This paper reports a numerical study on heat transfer improvement in a double backward-facing expanding channel using different convectional fluids. A finite volume method with the k-e standard model is used to investigate the effects of step, Reynolds number and type of liquid on heat transfer enhancement. Three types of conventional fluids (water, ammonia liquid and ethylene glycol) with Reynolds numbers varying from 98.5 to 512 and three cases for different step heights at a constant heat flux (q = 2000 W/m2) are examined. The top wall of the passage and the bottom wall of the upstream section are adiabatic, while the walls of both the first and second steps downstream are heated. The results show that the local Nusselt number rises with the augmentation of the Reynolds number, and the critical effects are seen in the entrance area of the first and second steps. The maximum average Nusselt number, which represents the thermal performance, can be seen clearly in case 1 for EG in comparison to water and ammonia. Due to the expanding of the passage, separation flow is generated, which causes a rapid increment in the local skin friction coefficient, especially at the first and second steps of the downstream section for water, ammonia liquid and EG. The maximum skin friction coefficient is detected in case 1 for water with Re = 512. Trends of velocities for positions (X/H1 = 2.01, X/H2 = 2.51) at the first and second steps for all the studied cases with different types of convectional fluids are indicated in this paper. The presented findings also include the contour of velocity, which shows the recirculation zones at the first and second steps to demonstrate the improvement in the thermal performance.

中文翻译：

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使用不同工作流体的双后向扩展通道中的传热改进

本文报告了使用不同对流流体改善双后向膨胀通道传热的数值研究。使用具有ke标准模型的有限体积方法研究阶跃、雷诺数和液体类型对传热增强的影响。研究了雷诺数从 98.5 到 512 不等的三种常规流体（水、氨液和乙二醇）以及在恒定热通量 (q = 2000 W/m2) 下不同台阶高度的三种情况。通道的顶壁和上游段的底壁是绝热的，而下游的第一和第二级的壁被加热。结果表明，局部努塞尔数随着雷诺数的增加而上升，关键效应出现在第一和第二步的入口区域。与水和氨相比，EG 在案例 1 中可以清楚地看到代表热性能的最大平均努塞尔数。由于通道的扩大，产生了分离流，导致局部表面摩擦系数迅速增加，特别是在水、氨液和EG下游段的第一和第二阶段。在 Re = 512 的水的情况 1 中检测到最大皮肤摩擦系数。 对于具有不同类型的所有研究案例，在第一步和第二步的位置（X / H1 = 2.01，X / H2 = 2.51）的速度趋势对流流体在本文中进行了说明。所提出的发现还包括速度的轮廓，