Experimental investigation of flow and thermal characteristics of synthetic jetissuing from sharp-edged orifices

The present experimental study reports the flow and heat transfer characteristics of a synthetic jet issuing from a sharp-edged orifice (diverging-shaped orifice). The experiments are carried out for a varied range of opening angles of sharp-edged orifices (theta = 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees), Reynolds number (Re = 3243-8143), different jet-to-surface spacings (z/d = 1-16), and for two different values of orifice thicknesses, t = 5 mm (t/d = 0.33) and 10 mm (t/d = 0.66). The hot-wire anemometry is used to study the flow characteristics of synthetic jet, while heat transfer characteristics are studied by using a thermal imaging technique. The time-averaged flow fields associated with sharp-edged orifices reveal that orifices with t = 5 mm and 10 mm exhibit saddle-backed and top-hat velocity profile shapes, respectively. The results show that for a square-edge orifice (theta = 0 degrees), the heat transfer rate decreases with an increase in orifice plate thickness from 5 to 10 mm, while the opposite trend in heat transfer is observed with sharp-edged orifice. The heat transfer rate with a 10 mm thick sharp-edged orifice is higher than the 5 mm thick sharp-edged orifice for all the tested opening angles. Furthermore, the results also show that for sharp-edged orifices, the heat transfer rate increases with the increase in opening angle from theta = 0 degrees to 60 degrees, while it decreases with further increasing from theta = 60 degrees to 120 degrees. The maximum value of average Nusselt number (Nu(avg)) is obtained for theta = 60 degrees for both the orifice thicknesses (t = 5 and 10 mm), and this effect is found to be more pronounced for t = 10 mm orifice. For sharp-edged orifice (theta = 60 degrees), the maximum enhancement in Nu(avg) is found to be 12.66% and 23% higher for t = 5 mm and 10 mm, respectively, compared to the equivalent square-edged orifice (theta = 0 degrees). The cause for variation in heat transfer rate with sharp-edged orifices is interpreted due to the effect of flow recirculation and mass flow rate. A correlation has been proposed for Nu(avg) as a function of different opening angles. The present finding is useful for the optimization of the synthetic jet geometrical parameters for the effective heat transfer rate.

Automated summary

This experimental study investigates the flow and heat transfer characteristics of a synthetic jet from a sharp-edged orifice. The study explores the effects of orifice opening angles, Reynolds number, jet-to-surface spacing, and orifice thickness on the flow and heat transfer. The results show that the heat transfer rate is influenced by the orifice thickness and opening angle, providing valuable guidance for optimizing the geometric parameters of synthetic jets.