On the Mechanism of Dropwise Condensation of Steam on Ion Implanted Metallic Surfaces

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Michael H. Rausch ◽  
Alfred Leipertz ◽  
Andreas P. Fröba
Keyword(s):  
Experimental Studies ◽  
Ambient Air ◽  
Contact Angles ◽  
Dropwise Condensation ◽  
Free Energies ◽  
Metallic Surfaces ◽  
Microscopic Mechanism ◽  
Theoretical Approaches ◽  
Type Contact ◽  
Ion Implanted

Our recent experimental studies indicate that nanostructured, chemically inhomogeneous surfaces are the origin of dropwise condensation of steam on ion implanted metals. Yet, the underlying microscopic mechanism governing this special condensation form is still not clear. We suggest a condensation model based on droplet nucleation and growth on elevated precipitates, resulting in short-term steam entrapment after droplet coalescence. According to the wetting theory, this transition state yields increased macroscopic contact angles. Condensation phenomena such as enlarging dropwise condensation areas in spite of increasing condensation rate become comprehensible by our model. Furthermore, it points out that for this special surface type, contact angles and surface free energies measured under ambient air conditions are not usable for predicting the condensation form of steam. Although the suggested microscopic model cannot be directly proved by experiment, its validity is supported by its capability of explaining experimental observations colliding with previous theoretical approaches.

Mechanism of Dropwise Condensation on Ion Implanted Metallic Surfaces

2010 ◽  
Author(s):  
Michael H. Rausch ◽  
Alfred Leipertz ◽  
Andreas P. Fro¨ba
Keyword(s):  
Ambient Air ◽  
Contact Angles ◽  
Dropwise Condensation ◽  
Free Energies ◽  
Metallic Surfaces ◽  
Short Term ◽  
Microscopic Mechanism ◽  
Theoretical Approaches ◽  
Modified Surfaces ◽  
Ion Implanted

In this work a model for the mechanism of dropwise condensation on ion implanted metallic surfaces is proposed. Considering experimental results for respective surfaces, the model is based on droplet nucleation and growth on preferably wetted, elevated precipitates, resulting in short-term steam entrapment after droplet coalescence. According to wetting theory this transition state yields increased macroscopic contact angles enabling dropwise condensation. Open condensation phenomena like enlarging dropwise condensation areas in spite of increasing condensation rate become comprehensible by our approach. Furthermore, the model points out that contact angles and surface free energies measured under ambient air conditions are not usable for predicting the condensation form of steam on the modified surfaces. Although the suggested microscopic mechanism cannot be directly proved by experiment, its capability of explaining experimental observations colliding with previous theoretical approaches supports its validity. The results also reveal that dropwise condensation of steam can originate from microscopically different mechanisms.

On the Characteristics of Ion Implanted Metallic Surfaces Inducing Dropwise Condensation of Steam

Langmuir ◽  
2010 ◽  
Vol 26 (8) ◽  
pp. 5971-5975 ◽  
Author(s):  
Michael H. Rausch ◽  
Alfred Leipertz ◽  
Andreas P. Fröba
Keyword(s):  
Dropwise Condensation ◽  
Metallic Surfaces ◽  
Ion Implanted

Experimental Study on the Origin of Dropwise Condensation of Steam on Ion Implanted Metallic Surfaces

2010 ◽  
Author(s):  
Michael H. Rausch ◽  
Alfred Leipertz ◽  
Andreas P. Fro¨ba
Keyword(s):  
Experimental Study ◽  
Free Energy ◽  
Ion Implantation ◽  
Surface Free Energy ◽  
Nano Particles ◽  
Saturated Steam ◽  
Chemical Inhomogeneity ◽  
Dropwise Condensation ◽  
Metallic Surfaces ◽  
Ion Implanted

