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首页> 外文期刊>International Journal of Heat Exchangers >Local Transient Behavior of a Compact Heat Exchanger Core During Brazing Equivalent Zonal (EZ) Approach
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Local Transient Behavior of a Compact Heat Exchanger Core During Brazing Equivalent Zonal (EZ) Approach

机译：紧凑型换热器芯在钎焊等效区带（EZ）时的局部瞬态行为

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This paper discusses temperature history of both the core and the associated manifold-shell surfaces exposed to a transient brazing cycle during the controlled atmosphere brazing process (CAB). A complex compact heat exchanger structure consisting of a sequence of extruded tubes with micro channels and multilouver fins, and framed with the manifold-shell assembles, was exposed to a ramp-up/dwell/rapid-quench radiation-convection heating-cooling materials processing sequence. A test sample was assembled using actual heat exchanger design elements (i.e., extruded tubes, multilouver fins, and manifold-shells.) Brazing was accomplished at the peak brazing temperature of 878 K in an experimental facility equipped with a transparent hot zone. The experimental regime mimicked a state-of-the-art manufacturing process utilized for the manufacturing of aluminum compact heat exchangers. Fin and tube surface temperatures were monitored continuously during both radiation heating and convective cooling of a sample. Heating was conducted in 99.999 % nitrogen, with the background oxygen level at the peak lower than 50 ppm, and the dew point temperature below -40℃. Numerical simulations of the model with an identical overall geometric structure as the one used in the experiments were performed using a novel Equivalent Zonal (EZ) approach. A solution of an inverse heat transfer problem utilizing a time-dependent finite-volume CFD code was obtained. The model consisted of a sequence of distinct equivalent heat transferring zones representing the fins and tubes, and adjacent zones representing manifold shells, having geometrical features identical to the actual design. Five tube zones, four alternating fin zones, and two manifold zones were included in the model. The comparison between experimental temperature data and numerical simulation performed under the same conditions indicates a very good agreement throughout the ramp-up brazing cycle, and in particular at the peak brazing temperature. The suggested EZ-approach to the modeling provides temperature-time data sensitive enough to indicate critical locations in the joint zones between the tubes and manifolds. These zones are prone to poor brazing conditions due to temperature non-uniformities, thus leading to manufacturing imperfections.
机译：本文讨论了在受控气氛钎焊过程（CAB）中暴露于瞬态钎焊循环的型芯和相关歧管壳表面的温度历史。复杂的紧凑型换热器结构由一系列带有微通道和多百叶窗散热片的挤压管组成，并与歧管壳组合件框在一起，并进行了斜升/保压/快速淬火辐射-对流加热-冷却材料处理序列。使用实际的换热器设计元素（即挤压管，百叶窗翅片和歧管壳）组装测试样品。在配备有透明热区的实验设备中，在878 K的峰值钎焊温度下完成钎焊。实验方案模仿了用于制造铝制紧凑型热交换器的最新制造工艺。在样品的辐射加热和对流冷却期间，连续监测翅片和管子的表面温度。在99.999％的氮气中加热，峰值背景氧含量低于50 ppm，露点温度低于-40℃。使用新颖的等效分区（EZ）方法对模型进行了数值模拟，该模型的整体几何结构与实验中使用的几何结构相同。利用时间相关的有限体积CFD代码获得了逆传热问题的解决方案。该模型由代表翅片和管子的一系列不同的等效传热区域和代表歧管壳体的相邻区域组成，其几何特征与实际设计相同。该模型包括五个管区，四个交替的翅片区和两个歧管区。在相同条件下进行的实验温度数据与数值模拟之间的比较表明，在整个斜焊过程中，特别是在峰值钎焊温度下，一致性非常好。建模中建议的EZ方法可提供足够敏感的温度时间数据，以指示管和歧管之间的接合区域中的关键位置。由于温度不均匀，这些区域易于出现不良的钎焊条件，从而导致制造缺陷。

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