Simultaneous droplet impingement dynamics and heat transfer on nano-structured surfaces

Shen, Jian Ren; Graber, Christof; Liburdy, James A.; Pence, Deborah V.; Narayanan, Vinod

doi:10.1016/j.expthermflusci.2009.02.003

Cited by 47 publications

(16 citation statements)

References 31 publications

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“…As reported in [35] and elsewhere, distinct stages are observed during impingement. In this case of non-splashing with heat transfer the stages are: initial impact (with a large temperature transient), boiling (if the surface temperature is high enough), evaporation (with near-constant wetting diameter and temperature), evaporation (with a receding contact line) and final dry-out.…”

Section: Impingement Processsupporting

confidence: 69%

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Droplet impingement dynamics: effect of surface temperature during boiling and non-boiling conditions

Shen

Liburdy

Pence

et al. 2009

J. Phys.: Condens. Matter

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This study investigates the hydrodynamic characteristics of droplet impingement on heated surfaces and compares the effect of surface temperature when using water and a nanofluid on a polished and nanostructured surface. Results are obtained for an impact Reynolds number and Weber number of approximately 1700 and 25, respectively. Three discs are used: polished silicon, nanostructured porous silicon and gold-coated polished silicon. Seven surface temperatures, including single-phase (non-boiling) and two-phase (boiling) conditions, are included. Droplet impact velocity, transient spreading diameter and dynamic contact angle are measured. Results of water and a water-based single-wall carbon-nanotube nanofluid impinging on a polished silicon surface are compared to determine the effects of nanoparticles on impinging dynamics. The nanofluid results in larger spreading velocities, larger spreading diameters and an increase in early-stage dynamic contact angle. Results of water impinging on both polished silicon and nanostructured silicon show that the nanostructured surface enhances the heat transfer for evaporative cooling at lower surface temperatures, which is indicated by a shorter evaporation time. Using a nanofluid or a nanostructured surface can reduce the total evaporation time up to 20% and 37%, respectively. Experimental data are compared with models that predict dynamic contact angle and non-dimensional maximum spreading diameter. Results show that the molecular-kinetic theory's dynamic contact angle model agrees well with current experimental data for later times, but over-predicts at early times. Predictions of maximum spreading diameter based on surface energy analyses indicate that these models over-predict unless empirical coefficients are adjusted to fit the test conditions. This is a consequence of underestimates of the dissipative energy for the conditions studied.

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Section: Impingement Processsupporting

confidence: 69%

“…The gold layer allows direct infrared imaging of the solid surface rather than the fluid. This method, along with detailed thermal results, are discussed in [35]. Results include the initial impact hydrodynamics, while looking at the ability of existing models to predict maximum spread distances.…”

Section: Introductionmentioning

confidence: 99%

Droplet impingement dynamics: effect of surface temperature during boiling and non-boiling conditions

Shen

Liburdy

Pence

et al. 2009

J. Phys.: Condens. Matter

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“…Control of surface texture to enhance CHF: Several attempts have been made to use micro and nanostructures, to delay the occurrence of dry-out, or minimize its effects, as reviewed by Lu and Kandlikar 131 . The mechanism by which these nanostructures enhance heat flux is still a matter of debate used to enhance CHF are copper nanowires 35,[232][233][234] , silicon nanowires 231,232 , carbon nanotubes 235 , zinc oxide nanoparticles 236 , nanoporous copper 237,238 , nanoporous zirconium 239 , nanoporous silicon 240 , and nanoporous aluminum oxide 241 . Figure 16 presents a micrograph of superhydrophilic silicon nanowires which achieved a 100% increase in the CHF value for water, as compared with smooth silicon 232 .…”

