Study On Liquid Cooling Technology Of Light Guide Mirror Under High Power Laser Beam

With the development of laser technology,the application of high power laser emission system is more extensive.However,in high power laser emission systems,the laser beam can reach the target in a predetermined direction only through the light guide mirror.Due to the large energy carried by the laser beam,it can cause thermal deformation of the light guide mirror and affect the final beam quality.Therefore,the light guide mirror cooling is important for reducing thermal deformation and improving the quality of the laser beam quality.In this thesis,the high power laser emission system is the research background and application.The research on the cooling of the light guide mirror is carried out,including the comparison and selection of cooling schemes,the proposal of indexes of liquid cooling effect,the theoretical analysis of liquid cooling technology,structural design and optimization of the cooling channels,the selection of cooling medium,study of the laser source on the cooling effect.Specifically described as follows:In view of the existing main cooling methods,a full investigation and analysis were conducted.The advantages and disadvantages of various cooling methods were compared.The channels liquid cooling scheme was adopted to cool the light guide mirror,restrain the thermal deformation,and improve the output quality of the beam.According to the project requirements and engineering need,the new evaluation indexes of liquid cooling effect are proposed,mainly including the temperature field of the mirror surface and the flow field of the channel.The heat transfer theory and the turbulence theory involved in the convective heat transfer are discussed in detail.Various factors that may affect the temperature field of the irradiation zone and the internal flow field of the channel under turbulent flow conditions are analyzed deeply.The numerical simulation theory is studied to analyze the algorithms and boundary conditions involved in numerical simulation.The numerical simulation method is used to analyze the influence of structure parameters of the cooling channels,channel layout,mirror materials and other factors on the temperature field of the mirror irradiation zone and the fluid flow characteristics in detail.And according to the results,optimize the structural parameters further.It can be seen that,for the single channel structure,the temperature field of the mirror irradiation zone is not symmetrically distributed with its geometric center,and the highest temperature point is located in the downstream of the flow channels;increasing the cross-sectional dimension of the flow channels can improve the heat exchange effect;the temperature distribution of different walls of the flow channel is not the same;the distance between the flow channels and the mirror surface has little influence on the temperature field of the light guide mirror;the liquid cooling effect of the double channel structure is better;and the property of the mirror materials also has some influence on the temperature field.But the pressure loss and the pressure loss coefficient decrease with the increase of the channel width and the channel height,and then decrease slightly with the channel interval.The bend width will cause the change of pressure loss coefficient.Analysis of the law of the coolant and laser source on the liquid cooling effect.The results show that: the larger the coolant fraction is,the worse the heat transfer effect is and the larger the pressure loss coefficient is.The larger the coolant velocity is,the better the heat transfer is,the larger the pressure loss is,the smaller the pressure loss coefficient is.The coolant temperature has also some influence on the cooling effect.The larger the laser power is,the larger the temperature rise of the light guide mirror is.The temperature rise of the mirror is different with time.In the early stage,the temperature rise increases rapidly and the later stage tends to be slow.