Interferometry based whole-field heat transfer measurements of an impinging turbulent synthetic jet

Abstract

The present work is concerned with exploring the potential of refractive index-based imaging techniques for investigating the heat transfer characteristics of impinging turbulent synthetic jets. The line-of-sight images of the convective field have been recorded using a Mach Zehnder interferometer. Heat transfer experiments have been conducted in infinite fringe setting mode of the interferometer with air as the working fluid. The effect of the excitation frequency of the synthetic jet on the resultant temperature distribution and local heat transfer characteristics has been studied. The fringe patterns recorded in the form of interferograms have first been qualitatively discussed and thereafter, quantitatively analyzed to determine the two-dimensional temperature field. Local heat transfer coefficients along the width of the heated copper block have been determined from the temperature field distribution thus obtained from the interferograms. The results have been presented in the form of interferometric images recorded as a function of frequency of the synthetic jet, corresponding two-dimensional temperature distributions and local variation of heat transfer coefficients. Interferometric measurements predicted maxima of the heat transfer coefficient at the resonance frequency of the synthetic jet and at a jet-to-plate surface spacing (z/d) of 3. These observations correlate well with the thermocouple-based measurements of temperature and heat transfer coefficient performed simultaneously during the experiments. The interferometry-based study, as reported in the present work for the first time in the context of synthetic jets, highlights the importance of refractive index-based imaging techniques as a potential tool for understanding the local heat transfer characteristics of synthetic jets.