He Cooled Granular Target Analytical Results and CFD Analysis
2010
A multidisciplinary scientific research center harnessing the world’s most powerful neutron source is going to be built in Lund: ESS, The European Spallation Source. Researchers will be able to study the materials of everyday life in all their rich diversity – from plastics and proteins to medicines and molecules – in order to understand how they are built up and how they work. ESS will become a hub in Europe’s research infrastructure
ESS consists of an accelerator and a target station. A first step is to accelerate protons close to the speed of light. This is achieved using front edge technology in a 600 m long linear accelerator. The protons are impinging materials such as lead, tungsten or mercury. When protons interact with heavy nuclei, neutrons are released from those nucleis: this reaction is called spallation. A large amount of energy is deposited by the proton beam into the target. This causes a temperature rise in the material and requires efficient cooling.
There are many different concepts for the target, one of them is a stationary target consisting of granular tungsten spheres and another one is a rotating target consisting of densely packed tungsten cylinders. This thesis will be about simulating the cooling of these target concepts. The cooling is achieved by helium flowing through the granular target.
As a first step analytical calculations are performed on a global level on the bed of tungsten spheres. This is done to study and get an understanding of how the essential parameters affect the cooling. The results are presented as graphs with the essential parameters and contour plots of the outlet helium temperature and pressure. The next step is to perform CFD calculations with ANSYS CFX, also on a global level with a porous domain acting as the tungsten spheres. The analytic calculations are used as a guideline to determine the properties of the boundary conditions. Finally CFD calculations are performed on the rotating target with the densely packed cylinders. These are performed on both larger and smaller scale.
The different analyses give an understanding of how the essential parameters affect the results of the granular targets. Requirements are set up and have to be fulfilled by the design. Unfortunately the results show that the stationary target with the tungsten spheres does not fulfill some important requirements. Conclusions were drawn that the rotating target is more viable than the stationary. The reasons for this can be read in the thesis.
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