ability to condense the refrigerant, resulting in reduced motor power when the roll compressor does not pump. By alternating two different working countries: the loaded state and the derived state. A solenoid contract and expand the spinning roll and/or scroll fixed, using axial compliance. The controller modifies load time, and unload time, adjusts the compressor capacity to the requested load. This type of scroll compressor while offering variable variable control, typically down to 20% of full flow, may experience significant efficiency downturns especially towards lower ranges of capacity control.
See also
- Vacuum pump
- Gas compressor
- Pump
- Compressed air batteries
References
External links
- Compressor Copeland 111, a video showing how a scroll compressor works
Source of the article : Wikipedia
0 Comments