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对倾斜单管和倾斜管排的自然对流换热进行了实验研究。试验管的外径为40毫米,长800毫米。试验在恒热流条件下进行,R_(αL)的范围是5×10~8～3×10~9,倾斜角度为θ=0°(水平放置),15°,30°和45°。对于倾斜管排,在每一倾斜角下进行了七种s/d的试验。根据实验结果,拟合了适用于倾斜角度为0°～45°、流动状态为紊流时的倾斜单管的自然对流换热通用准则关系式,填补了现有实验数据的空白。试验还揭示了不同倾斜角度下倾斜管排中各管的N_(u_L)随s/d的变化规律。试验发现,尽管倾斜单管的换热总比相应条件下水平单管差,但是在θ不太大时,倾斜管排的平均换热系数不仅不比水平管排低,而且可高出5～6%。因此,就工程实用来说,当换热器的水平尺寸受限制时,将自然对流换热管排布置成倾斜的方式是可取的。此时,从工程实用的观点,倾斜管排的换热完全可按相同条件下的水平管排的公式计算。用Mach-Zehnder干涉仅获得了流场显示图像,对合理的解释试验结果及进一步建立理论模型提供了依据。
Experiments were conducted on the natural convection heat transfer of inclined single-tube and inclined tube. The test tube has an outer diameter of 40 mm and a length of 800 mm. The experiment was carried out under constant heat flow conditions. The range of R_ (αL) was 5 × 10 ~ 8 ~ 3 × 10 ~ 9, and the tilting angles were θ = 0 ° (horizontal), 15 °, 30 ° and 45 °. For inclined tube rows, seven s / d tests were performed at each tilt angle. According to the experimental results, the general guideline for natural convection heat transfer of a tilted single tube with a tilt angle of 0 ° ~ 45 ° and a turbulent flow condition is fitted, filling up the blank of the existing experimental data. The experiment also revealed the variation law of N_ (u_L) with s / d of each tube in the inclined tube row under different inclination angles. It is found that although the heat transfer of inclined single tube is always worse than that of the corresponding single horizontal tube, the average heat transfer coefficient of the inclined tube is not only lower than that of the horizontal tube but also can be higher than 5 ~ 6 %. Therefore, in engineering practice, it is advisable to arrange the natural convection heat exchange tube arrangement to be inclined when the horizontal size of the heat exchanger is limited. At this point, from a practical point of view, the heat transfer of the inclined tube row can be calculated according to the formula of the horizontal tube row under the same conditions. Only Mach-Zehnder interference was used to obtain the image of the flow field, which provided a basis for the reasonable interpretation of the test results and further theoretical models.