Electrowetting-Based Coalescence of Droplets During Dropwise Condensation of Humid Air

2019 ◽  
Author(s):  
Enakshi Wikramanayake ◽  
Vaibhav Bahadur
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Electric Fields ◽  
Applied Electric Field ◽  
Growth Dynamics ◽  
Condensation Heat Transfer ◽  
Droplet Growth ◽  
Dropwise Condensation ◽  
Condensation Rate ◽  
Humid Air

Abstract Dropwise condensation yields higher heat transfer coefficients by avoiding the thermal resistance of the condensate film, seen during filmwise condensation. This work explores further enhancement of dropwise condensation heat transfer through the use of electrowetting to achieve faster droplet growth via coalescence of the condensed droplets. Electrowetting is a well understood microfluidic technique to actuate and control droplets. This work shows that AC electric fields can significantly enhance droplet growth dynamics. This enhancement is a result of coalescence triggered by various types of droplet motion (translation of droplets, oscillations of three phase line), which in turn depends on the frequency of the applied AC waveform. The applied electric field modifies droplet condensation patterns as well as the roll-off dynamics on the surface. Experiments are conducted to study early-stage droplet growth dynamics, as well as steady state condensation rates under the influence of electric fields. It is noted that this study deals with condensation of humid air, and not pure steam. Results show that increasing the voltage magnitude and frequency increases droplet growth rate and overall condensation rate. Overall, this study reports more than a 30 % enhancement in condensation rate resulting from the applied electric field, which highlights the potential of this concept for condensation heat transfer enhancement.

Computational Studies of EHD-Enhanced Condensation Heat Transfer on a Downward-Facing Horizontal Plate

2009 ◽  
Author(s):  
Payam Sharifi ◽  
Asghar Esmaeeli
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Phase Boundary ◽  
Electric Fields ◽  
Detailed Examination ◽  
Relative Magnitude ◽  
Condensation Heat Transfer ◽  
Horizontal Plate ◽  
Condensation Rate ◽  
Leaky Dielectric Model

This study aims to investigate the effect of uniform electric fields on the enhancement of condensation heat transfer from a downward facing horizontal plate by direct numerical simulations. The governing equations of fluid flow and electric field are solved using a front tracking/finite difference technique in the framework of Taylor’s leaky dielectric model. The electric force comprises of the dielectrophoretic and the Coulomb forces. Both forces act on the phase boundary and their relative magnitude and directions affect the condensation rate. For the results shown here, the condensate drops are more elongated compared to the those in zero-electric field. It is shown that the electric field enhances the condensation rate in two ways: by increasing the number of the drops that are generated per unit surface due to destablizing the interface and by increasing the frequency of drop generation and pinch off. The mechanism of elongation of the condensate drops are explained by detailed examination of the distribution of the electric field at the phase boundary.

A Heat Transfer Model of Dropwise Condensation Underneath a Horizontal Substrate

2011 ◽  
Vol 199-200 ◽  
pp. 1604-1608
Author(s):  
Yun Fu Chen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Contact Angle ◽  
Fractal Model ◽  
Condensation Heat Transfer ◽  
Droplet Growth ◽  
Transfer Model ◽  
Dropwise Condensation ◽  
Small Contact Angle ◽  
Horizontal Substrate

For finding influence of the condensing surface to dropwise condensation heat transfer, a fractal model for dropwise condensation heat transfer has been established based on the self-similarity characteristics of droplet growth at various magnifications on condensing surfaces with considering influence of contact angle to heat transfer. It has been shown based on the proposed fractal model that the area fraction of drops decreases with contact angle increase under the same sub-cooled temperature; Varying the contact angle changes the drop distribution; higher the contact angle, lower the departing droplet size and large number density of small droplets; dropwise condensation translates easily to the filmwise condensation at the small contact angle ;the heat flux increases with the sub-cooled temperature increases, and the greater of contact angle, the more heat flux increases slowly.

