City Research Online

Abstract

This study investigates the fluid flow and Conjugate Heat Transfer (CHT) in the clearance gaps during the operation of an optical Roots blower, which is a type of rotary Positive Displacement Machine (PDM) commonly used in energy generation and conversion systems. Leakage flow through clearance gaps between rotating and stationary elements of PDM’s is a major contributor to efficiency loss and reducing clearances can cause reliability issues, especially in oil-free PDMs. However, high fidelity measurements of flow and temperatures in clearances during operation of PDM and measurements of thermo-fluid-solid interaction in clearance gaps are not reported. To address this gap, the study employs three optical measurement techniques, namely Planar Laser-Induced Fluorescence (PLIF) to measure the air temperature in clearances, Particle Image Velocimetry (PIV) to measure flow velocities, and high-speed Infrared Thermography (IR) to measure lobe and casing surface temperatures. The data collected are post-processed and analyzed using specialized data visualization software. The study establishes a state-of-the-art experimental test rig to explore the physics of flow and heat transfer in clearance gaps, and the experimental data validate the numerical models of CHT in clearance flows. The results of the study provide new insights into the difference in clearance flow between stationary and running conditions and show the presence of secondary flows such as boundary layer and vortices, which are different from measurements in stationary condition. The findings from this study are used to implement new active control methods to control leakages through clearances.

The contributions of this study are the establishment of a experimental setup for exploring the physics of the flow and heat transfer in clearance gaps, the understanding of the difference in the clearance flow between stationary and running conditions, and experimental data for the validation of numerical models of CHT in clearance flows.

A new design for the tip shape of clearance has been proposed, which aims to reduce leakage flow. Additionally, an improved setup for Planar Laser-Induced Fluorescence (PLIF) has been proposed to accurately measure the temperature inside the clearance. Further work is planned to investigate clearance flows through different shapes of clearance gaps using both PLIF and PIV measurements

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses School of Science & Technology > Engineering

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