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Numerical and Experimental Study of Microchannel Performance on Flow Maldistribution

机译：流量分配不均的微通道性能数值与实验研究

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Miniaturized heat exchangers are well known for their superior heat transfer capabilities in comparison to macro-scale devices. While in standard microchannel systems the improved performance is provided by miniaturized distances and very small hydraulic diameters, another approach can also be followed, namely, the generation of local turbulences. Localized turbulence enhances the heat exchanger performance in any channel or tube, but also includes an increased pressure loss. Shifting the critical Reynolds number to a lower value by introducing perturbators controls pressure losses and improves thermal efficiency to a considerable extent. The objective of this paper is to investigate in detail collector performance based on reduced-order modelling and validate the numerical model based on experimental observations of flow maldistribution and pressure losses. Two different types of perturbators, Wire-net and S-shape, were analyzed. For the former, a metallic wire mesh was inserted in the flow passages (hot and cold gas flow) to ensure stiffness and enhance microchannel efficiency. The wire-net perturbators were replaced using an S-shaped perturbator model for a comparative study in the second case mentioned above. An optimum mass flow rate could be found when the thermal efficiency reaches a maximum. Investigation of collectors with different microchannel configurations (s-shaped, wire-net and plane channels) showed that mass flow rate deviation decreases with an increase in microchannel resistance. The recirculation zones in the cylindrical collectors also changed the maldistribution pattern. From experiments, it could be observed that microchannels with S-shaped perturbators shifted the onset of turbulent transition to lower Reynolds number values. Experimental studies on pressure losses showed that the pressure losses obtained from numerical studies were in good agreement with the experiments (<4%).
机译：与大型设备相比，小型热交换器以其卓越的传热能力而闻名。虽然在标准微通道系统中，通过最小化的距离和非常小的水力直径来提供改进的性能，但也可以采用另一种方法，即产生局部湍流。局部湍流增强了任何通道或管道中的热交换器性能，但同时也增加了压力损失。通过引入扰动器将临界雷诺数转换为较低值，可以控制压力损失并在相当大的程度上提高热效率。本文的目的是详细研究基于降阶建模的收集器性能，并基于对流量分布不均和压力损失的实验观察来验证数值模型。分析了两种不同类型的微扰器，即钢丝网和S型。对于前者，将金属丝网插入流动通道（热气流和冷气流）以确保刚度并提高微通道效率。在上述第二种情况下，使用S形扰动模型替换了丝网扰动器，以进行比较研究。当热效率达到最大值时，可以找到最佳质量流量。对具有不同微通道配置（S形，丝网和平面通道）的收集器的研究表明，质量流量偏差随微通道阻力的增加而减小。圆柱形收集器中的再循环区域也改变了分布不均的格局。从实验中可以看出，带有S形扰动的微通道将湍流转变的开始转移到了较低的雷诺数值。压力损失的实验研究表明，从数值研究获得的压力损失与实验吻合良好（<4％）。

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