Which type of cabin air compressor is considered positive-displacement?

The type of cabin air compressor that is considered positive-displacement is the Root blower. A positive-displacement compressor works by trapping a volume of air and then displacing it into the cabin, effectively increasing the pressure of the air. Root blowers achieve this through the use of two rotors that mesh together, creating pockets of air that are pushed into the system.

In contrast, centrifugal compressors, like the one mentioned in the first option, operate by converting kinetic energy into pressure energy through the rotation of an impeller, making them dynamic compressors rather than positive-displacement types. Electric heaters, listed as another option, do not compress air at all; instead, they provide heat to the existing cabin air without changing pressure. Turbochargers primarily function to force more air into an engine for combustion efficiency rather than serving as a standard cabin air compressor.

Understanding the mechanics of different types of compressors helps clarify why the Root blower is categorized as a positive-displacement unit, contributing effectively to cabin pressurization and air supply.