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首页> 外文期刊>Experimental Thermal and Fluid Science: International Journal of Experimental Heat Transfer, Thermodynamics, and Fluid Mechanics >Heat transfer enhancement in natural convection between vertical and downward inclined wall and air by pulsating jets
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Heat transfer enhancement in natural convection between vertical and downward inclined wall and air by pulsating jets

机译：通过脉动射流增强垂直和向下倾斜壁与空气之间自然对流的传热

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In this paper are reported the results of an experimental investigation about the heat transfer enhancement from vertical and downward inclined wall to air, in natural convection, by means of expired jets. The air was maintained at room temperature and the wall is heated by Joule effect. The temperature difference between the wall and the air was prefixed at 25 K and the wall placement had been varied from the vertical to different downward inclined positions(5°, 10°, 15°, 20°, 25° and 30°). The experimental results had shown an increase in the heat transfer coefficient, at the different wall inclinations, due to the jets; actually they had induced turbulence in the dynamic field, by interrupting the laminar flow. Our aim was to optimize the variables involved in the phenomenon, in order to find out the highest enhancement of the heat transfer coefficient values, caused by the jets. The variables were the number of active horizontal lines of jets, their activity and the inactivity time and their velocity. We had also investigated the conditions without jets and we found out that the heat transfer coefficient trend versus the downward inclination angles, could not be described by correlations present in literature. In fact, in the investigated range of the downward wall inclinations, the heat transfer coefficient did not may be simply correlated with the cosine of the angle, but it increased up to a maximum value, reached at 15°, and then decreased. The visualization by smoke had confirmed these results: the boundary layer thickness had followed this trend. In correspondence to the wall inclination equal to 15°, it reached its minimum value. Finally, to the purpose to link the experimental data, we had proposed a numerical correlation. The values calculated thanks to this one reported differences much lower than the computed experimental error.
机译：本文报道了通过自然射流对垂直和向下倾斜壁向空气传热的实验研究的结果，这些传热是通过对流射流实现的。将空气保持在室温下，并通过焦耳效应加热壁。墙壁和空气之间的温差为25 K，并且墙壁的位置从垂直位置更改为不同的向下倾斜位置（5°，10°，15°，20°，25°和30°）。实验结果表明，由于射流的影响，在不同的壁倾角下，传热系数都增加了。实际上，它们是通过中断层流在动态场中引起湍流的。我们的目的是优化与现象有关的变量，以找出由射流引起的传热系数值的最大提高。变量是射流的有效水平线的数量，其活动性，不活动时间和速度。我们还研究了无射流的情况，发现传热系数趋势与向下倾斜角之间的关系无法通过文献中的相关性来描述。实际上，在所研究的向下壁倾角范围内，传热系数可能不会简单地与角度的余弦相关，而是会增加到最大值，达到15°，然后降低。烟气的可视化已经证实了这些结果：边界层厚度遵循了这一趋势。对应于等于15°的壁倾角，它达到了最小值。最后，为了链接实验数据，我们提出了数值相关性。由于这一结果而计算出的值报告的差异远低于计算出的实验误差。

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