scholarly journals Near Field Condensation

2020 ◽  
Author(s):  
Xiao Yan ◽  
Feipeng Chen ◽  
Chongyan Zhao ◽  
Yimeng Qin ◽  
Xiong Wang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Population Density ◽  
Near Field ◽  
Condensation Heat Transfer ◽  
Droplet Growth ◽  
Dropwise Condensation ◽  
Droplet Transfer ◽  
Droplet Sizes ◽  
Departure Size ◽  
Contact Line Pinning

Abstract Dropwise condensation represents the upper limit of condensation heat transfer. Promoting dropwise condensation relies on surface chemical functionalization, and is fundamentally limited by the maximum droplet departure size. A century of research has focused on active and passive methods to enable the removal of ever smaller droplets. However, fundamental contact line pinning limitations prevent gravitational and shear-based removal of droplets smaller than 250 µm. Here, we break this limitation through near field condensation. By de-coupling nucleation, droplet growth, and shedding via droplet transfer between parallel surfaces, we enable the control of droplet population density and removal of droplets as small as 20 µm without the need for chemical modification or surface structuring. We identify droplet bridging to develop a regime map, showing that rational wettability contrast propels spontaneous droplet transfer from condensing surfaces ranging from hydrophilic to hydrophobic. To demonstrate efficacy, we perform condensation experiments on surfaces ranging from hydrophilic to superhydrophobic. The results show that near field condensation with optimal gap spacing can limit the maximum droplet sizes and significantly increase the population density of sub-20 µm droplets. Theoretical analysis and direct numerical simulation confirm the breaking of classical condensation heat transfer paradigms through enhanced heat transfer. Our study not only pushes beyond century-old phase change limitations, it demonstrates a promising method to enhance the efficiency of applications where high, tunable, gravity-independent, and durable condensation heat transfer is required.

Electrohydrodynamic Condensation Heat Transfer

1968 ◽  
Vol 90 (1) ◽  
pp. 98-102 ◽  
Author(s):  
H. Y. Choi
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Liquid Film ◽  
Electric Fields ◽  
Vertical Tube ◽  
Condensation Heat Transfer ◽  
Instability Waves ◽  
Condensing Heat Transfer ◽  
Electrohydrodynamic Force ◽  
Rayleigh Numbers

This paper describes the results of an investigation of the effects of strong electric fields on condensation heat transfer. Freon-113 is condensed inside a vertical tube, and the condensate interface is stressed by a radial d-c field. The effect of the field on condensing heat transfer can be summarized as follows: (a) The condensing heat transfer coefficient increases significantly with the electric field; (b) the increase is related to the appearance of instability waves at the liquid film interface. These effects suggest that the average liquid film thickness is significantly reduced at high electric field intensities. A tentative correlation is presented for the high field data. The correlation is presented in terms of modified Nusselt and Rayleigh numbers in which the characteristic length is the most unstable wavelength in the system, and the driving force acting on the film is an equivalent electrohydrodynamic force.

scholarly journals A Review on Heat Transfer of Nanofluids by Applied Electric Field or Magnetic Field

Nanomaterials ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 2386
Author(s):  
Guannan Wang ◽  
Zhen Zhang ◽  
Ruijin Wang ◽  
Zefei Zhu
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Electric Field ◽  
Electric Fields ◽  
Applied Electric Field ◽  
Heat Transfer Performance ◽  
Transfer Enhancement ◽  
Heat Transfer Medium ◽  
Conductivity Enhancement ◽  
Chaotic Convection

Nanofluids are considered to be a next-generation heat transfer medium due to their excellent thermal performance. To investigate the effect of electric fields and magnetic fields on heat transfer of nanofluids, this paper analyzes the mechanism of thermal conductivity enhancement of nanofluids, the chaotic convection and the heat transfer enhancement of nanofluids in the presence of an applied electric field or magnetic field through the method of literature review. The studies we searched showed that applied electric field and magnetic field can significantly affect the heat transfer performance of nanofluids, although there are still many different opinions about the effect and mechanism of heat transfer. In a word, this review is supposed to be useful for the researchers who want to understand the research state of heat transfer of nanofluids.

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