Effects of Channel and Ratchet Geometry on Passive Pumping in an Open-ended channel Configuration

Modern electronics have created increased demand for innovative cooling solutions. Typical forced convective cooling systems consist of pumps that circulate cooling fluid. However pumps can be unwieldy for many applications. This research is a continuation of work done at Oregon State University and Auburn University on the passive pumping of fluid in a preferential direction.\ud The geometry consisted of a channel with side walls comprised of 30-60 degree brass ratchets that were nominally 1 mm in pitch. Thin film heaters, located on the back side of the ratchets, were used to simulate the electronics heat source. The top and bottom sides of the channel were transparent to permit high speed visualization of boiling. A dielectric fluid, FC-72, was used as the working fluid. Several different geometries were considered including; different channel widths, asymmetric and symmetric surfaces, surfaces with flat sections, and half-pitch offset. Runs with similar conditions were chosen to compare the effect of the geometric changes on preferential bubble motion. Image processing was used to retrieve the velocity of the bubbles in the channel and the number of venting events to classify the performance.\ud The vapor bubbles exhibited a preferential direction in the direction of the ratchet with the lower angle. Bubble velocities up to 160 mm/s were observed during the tests. Symmetric ratchets and flat surfaces were observed to have no preferential direction