scholarly journals Kinetic and thermal simulation of water droplets in icing wind tunnels

2021 ◽  
Author(s):  
A. Fallast ◽  
A. R. Rapf ◽  
A. Tramposch ◽  
W. Hassler
Keyword(s):  
State Space ◽  
Test Object ◽  
Droplet Diameter ◽  
Ambient Air ◽  
Droplet Surface ◽  
Wind Tunnels ◽  
Droplet Temperature ◽  
Water Droplets ◽  
Test Conditions ◽  
The Impact

AbstractWithin the certification process of aircraft, tests under specific icing conditions are required. For such safety relevant tests—which are performed under defined and repeatable test conditions—specially equipped Icing Wind Tunnels (IWT) are required. In such IWTs, supercooled water droplets are created with the aid of a spray system injecting pre-tempered water droplets of specific diameters into the free stream air flow. Especially tests with a droplet size up to 2mm (Supercooled Large Droplets - SLDs) are of great importance. SLDs are difficult to generate under laboratory conditions in IWT since usually the available droplet flight time from the injection location to the impact position on the test object is insufficient to reliably cool down a droplet at least to freezing temperature. To investigate the limitations associated with the application of SLD, the current work provides a method to allow detailed insight into the behavior of droplets on the path from the injection spray nozzle to the test section. In this work a state space model of a single droplet is derived that combines the kinetic aspects, thermal properties as well as the governing differential equations for motion, convective heat transfer at the droplet surface and heat conduction inside the droplet. Beside the states for the droplet’s position and velocity in space, the state space vector comprises various fluid and thermodynamic parameters. The droplet-internal temperature distribution is modelled by a discrete one-dimensional spherical shell model that also incorporates the aggregate phase (freezing mass fraction) at each shell node. This approach allows, therefore, the simulation of potential droplet phase change processes (freezing/melting) as well. With the model at hand, the influence of various boundary conditions (initial droplet temperature, flow field, ambient air temperature, etc.) can be determined and evaluated. As a result, concrete measures to achieve a desired operating condition (e.g. droplet temperature at the test object) for various model assumptions can be derived. In addition, the simulation model facilitates the prediction of the droplet diameter threshold for ensuring a supercooled state upon the impact on the test object. The governing theoretical influences are described, and various simulation results for representative test conditions that occur at the Rail-Tec-Arsenal (RTA) in Vienna are presented.

Investigation of Droplet Impinging on a Heated Porous Surface Under Various Working Conditions; A Mathematical Modeling

2021 ◽  
pp. 2150015
Author(s):  
Mohammad Azadeh ◽  
Hamidreza Khakrah
Keyword(s):  
Droplet Diameter ◽  
High Surface ◽  
Adaptive Method ◽  
Porous Surface ◽  
Droplet Temperature ◽  
Surface Porosity ◽  
Two Phase ◽  
Air Interface ◽  
Accuracy Of Results ◽  
The Impact

This study numerically investigated the behavior of a Newtonian droplet impacting a heated porous surface. In this regard, a two-phase finite volume code was used for laminar flow. The time adaptive method was applied to enhance the accuracy of results and better convergence of the solving process. Also, the dynamic grid adaptation technique was adopted to predict the liquid-air interface precisely. The results were first validated against experimental data at different Weber numbers. Then the effect of variations in the droplet temperature was investigated on the spreading factor. The obtained results revealed that the rise in droplet temperature led to an increase in the maximum spreading diameter due to the reduction in the effects of viscosity, density, and surface tension. In the next step, the effects of droplet impact on the hydrophilic and superhydrophobic surfaces with the porosities of 20–80% were evaluated. The obtained results revealed that the increase in the surface porosity caused a decrease in the droplet diameter during the impact time. Also, at high surface porosity values, the decline in the contact angle influence on the droplet dynamic behavior was observed.

