Thermal Distortion Analysis And Constructal Design Of Large Size Water-cooling Mirror

In order to ensure the output laser beam, the thermal distortion of the reflecting surface of the laser mirror must be kept in a certain range. Water cooling is the main approach to mitigating the thermal distortion. However, with the development of high power laser, the conventional configuration of water-cooled mirror with straight flow channels is difficult to satisfy the requirement of large size mirror. Therefore, it is necessary to study the high performance large size water-cooled mirror.In this paper, finite element method (FEM) was used to analyze the conventional configuration of water-cooled mirror with straight flow channels, and design principle of key design dimensions was presented. Then based on the FEM model of single channel heat sink, the paper introduced a simplified calculation method with updating the temperature with time. The results was nearly the same to that from computational fluid dynamics (CFD) both on the trend and value. Subsequently, structural optimization of conventional configuration was performed. The optimized one could reduce the thermal distortion to a low level, with limited cooling performance of channel heat sinks.A new configuration with interdigitated channels was proposed for solving the problems of high flow resistance and non-uniform heat dissipation in large size conventional configuration. The relevant design principle of new configuration was deduced. Temperature field and thermal deformation of reflecting surface of mirror were analyzed by fluid-solid-heat coupling simulation. A comparative analysis of the new configuration and conventional straight channel water-cooled mirror was performed under the condition of equal mass flow rate and equal pressure drop, respectively. The numerical results demonstrated that the new configuration was better on the consistency of heat transfer coefficients than conventional straight cooling channel. Meanwhile, its peak deformation on the mirror surface decreased by around 1/3, and the peak-to-valley deformations along x direction and y direction were reduced by 40% and 60%, respectively, compared with the conventional configuration. Besides, the flow resistance of the new configuration was so small that the flow rate was about triple that of the conventional configuration, which enhanced its superiority on mitigating the thermal deformation on mirror surface. The new configuration of cooling channel provided a feasible solution for reducing the thermal deformation of large size laser mirror.Water test experiment was carried out to verify the validity of CFD results of the flow field of ?150 mm new configuration. And water pressure and flow rate were tested. The comparison with experimental results demonstrated that numerical results from CFD were valid.The study in this paper could be used as a reference to design high performance large size water-cooled mirror. Furthermore, further study on the fabrication process will be conducted.