In this work, passive fluid pumping during boiling using the concept of asymmetry in the geometry of the heated surface is studied experimentally. The geometry consists of a channel that is located within a chamber filled with dielectric fluid. The channel ends (inlet and outlet) are exposed to the chamber, such that the ends of the channel have the same pressure prior to the addition of heat. Two types of asymmetry are introduced on the heated surface, and their effect is assessed on the net bubble growth and motion within the open-ended channel. The first is a millimeter-scale asymmetry caused by contouring the vertical walls of the channel with repeating 60-30 degree ratchets. Microscale reentrant cavities located preferentially on one face of the ratchet is the second level of asymmetry. Asymmetry in the form of mm-scale ratchets with 60-30 degree angle in the absence of directionally oriented reentrant cavities has been studied in prior work \[1\]. The directional motion of slugs in open-ended channels has been observed in the prior study and a phenomenological model of slug motion based on a Couette-Poiseuille flow in the thin film between the vapor slug, and the ratchet walls was proposed. The addition of the second asymmetry of preferentially-located cavities brings about another potential mechanism- that of momentum transfer by the growing bubble to the surrounding fluid- as a contributor to bubble motion. To assess the contributing mechanisms and their impact on bubble and slug motion, experiments are performed with a dielectric fluid, FC-72, for various channel widths ranging from 3 mm to 10 mm and under varied subcooling ranging from 5-40 degree C and heat fluxes ranging from 1-10 W/cm^2^. Geometrical variants on the mm-scale include 60-30 degree faces with varied ratchet pitch of 1.5 mm and 3.0 mm. Cavities are located on the shallow side with one on every other two sides. High-speed videos of bubble ebullition, mergers and slug transport are recorded and analyzed to obtain growth rates, velocities, and frequency counts of slugs emanating from either end of the open-ended channel.


Assessment of Thermally-Actuated Pumping in an Open-Ended Channel With Multi-Scale Surface Asymmetry

Division / Sponsors: 
Heat Transfer Division (HTD), Fluids Engineering Division (FED)

Heat Transfer Summer Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2020/volume/83709

18th International Conference on Nanochannels, Microchannels, and Minichannels
Paper Proceedings: https://asmedigitalcollection.asme.org/ICNMM/ICNMM2020/volume/83693

Fluids Engineering Division Summer Meeting
Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2020/volume/83716

HT-ICNMM2020 - Virtual Conference, SHTC - Virtual Conference, FEDSM2020 - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.