Acoustic Cloud Condensation Nuclei Counter

2005 ◽  
Author(s):  
Abhijit Deshpande ◽  
Marcellin Zahui
Keyword(s):  
Water Surface ◽  
Cloud Condensation Nuclei ◽  
Droplet Diameter ◽  
Bubble Formation ◽  
Maximum Velocity ◽  
Acoustic Energy ◽  
Water Droplets ◽  
Condensation Nuclei ◽  
Micro Scale ◽  
The Impact

Analysis and simulation of an acoustic cloud condensation nuclei counter is presented. The instrument is capable of accurately counting the number of micro scale water droplets impacting a water surface. The sound produced underwater by the water droplets is determined when the droplets strike the water surface with an impact velocity equal to either their terminal or maximum velocity. First, the terminal velocities of the droplets are calculated using Stoke’s law and compared to measured velocities from Gunn and Kinzer. Then the maximum velocities that these droplets can sustain without breaking are calculated as a function of droplet diameter. Second, the sound due to droplet impact is estimated. Due to their size and water surface tension, there is no bubble formation at impact when the droplets are falling with terminal velocities. However conditions for regular bubble entrainments are established and limit velocities are calculated. Assuming that the micro water droplets can be accelerated, the maximum velocities for no bubble entrainments are calculated. The results show that the level of the sound produced by individual micro scale droplet falling with terminal velocity is so small that experimental verification is not possible. However, reasonable level of acoustic energy can be obtained by increasing the impact velocities of the droplets or by measuring the sound radiated by a group of impacting droplets. Finally, the droplets counting process is simulated using a water surface of one centimeter squared and a vertical growth chamber.

On high-speed impingement of cylindrical droplets upon solid wall considering cavitation effects

2018 ◽  
Vol 857 ◽  
pp. 851-877 ◽  
Author(s):  
Wangxia Wu ◽  
Gaoming Xiang ◽  
Bing Wang
Keyword(s):  
Phase Transition ◽  
Shock Wave ◽  
High Speed ◽  
Solid Wall ◽  
Fluid Model ◽  
Droplet Diameter ◽  
Droplet Surface ◽  
Rarefaction Waves ◽  
Two Phase ◽  
The Impact

The high-speed impingement of droplets on a wall occurs widely in nature and industry. However, there is limited research available on the physical mechanism of the complicated flow phenomena during impact. In this study, a simplified multi-component compressible two-phase fluid model, coupled with the phase-transition procedure, is employed to solve the two-phase hydrodynamics system for high-speed cylindrical droplet impaction on a solid wall. The threshold conditions of the thermodynamic parameters of the fluid are established to numerically model the initiation of phase transition. The inception of cavitation inside the high-speed cylindrical droplets impacting on the solid wall can thus be captured. The morphology and dynamic characteristics of the high-speed droplet impingement process are analysed qualitatively and quantitatively, after the mathematical models and numerical procedures are carefully verified and validated. It was found that a confined curved shock wave is generated when the high-speed cylindrical droplet impacts the wall and this shock wave is reflected by the curved droplet surface. A series of rarefaction waves focus at a position at a distance of one third of the droplet diameter away from the top pole due to the curved surface reflection. This focusing zone is identified as the cavity because the local liquid state satisfies the condition for the inception of cavitation. Moreover, the subsequent evolution of the cavitation zone is demonstrated and the effects of the impact speed, ranging from $50$ to $200~\text{m}~\text{s}^{-1}$ , on the deformation of the cylindrical droplet and the further evolution of the cavitation were studied. The focusing position, where the cavitation core is located, is independent of the initial impaction speed. However, the cavity zone is enlarged and the stronger collapsing wave is induced as the impaction speed increases.

scholarly journals Effect of relative humidity on heat transfer across the surface of an evaporating water droplet in air flow

2009 ◽  
Vol 624 ◽  
pp. 57-67 ◽  
Author(s):  
RYOICHI KUROSE ◽  
AKITOSHI FUJITA ◽  
SATORU KOMORI
Keyword(s):  
Heat Transfer ◽  
Relative Humidity ◽  
Heat Loss ◽  
Water Droplet ◽  
Rear Surface ◽  
Ambient Air ◽  
Droplet Surface ◽  
Droplet Temperature ◽  
Humidity Condition ◽  
Evaporation Heat

A three-dimensional direct numerical simulation (DNS) is applied to flows inside and outside an evaporating spherical water droplet in air, and the effect of relative humidity on the heat transfer between the droplet and ambient air is investigated. The initial air temperature is set to be 15 K higher than the initial droplet temperature. The results show that the local evaporation heat loss indicates the maximum on the front of the droplet and decreases on going from the front to the rear, and the reduction on the rear becomes marked for high-droplet Reynolds numbers. This is because the evaporation rate is suppressed on the rear surface by the presence of flow separations behind the droplet. The droplet temperature decreases in the low-humidity condition, whereas it increases in the high-humidity condition. This difference is caused by the heat balance of evaporation heat loss and convective heat gain from ambient air at the droplet surface.

