Kaspenberg et al. [] and Thiagarajan et al. [] observed passively generatedliquid motion on asymmetrically-textured surfaces during nucleate boilingof F -!". They fabricated these textured surfaces in the form of mm-scale

ratchets #ith re-entrant cavities located preferentially on the shallo# faceand indicated that the bubble gro#th and departure from these cavitiesoccurred normal to the shallo# face of the ratchets. They developed a semi-empirical model$ #ith the use of a simple force-balance model andexperimental data$ to demonstrate the e%ect of the non-vertical bubblegro#th on the net lateral liquid velocity. Thiagarajan et al. [] conductedsimilar pool boiling experiments but under reduced gravity &'.'(g) aboard a*oeing !"! aircraft &+ero-g ,nc.) carrying out parabolic maneuvers. ue to

negligible buoyancy force compared to surface tension$ the bubblediameters #ere at least times larger than compared to the experiments

carried out at (g []$ and consequentially #ere able to slide laterally alongthe surface &at / "!.0 mm1sec) after departure. They attributed this lateralmotion of bubbles to the pressure di%erences in the liquid 2lm beneath the

vapor bubble$ similar the observation made by 3in4e et al. [] for 3eidenfrostdroplets and by 3agubeau et al. [] for dry-ice dis4s.

From these studies$ it is apparent that a self-propelled 5o# exists in theliquid 2lm arising predominantly due to the asymmetry in the test-surface.