Experimental investigation of the effect of heat exchanger temperature on the behaviour of oscillatory flow

Thermoacoustic technologies are used for the conversion of acoustic power into thermal energy, or vice versa, by relying on the so-called thermoacoustic effect. This paper investigates the oscillatory flow features in a quarter-wavelength standing wave thermoacoustic device. The effect of the hot heat exchanger temperature on the flow characteristics is examined using the Particle Image Velocimetry (PIV) technique. Hot-Wire Anemometry (HWA) technique and theoretical predictions are applied for validation purposes. Four drive ratios (the ratio of acoustic pressure to the mean pressure) were tested, including 0.3%, 0.45%, 0.65%, and 0.83%. The experimental examination showed noticeable differences in the formation of vortical structures by varying the hot heat exchanger temperature. Symmetrical and asymmetrical vortex shedding is presented at both ends of the heat exchangers at the ambient and high temperatures, depending on the variation of acoustic amplitude and phase. The results showed that instabilities and disturbances from the edges of heat exchanger plates and vortex shedding may promote the formation of secondary boundary layers. The results revealed the deformation of vortical structures by increasing the temperature of hot heat exchanger within 150 °C. At the Stokes layer, the flow domain experiences high acoustic velocity in the presence of temperature due to the annular effect, which produces the ‘M’ shaped velocity profiles, while by increasing the drive ratio, the flow exhibits more pronounced nonlinear behaviour, including asymmetric velocity distributions and intensified vortex dynamics.