Theoretical and Experimental Studies on the Pseudo-Dropwise Condensation of a Binary Vapor Mixture

1996 ◽  
Vol 118 (1) ◽  
pp. 140-147 ◽  
Author(s):  
K. Hijikata ◽  
Y. Fukasaku ◽  
O. Nakabeppu
Keyword(s):  
Surface Tension ◽  
Experimental Studies ◽  
Marangoni Effect ◽  
Copper Plate ◽  
Droplet Growth ◽  
Dropwise Condensation ◽  
Vapor Mixture ◽  
Ethanol Mixture ◽  
Absolute Value ◽  
Critical Marangoni Number

When a water–ethanol binary mixture condenses on a flat plate, one observes that the liquid film condensate rises locally and eventually forms many droplets on the film. Usually, filmwise condensation is expected because both substances are completely soluble in each other and they wet a copper plate well. This paper presents the droplet growth mechanism during so-called pseudo-dropwise condensation. Instability analysis is used to determine the transition from filmwise condensation to pseudo-dropwise condensation theoretically. In a stress balance at the vapor–liquid interface, the analysis considers not only the surface tension itself, but also the surface tension variation due to changes in temperature and concentration, assuming saturation conditions at the interface. Numerical results indicate that the Marangoni effect plays a more important role than the absolute value of the surface tension in pseudo-dropwise condensation. The change in surface tension with temperature is not always negative; it becomes positive for certain mixtures due to the dependence on concentration. Pseudo-dropwise condensation is only realized when surface tension increases with temperature. This analysis qualitatively predicts the critical Marangoni number experimentally observed during water–ethanol mixture condensation.

Characteristics of Droplet Growth Behavior on Hydrophobic Micro-textured Surfaces

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Jae Bin Lee ◽  
Joo Hyun Moon ◽  
Minhaeng Cho ◽  
Seong Hyuk Lee
Keyword(s):  
Surface Tension ◽  
Surface Texturing ◽  
Copper Plate ◽  
Growth Behavior ◽  
Numerical Control ◽  
Droplet Growth ◽  
Dropwise Condensation ◽  
Textured Surfaces ◽  
Cnc Machine ◽  
Self Assembled Monolayer

For occurring dropwise condensation, the droplet growth behavior such as single droplet growth, coalescence, and fall-off of large droplets play a major role in regard to condensation heat transfer and water harvesting. The present study visualized the droplet growth behavior of dropwise condensation which might be controlled by the surface tension. We used three copper plate with different hole area fraction (i.e., ϕ=0, 0.148 and 0.439). Surface texturing was conducted by using a μ-computer numerical control (μ-CNC) machine and composed of micro-holes (diameter: 300 μm, depth: 200 μm) with 691 μm, 401 μm pitch. To make the hydrophobic surfaces, the copper surfaces were coated self-assembled monolayer (SAM). From the results, it was found that for only SAM coated surface, random coalescence occurred and affected the droplet growth significantly, whereas for textured SAM coated surfaces, the droplet started to be grown up at the textured holes and coalesced near the holes, indicating that capillary effects might affect the droplet growth mechanism. In particular, the fall-off time at which a coalesced droplet is removed away from the surface increased when the textured surfaces was used, because of surface tension effect increased by the textured holes.

SINGLE DROPLET GROWTH MODEL FOR DROPWISE CONDENSATION CONSIDERING NON-CONDENSABLE GAS

2018 ◽  
Author(s):  
Shaofei Zheng ◽  
Ferdinand Eimann ◽  
Christian Philipp ◽  
Ulrich Gross
Keyword(s):  
Growth Model ◽  
Droplet Growth ◽  
Dropwise Condensation ◽  
Single Droplet

On the Role of Marangoni Effects on the Critical Heat Flux for Pool Boiling of Binary Mixtures

1996 ◽  
Vol 118 (1) ◽  
pp. 103-109 ◽  
Author(s):  
W. R. McGillis ◽  
V. P. Carey
Keyword(s):  
Surface Tension ◽  
Heat Flux ◽  
Binary Mixtures ◽  
Critical Heat Flux ◽  
Full Range ◽  
Pool Boiling ◽  
Marangoni Effect ◽  
Restoring Force ◽  
Marangoni Effects

