Numerical simulation of the air flow inside a cavity combiner of the ALBA Synchrotron

Abstract

The main objective of the project is to simulate the air flow inside a cavity combiner of ALBA Synchrotron and its cooling efficiency as accurately as possible. For that, the thermal energy exchange inside of the cavity combiner will be calculated to identify the maximum wall temperatures. Moreover, the effect of the air flow rate on the refrigeration efficiency will be analyzed to optimize the system. To begin, a first set of simulations is carried out in order to become familiar with the CFX software and to analyze the model sensitivity to the mesh. Different configurations and sizes are tested to determine the best parameters to simulate the heat convection mechanisms. The location of the boundary conditions and their influence on the convergence are also considered. As a result, some modifications of the geometry are assumed to achieve well-placed boundary conditions that consist in extending the inlet and outlet pipes. With the new geometry and based on the previous knowledge, a second set of meshes are developed that lead to new results from which it is observed that the flow is not fully steady inside the cavity. Nevertheless, the fluctuations are assumed to be of low intensity and finally a steady state simulation of the thermal exchange with the optimal mesh is carried out. To define the wall heat flux induced by the electromagnetic fields generated in the system, the available information of the amperage distribution on the inner surfaces and the total amount of power provided by Alba Synchrotron is used. In the model, the radiation is neglected and only the heat transfer mechanism due to convection is considered. Consequently, the temperature distribution is obtained as a function of the available air mass flow rates. From these results, the relation between the flow behavior inside the cavity combiner and the heat extraction is studied. And finally, the minimum flow rate that guarantees that undesirable temperatures are achieved on the system is determined.