| Solid-state lasers are widely used in national defense construction,national economy,scientific research,daily life and other fields.However,due to the influence of heat effect,there are some problems such as limited output power,reduced output quality and safety risks.With the rapid development of high-power lasers,direct liquid-cooling solid-state lasers with micro-channel cooling system have attracted the attention of researchers because of their good ability of heat transfer and high output power.Based on the actual parameters of a small direct liquid-cooling solid-state laser,the calculation model of the micro-channel and gain module of the liquid-cooling system are established.The influence factors of flow and heat transfer characteristics in micro-channel are analyzed by numerical simulation using FLUENT and other software.On this basis,the thermal stress and optical path difference distribution of the gain module are studied,and the optimization parameters and security factors of the gain module are analyzed.The simulation results of flow and heat transfer characteristics in micro-channels show that transition Reynolds number increases with the increase of the height of the test section,the relative roughness of the wall and the contraction ratio of the inlet section;the slice heat load has no effect on the transition point;the increase of the heat load and the height of the test section reduces heat transfer,and the minimum Reynolds number or the minimum flow velocity exists under each heat load;that lower than the minimum flow rate is not conducive to the safe operation of the laser;the optimum design parameters of the micro-channel are obtained by simulation orthogonal experiment: the height of the test section is 0.5mm,the wall is smooth,and the contraction ratio of the inlet section is 9,in this case,the transition Reynolds number is 3100.The results of Thermal-Fluid-solid coupling simulation and optical path difference calculation show that when the thermal load is 800 W and the Reynolds number is 3100,the flow in the micro-channel is laminar,and the maximum Von Mises stress is 328.77 MPa.The optical path difference caused by the temperature gradient of the coolant and the slice offsets each other,so the optical path difference caused by the whole temperature gradient is uniform distributed except the edge.The distribution of optical path difference caused by thermal deformation is similar to that caused by slice deformation which is S-shaped with obvious peaks and troughs.Therefore,the distribution of total optical path difference is uneven,with the peak-to-trough value of 0.428 um.The results of parameter optimization and safety factor analysis of gain module show that the non-uniform distribution of optical path difference caused by cooling fluid can be reduced by countercurrent flow of the fluid,so the total optical path difference can be significantly reduced;the maximum stress on the slice and the peak-to-valley of optical path difference of gain module will be reduced with the increase of Reynolds number and the decrease of thermal load;the maximum thermal load on the slice will be decreased with the increase of Reynolds number.When the Reynolds number is 3100,the maximum heat load of the slice is 800 W.In conclusion,without affecting the physical properties of micro-channels,the height of the test section and the contraction ratio of the inlet section(the length of the inlet section is constant)should be increased,the wall should be smooth,the flow rate of cooling fluid should be as close as possible to the transition Reynolds number,and the heat load should not exceed the maximum heat load that slice can bear,so the high efficiency heat transfer of laser cooling system can be realized and the laser can run safely and smoothly.The research content of this paper provides guidance for the design and optimization of gain module of direct liquid-cooling solid-state laser,and puts forward feasible schemes to alleviate the thermal effect. |
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