The Marangoni effect on the critical heat flux (CHF) condition in pool boiling of binary mixtures has been identified and its effect has been quantitatively estimated with a modified model derived from hydrodynamics. The physical process of CHF in binary mixtures, and models used to describe it, are examined in the light of recent experimental evidence, accurate mixture properties, and phase equilibrium revealing a correlation to surface tension gradients and volatility. A correlation is developed from a heuristic model including the additional liquid restoring force caused by surface tension gradients. The CHF condition was determined experimentally for saturated methanol/water, 2-propanol/water, and ethylene glycol/water mixtures, over the full range of concentrations, and compared to the model. The evidence in this study demonstrates that in a mixture with large differences in surface tension, there is an additional hydrodynamic restoring force affecting the CHF condition.

Effects of Copper Extraction-Stripping Loops on Entrainment in Aqueous Raffinate

2014 ◽  
Vol 908 ◽  
pp. 18-21
Author(s):  
Yan Jun Liu ◽  
Xiao Rong Liu ◽  
Hui Li ◽  
Yong Sheng Li ◽  
Qing Li ◽  
...  
Keyword(s):  
Surface Tension ◽  
Solvent Extraction ◽  
Early Stage ◽  
Organic Chemical ◽  
Copper Extraction ◽  
Organic Chemicals ◽  
Stabilization Mechanism ◽  
Absolute Value ◽  
Copper Solvent Extraction ◽  
Average Size

Effects of extraction-stripping loops of organic phase on organic chemical entrainment in the aqueous raffinate in copper solvent extraction were studied in this paper. Results demonstrated that the total amount of organic chemicals lost in the aqueous raffinate decreased with the increase of times of extraction-stripping loops but reached largest at third loop. Entrainment was the dominate way of organic chemicals losing in the aqueous raffinate at early stage of the loops. The formation of entrainment and its stabilization mechanism was also studied. The average size of entrained droplet trended to increase with extraction-stripping loops increasing. Meanwhile, the absolute value of zeta potential trended to decrease. The surface tension of the aqueous raffinate increased after reaching the minimum value 41.3 mN/m at the 3rd loop. It showed that the formation of entrained droplets and its stability were mainly affected by the surface tension of aqueous raffinate.

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.

Concentration Dependence of the Surface Tension of Three and Four-Component Systems with Peculiarities in the Surface Tension Isotherms of Lateral Binary Melts

2021 ◽  
Vol 1022 ◽  
pp. 194-202
Author(s):  
R.Kh. Dadashev ◽  
R.A. Kutuev
Keyword(s):  
Experimental Data ◽  
Surface Tension ◽  
Concentration Dependence ◽  
Experimental Error ◽  
Binary Systems ◽  
Experimental Studies ◽  
Study Results ◽  
Component Systems ◽  
Minimum Depth ◽  
Surface Tension Isotherms

The experimental study results of the melts concentration dependence of the surface tension of the four-component indium-tin-lead-bismuth system and its constituent binary systems of indium-tin, indium-lead, indium-bismuth, tin-lead, tin-bismuth, lead-bismuth are presented in the paper. It is shown that the concentration dependence of the melts surface tension of the In-Sn-Pb-Bi four-component system can be predicted from the data on ST (surface tension) values of lateral binary systems. Features in the ST isotherms in the form of a minimum are observed only in the indium-tin lateral system from all lateral binaries. A distinctive feature of the detected minimum is that the minimum depth slightly exceeds the experimental error. Therefore, in addition to the fact that the area of average compositions was studied more thoroughly, we carried out the surface tension measurements by two independent methods. The experimental data obtained by both methods coincide within the experimental error and indicate the extremum availability on ST isotherms. Thus, ST experimental studies by two independent methods confirmed the presence of a flat minimum on ST isotherms of the indium-tin binary system increasing the reliability of the obtained data. The obtained outcomes and their comparison with experimental data have shown that the considered models for predicting surface properties based on data due to similar properties of lateral binary systems adequately reflect the experimental dependences. However, the prediction model based on Kohler's method of excess values describes the experimental curves more accurately.

