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使用Fluent软件对两种模型进行流体分析和流体-固体耦合热传导分析[10-11],流体分析部分使用收敛性好,计算结果相对可靠的k-ε标准湍流模型,该模型中ε是各向同性小尺度涡旋的机械能转为热能的速率,ε和k是两个需要求解的未知量,其运算方程分别为:
$$ \begin{split} \dfrac{{\partial (pk)}}{{\partial t}} +& \dfrac{{\partial (pk{u_i})}}{{\partial {x_i}}} = \dfrac{\partial }{{\partial {x_j}}}\left[ {\left(\mu + \dfrac{{{\mu _i}}}{{{\sigma _k}}}\right)\dfrac{{\partial k}}{{\partial {x_i}}}} \right] +\\ &({G_k} + {G_b} - {\rho _\varepsilon } - {Y_M} + {S_k}) \end{split} $$ (1) $$ \begin{split} \dfrac{{\partial (p\varepsilon )}}{{\partial t}} +& \dfrac{{\partial \left(p\varepsilon {u_i}\right)}}{{\partial {x_i}}} = \dfrac{\partial }{{\partial {x_j}}}\left[ {\left(\mu + \dfrac{{{\mu _i}}}{{{\sigma _k}}}\right)\dfrac{{\partial \varepsilon }}{{\partial {x_i}}}} \right]+ \\ &\left[ {{C_{1\varepsilon }}\dfrac{\varepsilon }{k}({G_k} + {C_{3\varepsilon }}{G_b}) - {C_{2\varepsilon }}\rho \dfrac{{{\varepsilon ^2}}}{k} + {S_\varepsilon }} \right] \end{split} $$ (2) 式中:Gk为由于平均梯度引起的湍流动能k的产生项;Gb为浮力产生的湍流动能k的产生项;YM代表可压缩的湍流脉动扩张贡献;C1ε、C2ε和C3ε为经验常数;Sk和Sε为用户定义的源项[12]。对于热传导部分采用三维有热源的瞬态热传导模型,其表达式如下:
$$\rho {\rm{c}}\dfrac{{\partial T}}{{\partial t}} = k\left(\dfrac{{{\partial ^2}T}}{{\partial {x^2}}} + \dfrac{{{\partial ^2}T}}{{\partial {y^2}}} + \dfrac{{{\partial ^2}T}}{{\partial {{\textit{z}}^2}}}\right) + qv$$ (3) 式中:ρ,c,k分别为介质的密度、比热容和导热系数;n代表介质的法线方向;h为介质表面和周围冷却液体的对流换热系数;qv为材料的热源强度。
$$\begin{split} &\\ - k\frac{{\partial T}}{{\partial n}} = h({T_S} - {T_f}) \end{split}$$ (4) 式中:Ts为水冷板表面温度;Tf为冷却液温度。
$${{T}}(x,y,{\textit{z}};0) = {T_0}(x,y,{\textit{z}})$$ (5) 公式(5)为初始条件,式中T0是初始温度。Fluent软件在求解以上3个导热方程时使用有限元分析法,将分析的对象划分成有限多个单元,根据能量守恒原理求解一定边界条件和初始条件下各个节点的热平衡方程得出各节点温度,从而求解出温度梯度变化[13-14]。
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数值模拟计算中边界条件设置如下:
(1)整个系统共8个体热源,发热功率是80 W;
(2)水冷板材质为6061铝合金,出水口设置为压力出口;
(3)水冷机额定输出的冷却液使用去离子水,流速为15 L/min,水温恒定20 ℃;
(4)热源和各模块水冷板的接触面、流体与水流通道的接触面采用耦合边界条件,实现热传导;
(5)冷却系统装置外壁面定义为绝热面(忽略外界温度),不考虑自然对流和辐射换热。
Design of atypical macro-channel water cooling system for semiconductor lasers
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摘要: 针对大功率半导体激光器散热系统展开设计研究。首先,对水冷散热系统的流体通道中的冷却液进行了流体分析,结果表明在传统矩形流体通道结构中,冷却液在进液口处和弯度较小处容易产生湍流空洞。湍流空洞不仅会产生空泡腐蚀效应,还会导致靠近热源的上层冷却液填充不充分,降低系统的散热效率;其次,在传统流体通道结构的基础上,提出了一种非典型宏通道结构的优化模型。采用有限元分析软件Fluent分别对散热模型的分布和激光器模块器件的分布进行了数值模拟,流场结果表明优化模型中冷却液流动时没有湍流空洞产生,散热系统可靠性更高,冷却液在流体通道的上层填充效果更好,同时解决了传统模型中流体在局部流道中流速缓慢的问题,使散热系统具备更良好的散热性能。接着又通过温度场仿真结果得出,优化模型搭建的散热系统工作时激光器最高温度可降低2 ℃,且热源1上温度更均匀,热源3上温度降低1.25 ℃;最后,在激光器满功率输出情况下进行的散热实验对比,获得的实验数据与仿真结果基本一致。Abstract: Comprehensive study on the cooling system of high-power semiconductor laser was carried out. Firstly, fluid analysis of the coolant in the channels of the cooling system was conducted, and the corresponding results showed that turbulent cavities were formed easily at the inlet and places with small comprehensive study on the cooling system of high-power semiconductor laser was carried out. Firstly, fluid analysis of the coolant in the channels of the cooling system was conducted, and the corresponding results showed that turbulent cavities were formed easily at the inlet and places with small curvatures. Turbulent cavities may not only cause the cavitation corrosion effect, but also cause the upper fluid channel near the heat source was not fully filled with coolant. In addition, turbulent cavities will also reduce the heat dissipation efficiency of the cooling system; Secondly, based on the traditional fluid channel structure, an optimized atypical macro-channel structure was proposed. The distribution of the heat dissipation model and the distribution of the laser module components were numerically simulated using Fluent that the finite element analysis software. The simulation results showed that no turbulence cavities were generated when the coolant flows in the fluid channel of the optimized model, and the upper layer of the fluid channel can be better filled with coolant. Simultaneously, the optimized model solved the problem of slow fluid velocity in the localized area of fluid channel of the classical model, not only improved the heat dissipation performance of the cooling system, but also improved the reliability of the cooling system. Additionally, according to the temperature field simulation results, the highest working temperature of the laser was decreased by 2 ℃ when applying the optimized cooling system. And the temperature on heat source-1 was more uniformly-distributed, while the temperature on heat source-3 was reduced by 1.25 ℃; Finally, the cooling system experiments were carried out and the results were well-matched with our simulation results.
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Key words:
- cooling system /
- semiconductor laser /
- Fluent /
- flow field analysis /
- temperature field analysis
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