Film thickness measurement techniques applied to micro-scale two-phase flow systems

Tibiriçá, Cristiano; Nascimento, Francisco Júlio do; Ribatski, Gherhardt

doi:10.1016/j.expthermflusci.2009.03.009

Cited by 101 publications

(54 citation statements)

References 58 publications

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“…[1] 。因此，临界热负荷是工业系统设计和操作的重要参数之一 [2] 。保持近壁微液膜的完整性对避免局部烧干、防止传热恶化有着重要的意义。针对流动沸腾，国内外学者对临界热负荷的产生进行了广泛的研究 [3][4][5] ，提出了相应的机理模型，如液膜流动模型 [6] 、近壁面气泡拥堵模型 [7] 、微液层干涸模型 [8] 和界面分离模型 [9] 等。在众多的临界热负荷预测模型中，THEOFANOUS 等 [10][11] 针对临界热负荷产生机理提出尺度分离理论具有更好的发展前景。原始的尺度分离理论是针对池沸腾提出的，认为临界热负荷的产生与远离壁面的宏观液膜行为无关，而主要受加热表面近壁微液膜的动力学行为影响。THEOFANOUS 等 [12] 认为尺度分离理论同样适合流动沸腾。目前，基于薄膜液层概念的液膜动力学机理模型和数值模拟有较多的研究成果 [13][14] 。 ORON 等 [15] 基于长波理论对薄液膜波动特性进行了系统总结，提出了液膜波动预测模型。CRASTER 等 [16] 在 ORON 等 [20] ，测量的范围限于 400 μm 至 23 mm [18] 。在电阻法中，探针接触气相和液相时的输出阻抗会有明显区别，因而在气液两相流检测中应用最广，可以用来测量气泡的频率、局部空隙率以及液膜厚度 [21] 。由于电阻法是一种接触式测量方法，其分辨率受到探针尺寸和探针定位系统的限制。依据不同的探针设计方法，测量范围可达到 50 μm 至 1.2 mm [18] 。光学法的原理基于光在经过不同介质或不同相的交界面时发生的光学现象。光学法也分为很多类别，利用光的衰减来检测界面行为较为简便，但是其测量误差相对较高 [22] 。光扫描法 [23] 精度高、准确度高，但是对于本文的研究对象，其测量范围很窄。光的干涉法也是一种测量液膜厚度较为精确的方法 [24] ,但是整个测量装置需要配备复杂的光学处理系统，而且测 …”

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Experimental Study on the Dynamics of a Thin Liquid Film under Shearing Force

Wang¹

2017

JME

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： The "scales-separation" phenomenon indicates that high heat-flux boiling and boiling crisis is dominated by micro-hydrodynamics of liquid microlayer on the heater surface. The techniques for liquid film measurement such as acoustic methods, nucleonic techniques, electrical methods, and optical methods are discussed in detail. Accordingly, a confocal optical sensor system is used to detect the dynamics of liquid film sheared by the co-flowing air from above in a horizontal aluminum channel. The impact of the gas shearing on film behaviors is analyzed and the integrity of liquid film is discussed in detail. The results indicate that the liquid film thickness decreases due to the entrainment and shows a linear or nonlinear variation under different flow conditions. Additionally, for a specific surface, the critical film thickness for an integral film is found to have no relation with the gas and liquid flow rates but the fluctuation of the liquid film increases with the increasing gas velocity.

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Experimental Study on the Dynamics of a Thin Liquid Film under Shearing Force

Wang¹

2017

JME

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“…Several distinct benefits to the slug flow regime result from this unique morphology; specifically, heat and mass transfer processes benefit from the high gas-phase surface-to-volume ratio [1], enhanced mixing, and presence of very thin liquid films [3], thus offering advantages relative to other flow regimes in chemical processing, thermal management and other applications. Despite these advantages, quantitative investigation of liquid-gas interface geometries in the slug flow regime has been limited mainly by the lack of suitable metrological techniques [4]. Characterization of the liquid film structure would aid in improved performance prediction capabilities that would benefit device design.…”

Section: Introductionmentioning

confidence: 99%

“…Detailed information specific to vapor bubble geometry and liquid film thickness in microchannel slug flows has not been reported to date. Tibirica et al [4] presented an exhaustive review of extant metrological techniques targeted towards thin film measurements and attributed this lack of film characterization to difficulties associated with performing measurements at a sufficiently high speed in a non-intrusive manner. Han and Shikazono [11] successfully deployed laser focus displacement meters in the investigation of liquid film thickness at the channel sidewall and corner in microchannels of square cross-section ranging in hydraulic diameter of 0.3 mm to 1 mm.…”

Section: Introductionmentioning

confidence: 99%

Characterization of liquid film thickness in slug-regime microchannel flows

Patel

Weibel

Garimella

2017

International Journal of Heat and Mass Transfer

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An experimental investigation is conducted to examine the effects of operating conditions and channel size on the liquid film thickness of vapor bubbles in adiabatic air-water flows within the slug flow regime. Acrylic test sections are fabricated to contain a single microchannel of square cross-section with hydraulic diameters of 510 μm and 1020 μm. High-speed visualizations are used to map the flow regimes in these channels in order to determine the range of liquid and gas flow rates for which slug-regime flows are sustained. Subsequently, a tomographic optical imaging technique is employed to quantitatively reconstruct the liquid-gas interface of vapor bubbles at selected operating conditions. This technique relies on visualization of fluorescent particles seeded into the liquid phase in order to identify the phase boundaries within thin sections of the flow. Using the reconstructions, the thickness of the liquid film in the corner of the square channel cross-section is extracted. This film thickness is found to decrease with increasing capillary number, and a simple expression is proposed for calculation of the film thickness; predictions from this model match the measurements with a mean absolute error (MAE) of 21.6%; 85.7% of all predicted data points fall within an error band of ±30%. Additionally, film thickness data from the literature are compared to model predictions and a comparable MAE of 21.8% is found with 77.8% of data points falling within an error band of ±30%.

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“…In many semi-empirical analyses for flow boiling heat transfer, slug flows with elongated bubbles or annular flows are often assumed as reference flow patterns and in the analysis the liquid film thickness is treated as one of the main parameters [1,2]. Once the local liquid film thickness is determined, it becomes easier to estimate the two-phase parameters, such as the void fraction and the liquid and gas velocities, as well as the acceleration pressure drop and the fluid inventory along the channels [3].…”

Section: Introductionmentioning

confidence: 99%