Visualization of the impact of water drops on a hot surface: effect of drop velocity and surface inclination

2006 ◽  
Vol 42 (10) ◽  
pp. 885-890 ◽  
Author(s):  
Gian Piero Celata ◽  
Maurizio Cumo ◽  
Andrea Mariani ◽  
Giuseppe Zummo
Keyword(s):  
Surface Effect ◽  
Drop Velocity ◽  
Water Drops ◽  
Surface Inclination ◽  
Hot Surface ◽  
The Impact

scholarly journals Superhydrophobicity in perfection: the outstanding properties of the lotus leaf

2011 ◽  
Vol 2 ◽  
pp. 152-161 ◽  
Author(s):  
Hans J Ensikat ◽  
Petra Ditsche-Kuru ◽  
Christoph Neinhuis ◽  
Wilhelm Barthlott
Keyword(s):  
Chemical Composition ◽  
Water Repellency ◽  
Contact Angles ◽  
Dense Layer ◽  
Lotus Effect ◽  
Nano Structure ◽  
Lotus Leaf ◽  
Water Drops ◽  
The Impact ◽  
Unique Chemical

Lotus leaves have become an icon for superhydrophobicity and self-cleaning surfaces, and have led to the concept of the ‘Lotus effect’. Although many other plants have superhydrophobic surfaces with almost similar contact angles, the lotus shows better stability and perfection of its water repellency. Here, we compare the relevant properties such as the micro- and nano-structure, the chemical composition of the waxes and the mechanical properties of lotus with its competitors. It soon becomes obvious that the upper epidermis of the lotus leaf has developed some unrivaled optimizations. The extraordinary shape and the density of the papillae are the basis for the extremely reduced contact area between surface and water drops. The exceptional dense layer of very small epicuticular wax tubules is a result of their unique chemical composition. The mechanical robustness of the papillae and the wax tubules reduce damage and are the basis for the perfection and durability of the water repellency. A reason for the optimization, particularly of the upper side of the lotus leaf, can be deduced from the fact that the stomata are located in the upper epidermis. Here, the impact of rain and contamination is higher than on the lower epidermis. The lotus plant has successfully developed an excellent protection for this delicate epistomatic surface of its leaves.

Optimizing and Predicting CHF in Spray Cooling of a Square Surface

1996 ◽  
Vol 118 (3) ◽  
pp. 672-679 ◽  
Author(s):  
I. Mudawar ◽  
K. A. Estes
Keyword(s):  
Flow Rate ◽  
Flux Distribution ◽  
Spray Cooling ◽  
Liquid Volume ◽  
Optimum Configuration ◽  
New Correlation ◽  
Impact Area ◽  
Hot Surface ◽  
The Impact ◽  
Volumetric Flux

Spray cooling of a hot surface was investigated to ascertain the effect of nozzle-to-surface distance on critical heat flux (CHF). Full cone sprays of Fluorinert FC-72 and FC-87 were used to cool a 12.7 × 12.7 mm2 surface. A theoretical model was constructed that accurately predicts the spray’s volumetric flux (liquid volume per unit area per unit time) distribution across the heater surface. Several experimental spray sampling techniques were devised to validate this model. The impact of volumetric flux distribution on CHF was investigated experimentally. By measuring CHF for the same nozzle flow rate at different nozzle-to-surface distances, it was determined CHF can be maximized when the spray is configured such that the spray impact area just inscribes the square surface of the heater. Using this optimum configuration, CHF data were measured over broad ranges of flow rate and subcooling, resulting in a new correlation for spray cooling of small surfaces.

scholarly journals IMPACT OF FIBER DIAMETER ON-ROAD PERFORMANCE OF CEMENT-STABILIZED MACADAM

