Speaker
Description
The broad applicability and effectiveness of impinging synthetic jets (SJs) in thermal management have motivated extensive efforts to refine their design through systematic examination of key parameters, including stroke length and Reynolds number [1–2]. Earlier investigations [3–4] have demonstrated that nozzle geometry plays a significant role in determining the heat transfer of impinging SJs. However, these studies did not consider the temporal or spatial evolution of the heat transfer coefficient on the impinged plate, as the results were limited to time-averaged pointwise measurements.
The current work focuses on the influence of the nozzle exit section shape (NESS) on the heat transfer behaviour of SJs. Four different shapes are comparatively assessed: the circular (C), the triangle (T), the square (S) and the rectangular (R) NESS. To capture the spatio-temporal evolution of the heat transfer behaviour, phase-locked 2D infrared thermography measurements are carried out for five nozzle-to-plate distances: H/D ∈ [2,4,6,8,10] The Reynolds and Strouhal numbers are kept constant to Re = 3500 and Sr =0.068.
The heat transfer behaviour is significantly modified by the NESS, especially for short impingement distances. Upon ejection, the coherent vortical structures inherit the geometry of the issuing nozzle, hence the Nu maps show the signature of the impinging vortical structures. Whereas, as the vortical structures are convected downstream, they lose their geometrical coherence due to inertial instabilities and, at high nozzle-to-plate distances, the SJ’s thermal footprint on the foil is almost bell-shaped, with all NESSs achieving a heat transfer similar to the circular nozzle.
Additionally, phase-averaged measurements revealed the complex evolution of the heat transfer coefficient during the actuation period of the SJ.
References
$\left[1\right]$ Carlo Salvatore Greco et al. “Effects of the stroke length and nozzle-to-plate distance on synthetic jet im pingement heat transfer”. In: Int. J. Heat Mass Transf. 117 (2018), pp. 1019–1031. DOI: 10.1016/j.ijheatmasstransfer.2017.09.118.
$\left[2\right]$ M. Chaudhari et al. “Heat transfer characteristics of synthetic jet impingement cooling”. In: Int. J. Heat Mass Transf. 53.5 (2010), pp. 1057–1069. DOI: https://doi.org/10.1016/j.ijheatmasstransfer.2009.11.005.
$\left[3\right]$ P. Gulati et al. “Influence of the shape of the nozzle on local heat transfer distribution between smooth flat surface and impinging air jet”. In: Int. J. Therm. Sci. 48.3 (2009), pp. 602 617. ISSN: 1290-0729. DOI: https://doi.org/10.1016/j.ijthermalsci.2008.05.002.
$\left[4\right]$ M. Chaudhari et al. “Effect of orifice shape in synthetic jet based impingement cooling”. In: Exp. Therm. Fluid Sci. 34.2 (2010), pp. 246–256. DOI: https: //doi.org/10.1016/j.expthermflusci.2009.11.001.
