The present study has been numerically surveyed the effect of different expansion angles on the heat transfer and pressure drop characteristics of a sudden expansion in a microtube. For this purpose, Cu/water nanofluids flowing with Reynolds numbers (Re) of 10, 25, 50, and 100 through expansion angles of 30º, 45º, 60º, and 90º were modeled. Governing equations were solved by the finite volume method (FVM). The findings indicated that the heat transfer coefficient (HTC) could enhance by nanoparticles concentration and Re augmentation. Also, It was revealed that HTC of a sudden expansion with an angle of 45º has optimum hydrodynamic performance; then, sudden expansions of 30º, 90º, and 60º are followed. The highest HTC was achieved for a microtube containing 4 vol.% nanofluids at Re = 100 with a 45º expansion angle, 43.63% higher than conventional expansion angle (90º) working with distilled water at Re = 10. By comparing HTC at various angles, it can be found that there is a 14.57% further HTC by changing the expansion angle from α = 90º with α = 45º. Furthermore, the pressure drop investigation showed that the expansion angle with α = 30º has the lowest pressure drop. In contrast, α = 45º produced the highest pressure drop because of giant vortices created along the tube wall. The velocity streamlines and contours explained the reason for a lower pressure drop of α = 30º, 45º, and 60º which was regular streamlines along the tube wall due to the Coanda effect.

本研究已经对不同膨胀角度对微管中突然膨胀的传热和压降特性的影响进行了数值调查。为此，模拟了雷诺数 (Re) 为 10、25、50 和 100 且膨胀角为 30º、45º、60º 和 90º 的 Cu/水纳米流体。控制方程通过有限体积法 (FVM) 求解。研究结果表明，传热系数（HTC）可以通过纳米颗粒浓度和 Re 增加来提高。此外，还揭示了45°角突然膨胀的HTC具有最佳的流体动力学性能；然后，30º、90º 和 60º 的突然膨胀紧随其后。在 Re = 100 和 45º 扩展角 43 时，含有 4 vol.% 纳米流体的微管实现了最高的 HTC。在 Re = 10 时使用蒸馏水比常规膨胀角 (90º) 高 63%。通过比较不同角度下的 HTC，可以发现，通过将膨胀角从 α = 90º 更改为 α = 45º。此外，压降调查表明，α = 30º 的膨胀角具有最低的压降。相比之下，α = 45º 产生的压降最大，因为沿管壁产生了巨大的涡流。速度流线和等高线解释了 α = 30º、45º 和 60º 压降较低的原因，这是由于附壁效应导致的沿管壁的规则流线。此外，压降研究表明，α = 30º 的膨胀角具有最低的压降。相比之下，α = 45º 产生的压降最大，因为沿管壁产生了巨大的涡流。速度流线和等高线解释了 α = 30º、45º 和 60º 压降较低的原因，这是由于附壁效应导致的沿管壁的规则流线。此外，压降调查表明，α = 30º 的膨胀角具有最低的压降。相比之下，α = 45º 产生的压降最大，因为沿管壁产生了巨大的涡流。速度流线和等高线解释了 α = 30º、45º 和 60º 压降较低的原因，这是由于附壁效应导致的沿管壁的规则流线。