2017 ◽  
Vol 12 (1) ◽  
pp. 12-20 ◽  
Author(s):  
Zhijun Liu ◽  
Dongquan Wang ◽  
Xiaobi Wei ◽  
Liangliang Wang
Keyword(s):  
Water Loss ◽  
Loss Rate ◽  
Surface Effect ◽  
Fiber Diameter ◽  
Base Material ◽  
The Road ◽  
Water Loss Rate ◽  
Reinforced Cement ◽  
Road Performance ◽  
The Impact

Cement-stabilized macadam is the most widely used road base material in road engineering. The current study investigated the impact of fiber diameter on its performance. The authors prepared polyester fibers with diameters of 20, 35, 70, and 105 μm and added them to cement-stabilized macadam. Then, the indoor shrinkage tests and mechanical property tests at different ages were conducted. Then, the property changes of the polyester-reinforced cement-stabilized macadam were analysed. The water loss rate of the polyester-reinforced cement-stabilized macadam is subject to the combined influence of the “water loss surface effect” and “water loss porthole effect.” With increasing fiber diameter, the water loss surface effect becomes stronger, and the water loss porthole effect gradually decreases; thus, the overall effect transitions from the latter to the former. Moreover, the water loss rate shows an increasing trend of decreasing to its minimum. Therefore, with increasing fiber diameter, the average dry shrinkage coefficient of the polyester-reinforced cement-stabilized macadam first increases and then decreases, while the temperature shrinkage coefficients increase. The change in the fiber diameter does not significantly affect the compressive resilient modulus of the polyester-reinforced cement-stabilized macadam if the fiber content remains constant. These findings demonstrate the functional mechanism of the fiber diameter on the road performance of cement-stabilized macadam, thus improving our understanding of the road performance of the polyester-reinforced cement-stabilized macadam and laying a solid theoretical foundation for its many applications.

scholarly journals Experimental Research on the Impact of Interface Temperature on the Adhesion Properties of Clay under the Condition of Different Contacting Time

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Tao Qiu ◽  
Yonggang Zhang
Keyword(s):  
Adhesion Force ◽  
Interface Temperature ◽  
Heating Process ◽  
Adhesion Properties ◽  
Interfacial Temperature ◽  
Short Time ◽  
Hot Surface ◽  
Shield Machine ◽  
The Impact

Mud cakes are very likely to occur at the shield cutter when the shield machine passes through a clay stratum, which adhere to the cutter and reduce the excavation efficiency. Due to the thrust of the cutter, the mud cakes are compacted and cause friction at the soil-structure interface, which results in high temperature and aggravates the adhesion, and the effect tends to become stronger as the heating process lasts. In this paper, the effects of the interface temperature and the contacting time between the soil and the hot surface on the adhesion properties of the soil were studied by a self-made adhesion test device. According to the findings, at low interfacial temperature (≤40°C), both the adhesion force and the amount of adhered soil were insignificant in a short term, and the effects were found to be strengthened as the contacting time went on; at the high interfacial temperature (≥50°C), very significant soil adhesion occurred at the structure surface within a short time, and as the contacting time increased, the amount of the adhered soil decreased rapidly while the adhesion force kept increasing, and both tended to remain a constant and become independent with the temperature after a long-term contact. This study is of guiding significance for understanding the formation and development of the shield mud cakes during shield construction.

Model studies of ships as an element of maritime transport

2018 ◽  
Vol 121 ◽  
pp. 267-276
Author(s):  
Waldemar Mironiuk
Keyword(s):  
Surface Effect ◽  
Mineral Resources ◽  
Weather Conditions ◽  
Model Studies ◽  
Initial Stability ◽  
Damage Stability ◽  
Long Time ◽  
Current Operation ◽  
The Impact ◽  
And Training

