Microspray flow/thermal characteristics via a micro-piezoelectric atomizer with single and multiple arrays of micronozzles

• Published in: Experimental thermal and fluid science 2018-05, Vol.93, p.96-107
• Main Authors: Hsieh, Shou-Shing, Yeh, Yi-Fan, Li, Yi-Fang
• Format: Article
• Language: English
• Subjects: Arrays; Atomizing; Cooling; Cooling and boiling curve; Cooling rate; Downstream; Flow characteristics; Flow rates; Heat flux; Impingement; Mass flow rate; Microholes; Microspray cooling; Piezoelectric actuator; Piezoelectricity; Size distribution; Temperature distribution; Thermal energy; Velocimetry; Velocity; Velocity measurement
• ISSN: 0894-1777; 1879-2286
• DOI: 10.1016/j.expthermflusci.2017.12.023

•Effect of the spray height on the cooling performance has been extensively studied.•At the spray height H = 50 mm, the biggest cooling rate can reach −15 °C/s.•The maximum steady state CHF can be up to 259 W/cm2 with a HTC of 2.0 W/cm2 K. An experimental study on the flow characteristics (only for a single microhole) and cooling performance (multiple array of microholes) of water spray impingement on a polished copper plate using a commercial piezoelectric (PZT) atomizer with multiple arrays of micronozzles (∼900 holes) was conducted. Microholes of dj = 35 µm were used and tested with a total volumetric flow rate of 0.361–22.5 cm3/min and a corresponding mass flow rate of 6 × 10−6 kg/s–3.7 × 10−4 kg/s using seven spray heights of 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm and 90 mm. µPIV and IPI optical velocimetry, as well as temperature distribution and a droplet size analyzer, were used to measure the downstream local velocity and temperature profile during the spray flight and its associated droplet size distribution for single and multiple arrays of micronozzles. Results of the flow characteristics show that a well-mixed atomization can be found at a spray height of 50 mm, and the spray pattern keeps its symmetry as the flow proceeds downstream. A very rapid cooling rate of −15 °C/s can be reached at the critical heat flux (CHF) for dj = 35 µm with a spray height of H = 50 mm. The effect of the spray height was examined, and it was found that the best cooling performance for a spray height of 50 mm with a CHF can be up to 259 W/cm2 (steady) and 209 W/cm2, respectively.