Digital Holographic Interferometry for Temperature Field Measurements in Flowing Gases and Liquids

Ing. Gramoz Cubreli

Doctoral thesis

Abstract:

This Ph.D. dissertation introduces and elaborates the optical technique known as Digital Holographic Interferometry (DHI) in the field of applied fluid mechanics for the purpose of investigating the properties and visualization of flowing gases and liquids. The work deals mostly with the general aspects of using digital holographic interferometry as the main technique of investigation, deepening in some of its technical aspects for data treatment and visualization. It gradually present the evolving process of studying different forms of temperature fields, based on the distribution of its refractive index, starting with simple 2D distribution toward 3D distribution that is treated with tomographic approach. It brings to light main concepts and possibilities of using this technique for the field of fluid mechanics. Apart the general theoretical background introduced in the beginning of this thesis, each chapter contains an introduction to some more theoretical and technical aspects of the optical setup and data treatment that are needed for a better and full understanding of the process of capturing, treating and presenting the data. General conclusions are drawn at the end of each chapter. Throughout our work, we have achieved a deviation below tenths of degree Celsius between the temperature registered from the thermocouples, ANSYS simulations and the one measured by the optical technique for the case of heat measurements in water, falling within 5% of error margin for the case of a 2D temperature field. For the case of a 3D temperature field from a pulsatile jet with water as its working fluid, we estimated that the relative uncertainty of the temperature field measurement near the orifice is below 5%, compared to the relative uncertainty increasing up to 15% further from the orifice. We also achieved an increase of the range of measurement for the case of two-wavelength digital holographic interferometry. Each investigation is accompanied with a whole-field picture of visualizing the temperature and other important properties of the fluid/gas under study, which is one of the main advantages of this optical technique.

Abstract:

This Ph.D. dissertation introduces and elaborates the optical technique known as Digital Holographic Interferometry (DHI) in the field of applied fluid mechanics for the purpose of investigating the properties and visualization of flowing gases and liquids. The work deals mostly with the general aspects of using digital holographic interferometry as the main technique of investigation, deepening in some of its technical aspects for data treatment and visualization. It gradually present the evolving process of studying different forms of temperature fields, based on the distribution of its refractive index, starting with simple 2D distribution toward 3D distribution that is treated with tomographic approach. It brings to light main concepts and possibilities of using this technique for the field of fluid mechanics. Apart the general theoretical background introduced in the beginning of this thesis, each chapter contains an introduction to some more theoretical and technical aspects of the optical setup and data treatment that are needed for a better and full understanding of the process of capturing, treating and presenting the data. General conclusions are drawn at the end of each chapter. Throughout our work, we have achieved a deviation below tenths of degree Celsius between the temperature registered from the thermocouples, ANSYS simulations and the one measured by the optical technique for the case of heat measurements in water, falling within 5% of error margin for the case of a 2D temperature field. For the case of a 3D temperature field from a pulsatile jet with water as its working fluid, we estimated that the relative uncertainty of the temperature field measurement near the orifice is below 5%, compared to the relative uncertainty increasing up to 15% further from the orifice. We also achieved an increase of the range of measurement for the case of two-wavelength digital holographic interferometry. Each investigation is accompanied with a whole-field picture of visualizing the temperature and other important properties of the fluid/gas under study, which is one of the main advantages of this optical technique.

Keywords

Digital holographic interferometry, temperature fields, spatial-carrier, Fourier Transform, convection, water, pulsatile jets, tomography

Language used: English

Date on which the thesis was submitted / produced: 31. 1. 2022

Thesis defence

• Supervisor: doc. Ing. Petra Dančová, Ph.D.

Technical University of Liberec

Faculty of Mechanical Engineering

Doctoral programme / field:
Machines and Equipment / Machine and Equipment Design