Transport of large amounts of cargo, mining and exploiting natural mineral resources, carrying large number of passengers by sea are characterized by high risk, even if the latest technologies are employed. It is not a long time ago that thousands of people lost their lives in catastrophes of ships, off-shore oil rigs and other marine objects. It is estimated that around 80% of accidents at sea are caused by making wrong decisions by persons keeping watch on the bridge, especially during difficult navigational and weather conditions. Accidents can also be caused by lack of skills necessary for crews or absence of appropriate tools. Therefore, it is important that seafarers should be trained in accordance with the highest standards. The scope of crew research and training may include both static, dynamic and damage stability. This stand bad also enables the analysis of the influence of the free surface effect of the liquid occurring in the compartments or tanks after damage to the ship's hull and the analysis of the impact of cargo operation on the ship's initial stability. Experiences gained on the research stand lead to a better understanding of the phenomena occurring in the current operation of the ship and to improve the safety of swimming. The aim of this article is presentation selected scenarios for the model tests of vessels and to familiarize with the construction of selected types of ship models and the capabilities of stability test stands in the aspect of improving the safety at sea.

The Effect of the Surface Inclination on the Hydrodynamics and Thermodynamics of Leidenfrost Droplets

2014 ◽  
Vol 30 (2) ◽  
pp. 145-151 ◽  
Author(s):  
P. Pournaderi ◽  
A. R. Pishevar
Keyword(s):  
Contact Time ◽  
Heat Removal ◽  
Total Heat ◽  
Vapor Layer ◽  
Accurate Calculation ◽  
Simulation Process ◽  
Mesh Resolution ◽  
Surface Inclination ◽  
Hot Surface ◽  
Maximum Spreading

ABSTRACTIn this research, the effect of the surface inclination on the hydrodynamics and heat transfer of droplets impinging on very hot surfaces is studied. The applied numerical algorithm is based on the accurate calculation of the vaporization rate in the simulation process using a combination of the level set and ghost fluid methods. Also a mesh clustering technique is utilized to create sufficient mesh resolution near the surface in order to take into account the effect of the thin vapor layer between droplet and very hot surface. The results are verified against available experiments. The effect of the surface inclination on the droplet maximum spreading radius, droplet contact time and total heat removal from the surface is considered. Results show that for the studied regime, the maximum spreading radius of the droplet is decreased with an increase in the surface inclination while the droplet contact time on the surface is independent from the surface inclination. For inclinations greater than 45°, the total heat removal is decreased considerably with an increase in the inclination angle. For smaller inclinations, the dependency of the total heat removal on the surface inclination is not strong.

Regimes during liquid drop impact on a liquid pool

2015 ◽  
Vol 768 ◽  
pp. 492-523 ◽  
Author(s):  
Bahni Ray ◽  
Gautam Biswas ◽  
Ashutosh Sharma
Keyword(s):  
Vortex Ring ◽  
Liquid Drop ◽  
Liquid Pool ◽  
Ring Formation ◽  
Gas Bubble ◽  
Jet Formation ◽  
Vortex Ring Formation ◽  
Water Drops ◽  
Regime Map ◽  
The Impact

Water drops falling on a deep pool can either coalesce to form a vortex ring or splash, depending on the impact conditions. The transition between coalescence and splashing proceeds via a number of intermediate steps, such as thick and thin jet formation and gas-bubble entrapment. We perform simulations to determine the conditions under which bubble entrapment and jet formation occur. A regime map is established for Weber numbers ranging from 50 to 300 and Froude numbers from 25 to 600. Vortex ring formation is seen for all of the regimes; it is greater for the coalescence regime and less in the case of the thin jet regime.

An experimental investigation of fluid flow resulting from the impact of a water drop with an unyielding dry surface

1981 ◽  
Vol 373 (1755) ◽  
pp. 419-441 ◽  
Keyword(s):  
Water Drop ◽  
Roughness Parameter ◽  
Fluid Velocities ◽  
Spatial Dimensions ◽  
Water Drops ◽  
The Moment ◽  
High Degree ◽  
First Contact ◽  
The Impact

