How to Read a Compressor Map for Dummies
Compressor Maps
Compressor maps are developed by the manufacturer of dynamic compressors. They are compressor equivalents of the pump performance curves. It is the performance chart of a specific compressor which manufacturer calculates and draws up for the unique pattern characteristics of that compressor. An example of an air compressor from a car turbocharger is shown in figure – i.
Effigy 1: Sample air compressor map
Compressor maps are two dimensional and has all the information an engineer needs for design purposes. In the sample compressor map represented in figure-1, the blue curved lines represent compressor curves for different impeller speed values with the uppermost line being the maximum speed that the compressor can reach. The skewed ellipses are the efficiency "islands" or the efficiency areas. The Y axis is the pressure level ratio which is explained below and the X axis is the "air / gas flow earlier the turbo". To read of a point from the compressor map is straight forrard. For case the red circled signal on the map, represents compressor output of 520 CFM (corrected air flow) at a pressure ratio of ii.1. At this point the compressor is spinning at 144000 rpm and has an efficiency of merely 61% (indicated by the corresponding efficiency area).
The Y axis (Vertical Axis)
Y axis of a compressor maps indicates pressure ratio. Pressure level ratio is the ratio of the compressor discharge pressure level to the compressor suction force per unit area. If the compressor suction pressure is known, pressure ratio can be decided to achieve required output. For example if the inlet pressure level is 1bar (Atmospheric pressure level) and it is required to boost the gas to a pressure of 2 bar, then the force per unit area ratio needs to be two. The same principal applies to industrial compressors except that they take higher pressure ratios, peculiarly multi-stage compressors. The following is a formula of the calculation that has just been described:
Outlet pressure level = Inlet pressure × pressure ratio
Thus if at sea level a certain compressor gives an outlet pressure of 2 bar and so yous take the compressor to a much college elevation the outlet pressure will be lower because the inlet pressure has dropped.
Efficiency Islands / Efficiency Areas
The "ellipses" can be used just like contours on geographical maps, except that here they prove a range of efficiencies. Usually the efficiency islands converge to the centre of the compressor map equally shown in effigy-1, where the efficiency is at its maximum. This line where the efficiency islands on compressor maps converge is known as "Summit Efficiency Line". Commonly operating the compressor about "Peak Efficiency Line" is always the most desirable as the about possible work output can be obtained using aforementioned or less work input.
Surge and Choke lines (Orange)
The orangish line on the left hand side is the Surge line and the Orange line on the right hand side is the asphyxiate line. If the compressor operates on the left of the surge line, this can issue in compressor surge. Compressor surge is a pulsating back flow of gas through the device. Compressor surge is a highly undesirable phenomenon as it can mechanically impairment compressor parts and must be avoided.
If the compressor operates on the right of the choke line and so the compressor will feel choked menses. Choked flow is when the menses reaches the speed of sound and this is a problem considering information technology limits the maximum flow rate through the compressor. Thus the asphyxiate line on a compressor map signifies its maximum flow charge per unit limit. When designing a compressor system careful consideration needs to be taken to make sure that the designed operating point does not fall outside the surge and choke lines.
Max Flow and Max Pressure level
The maximum flow that a compressor can handle is hands constitute on the sample compressors map, in effigy-i. The point of maximum flow is the extreme right point on the map. The red circled point in figure-one happens to exist the betoken of maximum menstruation. If more menstruation needs to be pushed through and so a different compressor is required. At the maximum flow point, compressor efficiency is at its lowest so it is highly desirable to utilize a unlike compressor.
The maximum discharge force per unit area that a compressor can achieve is found using the uppermost bespeak on the map. At this point the force per unit area ratio can be found and using the formula to a higher place the outlet pressure can be calculated.
Compressor maps are very important in design of systems considering they give you vital information on surge, asphyxiate and compressor speeds. They as well let you lot know if your compressor is going to be efficient plenty for your application.
Source: https://www.enggcyclopedia.com/2012/01/compressor-maps/
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