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Centrifugal compressors, (sometimes referred to as radial compressors) are a special class of radial-flow work-absorbing turbomachinery that includes pumps, fans, blowers and compressors.
The earliest forms of these dynamic-turbomachines were pumps, fans and blowers. What differentiates these early turbomachines from compressors is that the working fluid can be considered incompressible thus permitting accurate analysis through Bernoulli's equation. In contrast, modern centrifugal compressors are higher in speed and analysis must deal with compressible flow.
For purposes of definition, centrifugal compressors often have density increases greater than 5 percent. Also, they often experience relative fluid velocities above Mach 0.3 when the working fluid is air or nitrogen. In contrast, fans or blowers are often considered to have density increases of less than 5 percent and peak relative fluid velocities below Mach 0.3
In an idealized sense, the dynamic compressor achieves a pressure rise by adding kinetic-energy/velocity to a continuous flow of fluid through the rotor or impeller. This kinetic energy is then converted to an increase in static pressure by slowing the flow through a diffuser.
Additional recommended knowledge
Centrifugal compressors are used throughout industry because they have fewer rubbing parts, are relatively energy efficient, and give higher airflow than a similarly sized reciprocating compressor (i.e. positive-displacement). Their primary drawback is that they cannot achieve the high compression ratio of reciprocating compressors without multiple stages. Centrifugal fan/blowers are more suited to continuous-duty applications such as ventilation fans, air movers, cooling units, and other uses that require high volume with little or no pressure increase. In contrast, multi-stage centrifugal compressors often achieve discharge pressures of 8,000 to 10,000 psi (59 MPa to 69MPa) re-injecting natural gas back into oil fields to increase oil production.
Centrifugal compressors are often used in small gas turbine engines like APUs (auxiliary power units) and smaller aircraft gas turbines. A significant reason for this is that with current technology, the equivalent flow axial compressor will be less efficient due primarily to tip-clearance losses. There are few single stage centrifugal compressors capable of pressure-ratios over 10:1, due to stress considerations which severely limit the compressor's safety, durability and life expectancy.
For aircraft gas-turbines; centrifugal flow compressors offer several advantages including simplicity of manufacture, relatively low cost, low weight, low starting power requirements, and operating efficiency over a wide range of rotational speeds. In addition, a centrifugal compressor’s short length and spoke-like design allow it to accelerate air rapidly and immediately deliver it to the diffuser in a short distance. The most significant drawback is the relatively larger frontal area/unit flow. For these reasons and others, aircraft gas turbines that utilize centrifugal stages within the compressor tend to be smaller and are used in turboshaft or turboprop applications (ref List of aircraft engines). These smaller compressor configurations vary, but generally fall into one of two categories; the axi-centrifugal and the 2-stage centrifugal. Tip speeds of centrifugal compressors can often reach Mach-1.3. In current 2-stage gas-turbines, the high pressure rise per stage allows these modern compressors to obtain overall compression ratios of 15:1.
A partial list of centrifugal compressor applications include:
Many centrifugal compressors have one or more of the following operating limits:
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Centrifugal_compressor". A list of authors is available in Wikipedia.|