It is well known that compressors, such as the Roots compressor, with no internal compression have a low efficiency. Two approaches (1, 2) to the efficiency analysis are compared here, and the correct approach is identified. The results for the efficiency of ideal systems are placed in context by considering typical applications, along with methods for improving the efficiency. The significance of the internal leakage losses reported elsewhere is established and comparisons are made with the inherent thermodynamic losses. The analysis is extended to cover compressors with some internal compression, such as sliding vane and screw compressors, when they are operating away from their design point.
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