ABSTRACT In a double-pipe heat exchanger, heat transfer enhancement can be carried out by active or passive methods. In the present study, heat transfer characteristics are studied by the addition of hemispherical turbulators placed in the annulus region in a double-pipe heat exchanger. The turbulators are placed in the annulus region on the inner pipe separated at 90° to each other around the circumference. Studies have been carried out for various diameter ratios of 0.29, 0.44, and 0.58 and different pitch ratios of 1.47, 4.41 and 7.35. Water is taken as the fluid flowing in the inner pipe and air in the annulus. The numerical simulation is carried out to study various thermal parameters such as the Nusselt number (Nu), friction factor and thermohydraulic performance index. It is observed that the addition of the hemispherical turbulators in the double-pipe heat exchanger enhanced the air turbulence. The Nusselt number and the heat transfer rate increased but caused an undesirable increase in the friction factor compared to the bare pipe. Decreasing the pitch ratio as well as increasing the diameter ratio led to an increase in the heat transfer rate and Nu.

中文翻译：

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半球形湍流器在双管换热器中增强传热的作用

摘要 在双管换热器中，传热增强可以通过主动或被动方法进行。在本研究中，通过在双管换热器的环形区域添加半球形湍流器来研究传热特性。湍流器放置在内管上的环形区域中，围绕圆周彼此分开 90°。已经针对 0.29、0.44 和 0.58 的各种直径比和 1.47、4.41 和 7.35 的不同节距比进行了研究。水被视为在内管中流动的流体和在环空中的空气。进行数值模拟以研究各种热参数，如努塞尔数（Nu）、摩擦系数和热工水力性能指标。观察到，在双管换热器中加入半球形湍流器增强了空气湍流。与裸管相比，努塞尔数和传热率增加，但导致摩擦系数增加，这是不希望的。降低螺距比以及增加直径比导致传热率和 Nu 增加。