I recently attended the 31st International Symposium on Rarefied Gas Dynamics held at the University of Strathclyde in Glasgow, Scotland. The event was a great success in all its facets. There was a remarkable turnout and both the oral presentations and poster display were of the highest scientific level. During the week-long event, we were delighted with several invited talks by some of the world’s leading figures in the field of rarefied gas dynamics. Several members of the Micro- and Nano-Flows Group for Engineering based at Edinburgh, Warwick, or Daresbury, participated in the symposium in a variety of roles.
In this blog entry, I want to focus on a talk I attended, entitled “Periodically patterned radiometric pumps – Novel configurations and further applications” by A. Lotfian, E. Roohi, and S. Stefanov. It was delivered by Dr. S. Stefanov of the Bulgarian Academy of Sciences. The worked consisted on the numerical simulation of the flow and temperature fields of the gas in the channel formed between a patterned or ratchet surface on one side and a flat or, alternatively, ratchet surface on the other. The radiometric pumping effect is generated by imposing a uniform temperature difference between both surfaces and by periodically changing the reflective property of the surface in the ratchet, namely, by alternating between a section reflecting specularly and another diffusely. Another configuration studied consisted of alternating a hot surface section with a cold one on the same side. The effect of these perturbations is to create a net force and flow along the direction of the surfaces. This net force can be used to generate motion if one of the surfaces is allowed to move, such as with a rotor.
In total, they investigated seven novel configurations. A configuration very similar to the ones considered in this work can be seen here. For the analysis, they used the solver dsmcFoam+, an implementation of Direct Simulation Monte Carlo (DSMC) in the open source package OpenFoam+, parallelized using MPI. They found that the maximum pumping velocity is observed in a zigzag channel with teeth machined on both sides. On the other hand, the maximum radiometric force was attained in a channel with a flat wall on one side and double ratchets on the other wall.
Details about a numerical study like the one described in this entry can be found in this open-access article.