TurboTime Podcast: Part I: Compressor Maps with the Myth Busters

In this two-part episode of the TurboTime Podcast, Klaus Burn of Ebara Elliott Energy, and Rainer Kurz of RKSBenergy LLC, discuss compressor maps. The duo explains what compressor maps are, what they are useful for, how they fit into the process, and where head, flow, and efficiency islands fit in.

“In its most basic form, a compressor map is a graphical representation of how a centrifugal compressor behaves,” Brun said. “It's somewhat of an oversimplification because more factors play into it; but overall, it gives an accurate representation of what a compressor does within the system that it operates. A standard compressor map has an X and Y axis. The Y axis has something called head—isentropic or polytropic head. Sometimes you also see pressure ratio or a discharge pressure or a fixed section pressure. On the X axis is flow, and most of the time it’s volumetric flow. Sometimes you see mass flow, but that's not very common. Compressor maps also have a surge line on the left and on the right side of the map you have a choke or stonewall area. And finally, you have efficiency islands, and they correspond to the efficiency of the compressor. Not all compressor maps show them.”

Kurz further described efficiency islands: “Efficiency islands refer to the fact that these maps are three-dimensional, but we can only put them in two dimensions on paper. The three axes you want to display are head, flow, and efficiency. You use the efficiency lines in a very similar way to elevation lines. Also, the coordinates of the map that are directly affected by the compressor aerodynamics are head and flow. You can translate head into pressures or pressure ratios, and you can translate actual flow into mass flow, but ultimately what happens aerodynamically in the compressor is described by head and actual flow.”