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首页> 外文期刊>International Journal of Heat and Mass Transfer >Milliscale confined impinging slot jets: Laminar heat transfer characteristics for an isothermal flat plate
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Milliscale confined impinging slot jets: Laminar heat transfer characteristics for an isothermal flat plate

机译：毫米级受限撞击槽式射流：等温平板的层流传热特性

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摘要

Heat transfer and overall visualized flow characteristics of confined, laminar milli-scale slot jets are investigated, as they impinge upon an isothermal flat target plate, with a fully-developed profile at the nozzle exit. The effects of Reynolds number Re and normalized nozzle-to-plate distance ratio H/B are investigated for Re = 120-200, H/B= 2-10, and B = 1.0 mm, with a nozzle aspect ratio of y/B = 50. Instantaneous visualizations of overall slot jet flow structure show unsteady lateral distortions of jet columns at experimental conditions corresponding to the presence of continuous sinusoidal oscillations. Also apparent in flow visualization sequences are smoke signatures associated with instantaneous vortex structures which form as secondary flows develop in fluid which, initially, is just adjacent to the jet column. For each Reynolds number considered, local stagnation region Nusselt numbers Nu_0 decrease dramatically as HjB increases to become greater than 7.2-13.2, as the Reynolds number is maintained constant at a value from 200 to 120, changes which occur just as continuous sinusoidal oscillation of the jet column begins to develop. The further development of continuous sinusoidal oscillating motion results in an approximate collapse of stagnation region Nusselt numbers measured at different Re and HjB values. When surface thermal boundary condition data are compared, the constant surface temperature data are generally higher than the constant surface heat flux data near the stagnation location, and lower at locations where x/B is greater than 1-2. The constant surface temperature data also show relatively low values with only very small changes with x/B, for x/B values which are greater than about 5.0. As such, the results illustrate the sensitivity of Nusselt numbers for laminar boundary layer and laminar slot jet flows to thermal boundary condition, as well as the restrictions on near-wall temperature gradients which result from a constant surface temperature thermal boundary condition.
机译：研究了密闭的层状毫米级狭缝射流的传热和整体可视化流动特性，因为它们撞击到等温的扁平靶板上，并且在喷嘴出口处具有完全展开的轮廓。对于Re = 120-200，H / B = 2-10和B = 1.0 mm，以y / B的喷嘴纵横比，研究了雷诺数Re和归一化的喷嘴到板的距离比H / B的影响。 = 50.整体缝隙射流流动结构的瞬时可视化结果显示，在实验条件下射流柱的不稳定横向变形与连续正弦振动的存在相对应。在流动可视化序列中也很明显的是与瞬时涡旋结构相关的烟雾特征，这些涡旋结构是随着二次流动在最初与喷射塔相邻的流体中发展而形成的。对于每个考虑的雷诺数，当HjB增大到大于7.2-13.2时，局部停滞区域Nusselt数Nu_0急剧减小，因为雷诺数保持恒定在200到120的值，这种变化的发生就像连续的正弦振动一样。射流柱开始发展。连续正弦振荡运动的进一步发展导致停滞区域Nusselt数在不同Re和HjB值下的近似崩溃。当比较表面热边界条件数据时，恒定表面温度数据通常高于停滞位置附近的恒定表面热通量数据，而在x / B大于1-2的位置则较低。恒定的表面温度数据还显示出相对较低的值，并且随x / B的变化很小，因为x / B值大于约5.0。这样，结果说明了层流边界层和层流缝隙射流的Nusselt数对热边界条件的敏感性，以及由于恒定的表面温度热边界条件导致的近壁温度梯度的限制。

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