The presented work provides new perspectives on the origin of dropwise condensation of steam on ion implanted metallic surfaces. For the experimental study metallic samples made of different materials implanted with various ion species were used. Condensation experiments with saturated steam and surface analysis via contact angle and surface free energy measurements, atomic force microscopy and scanning electron microscopy were performed. It could be shown that available explanation approaches for the appearance of dropwise condensation based on a reduction of the metal surface free energy by ion implantation have to be discarded. Our results rather suggest a nucleation mechanism proceeding on surfaces featuring nano-scale surface roughness and chemical inhomogeneity. These characteristics seem to be induced by nano-particles precipitated due to supersaturation of the metal substrate with the doping elements. On unimplanted high-alloyed materials like stainless steel, dropwise condensation was found to develop spontaneously because of strong oxidation effects. Obviously the latter naturally produce surface modifications which are similar to those obtained artificially by ion implantation.

Synthesis and Experimental Studies on Supramolecular Synthons of Aminoguanidinium Carboxylates: A Case Study of π-HoleBonded Carbon Bonding via Theoretical Approaches

2018 ◽  
Vol 3 (35) ◽  
pp. 10032-10048
Author(s):  
Govindarajan Radha ◽  
Baskaran Vijaya Pandiyan ◽  
Palanisamy Deepa ◽  
Subbiah Govindarajan ◽  
Ponmalai Kolandaivel ◽  
...  
Keyword(s):  
Experimental Studies ◽  
Supramolecular Synthons ◽  
Theoretical Approaches ◽  
Carbon Bonding

scholarly journals Air Pollution Monitoring and Control System for Subway Stations Using Environmental Sensors

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Gyu-Sik Kim ◽  
Youn-Suk Son ◽  
Jai-Hyo Lee ◽  
In-Won Kim ◽  
Jo-Chun Kim ◽  
...  
Keyword(s):  
Air Quality ◽  
Air Pollutants ◽  
Linear Regression Analysis ◽  
Experimental Studies ◽  
Ambient Air ◽  
Pollution Monitoring ◽  
Scattering Method ◽  
Environmental Sensors ◽  
Monitoring And Control ◽  
Subway Stations

The metropolitan city of Seoul uses more energy than any other area in South Korea due to its high population density. It also has high emissions of air pollutants. Since an individual usually spends most of his/her working hours indoors, the ambient air quality refers to indoor air quality. In particular, PM10concentration in the underground areas should be monitored to preserve the health of commuters in the subway system. Seoul Metro and Seoul Metropolitan Rapid Transit Corporation measure several air pollutants regularly. In this study, the accuracy of an instrument for PM measurement using the light scattering method was improved with the help of a linear regression analysis technique to continuously measure thePM10concentrations in subway stations. In addition, an air quality monitoring system based on environmental sensors was implemented to display and record the data of PM10, CO2, temperature, and humidity. Through experimental studies, we found that ventilation fans could improve air quality and decrease PM10concentrations in the tunnels effectively by increasing the air flow rate.

Determining Parametric Effects for Droplet Evaporation on Nanoporous Superhydrophillic Surfaces Using Machine Learning Techniques

2021 ◽  
Author(s):  
Emma R. McClure ◽  
Van P. Carey
Keyword(s):  
Machine Learning ◽  
Cooling System ◽  
Spray Cooling ◽  
Droplet Evaporation ◽  
Contact Angles ◽  
Machine Learning Techniques ◽  
Metallic Surfaces ◽  
Droplet Spreading ◽  
Droplet Vaporization ◽  
Speed Accuracy

Abstract Experimental results demonstrate that droplet vaporization on metal surfaces can be significantly enhanced with the application of a nanoporous, superhydrophilic surface coating. A thin layer of ZnO nanopillars can be easily seeded and grown on most metallic surfaces to achieve nanoscale pores between pillars, and ultra-low apparent contact angles. These surface coatings have the potential to improve spray cooling processes, and can be easily scaled up to larger and more complex heat exchangers. In order to characterize the potential improvement to a spray cooling system it is important to understand the dependence on system parameters, and to have a clear model of droplet vaporization on such surfaces. There are a number of surface and impact parameters that will affect the droplet spreading and subsequent vaporization on the surface. The surface contact angle, wicking speed and impact velocity all interact to affect the maximum spread of the droplet and the speed at which the droplet reaches this state. Along with variations in droplet volume and wall superheat, the model for droplet vaporization becomes more complex and nonlinear. Instead of exploring a single parameter at a time, machine learning tools can be utilized to determine the dependence of droplet evaporation time on these parameters simultaneously. In this study a genetic algorithm and a neural network were used to develop a droplet evaporation model for these superhydrophilic surfaces. Each algorithm demonstrated clear advantages depending on whether speed, accuracy, or an explicit mathematical model was prioritized.