Boiling Heat Transfer Rates for Small Precisely Placed Water Droplets on a Heated Horizontal Plate

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Sally M. Sellers ◽  
W. Z. Black
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Weber Number ◽  
Droplet Diameter ◽  
The Other ◽  
Droplet Generator ◽  
Water Droplets ◽  
Transfer Rates ◽  
The Impact

Two small horizontal surfaces, heated to temperatures up to 220°C, were cooled by small (50–300 mm diameter) room-temperature droplets at 1 atmosphere pressure. One surface was a 10×10 mm thin-film nichrome heater that was used to measure heat fluxes below 100 W/cm2. The other surface, used for fluxes in excess of 100 W/cm2, was a solid copper heater with an 8×8 mm exposed surface. A continuous jet droplet generator coupled with two mutually perpendicular deflection plates was used to manipulate the path of constant diameter water droplets so that the impact of the drops could be precisely located on the heated surfaces. The droplet generator and the deflection plates were employed so that the effect of the impact frequency, droplet diameter, droplet velocity and spacing on the resulting heat transfer rates could be studied under controlled conditions. Optimal droplet spacing between 0.75 and 1.5 times the droplet diameter increased the critical heat flux approximately 30 percent above the value that was achieved when the drops were deposited in one location. For area-averaged mass flow rates less than about 0.08 g/(cm2s), there was no trend in the critical heat flux with the Weber number. However, for larger mass flux rates, the critical heat flux increased with an increasing Weber number. The measured critical heat flux values were roughly twice the heat flux of traditional pool boiling for identical superheat temperatures. Two droplet cooling dimensionless critical heat flux correlations are proposed as a function of Weber and Strouhal numbers; one for a single stream of drops and the other for drops that are spaced across the heated surface. The correlation for the spaced droplets is a function of a dimensionless droplet spacing on the heater.

Key Aspects of Assessing Effectiveness and Efficiency of Implementation of the Federal Clean Air Project on the Example of the Comprehensive Emission Reduction Action Plan in Nizhny Tagil

2020 ◽  
pp. 48-60
Author(s):  
SV Yarushin ◽  
DV Kuzmin ◽  
AA Shevchik ◽  
TM Tsepilova ◽  
VB Gurvich ◽  
...  
Keyword(s):  
Emission Reduction ◽  
Action Plan ◽  
Local Population ◽  
Ambient Air ◽  
Ambient Air Pollution ◽  
Mortality And Morbidity ◽  
Industrial Enterprises ◽  
Clean Air ◽  
Effectiveness And Efficiency ◽  
The Impact

Introduction: Key issues of assessing effectiveness and economic efficiency of implementing the Federal Clean Air Project by public health criteria are considered based on the example of the Comprehensive Emission Reduction Action Plan realized in the city of Nizhny Tagil, Sverdlovsk Region. Materials and methods: We elaborated method approaches and reviewed practical aspects of evaluating measures taken in 2018–2019 at key urban industrial enterprises accounting for 95 % of stationary source emissions. Results: Summary calculations of ambient air pollution and carcinogenic and non-carcinogenic inhalation health risks including residual risks, evaluation of the impact of air quality on urban mortality and morbidity rates, economic assessment of prevented morbidity and premature mortality cases have enabled us not only to estimate health effects but also to develop guidelines for development and implementation of actions aimed at enhancing effectiveness and efficiency of industrial emission reduction in terms of health promotion of the local population. Conclusions: We substantiate proposals for the necessity and sufficiency of taking remedial actions ensuring achievement of acceptable health risk levels as targets of the Comprehensive Emission Reduction Action Plan in Nizhny Tagil until 2024 and beyond.

scholarly journals The impact of measures to reduce ambient air PM<sub>10</sub> concentrations originating from road dust, evaluated for a street canyon in Helsinki

