Spatiotemporally resolved heat transfer measurements in falling liquid-films by simultaneous application of planar laser-induced fluorescence (PLIF), particle tracking velocimetry (PTV) and infrared (IR) thermography
Spatiotemporally resolved heat transfer measurements in falling liquid-films by simultaneous application of planar laser-induced fluorescence (PLIF), particle tracking velocimetry (PTV) and infrared (IR) thermography
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DOI：
10.1016/j.expthermflusci.2018.11.001
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发表时间：
2019-10
影响因子：
3.2
通讯作者：
A. Charogiannis;C. Markides
中科院分区：
文献类型：
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作者：
A. Charogiannis;C. Markides
我们提出了一种光学技术，结合同时平面激光诱导荧光（PLIF），粒子跟踪测速（PTV）和红外（IR）热成像的空间和时间分辨测量的膜高度，2-D速度和2-D自由表面温度的液体薄膜下降在倾斜的，连续加热的玻璃基板。使用此信息和知识的壁温，局部和瞬时传热系数（HTC）和努塞尔数，Nu，也恢复沿着波的液体膜与Kapitza数，Ka= 180，普朗特数，Pr= 77。通过使用这种技术，在雷诺数Re= 18-66范围内，波频率设定为fw = 7、12和17 Hz，壁面热通量设定为q = 2.5 W cm− 2的情况下，对降膜流动进行了研究。在q今= 0 W cm− 2的等效（即平均流Re相同）流中也收集了补充数据。进行质量保证实验，揭示PLIF/PTV衍生的膜高度，界面/体积速度和流速之间的偏差高达2-3%，以及在一系列条件下对平膜的分析预测和直接测量，而基于IR的温度测量在热电偶测量的1° C范围内。高度本地化的膜的高度，速度，流量和界面温度的数据产生沿着检查波拓扑结构的相位/波锁定平均。热通量的应用（q ~= 2.5 W cm− 2）导致所研究的膜的显著“变薄”（平均18%），而平均体积速度通过增加类似的程度来补偿，以保持施加的流速。在加热的情况下获得的轴向速度分布是抛物线，但“更充分”相比，等效的等温流，不包括任何波区的接口斜率高。由于Re减少，在壁处施加的加热穿透膜，导致在HTC和较薄的膜区域中的膜高度之间的显著耦合。当施加的波频率增加时，观察到较窄范围的HTC，这与膜拓扑结构的演变和成像位置上游的流体流的相关重新分配有关，因为液体粘度降低。的本地和瞬时Nu强烈耦合到膜的高度和经验的变化，随着f w减少而增加。
We present an optical technique that combines simultaneous planar laser-induced fluorescence (PLIF), particle tracking velocimetry (PTV) and infrared (IR) thermography for the space-and time-resolved measurement of the film-height, 2-D velocity and 2-D free-surface temperature in liquid films falling over an inclined, resistively-heated glass substrate. Using this information and knowledge of the wall temperature, local and instantaneous heat-transfer coefficients (HTCs) and Nusselt numbers, Nu, are also recovered along the waves of liquid films with Kapitza number, Ka= 180, and Prandtl number, Pr= 77. By employing this technique, falling-film flows are investigated with Reynolds numbers in the range Re= 18–66, wave frequencies set to f w= 7, 12 and 17 Hz, and a wall heat flux set to q ̇= 2.5 W cm− 2. Complementary data are also collected in equivalent (ie, for the same mean-flow Re) flows with q ̇= 0 W cm− 2. Quality assurance experiments are performed that reveal deviations of up to 2–3% between PLIF/PTV-derived film heights, interfacial/bulk velocities and flow rates, and both analytical predictions and direct measurements of flat films over a range of conditions, while IR-based temperature measurements fall within 1° C of thermocouple measurements. Highly localized film height, velocity, flow-rate and interface-temperature data are generated along the examined wave topologies by phase/wave locked averaging. The application of a heat flux (q ̇= 2.5 W cm− 2) results in a pronounced “thinning” of the investigated films (by 18%, on average), while the mean bulk velocities compensate by increasing by a similar extent to conserve the imposed flow rate. The axial-velocity profiles that are obtained in the heated cases are parabolic but “fuller” compared to equivalent isothermal flows, excluding any wave-regions where the interface slopes are high. As the Re is reduced, the heating applied at the wall penetrates through the film, resulting in a pronounced coupling between the HTC and the film height in thinner film regions. When the imposed wave frequency is increased, a narrower range of HTCs is observed, which we link to the evolution of the film topology and the associated redistribution of the fluid flow upstream of the imaging location, as the liquid viscosity decreases. The local and instantaneous Nu is strongly coupled to the film height and experiences variations that increase as f w is reduced.