Abstract Channels with ribs/baffles are widely applied in thermal engineering applications such as heat exchangers, solar water/air heaters and gas turbine cooling. In the present work, inclined and transverse twisted-baffles (I-TBs/T-TBs) are developed for heat transfer enhancement in a channel. The effects of Reynolds number (Re = 4000, 8000, 12,000, 16,000 and 20,000) roughness pitch ratios (p/w = 4.0, 6.0, 8.0, 10.0 and 12.0) and baffle twist ratios (y/w = 2.0, 3.0, 4.0 and 5.0 corresponding to twisted-baffle loop numbers (N) of 5, 7, 8 and 9) were investigated using air (Prandtl number, Pr = 0.7) as a working fluid. Heat transfer behavior was examined using thermochromic liquid crystal temperature measurements. Typical transverse and inclined baffles were also tested for comparison. Heat transfer, flow friction and thermal performance are reported in terms of Nusselt numbers (Nu), Nusselt number ratios (Nu/Nus), friction factors (f), friction factor ratios (f/fs) and thermal performance indices (η). Experimental results reveal that under most conditions examined, I-TBs show better heat transfer, lower frictional losses and higher thermal performance than TBs, IBs and T-TBs. For I-TBs, maximum heat transfer and thermal performance are obtained at a moderate pitch ratio (p/w = 6.0). However, in cases of T-TBs, heat transfer and thermal performance monotonically increase with a decreasing pitch ratio. Friction losses caused by both I-TBs and T-TBs decrease considerably with increasing pitch ratio. For I-TBs, heat transfer and thermal performance monotonically increase with increasing twist ratios. However, for T-TBs, maximum heat transfer and thermal performance are obtained at y/w = 3.0. Over the present studied range, a channel with I-TBs having optimal geometry (p/w = 6.0 and y/w = 5.0) yields maximum thermal performance indices, as high as 1.98, which is greater than the maximum values yielded by channels with T-TBs, TBs, IBs, and smooth channels, by around 74.1%, 98%, 52.5% and 98.3%.

中文翻译：

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在具有倾斜和横向扭曲挡板的通道中使用热致变色液晶温度测量来可视化传热特性

摘要 带肋/折流板的通道广泛应用于换热器、太阳能水/空气加热器和燃气轮机冷却等热工程应用中。在目前的工作中，倾斜和横向扭曲挡板 (I-TBs/T-TBs) 被开发用于增强通道中的传热。雷诺数 (Re = 4000、8000、12,000、16,000 和 20,000) 粗糙度间距比 (p/w = 4.0、6.0、8.0、10.0 和 12.0) 和挡板扭曲比 (y/w, 4.02.0) 的影响使用空气（普朗特数，Pr = 0.7）作为工作流体研究了对应于扭曲挡板回路数（N）为 5、7、8 和 9）的 5.0 和 5.0。使用热致变色液晶温度测量来检查传热行为。还测试了典型的横向和倾斜挡板以进行比较。传播热量，流动摩擦和热性能以努塞尔数 (Nu)、努塞尔数比 (Nu/Nus)、摩擦因数 (f)、摩擦因数比 (f/fs) 和热性能指数 (η) 报告。实验结果表明，在检查的大多数条件下，I-TB 比 TB、IB 和 T-TB 显示出更好的传热、更低的摩擦损失和更高的热性能。对于 I-TB，在适度的节距比 (p/w = 6.0) 下可获得最大的传热和热性能。然而，在 T-TB 的情况下，传热和热性能随着节距比的降低而单调增加。由 I-TB 和 T-TB 引起的摩擦损失随着节距比的增加而显着降低。对于 I-TB，传热和热性能随着捻比的增加而单调增加。然而，对于 T-TB，在 y/w = 3.0 时获得最大传热和热性能。在目前研究的范围内，具有最佳几何形状（p/w = 6.0 和 y/w = 5.0）的 I-TB 通道产生最高热性能指数，高达 1.98，大于具有T-TBs、TBs、IBs 和平滑通道，分别约为 74.1%、98%、52.5% 和 98.3%。