流体直接冷却薄板条介质温度及应力的解析表达

The analytic expressions of temperature and stress in directly liquid cooled thin slab laser

基于对流传热和热传导原理,建立了流体直接冷却均匀抽运薄板条激光工作介质的热效应分析模型,采用平面应力近似和最小功原理,得到了板条工作介质内部温度分布和应力分布的解析表达式.研究了不同流道厚度时对流热交换系数和冷却液温升与流体流速的关系,分析了流道厚度对工作介质的温度分布和应力分布的影响规律,讨论了之字形和直通光路时,热致波前畸变随产热功率的变化趋势.结果表明:层流和湍流时,较厚的流道可以实现更好的热管理效率;增益介质中的热分布关于中心平面对称,纵向最大温升出现在出水口端,最大应力畸变集中在板条两端及其侧边;流道厚度较大时,工作介质更易形成一维的温度梯度,产生的应力更小;之字形光路可以明显缓解热光效应导致的波前畸变.

In this paper, based on the convective heat transfer and conduction principle, the thermal effect analysis model of the directly liquid cooled uniformly pumped thin slab laser is established. The approximate plane stress and the principle of minimum are introduced to describe thermal stress distribution in the thin slab. Firstly, the relationships between the flow velocities in different flow channel thickness values and the convection heat transfer coefficients and also the relationship between flow velocity and coolant temperature rise are studied. Moreover, the influences of different flow channel thickness values on temperature field and thermal stress distribution are analyzed. Finally, the variation trends of wave-front phase distortion with the change of heat power in the case of zig-zag path and direct path are investigated,respectively. The results reveal that thicker flow channel can achieve stronger heat treatment effects in an appropriate range of the cooled liquid flow rate, and the thermal profile is symmetrical with respect to the center plane of slab. In addition, the longitudinal maximum temperature rise occurs in the outlet; the maximum stress distortions centralize on the both ends and partial sides of slab. It is worthy to mention that the one-dimensional temperature gradient and smaller stress form more probably for thicker flow channel. Furthermore, zig-zag path can alleviate obviously wave-front aberration due to thermo-optic effect. In this paper the thermal effect of the liquid direct cooled thin slab laser is investigated. The research results are beneficial to the design and optimization of the directly liquid cooled thin slab laser.