Increasing the diodicity of ceramic Tesla valves by exploiting the design freedom of additive manufacturing : A study in design optimizations of Tesla valves for ceramic 3D printing

Abstract: The work presented in this thesis was conducted at Uppsala University and at Fraunhofer IKTS, Dresden. The thesis aims to study design optimizations for increasing the diodicity and thereby performance of a Tesla valve, a type of “no moving parts” (NMP) valve, through design freedoms offered by ceramic additive manufacturing. Tesla valves are capable of creating a pressure differential across them purely by virtue of mechanical design, and do not employ any moving parts. By geometry manipulation, Tesla valves enable fluid to flow in a way that hinders its own flow, thereby creating fluidic resistance and increasing pressure in one fluid direction, while allowing relatively unimpeded flow in the opposite direction. The manufacture of Tesla valves in the past has been restricted to simple geometries because conventional manufacturing processes such as CNC machining are unable to produce intricate geometries, something that Tesla valves require. With the recent innovations in additive manufacturing, design of these complex geometries has become feasible but still requires further research. Prior literature has only explored relatively simpler constructs of Tesla valves, not fully utilizing the design freedoms offered by additive manufacturing. In this thesis, ceramic additive manufacturing and stereolithography has been used to manufacture complex Tesla valves. In addition to just complex design, this thesis also presents design optimizations that can be utilized for simpler Tesla valves for increasing a metric known as diodicity. Diodicity refers to the ratio of reverse to forward pressure difference, and a high diodicity of a valve indicates that the valve is able to hinder fluid flow more effectively in one direction than the opposite. Additive manufacturing boasts an ability to construct complex geometries, due to the layer-by-layer process of building the final component. Stereolithography (in particular, ceramic stereolithography) is capable of producing parts that have high resolution and dimensional accuracy, while also maintaining desirable material properties, such as resistance to high temperatures and mechanical durability. Since the envisioned Tesla valve is to be used at elevated temperatures, this makes stereolithography a viable method of producing Tesla valves for aerospace applications. Design optimizations were carried out and subsequently verified for effectiveness through fluid flow simulations and practical evaluations. Certain design optimizations were shown to have drastic effects on the diodicity of the Tesla valve, and these have been subsequently incorporated into the designs of the Tesla valve in an effort to increase the diodicity of the designed Tesla valves. For practical evaluation, the optimized Tesla valves were 3D printed through ceramic stereolithography and stereolithography and extensively tested on a testing rig, with experimental parameters congruent to the fluid flow parameters applied during fluid flow simulations. It was found that the results of the fluid flow simulations and experimental testing were somewhat consistent with each other, and that it is feasible to produce optimized Tesla valves through ceramic stereolithography. However, it was found through practical evaluation that certain design optimizations were found to have little to no effect on the diodicity of the final Tesla valve, with some optimizations even reducing the diodicity.