The flow of fluid associated with the impact of water drops of radius R at a speed V onto unyielding dry metal surfaces of known roughness R a is described. Spatial dimensions of the deforming drop are normalized by transformations of the kind x ' — x/R , and time scales are normalized according to t ' = tV/R , to permit comparison of events where or differ. It is shown that the primary influence of the surface roughness parameter R a is the determination of the condition for the ejection of secondary droplets by the excitation of an instability in the developing watersheet; provided R a ≪ R , it is possible to evaluate the condition to a high degree of accuracy, and for R a = 0.84 μm it is found to be α4/3 RV 1.69 > 7.4, where α is the eccentricity of the drop at the moment of impact. Deceleration of the drop apex does not commence until > 0.6, contrary to the prediction of Engel (1955) but in good agreement with that of Savic & Boult (1957). Close examination of the very early stages of impact suggests strongly that the so-called watersheet originates at a moment t ' — 0.01 after first contact, regardless of the absolute values of R, V or R a ; the initial normalized watersheet velocity is of order 5. Where there is ejected material, its normalized velocity at the moment of ejection is of the order of 20 % greater than that of the watersheet substrate. Simple calculations also suggest that initial fluid velocities greater than 10 are required immediately before the initiation of the watersheet ( t '< 0.01). Impacts at speeds considerably greater than the appropriate terminal fall speed in air show no deviations in character from those investigated at much lower speeds. A simple subsidiary experiment also suggests that greater impact velocities are required to produce splashing on inclined targets.

78 A Retrospective Review of Contact Burns Occurring over the Past Five Years and the Impact of Daily High Temperatures

2021 ◽  
Vol 42 (Supplement_1) ◽  
pp. S54-S54
Author(s):  
Kevin N Foster ◽  
Tiffany Hockenberry ◽  
Derek Murray ◽  
Karen J Richey
Keyword(s):  
High Temperatures ◽  
External Surface ◽  
Group Versus ◽  
Retrospective Chart Review ◽  
Climate Data ◽  
Burn Center ◽  
Number Of Patients ◽  
June July ◽  
Hot Surface ◽  
The Impact

Abstract Introduction Thermal burns as a result of contact with a hot surface are a frequent cause of injury. A unique subset of contact burns are those sustained as a result of exposure to a hot surface during summer days in geographic areas with excessive ambient temperatures. Under these conditions, external surface temperatures can reach 180 degrees Fahrenheit, and deep cutaneous burns can happen with only a brief contact. Often exposure occurs in patients with impairments that prevent them from removing themselves from such contact in an expeditious fashion leading to severe injury. The purpose of this study was to review and analyze patients admitted to a southwest burn center with burns caused by contact with a hot external surface during the summertime months. Methods This was a retrospective chart review of patients admitted to our regional burn center over a 6-year period, whose burns were sustained from contact with the ground during the months of June, July, and August. Patients were stratified into two groups those whose injuries occurred from 2015 – 2019 and those that occurred in 2020. Climate data was collected from the National Oceanic and Atmospheric Administration website. Results The mean high daily temperature for June, July, and August 2020 was 108.5oF compared to 106.3oF for June, July and August of the preceding five years 2015 to 2019 (p &lt; 0.0001) The number of days during this 3-month period with high temperatures exceeding 110oF was 48 for 2020 compared to a mean of 24 for years 2015 to 2019 (p &lt; 0.0001). Correspondingly, there were 104 inpatient admissions for contact burns during this 3-month period in 2020 compared to a mean of 70 patients each year for 2015 to 2019, a 49% increase. There was no difference in age, gender, % TBSA burned, length of stay, or comorbidities in the two groups of patients. There were differences noted in the ethnicity compositions between the two groups. While alcohol use was not different between the two groups, the admission blood alcohol level was significantly greater in the 2020 group versus the 2015–2019 group (p=.0477). Additionally, the 2020 group demonstrated significantly greater illicit drug use than the 2015 to 2019 group (p.0098). Conclusions This study shows that increasing summertime temperatures in the southwest USA results in a corresponding increase in the number of patients with hot surface contact burns, and this increase is also associated with significantly great drug and alcohol abuse.

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