The custom high speed centrifugal compressor is popular for pneumatic conveying, as it is highly efficient while being much lighter than compressors which operate through the movement of gas. Its polytropic efficiency is greater than eighty percent, and it is usually built with stainless steel or aluminum. A customized accelerometer is provided for the purpose of preventative maintenance.
Many of the blowers and compressors used today, particularly for refrigeration, are effective and consist of mechanical parts which are optimal. Additionally, they can be mass produced, making them widely available and affordable. However, centrifugal compression still has a number of advantages. It utilizes impellers which are simple in design and low in cost as the primary element, instead of the intricate surfaces and excessive tolerances which are seen in most standard compressors.
Furthermore, centrifugal compressors do their best when operating at higher speed. Their speed will increase while the flow volume will decrease. A two stage compressor can achieve RPMs higher than 100,000. However, at this rate the loss of rotor windage must be taken into consideration. Windage is almost completely proportional to fourth diameter power and about a third of RPM power. This means that great care must be taken when choosing the diameter of the motor, especially when one is needed which is hermetically cooled.
Choosing The Motor And Drive
There are three types of motors which can be used with a centrifugal compressor that is high speed, and these are permanent magnet, switch reluctance and induction. Research conducted on these three motor variants has found that all of them can provide electrical efficiency which is in the moderate 90s. Despite this, switch reluctance motors seem to be at a windage disadvantage as a result of the cross section which is cruciform. Permanent magnet motors are compact and thus have greater efficiency, but can be expensive as a result of higher speed. Induction motors are the most cost effective and popular of the three.
Commercial drives are available in PWM (pulse width modulation) and 6 step that provide 900 Hz. Those that require drives which are higher speed can have them custom built as needed. Since these drives can be as costly as the centrifugal compressor itself, researchers have been developing various ways to lower manufacturing costs. This will allow the compressors and drives to be competitive with and even surpass existing technologies.
Centrifugal compression is distinct in that it necessitates greater minimum frequency when compared to the other compression options available on the market. At the same time, it is superior at utilizing its capabilities. Another factor that must be considered is critical shaft speed, which is determined by the stiffness of the shaft, rotor mass and bearing. Generally speaking, shafts with a smaller diameter are preferable for windage which is low, but may cause the shaft to stiffen, which requires the creation of damping which is adequate.