Ferrohydrodynamic Capillary Convection

2018 ◽  
Vol 11 (2) ◽  
Author(s):  
Francisco J. Arias ◽  
Salvador A. De Las Heras
Keyword(s):  
Magnetic Field ◽  
Surface Tension ◽  
Concentration Gradient ◽  
Deductive Reasoning ◽  
Marangoni Convection ◽  
Marangoni Effect ◽  
Magnetic Fluids ◽  
Homogeneous Magnetic Field ◽  
Gradient Field ◽  
Two Fluids

Abstract In this work, consideration is given to capillary convection on ferrofluids from the concentration gradient induced when a nonhomogeneous magnetic field is applied. It is known that mass transfer along an interface between two fluids can appear due to a gradient of the surface tension in the so-called Marangoni effect (or Gibbs–Marangoni effect). Because the surface tension is both thermal and concentration dependent, Marangoni convection can be induced by either a thermal or a concentration gradient, where in the former case, it is generally referred as thermocapillary convection. Now, it has been theoretically and experimentally demonstrated that a ferrofluid under the action of a non-homogeneous magnetic field can induce a concentration gradient of suspended magnetic nanoparticles, and also the effect of Fe3O4 nanoparticles on the surface tension has been measured. Therefore, by deductive reasoning and taking into account the above mentioned facts, it is permissible to infer ferrohydrodynamic capillary convection on magnetic fluids under the presence of a magnetic gradient field. Utilizing a simplified physical model, the phenomenon was investigated and it was found that ferrohydrodynamic-Marangoni convection could be induced with particle size in the range up to 10 nm, which is the range of magnetic fluids to escape magnetic agglomeration.

scholarly journals Determination of the full deformation tensor by multi-Bragg fast scanning nano X-ray diffraction

2020 ◽  
Vol 53 (1) ◽  
pp. 99-106
Author(s):  
Andreas Johannes ◽  
Jura Rensberg ◽  
Tilman A. Grünewald ◽  
Philipp Schöppe ◽  
Maurizio Ritzer ◽  
...  
Keyword(s):  
Surface Tension ◽  
Single Crystal ◽  
Spatial Resolution ◽  
Deformation Tensor ◽  
X Ray Diffraction ◽  
Projected Area ◽  
Absolute Value ◽  
X Ray ◽  
Grown Single Crystal

This work showcases a method to map the full deformation tensor in a single micro-sized crystal. It is shown that measuring the position of two Bragg reflections in reciprocal space is sufficient to obtain the full deformation tensor, if the condition of incompressibility of the material is imposed. This method is used to reveal the surface tension induced deformation at the edges of an as-grown single-crystal VO2 microwire. All components of the deformation tensor of the microwire were measured down to an absolute value of 10−4 in an 8 × 14 µm projected area of the wire. With a beam-defined spatial resolution of 150 × 150 nm, the measurement time was merely 2.5 h.

scholarly journals THE ROLE OF SURFACE TENSION IN BREAKING WAVES

1972 ◽  
Vol 1 (13) ◽  
pp. 22 ◽  
Author(s):  
Robert L. Miller
Keyword(s):  
Surface Tension ◽  
Natural Waters ◽  
Experimental Studies ◽  
Breaking Waves ◽  
Engineering Model ◽  
Constant Depth ◽  
Model Studies ◽  
Limit Form ◽  
Satisfactory Theory

Breaking criteria in the vicinity of the crest, such as limit crest angle and limit form, and larger dimensions such as limit height (H/L) and breaker height (Hb/db)» are found experimentally to be significantly affected by change in surface tension. A number of wave types were examined, including periodic waves, solitary waves, and standing waves, over both constant depth and uniform slopes. Variations in natural waters in some cases were found to be of equivalent magnitude to those induced for the experiments. The conclusion is drawn that surface tension should be taken into account in development of a satisfactory theory of breakers. It is also an important factor in experimental studies, particularly engineering model studies involving breaking waves.

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