Drag Reduction and Leidenfrost Effect on Submerged Ratcheted Cylinder

Abstract

This paper presents experimental investigations of submerged self-propulsion due to the Leidenfrost effect. We aim to identify and quantify the forces governing the free-fall of heated cylinders at temperatures between 25 °C and 550 °C. Understanding the forces involved within three-phase systems is essential when designing sensitive instruments, such as microelectronic devices. Cylinders with sizes in the range of tens of millimeters are released into a vertical column filled with Novec 7000. Experiments were conducted to investigate five topological designs, and bored-out hollows within the cylinders forced vertical free-fall. The control cylinder was smooth, while the others had ratchet teeth engraved on their surface. Ratcheted cylinders were manufactured in pairs to compare ratchet directionality. An in-house tracking tool reduced experimental error and measurement noise. The time taken to reach terminal velocity increases with initial temperature while terminal velocity decreases, respectively. The depth at which terminal velocity occurs also decreases with increasing initial temperature. The existence of submerged self-propulsion has been identified by comparing ratcheted cylinders of opposing directionality. A theoretical mechanism for the action of the viscous friction force that drives self-propulsion has been developed. The viscous friction force has been quantified to be between 0.04–3.28 mN.