scholarly journals Dropwise condensation induced on chromium ion implanted aluminum surface

2019 ◽  
Vol 51 (1) ◽  
pp. 84-94 ◽  
Author(s):  
Kiwook Kim ◽  
Youngjin Lee ◽  
Ji Hwan Jeong
Keyword(s):  
Aluminum Surface ◽  
Dropwise Condensation ◽  
Chromium Ion ◽  
Ion Implanted

Temperature-Dependent Wettability of Water on a Nickel Surface at Pressurized Condition: A Molecular Dynamics Study

2019 ◽  
Author(s):  
Dong-Lei Zeng ◽  
Biao Feng ◽  
Jia-Wen Song ◽  
Li-Wu Fan
Keyword(s):  
Contact Angle ◽  
Hydrogen Bonds ◽  
Average Energy ◽  
Contact Angles ◽  
Nickel Surface ◽  
Free Energies ◽  
Water Droplets ◽  
Temperature Dependent ◽  
Interfacial Free Energies ◽  
Solid Liquid

Abstract Temperature-dependent wettability of water droplets on a metal surface in a pressurized environment is of great theoretical and practical significance. In this paper, molecular dynamic simulation is used to study this problem by relating the temperature-dependent apparent contact angles to the changes in solid-liquid and solid-vapor interfacial free energies and hydrogen bonds in the nano-sized water droplets with increasing the temperature. The temperature range of interest is set from 298 K to 538 K in a 20 K interval under a constant pressure of 7 MPa. The results show that the contact angle in general decreases with raising the temperature and decreasing trend can be divided into two sections with different slopes. The contact angle drops slowly when the temperature is below 458 K as a critical point. Beyond this point, the contact angle shows a much steeper decrease. The difference between solid-vapor and solid-liquid interfacial free energies is found to decrease slightly with temperature. Combining with that the surface tension drops with increasing the temperature, a decreasing trend of the contact angle is expected according to the Young’s equation. As the temperature increases, the number and average energy of the hydrogen bonds both decrease, and the hydrogen bonds tend to aggregate at the bottom of the nano-droplets.

scholarly journals Experimental evidence of the rear capture of aerosol particles by raindrops

2017 ◽  
Vol 17 (6) ◽  
pp. 4159-4176 ◽  
Author(s):  
Pascal Lemaitre ◽  
Arnaud Querel ◽  
Marie Monier ◽  
Thibault Menard ◽  
Emmanuel Porcheron ◽  
...  
Keyword(s):  
Experimental Evidence ◽  
Size Range ◽  
Collection Efficiency ◽  
Aerosol Particles ◽  
Experimental Studies ◽  
Laboratory Measurements ◽  
Experimental Proof ◽  
Theoretical Approaches ◽  
Capture Mechanism ◽  
Mode Size

Abstract. This article presents new measurements of the efficiency with which aerosol particles of accumulation mode size are collected by a 1.25 mm sized raindrop. These laboratory measurements provide the link to reconcile the scavenging coefficients obtained from theoretical approaches with those from experimental studies. We provide here experimental proof of the rear capture mechanism in the flow around drops, which has a fundamental effect on submicroscopic particles. These experiments thus confirm the efficiencies theoretically simulated by Beard (1974). Finally, we propose a semi-analytical expression to take into account this essential mechanism to calculate the collection efficiency for drops within the rain size range.

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