“…Nevertheless, we achieve DR > 0 together with a heat transfer increase for this geometry. Interface deformations, which have been neglected here, tend to reduce DR and increase convection further (Cartagena et al 2018;Ciri & Leonardi 2021;Sundin, Zaleski & Bagheri 2021).…”
Section: Heat Flux To Drag Ratiomentioning
confidence: 99%
“…Interface deformations, which have been neglected here, tend to reduce and increase convection further (Cartagena et al. 2018; Ciri & Leonardi 2021; Sundin, Zaleski & Bagheri 2021). Figure 12.( a ) The root-mean-squared wall-normal velocity for turbulent flow over LIS (——, ; — — —, dispersive component ; , random component ; , smooth-wall reference).…”
Liquid-infused surfaces can reduce friction drag in both laminar and turbulent flows. However, the heat transfer properties of such multi-phase surfaces have still not been investigated to a large extent. We use numerical simulations to study conjugate heat transfer of liquid-filled grooves. It is shown that heat transfer can increase for both laminar and turbulent liquid flows due to recirculation in the surface texture. Laminar flow simulations show that for the increase to be substantial, the thermal conductivity of the solid must be similar to the thermal conductivity of the fluids, and the recirculation in the grooves must be sufficiently strong (Péclet number larger than 1). The ratio of the surface cavity to the system height is an upper limit of the direct contribution from the recirculation. While this ratio can be significant for laminar flows in microchannels, it is limited for turbulent flows, where the system scale (e.g. channel height) usually is much larger than the texture height. However, heat transfer enhancement of the order of
$10\,\%$
is observed (with a net drag reduction) in a turbulent channel flow at a friction Reynolds number
${{Re}}_\tau \approx 180$
. It is shown that the turbulent convection in the bulk can be enhanced indirectly from the recirculation in the grooves.
“…Nevertheless, we achieve DR > 0 together with a heat transfer increase for this geometry. Interface deformations, which have been neglected here, tend to reduce DR and increase convection further (Cartagena et al 2018;Ciri & Leonardi 2021;Sundin, Zaleski & Bagheri 2021).…”
Section: Heat Flux To Drag Ratiomentioning
confidence: 99%
“…Interface deformations, which have been neglected here, tend to reduce and increase convection further (Cartagena et al. 2018; Ciri & Leonardi 2021; Sundin, Zaleski & Bagheri 2021). Figure 12.( a ) The root-mean-squared wall-normal velocity for turbulent flow over LIS (——, ; — — —, dispersive component ; , random component ; , smooth-wall reference).…”
Liquid-infused surfaces can reduce friction drag in both laminar and turbulent flows. However, the heat transfer properties of such multi-phase surfaces have still not been investigated to a large extent. We use numerical simulations to study conjugate heat transfer of liquid-filled grooves. It is shown that heat transfer can increase for both laminar and turbulent liquid flows due to recirculation in the surface texture. Laminar flow simulations show that for the increase to be substantial, the thermal conductivity of the solid must be similar to the thermal conductivity of the fluids, and the recirculation in the grooves must be sufficiently strong (Péclet number larger than 1). The ratio of the surface cavity to the system height is an upper limit of the direct contribution from the recirculation. While this ratio can be significant for laminar flows in microchannels, it is limited for turbulent flows, where the system scale (e.g. channel height) usually is much larger than the texture height. However, heat transfer enhancement of the order of
$10\,\%$
is observed (with a net drag reduction) in a turbulent channel flow at a friction Reynolds number
${{Re}}_\tau \approx 180$
. It is shown that the turbulent convection in the bulk can be enhanced indirectly from the recirculation in the grooves.
“…LIS can self-repair and are not sensitive to hydrostatic pressure, thereby being more robust than superhydrophobic surfaces (SHS) if designed properly (Wong et al. 2011; Wexler, Jacobi & Stone 2015; Sundin, Zaleski & Bagheri 2021).…”
Section: Introductionmentioning
confidence: 99%
“…The fluid-fluid interfaces and mobility of the lubricant give rise to a slipping effect of the external flow. LIS can self-repair and are not sensitive to hydrostatic pressure, thereby being more robust than superhydrophobic surfaces (SHS) if designed properly (Wong et al 2011;Sundin, Zaleski & Bagheri 2021).…”
Using numerical simulations, we investigate the effects of Marangoni stresses induced by surfactants on the effective slip length of liquid-infused surfaces (LIS) with transverse grooves. The surfactants are assumed soluble in the external liquid shearing the surface and can adsorb onto the interfaces. Two different adsorption models are used: a classical Frumkin model and a more advanced model that better describes the decrease of surface tension for minuscule concentrations. The simulations show that LIS may face even more severe effects of surfactants than previously investigated superhydrophobic surfaces. Constructing an analytical model for the effective slip length, we can predict the critical surfactant concentration for which the slip length decreases significantly. This analytical model describes both adsorption models of LIS on a unified framework if properly adjusted. We also advance the understanding of when surfactant advection gives rise to highly skewed interfacial concentrations: the so-called partial stagnant cap regime. To a good approximation, this regime can only exist below a specific surfactant concentration given by the Marangoni number and the strength of the surfactants.
“…Equation (2.5) was solved using the built-in implementation of the algorithm by Weymouth & Yue (2010), computing the fluxes of on the faces of each cell, and updating accordingly. The equation for the dynamic contact angle (2.8) was solved using the implementation reported by Sundin, Zaleski & Bagheri (2021). Boundary conditions were implemented through a ghost layer (a layer of cells outside the computational domain where numerical quantities can be imposed). The curvature of the interface was calculated using height functions.…”
The motion of the three-phase contact line between two immiscible fluids and a solid surface arises in a variety of wetting phenomena and technological applications. One challenge in continuum theory is the effective representation of molecular motion close to the contact line. Here, we characterize the molecular processes of the moving contact line to assess the accuracy of two different continuum two-phase models. Specifically, molecular dynamics simulations of a two-dimensional droplet between two moving plates are used to create reference data for different capillary numbers and contact angles. We use a simple-point-charge/extended water model. This model provides a very small slip and a more realistic representation of the molecular physics than Lennard-Jones models. The Cahn–Hilliard phase-field model and the volume-of-fluid model are calibrated against the drop displacement from molecular dynamics reference data. It is shown that the calibrated continuum models can accurately capture droplet displacement and droplet break-up for different capillary numbers and contact angles. However, we also observe differences between continuum and atomistic simulations in describing the transient and unsteady droplet behaviour, in particular, close to dynamical wetting transitions. The molecular dynamics of the sheared droplet provide insight into the line friction experienced by the advancing and receding contact lines. The presented results will serve as a stepping stone towards developing accurate continuum models for nanoscale hydrodynamics.
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