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 optimized 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 versus Reynolds number. Measurement uncertainties are discussed.
Highlights
The operation of thermoacoustic devices relies on very complex fluid flow and energy transfer interactions between an oscillatory compressible flow and a solid material
A simplified schematic of a standing-wave thermoacoustic engine is shown in Fig. 1: a “stack” of parallel plates and adjacent hot and cold plate heat exchangers are placed in an acoustic resonator
In standard applications such as internal combustion engines or jet flows, the temperature fields are investigated within relatively unobstructed imaging domains; and the temperature distributions may have large temperature gradients, the main focus is the nature of the temperature distribution, not an accurate estimation of the temperature gradient for heat transfer calculations
Summary
The operation of thermoacoustic devices (engines or refrigerators) relies on very complex fluid flow and energy transfer interactions between an oscillatory compressible flow and a solid material. Imposing an acoustic field in the vicinity of the solid may create a temperature gradient within it due to “heat pumping” phenomena The key to these so-called “thermoacoustic effects” [1,2] is the relative phasing between pressure and velocity oscillations, which allows the fluid to undergo a thermodynamic cycle, somewhat similar to the Stirling cycle. These phenomena form a basis for constructing thermoacoustic engines, coolers and heat pumps, whose main advantages include the simplicity of construction and lack of moving parts. Using the terminology adopted by MST this work can be classified as “the application of existing techniques in novel situations”
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