The characteristics of horizontally opposed water jets in the absence and presence of an impinging air jet are investigated visually with high speed camera and quantitatively using phase Doppler anemometry (PDA). In the absence of air jet, the size of the circular water sheet variation with water jet Reynolds number and Weber number is in agreement with previous findings. The average droplet diameter is found to scale with Weber number and density ratio. Breakup phenomena are captured and described for various combinations of water and air flowrates, which indicate the significant role the air jet plays in promoting water jets atomization. Quantitative measurements using phase Doppler anemometry (PDA) reveals the effects of water flowrates on the generated droplets' size, velocity and root mean square (RMS) distributions and air mass flowrates on the droplets' size distribution along the vertical axis. At various combinations of water flowrates and air mass flowrates, the droplet Sauter mean diameter (D 32 ) along the centerline of the spray, first decreases as a result of the breakup and then increases slight possibly due to the coalesce of droplets or preferential dispersion of different droplet sizes after break was complete. Larger water flowrates result in larger D 32 , while larger air mass flowrates lead to smaller D 32 values. Variation of D 32 /d, where d is the pipe diameter, against the air liquid momentum ratio reveals that the horizontally opposed impinging jet arrangement leads to better atomization than the one with liquid jet impingement angle of 90°.
Bubble
dynamics plays an important role in boiling heat transfer,
and surface wettability affects bubble behaviors. In the present work,
the effects of surface superhydrophilicity (SHI) and superhydrophobicity
(SHO) on bubble dynamics are experimentally studied by observing the
formation and motion behaviors of air bubbles and vapor bubbles on
varied surfaces. For air bubbles to better mimic vapor bubbles, the
air bubbles are introduced in a water pool by injecting airflow from
a through hole of the surface. Air bubble tests are first conducted
on homogeneous SHO and SHI surfaces, respectively. It is observed
that surface wettability significantly affects the bubble size and
departure frequency. To discover the dynamic behaviors of a bubble
under both SHI and SHO, a biphilic surface with SHI and SHO areas
is fabricated, and air bubbles are injected right on the biphilic
border between the two areas. It is observed the wettability contrast
significantly displaces the air bubbles, which spread only onto the
SHO area. The biphilic surface is fabricated for the pool boiling
test. Vapor bubbles are observed at different stages of the nucleate
boiling, showing surface effects similar to the observations of air
bubbles. Not only does this study present the influence of surface
wettability on air and vapor bubble behaviors but also it provides
useful implications for understanding and optimizing the biphilic
surface design for enhancing boiling heat transfer.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.