CFD and FEM Analysis of Passive Variable Flow Controller

Abstract

In this report we develop a novel design for a passively controlled valve that utilizes different shapes of the bimetallic vane-based controller inside the cooling channel. By taking advantage of the deformation characteristic of the bimetallic vane, additional flow areas would be generated to allow more coolant to flow. The pressure drop across the cooling channel would also decrease accordingly, which allows more heat transfer to take place, and eventually, realize the purpose of reactivity control.

The report (with appendices) describes Finite Element Method (FEM) simulations to evaluate the deflection of bimetallic membranes for multiple materials, shapes, and thicknesses Further, Computational Fluid Dynamics (CFD) simulations for various flow controller shapes and configurations to work towards optimization of the device geometry from a flow control capabilities standpoint are documented. The flow control capabilities were evaluated based on the pressure drop across the fully open and fully closed device for different fluid mass flow rates and temperatures. Preliminary results show a good device candidate that allows to reach up to three times in pressure drop difference between fully closed and fully open devices.

The feasibility of the device was tested using CFD and FEM simulations, demonstrating that such a straightforward device geometry could provide a pressure drop alteration of up to 46%-56%, depending on the selected geometry and temperature over a broad range of flow velocities. It is critical to note that the proposed geometries are conceptual studies and not the final designs, and careful consideration should be given to material selection to ensure good corrosion and fatigue resistance in the flow media and certain operating conditions. Therefore, measures would also be needed to prevent electrochemical corrosion at the bonding layer of the bimetallic strip or at the interface, for example, using thin buffer layers or encapsulating strips. Lastly, any radiation enhanced fatigue or corrosion effects would need to be studied and measured carefully. A possible direction for future work regarding the utilization of bimetallic devices for flow control could involve investigating various engineering approaches to use bimetallic features as motion actuators. These actuators could be mounted outside of the actual flow and actuated thermally through heat conduction through the walls. This approach might help reduce the requirement for high corrosion resistance if the valve is in the flow; however, additional attention would need to be given to sealing the moving parts.