Heat Transfer Enhancement During Dropwise Condensation Over Wettability-Controlled Surfaces

Bortolin, Stefano; Tancon, Marco

doi:10.1007/978-3-030-82992-6_3

Cited by 8 publications

(4 citation statements)

References 66 publications

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“…In equation (2), n(r) is the drop-size density of small droplets, growing by direct condensation, N(r) is the drop-size density of large droplets, growing mainly by coalescence, and re is the effective radius, which can be expressed as re = (4 Ns 0.5 ) -1 .…”

Section: Droplet Population and Heat Flux: Pbm Vs Ibmmentioning

confidence: 99%

“…However, by reducing the wettability of the subcooled wall, a more efficient condensation mechanism, known as dropwise condensation (DWC), can be achieved. Because the heat transfer coefficient (HTC) during DWC can be up to 10 times higher compared to FWC [1,2], heat exchangers can be significantly downsized or the driving temperature difference of the process can be reduced, leading to economic and energy savings.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of dropwise condensation of water through an efficient individual-based model

Tancon,

Abbatecola,

Mirafiori

et al. 2024

J. Phys.: Conf. Ser.

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In recent years, researchers have directed their studies towards solutions aimed at enhancing heat exchangers effectiveness. In this context, dropwise condensation (DWC) has been identified among the most promising solutions to increase the condensation heat transfer coefficient (HTC). In fact, DWC provides heat transfer coefficients up to ten times higher than those achievable during filmwise condensation (FWC), resulting in both economic and energy benefits. The DWC phenomenon is usually modelled by combining the heat exchanged through a single droplet and the drop-size distribution. The latter can be divided into a distribution of large droplets N(r), determinable analytically by semi-empirical models, and a distribution of small droplets n(r), typically determined through statistical approaches called population-based models. Another possibility for the determination of the droplet-size density is to simulate the DWC process by an individual-based model (IBM). In this case, each drop is tracked throughout its entire life cycle (nucleation, growth, coalescence, sliding), and the drop-size distribution is obtained as a result. In this paper, a new IBM for the simulation of DWC of steam is proposed. The developed model allows for the simulation of more than 10 million droplets while keeping an acceptable simulation time thanks to the implementation of parallel computing. The predictions obtained from the model, in terms of drop-size distribution and condensation heat flux, are compared against both PBM results and experimental data.

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Section: Droplet Population and Heat Flux: Pbm Vs Ibmmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Investigation of dropwise condensation of water through an efficient individual-based model

Tancon,

Abbatecola,

Mirafiori

et al. 2024

J. Phys.: Conf. Ser.

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“…During dropwise condensation (DWC) the vapor phase changes to liquid phase forming discrete droplets on the surface whose temperature is below the dew temperature of the condensing fluid. It is well established that DWC allows to reach very high values of the heat transfer coefficient compared to filmwise condensation (FWC) 71 . The creation of surfaces that can promote DWC is one of the main issues.…”

Section: Effect Of Gravity During Dropwise Condensationmentioning

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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“…This condensation mode is called dropwise condensation (DWC). During condensation of pure steam, promoting DWC can enhance the heat transfer performance by an order of magnitude compared to filmwise condensation (FWC) [1,2]. On the other hand, it should be noted that the possible advantage given by DWC during condensation in presence of non-condensable gases (NCGs) is not well established.…”

Section: Introductionmentioning

confidence: 99%

Experimental analysis of drop size distribution and nucleation site density during dropwise condensation from humid air flow

Mirafiori

Tancon

Bortolin

et al. 2023

J. Phys.: Conf. Ser.

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Condensation of the water vapor present in the air is a heat and mass transfer process encountered in many applications as humid air dehumidification and water harvesting. Depending on the wettability characteristics of the surface, condensation can take place in filmwise mode or in dropwise mode with the formation of discrete liquid droplets over the condensing surface. While dropwise condensation (DWC) of pure steam was found to promote a considerable enhancement of the heat transfer compared to filmwise condensation, when dealing with humid air DWC more investigation is needed. Modeling of DWC from humid air requires the calculation of the heat flow rate through a single droplet and the determination of the drop-size distribution. The heat exchanged through a single droplet depends on the heat and mass transfer resistances, while the drop-size distribution is also affected by nucleation site density and droplets mobility. Therefore, to better understand the DWC phenomenon with humid air and for the validation of the models, it is necessary to measure the heat flux (total and latent), droplet population and nucleation site density. In the present work, condensation tests from humid air are performed over two square (40 mm x 40 mm) aluminum samples that display different wettability. The experimental apparatus consists of a closed air loop with two main components: the environmental chamber and the test chamber. The air is conditioned in the environmental chamber and then it flows inside the test section where the vapor present in the humid air is condensed over the vertical metallic sample. Two variable speed fans are used to circulate the air. The test section is designed for heat and mass transfer measurements and for simultaneous visualization of the condensation process. As a peculiar characteristic of the present experimental technique, all the test section assembly is suspended on a high precision balance allowing a precise measurement of the mass of condensate. The effect of surface wettability on the heat and mass transfer during DWC is investigated. Time-lapse videos of the condensation process are acquired at different magnifications. By using a homemade MATLAB® program for droplet detection, recorded images are analysed allowing the determination of both the drop size density distribution (small and large droplet population) and the nucleation sites density.

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Heat Transfer Enhancement During Dropwise Condensation Over Wettability-Controlled Surfaces

Cited by 8 publications

References 66 publications

Investigation of dropwise condensation of water through an efficient individual-based model

Investigation of dropwise condensation of water through an efficient individual-based model

Condensation heat transfer in microgravity conditions

Experimental analysis of drop size distribution and nucleation site density during dropwise condensation from humid air flow

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