Film thickness, interfacial waviness and heat transfer during downflow condensation of R134a

Berto, Arianna; Lavieille, Pascal; Azzolin, Marco; Bortolin, Stefano; Miscevic, Marc

doi:10.1016/j.applthermaleng.2022.118808

Cited by 15 publications

(2 citation statements)

References 53 publications

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“…For conventional horizontal channels (D h > 3 mm), condensation models differentiate between gravity-dominated flow regime, where the heat transfer coefficient is sensitive to the saturation-to-wall temperature difference driving force, and shear-dominated flow regime, owing to the influence of mass flux and vapor quality [42][43][44][45][46][47] . For mini-/micro-channels, since the gravity effect condensation is expected to be less important, correlations developed for condensation inside circular conventional tubes may not be able to accurately predict the heat transfer coefficient, especially at small mass flux [48][49][50][51] .…”

Section: Numerical and Analytical Studiesmentioning

confidence: 99%

Condensation heat transfer in microgravity conditions

et al. 2023

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In the present paper, a thorough review of the experimental and numerical studies dealing with filmwise and dropwise condensation under microgravity is reported, covering mechanisms both inside tubes and on plain or enhanced surfaces. The gravity effect on the condensation heat transfer is examined considering the results of studies conducted both in terrestrial environment and in the absence of gravity. From the literature, it can be inferred that the influence of gravity on the condensation heat transfer inside tubes can be limited by increasing the mass flux of the operating fluid and, at equal mass flux, by decreasing the channel diameter. There are flow conditions at which gravity does exert a negligible effect during in-tube condensation: predictive tools for identifying such conditions and for the evaluation of the condensation heat transfer coefficient are also discussed. With regard to dropwise condensation, if liquid removal depends on gravity, this prevents its application in low gravity space systems. Alternatively, droplets can be removed by the high vapor velocity or by passive techniques based on the use of condensing surfaces with wettability gradients or micrometric/nanometric structuration: these represent an interesting solution for exploiting the benefits of dropwise condensation in terms of heat transfer enhancement and equipment compactness in microgravitational environments. The experimental investigation of the condensation heat transfer for long durations in steady-state zero-gravity conditions, such as inside the International Space Station, may compensate the substantial lack of repeatable experimental data and allow the development of reliable design tools for space applications.

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Section: Numerical and Analytical Studiesmentioning

confidence: 99%

Condensation heat transfer in microgravity conditions

et al. 2023

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“…When investigating the condensation heat transfer in the micro-scale, there is an intrinsic difficulty in measuring accurately such small thicknesses of the condensate (below 100 µm). Among the few studies available in the literature, Berto et al [5][6][7] performed liquid film thickness measurements of R245fa, R134a and HFE-7000 during condensation inside a 3.38 mm channel using shadowgraphy and chromatic confocal imaging. Han et al [8] employed a laser confocal displacement meter for measuring the liquid film thickness during IOP Publishing doi:10.1088/1742-6596/2766/1/012131 2 annular flow of degassed water and air inside tubes with 0.3, 0.5 and 1.0 mm inner diameters.…”

Section: Introductionmentioning

confidence: 99%

Measuring liquid film thickness during downflow condensation in a minichannel

Berto,

Azzolin,

Lavieille

et al. 2024

J. Phys.: Conf. Ser.

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The availability of experimental liquid film thickness data during in-tube condensation heat transfer is fundamental for the development of reliable correlations for the design of condensers. During annular flow condensation, the heat transfer is directly linked to the liquid film thickness, as the main thermal resistance is due to thermal conduction through the film of condensate. Therefore, understanding the liquid film characteristics is paramount for modelling two-phase annular flows. Although several prediction methods for liquid film thickness are available in the literature, they are mainly related to air-water adiabatic experiments. More liquid film thickness data are required for a better understanding of the condensation phenomena and for the development of more accurate models. In this work, the liquid film thickness characteristics of R245fa, R134a and HFE-7000 have been investigated during condensation inside a vertical channel with 3.38 mm inner diameter. Shadowgraphy and chromatic confocal imaging were used to detect the evolution of the liquid film thickness with high temporal resolution. The experimental data were useful to address the existence of a dependence of the liquid film thickness on dimensionless numbers. The combination of two dimensionless numbers, specifically the vapor Weber number and the Reynolds number of the liquid phase, allows to better catch the liquid film thickness trends with the varying operating conditions.

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