Application of planar laser-induced fluorescence measurement techniques to study the heat transfer characteristics of parallel-plate heat exchangers in thermoacoustic devices

Abstract

This paper describes the development of an experimental arrangement and the application of acetone-based Planar Laser Induced Fluorescence (PLIF) measurement techniques to study the unsteady characteristics of heat transfer processes in the parallel-plate heat exchangers of thermoacoustic devices. The experimental rig is a quarter-wavelength acoustic resonator where a standing wave imposes oscillatory flow conditions. Two mock-up heat exchangers: "hot" and "cold", have their fins kept at constant temperatures by electrical heating and water cooling, respectively. A purpose-designed acetone tracer seeding mechanism is used for PLIF temperature measurement. Acetone concentration is optimised from the viewpoint of PLIF signal intensity. Two-dimensional temperature distributions in the gas surrounding the heat exchanger plates, as a function of phase angle in the acoustic cycle, are obtained. Local and global (instantaneous and cycle-averaged) heat flux values on the fin surface are estimated and used to obtain the dependence of the space-cycle averaged Nusselt vs. Reynolds number. Measurement uncertainties are discussed.

Heat transfer augmentation in unsteady conjugate thermal systems – Part II: Applications

“…Such a method is employed herein, by using the temperature-sensitive dye Rhodamine B. Fluorescence methods have proven popular in evaluating the heat exchange of microchannel devices [26,29], in plate heat exchangers with oscillating flow [27,28] and has also been used to measure fluid film temperatures elsewhere [30,31].…”

The Effect of Temperature Field on Low Amplitude Oscillatory Flow within a Parallel-Plate Heat Exchanger in a Standing Wave Thermoacoustic System

“…[7,9,18]) the natural convection effect was neglected. This effect however was observed in many experimental works [1,11,17].…”

“…However, the presence of a temperature gradient on solid boundaries is necessary for the thermoacoustic effect to take place. Temperature effects must be considered to account for additional phenomena such as temperature-driven buoyancy [11,[15][16][17][18] and non-linear effects [4] that could affect the flow symmetry. Experimental studies often reveal signs of nonlinearities that are insufficiently addressed by the linear model [1,11].…”

“…Current computational fluid dynamics (CFD) study aims to improve the understanding of physical processes involved in the phenomena reported in the earlier experimental work of Shi et al [17]. However, bearing in mind more complex operating conditions (e.g., tilted-angle solar powered systems [19,20] or space applications), the scope of CFD is somewhat wider and extends to include gravity effects and effects of the device orientation on the physics of thermo-fluid processes across the heat exchanger plates.…”

“…The novelty of this study stems from the fact that the model used attempts to take into account a far wider range of physical effects which are commonly neglected in numerical works related to thermoacoustics (i.e., natural convection or the use of a full array of plates to handle asymmetrical flow features). This is undertaken to explain the phenomena reported in [11,17]. In addition, the study of device orientation provides a new perspective of the importance of considering such seemingly minor details in modelling heat transfer phenomena in thermoacoustics.…”