Modulated heat transfer tube with short conical-mesh inserts: A linking from microflow to macroflow
Modulated heat transfer tube with short conical-mesh inserts: A linking from microflow to macroflow
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DOI：
10.1016/j.ijheatmasstransfer.2015.05.051
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发表时间：
2015-10
影响因子：
5.2
通讯作者：
Zhenle Cao;Jinliang Xu
中科院分区：
文献类型：
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作者：
Zhenle Cao;Jinliang Xu
本文提出了一种新的方法，即利用微流体通过网孔来调节流场和温度场。通过在管内悬挂连续的锥形网格插入物来构造调制传热管。针对锥形网格内三维网孔（10-100 μm）较多的问题，采用网孔等当量直径准则和网孔总通流面积准则，通过网孔三维到二维的转换，对层流区进行了数值模拟。多尺度网格生成将微孔的微米尺度和管的宏观尺度联系起来。MHTT的努塞尔数是光管的1.4-4.1倍，性能评价指标PEC高达2.2，在低流量泵送成本下表现出良好的强化传热效果。完美的MHTT性能来自于独特的流场：管壁附近具有大速度和梯度的附着水力边界层、网状插入物上游的弱循环流动区域和网状插入物下游的弱正流动区域。在管壁上形成了一层薄的热边界层，强化了传热。优化了锥形网片的周期单位长度和直径δ。发现并解释了随Re增大NuversusRe斜率的变化。存在PPI（每英寸孔隙数）和Re（雷诺数）的最佳匹配。在低Re时建议采用LowPPImesh插入件，而highPPImesh插入件则使流线变形，偏离理想流场和温度场。同时，高PPImesh插入物在高Re下具有更好的性能。LowPPImesh插入物具有良好的性能，可以通过提高PPI来进一步改善。由于金属丝网筛的商品化和价格低廉，MHTT具有广阔的工程应用前景。
This paper creates new method that uses microflows through mesh pores to modulate flow and temperature fields. Modulated heat transfer tube (MHTT) was constructed by suspending consecutive conical-mesh inserts in a tube. Because there are too many 3D mesh pores (10–100 μm size) for a conical mesh insert, numerical simulations in laminar flow regime were performed by an 3D to 2D conversion of mesh pores applying equal equivalent diameter criterion and total flow area criterion of mesh pores. The multiscale grid generation linked micron scale of mesh pores and macroscale of the tube. Covering the present data ranges, MHTT had Nusselt numbers which are 1.4–4.1 times of that in a bare tube,PEC(performance evaluation criterion) was up to 2.2, demonstrating excellent heat transfer enhancement at low flow rate pumping cost. The perfect MHTT performance comes from the distinct flow field: an attached hydraulic boundary layer having large velocity and its gradient near the tube wall, a weak circulating flow region upstream of the mesh insert and a weakly positive flow region downstream of the mesh insert. A thin thermal boundary layer on the tube wall was reached to enhance heat transfer. The periodic unit lengthSand diameter of the conical mesh insertδwere optimized. The varied slopes ofNuversusRewere found and explained while increasingRe. There are best matches ofPPI(pores per inch) andRe(Reynolds number). LowPPImesh insert was suggested at lowRe, highPPImesh insert deformed streamlines to deviate from the perfect flow and temperature fields. Meanwhile, highPPImesh insert had better performance at highRe. LowPPImesh insert had good performance, which can be further improved by raisingPPI. Because metallic mesh screen is commercialized and cheap, MHTT has wide potential engineering applications.