2019 ◽  
Vol 19 (17) ◽  
pp. 11199-11212 ◽  
Author(s):  
Ana Stojiljkovic ◽  
Mari Kauhaniemi ◽  
Jaakko Kukkonen ◽  
Kaarle Kupiainen ◽  
Ari Karppinen ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Air Quality ◽  
Street Canyon ◽  
Dust Emission ◽  
Road Dust ◽  
Ambient Air ◽  
Air Quality Measurements ◽  
Emission Models ◽  
The Impact ◽  
Quality Measurements

Abstract. We have numerically evaluated how effective selected potential measures would be for reducing the impact of road dust on ambient air particulate matter (PM10). The selected measures included a reduction of the use of studded tyres on light-duty vehicles and a reduction of the use of salt or sand for traction control. We have evaluated these measures for a street canyon located in central Helsinki for four years (2007–2009 and 2014). Air quality measurements were conducted in the street canyon for two years, 2009 and 2014. Two road dust emission models, NORTRIP (NOn-exhaust Road TRaffic Induced Particle emissions) and FORE (Forecasting Of Road dust Emissions), were applied in combination with the Operational Street Pollution Model (OSPM), a street canyon dispersion model, to compute the street increments of PM10 (i.e. the fraction of PM10 concentration originating from traffic emissions at the street level) within the street canyon. The predicted concentrations were compared with the air quality measurements. Both road dust emission models reproduced the seasonal variability of the PM10 concentrations fairly well but under-predicted the annual mean values. It was found that the largest reductions of concentrations could potentially be achieved by reducing the fraction of vehicles that use studded tyres. For instance, a 30 % decrease in the number of vehicles using studded tyres would result in an average decrease in the non-exhaust street increment of PM10 from 10 % to 22 %, depending on the model used and the year considered. Modelled contributions of traction sand and salt to the annual mean non-exhaust street increment of PM10 ranged from 4 % to 20 % for the traction sand and from 0.1 % to 4 % for the traction salt. The results presented here can be used to support the development of optimal strategies for reducing high springtime particulate matter concentrations originating from road dust.

scholarly journals The Impact of Ambient Atmospheric Mineral-Dust Particles on the Calcification of Lungs

Minerals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 125
Author(s):  
Mariola Jabłońska ◽  
Janusz Janeczek ◽  
Beata Smieja-Król
Keyword(s):  
Mineral Dust ◽  
Smoking Habit ◽  
Lower Lobe ◽  
Ambient Air ◽  
Dust Particles ◽  
Masking Effect ◽  
Amorphous Calcium Carbonate ◽  
Calcium Salts ◽  
The Impact ◽  
First Time

For the first time, it is shown that inhaled ambient air-dust particles settled in the human lower respiratory tract induce lung calcification. Chemical and mineral compositions of pulmonary calcium precipitates in the lung right lower-lobe (RLL) tissues of 12 individuals who lived in the Upper Silesia conurbation in Poland and who had died from causes not related to a lung disorder were determined by transmission and scanning electron microscopy. Whereas calcium salts in lungs are usually reported as phosphates, calcium salts precipitated in the studied RLL tissue were almost exclusively carbonates, specifically Mg-calcite and calcite. These constituted 37% of the 1652 mineral particles examined. Mg-calcite predominated in the submicrometer size range, with a MgCO3 content up to 50 mol %. Magnesium plays a significant role in lung mineralization, a fact so far overlooked. The calcium phosphate (hydroxyapatite) content in the studied RLL tissue was negligible. The predominance of carbonates is explained by the increased CO2 fugacity in the RLL. Carbonates enveloped inhaled mineral-dust particles, including uranium-bearing oxides, quartz, aluminosilicates, and metal sulfides. Three possible pathways for the carbonates precipitation on the dust particles are postulated: (1) precipitation of amorphous calcium carbonate (ACC), followed by its transformation to calcite; (2) precipitation of Mg-ACC, followed by its transformation to Mg-calcite; (3) precipitation of Mg-free ACC, causing a localized relative enrichment in Mg ions and subsequent heterogeneous nucleation and crystal growth of Mg-calcite. The actual number of inhaled dust particles may be significantly greater than was observed because of the masking effect of the carbonate coatings. There is no simple correlation between smoking habit and lung calcification.

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