A Parametric Study on the Starting Transients of a Vacuum Ejector-Diffuser System

TL;DR

This paper investigates the transient behavior of a vacuum ejector-diffuser system through numerical simulations and experiments, revealing an inertial effect that causes oscillations in flow direction and pressure, influenced by geometric and flow parameters.

Contribution

It introduces a detailed analysis of the inertial effects and transient flow behavior in vacuum ejector systems, validated by experiments, and explores how design parameters affect these dynamics.

Findings

Inertial effect causes flow oscillations and recirculation zone movement.

Pressure and mass flux depend on jet thickness and chamber volume.

Inertial effects decrease with smaller jet thickness, larger chamber volume, and higher primary jet pressure.

Abstract

In this endeavor, the transients persisting in a vacuum ejector system (put reference of my old paper) is studied by numerically simulating the flow field, and experimentally validating the simulated results. An inertial effect was discovered in the study due to which the direction of mass flux changes. As a result of this, the recirculation zone moves forward and backward during the transients and the pressure in the secondary chamber rises and falls. The system behaves as a damped oscillatory flow in which the direction of mass flux keeps on changing and finally settles down to a state where there is no mass flux in either direction. The movement of recirculation zone due to this inertial effect is studied in more detail for various flow and geometric parameters. The results obtained show that the pressure and mass flux through the secondary chamber depend highly on both the thickness of the primary and secondary jet and the chamber volume. The inertial effect reduces with the reduction in thickness of primary and secondary flow. The inertial effect is found to be decreasing with increasing secondary chamber volume. It is also found that, the inertial effect decreases as the primary jet pressure increases, for all other parameters remaining the same. The computationally simulated flow field and the pressure on the secondary chamber are compared with the experimental data and found to be matching fairly well.