Abstract
This work aims to develop reliable laser-based measurement techniques to enable fundamental heat transfer and fluid flow studies in thermoacoustic systems. The challenge is to better understand the modes of energy transfer between the key components, such as stacks (or regenerators) and the hot and cold heat exchangers (located on two sides of the stack/regenerator structure), under the oscillatory flow conditions imposed by the acoustic field. The measurement methodologies adopted in this work include combined two-dimensional temperature and velocity field measurements using Planar Laser-Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV), respectively. These are investigated around the fins of a pair of mock-up heat exchangers placed side by side in a quarter-wavelength standing-wave acoustic resonator, to mimic the working conditions of a thermoacoustic system. The fins are kept at constant temperatures by means of resistive heating and water cooling, respectively. The velocity and temperature field distributions for 20 phases in the acoustic cycle have been obtained. The impact of the inertial, viscous and thermal effects on the time-dependent local temperature and velocity distributions is discussed. Mutual interaction between both fields is also shown. Future work towards obtaining useful heat transfer correlations in oscillatory conditions is outlined.
Highlights
Introduction and backgroundThermoacoustic engines and refrigerators rely on a thermal interaction between an oscillatory compressible flow and solid structures such as thermoacoustic stacks and heat exchangers.The role of these solid structures is to either produce acoustic power, due to an imposed temperature gradient, or to produce a refrigeration effect, induced by an acoustic excitation
The objective of this work is to develop and demonstrate the appropriate experimental techniques to include Planar Laser Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV) to enable detailed studies of heat transfer and fluid flow processes taking place on the micro-scale of the oscillatory flow around the solid surfaces that form the main components of the thermoacoustic devices
The combined measurement techniques of PIV and acetone-based PLIF have been developed to study the fluid flow and heat transfer processes in the oscillatory flow within a cold and hot heat exchanger setup, which mimics the physics of thermoacoustic processes
Summary
Thermoacoustic engines and refrigerators rely on a thermal interaction between an oscillatory compressible flow and solid structures such as thermoacoustic stacks (regenerators) and heat exchangers. The objective of this work is to develop and demonstrate the appropriate experimental techniques to include Planar Laser Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV) to enable detailed studies of heat transfer and fluid flow processes taking place on the micro-scale of the oscillatory flow around the solid surfaces that form the main components of the thermoacoustic devices. This kind of data can potentially be used to obtain both local and global (as well as instantaneous and/or cycle-averaged) heat transfer rates, which could be used for devising new heat transfer correlations. CFD codes that could be used for predicting the performance of thermoacoustic systems
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