The origin of gas pulsations in rotary PD compressors: ΔP or ΔU?

Abstract

This paper is a continuing work from the same authors on the same topic by analogizing the transient shock tube process to the gas pulsation phenomena [1, 2]. It has been demonstrated in the previous theoretical investigation that gas pulsations can be generated either by a sudden velocity change (ΔU) say from a piston or lobe movement, or by the sudden opening of a pressure difference (Δp4i) such as during the discharge phase of a rotary PD (Positive Displacement) compressor (screw, scroll or Roots) under UC (Under-Compression) or OC (Over-Compression) conditions. It is further reasoned that the more dominant pulsation source should be from the Ap41 induced source, but without backing from experiments.This paper is aimed at validating the theoretical predictions through experimental investigation conducted on a Roots blower, a special 100% UC case. This further clarification is important not only to prove the theory, but would pave the way for potential gas pulsation control methods if exact origin and nature of gas pulsations can be located and understood. Two schemes of tests under different load and speed conditions were carried out and results confirm the previous analytical conclusion that the dominant source of the gas pulsations for the 100% UC case is mainly from the sudden release of a pressure difference (Δp41) while the non-uniform rotor movement (ΔU) induced pulsation is about one order of magnitude lower. More experimental work on other types of rotary compressors such as screw or scroll is desirable in the future.