Section: (Up To 400%) By Coating Silicon Surfaces With Carbon Nanotubesmentioning

confidence: 99%

Surface engineering for phase change heat transfer: A review

Attinger

Frankiewicz

Betz

et al. 2014

MRS Energy & Sustainability

325

195

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Among numerous challenges to meet the rising global energy demand in a sustainable manner, improving phase change heat transfer has been at the forefront of engineering research for decades. The high heat transfer rates associated with phase change heat transfer are essential to energy and industry applications; but phase change is also inherently associated with poor thermodynamic efficiencies at low heat flux, and violent instabilities at high heat flux. Engineers have tried since the 1930's to fabricate solid surfaces that improve phase change heat transfer. The development of micro and nanotechnologies has made feasible the high-resolution control of surface texture and chemistry over length scales ranging from molecular levels to centimeters. This paper reviews the fabrication techniques available for metallic and siliconbased surfaces, considering sintered and polymeric coatings. The influence of such surfaces in multiphase processes of high practical interest, e.g. boiling, condensation, freezing, and the associated physical phenomena are reviewed. The case is made that while engineers are in principle able to manufacture surfaces with optimum nucleation or thermofluid transport characteristics, more theoretical and experimental efforts are needed to guide the design and cost-effective fabrication of surfaces that not only satisfy the existing technological needs, but also catalyze new discoveries.

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“…We consider a spherical water droplet of diameter d 0 =1.29 × 10 −3 m impinging with the pre-impact speed u imp =1.18 m/s, and initial surfactant concentrations, c 0 = 2000 and C Γ (x, 0) = 0. An equilibrium contact angle θ 0 e =46 • has been observed in the experimental study [58] for a clean water droplet on a polished silicon surface, and it is used here. Using L=d 0 and U =1.18 m/s as characteristic values, we get Re=1522, We=25 and Fr=110.…”

Section: Computational Examples Of Soluble Surfactant Droplet Impingementioning

confidence: 99%

Simulations of impinging droplets with surfactant-dependent dynamic contact angle

Ganesan

2015

Journal of Computational Physics

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An arbitrary Lagrangian-Eulerian (ALE) finite element scheme for computations of soluble surfactant droplet impingement on a horizontal surface is presented. The numerical scheme solves the time-dependent Navier-Stokes equations for the fluid flow, scalar convection-diffusion equation for the surfactant transport in the bulk phase, and simultaneously, surface evolution equations for the surfactants on the free surface and on the liquid-solid interface. The effects of surfactants on the flow dynamics are included into the model through the surfactant-dependent surface tension and dynamic contact angle. In particular, the dynamic contact angle (θ d ) of the droplet is defined in terms of the surfactant concentration at the contact line and the equilibrium contact angle (θ 0 e ) of the clean surface using the nonlinear equation of state for surface tension. Further, the surface forces are included in the model as the surface divergence of the surface stress tensor that allows to incorporate the Marangoni effects without calculating the surface gradient of the surfactant concentration on the free surface. In addition to a mesh convergence study and validation of the numerical results with experiments, the effects of adsorption and desorption surfactant coefficients on the flow dynamics in wetting, partially wetting and non-wetting droplets are studied in detail. It is observed that the effect of surfactants are more in wetting droplets than in the non-wetting droplets. Further, the presence of surfactants at the contact line reduces the equilibrium contact angle further when θ 0 e is less than 90• , and increases it further when θ 0 e is greater than 90• . The presence of surfactants has no effect on the contact angle, when θ 0 e = 90• . The numerical study clearly demonstrates that the surfactant-dependent contact angle has to be considered, in addition to the Marangoni effect, in order to study the flow dynamics and the equilibrium states of surfactant droplet impingement accurately. The proposed numerical scheme guarantees the conservation of fluid mass and of the surfactant mass well.

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Simultaneous droplet impingement dynamics and heat transfer on nano-structured surfaces

Cited by 47 publications

References 31 publications

Droplet impingement dynamics: effect of surface temperature during boiling and non-boiling conditions

Droplet impingement dynamics: effect of surface temperature during boiling and non-boiling conditions

Surface engineering for phase change heat transfer: A review

Simulations of impinging droplets with surfactant-dependent dynamic contact angle

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