Toward the design of low flow-rate multijet impingement spray atomizers

Abstract

When setting the baseline for discussing options toward a more efficient use of water resources, one of the drivers for decoupling economic growth and environmental impact is the development of resource-efficient innovations and instruments. One of such fields of interest is the design of water efficient showerheads, which provide a good shower experience, while consuming low flow rates (<3l/min), and potentiating energy savings for heating water. As a step forward in this challenge, the approach followed in this work is motivated by the need to develop tools for designing tailored sprays toward a high degree of efficiency in water usage. However, in order to design tailored sprays, it is important to establish a proper relation between the atomizer’s geometric configuration, operating conditions and the desired characteristics for the spray droplets (size and velocity). Therefore, this work focus on this tailoring through a multijet impingement atomization strategy using 2 and 3 impinging jets. An investigation is reported on the parametric effects on the dynamic characteristics of droplets of jet-impingement angle (40–90°) and pre-impingement distances (2.5–7.5mm), for a range of jet Weber numbers (20<Wej<500). The size of droplets is measured by image analysis, and their velocity by a Particle Tracking Velocimetry algorithm. The results evidence the similarities between droplet characteristics of sprays produced by 2- and 3-impinging jets, although the geometric effects induced by the jets’ impingement angle are more relevant for the 3-impinging jets spray, while negligible for the 2-impinging jets spray. Moreover, empirical correlations for the arithmetic (d10) and Sauter (d32) mean diameters, normalized by the jet diameter (dj), as well as drop velocity normalized by the jet velocity (ud/uj) are devised as tools for designing tailored multijet impingement sprays for low-flow rate water applications.