Investigation of dimpled fins for heat transfer enhancement in compact heat exchangers
Investigation of dimpled fins for heat transfer enhancement in compact heat exchangers
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DOI：
10.1016/j.ijheatmasstransfer.2007.09.013
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发表时间：
2008-06-01
影响因子：
5.2
通讯作者：
Tafti, Danesh K.
中科院分区：
文献类型：
--
作者：
Elyyan, Mohammad A.;Rozati, Ali;Tafti, Danesh K.
直接模拟和大涡模拟是在 Re-H=200 至 15,000 的雷诺数范围内具有凹痕和突起的翅片组中进行的，包括层流、过渡和完全湍流状态。研究了两种凹坑突出几何形状，其中针对两种不同的通道高度或翅片节距研究了相同的压印图案，情况 I 的翅片节距是情况 2 的两倍。较小的翅片节距配置（情况 2）在 Re-H=450 时产生流动不稳定性，而情况 I 在 Re-H=900 时经历转变。在情况 I 转变为湍流之前，情况 2 在低雷诺数状态下表现出较高的努塞尔数和摩擦系数，之后，在完全湍流状态下，两者之间的差异显着减小。凹坑腔内和凹坑边缘处产生的涡流主要有助于凹坑侧上的传热增强，而突出部之间的流动冲击和加速主要有助于突出侧上的传热。虽然在低雷诺数情况下，摩擦阻力在案例 I 中占主导地位，但在案例 2 中，形状阻力和摩擦阻力的贡献相等。随着雷诺数增加到完全湍流，形状阻力在两种情况下都占主导地位，约占总损失的 80%。虽然这两种几何形状在湍流状态下都是可行的并且与其他增强表面相比具有竞争力，但情况 2 具有相对于翅片节距的较大特征尺寸更适合低雷诺数状态 Re-H < 2000，该状态构成了典型紧凑型热交换器的大部分工作范围。 (c) 2007 Elsevier Ltd. 保留所有权利。
Direct and Large-Eddy simulations are conducted in a fin bank with dimples and protrusions over a Reynolds number range of Re-H=200 to 15,000, encompassing laminar, transitional and fully turbulent regimes. Two dimple-protrusion geometries are studied in which the same imprint pattern is investigated for two different channel heights or fin pitches, Case I with twice the fin pitch of Case 2. The smaller fin pitch configuration (Case 2) develops flow instabilities at Re-H=450, whereas Case I undergoes transition at Re-H=900. Case 2, exhibits higher Nusselt numbers and friction coefficients in the low Reynolds number regime before Case I transitions to turbulence, after which, the differences between the two decreases considerably in the fully turbulent regime. Vorticity generated within the dimple cavity and at the dimple rim contribute substantially to heat transfer augmentation on the dimple side, whereas flow impingement and acceleration between protrusions contribute substantially on the protrusion side. While friction drag dominates losses in Case I at low Reynolds numbers, both form and friction drag contributed equally in Case 2. As the Reynolds number increases to fully turbulent flow, form drag dominates in both cases, contributing about 80% to the total losses. While both geometries are viable and competitive with other augmentation surfaces in the turbulent regime, Case 2 with larger feature sizes with respect to the fin pitch is more appropriate in the low Reynolds number regime Re-H < 2000, which makes up most of the operating range of typical compact heat exchangers. (c) 2007 Elsevier Ltd. All rights reserved.