Particle Image Velocimetry (PIV) is a state-of-the-art non-intrusive optical flow measurement method based on the recording images of the movement of flow-following particles added to the liquid in the investigated flow domain. PIV is in use at BME Institute of Nuclear Techniques (NTI) since 2007, and has been applied for such investigations as coolant mixing, heat transfer of the fuel rod of the training Reactor or thermal-hydraulics characteristics of the MSFR molten salt reactor concept core. With the application of Matched Index of Refraction (MIR) method it is possible to investigate the flow field in complex geometries. By matching the refractive indices of the model material and the working fluid the flow domain behind a solid model part becomes visible for the optical method, thus allowing the measurement in geometries such as rod bundles.
Most of the publications in the international literature focus on rectangular lattice geometries as these are common for fuel rod bundles applied in western pressurized water reactors (PWRs). However in case of VVER reactors and some Generation IV reactor types hexagonal lattice is applied. So far only a limited number of publications presented PIV measurement results on hexagonal lattice rod bundle PIV measurements. Main purpose of the work proposed here is to develop an appropriate experimental model of hexagonal fuel rod bundles that can be applied with PIV for VVER-1200 relevant geometries. The measurement data would lead to a deeper understanding of flow behavior in such geometries, and would be invaluable for validating computational models and simulation results like CFD or subchannel code calculations. Such an experimental model would be a new, state-of-the-art and unique facility even in terms of international comparison. One of the objectives of the PhD research is to deliver new CFD-grade experimental data, which would be applicable for the validation of CFD codes and models. The research work could contribute to the development and optimization of spacer girds with mixing vanes for pressurized water reactors. Further task of the PhD candidate is to enhance the evaluation methods and tools used for PIV measurement data processing.
The PhD candidate would perform the following tasks:
- Study the latest findings of the international literature on Particle Image Velocimetry, Matched Index of Refraction and their application in nuclear reactor thermal-hydraulics.
- Select the applicable model and liquid materials for such an experimental model.
- Design a hexagonal fuel rod bundle experimental model that will be used for extensive series of PIV measurements in VVER-1200 fuel pin bundle and spacer grid relevant geometries.
- Perform measurements on the experimental model, analyze the measurement results and discuss the flow characteristics of different rod bundles.
- Compare the PIV results with other highly sophisticated measurements like LDA (if available).
- Investigate the possibilities of two phase flow PIV measurements in VVER-1200 relevant geometries.
- Propose more advanced evaluation methods and image processing tools used for PIV measurement data processing.
- Discuss different options of geometry modifications and their effects on rod bundle thermal-hydraulics, including the effects of different spacer grids and mixing vanes on flow behavior.
- Documentation of measurement results on a level which is applicable for validation of numerical models and codes.
- Adequate knowledge of nuclear reactor thermal hydraulics and Computational Fluid Dynamics or deep knowledge in precision mechanics and optics
- Capabilities and good manual skill in design, construction and operation of experimental setups and test rigs
- Basic knowledge of measurement techniques applied in thermal-hydraulics
- Good knowledge and experience in lasers, precision mechanics and optics
- Affinity for using computational modelling tools, applying experimental methods
- Good level of English
- Diligence, precision, commitment