Natural convection heat transfer from a vertical plate—II. With gas injection and transverse magnetic field
Natural convection heat transfer from a vertical plate—II. With gas injection and transverse magnetic field
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垂直板的自然对流换热——注气和横向磁场
DOI：
10.1016/0017-9310(94)90225-9
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发表时间：
1994
影响因子：
5.2
通讯作者：
P. Lykoudis
中科院分区：
文献类型：
--
作者：
A. Tokuhiro;P. Lykoudis
在竖直封闭腔内进行了一面加热、另一面冷却的自然对流换热实验。从一排皮下注射管中沿加热板底部沿着向上注射氮气泡。垂直于加热表面施加幅度为0.07 B ~ 0.50特斯拉的横向磁场。所施加的热通量的范围为370 Ω·m-16 000 W·m-2，对应于10 5 Ω·Bo·m-10 9的修改的Boussinesq数范围。气体注入速率范围为0.9 × 10 - 4g × 9.2 cm 3 s-1。用热电偶和双电导探针测量了局部传热和空隙率。实验结果表明，对于低的热通量率，一个小的磁场强度（B <$0.07 T）显着降低的传热系数在气体注入的存在下，在没有磁场的情况下，提高传热系数的两到三倍，相对于单相的结果。这种下降是由于层流对流和气泡引起的液体运动的抑制。在较高的热通量，在磁场的存在下的传热系数的降低是不太显着的。然而，随着磁场强度的增加，努塞尔数在这些较高的热通量下降。当磁场强度在B = 0.25-0.35 T范围内时，气泡尺寸和气泡速度的增加使传热系数的连续下降趋于稳定。在较高的电场强度（B <0.50 T）的温度曲线表明传导为主的传热机制。
A natural convection heat transfer experiment was conducted in mercury with gas injection in a vertical enclosure heated on one face at constant heat flux and cooled on the opposite face. Nitrogen gas bubbles were injected from a row of hypodermic tubes facing upwards along the bottom of the heated plate. A transverse magnetic field of magnitude 0.07⩽ B⩽ 0.50 Tesla was imposed perpendicular to the heated surface. The range of the applied heat flux was 370⩽ q “⩽ 16 000 W m t-2, corresponding to a modified Boussinesq number range of 10 5⩽ Bo∗ x⩽ 10 9. The gas injection rate range was 0.9⩽ Q g⩽ 9.2 cm 3 s− 1. Local heat transfer and void measurements were made with thermocouple and double-conductivity probes. Experimental results showed that for low heat flux rates, a small magnetic field intensity (B∼ 0.07 T) significantly reduced the heat transfer coefficient in the presence of gas injection which in the absence of the magnetic field enhanced the heat transfer coefficient two-to three-fold relative to the single-phase result. The decrease was attributed to the suppression of both the laminar convection and the bubble-induced liquid motion. At higher heat fluxes, the decrease in the heat transfer coefficient in the presence of the magnetic field was less significant. Nevertheless, with increasing field intensity the Nusselt number decreased at these higher heat fluxes. An increase in the bubble size and bubble velocity stabilized the continuous decrease in the heat transfer coefficient for field intensities in the range B∼ 0.25–0.35 T. At higher field intensities (B∼ 0.50 T) temperature profiles indicated a conduction-dominated heat transfer mechanism.