scholarly journals Comparing Internal Flow in Freezing and Evaporating Water Droplets Using PIV

Water ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1489
Author(s):  
Linn Karlsson ◽  
Anna-Lena Ljung ◽  
T. Staffan Lundström
Keyword(s):  
Natural Convection ◽  
Marangoni Convection ◽  
Flow Direction ◽  
Flow Behavior ◽  
Internal Flow ◽  
Freezing Process ◽  
Complex Nature ◽  
Water Droplets ◽  
Wide Range ◽  
Jet Printing

The study of evaporation and freezing of droplets is important in, e.g., spray cooling, surface coating, ink-jet printing, and when dealing with icing on wind turbines, airplane wings, and roads. Due to the complex nature of the flow within droplets, a wide range of temperatures, from freezing temperatures to heating temperatures, have to be taken into account in order to increase the understanding of the flow behavior. This study aimed to reveal if natural convection and/or Marangoni convection influence the flow in freezing and evaporating droplets. Droplets were released on cold and warm surfaces using similar experimental techniques and setups, and the internal flow within freezing and evaporating water droplets were then investigated and compared to one another using Particle Image Velocimetry. It was shown that, for both freezing and evaporating droplets, a shift in flow direction occurs early in the processes. For the freezing droplets, this effect could be traced to the Marangoni convection, but this could not be concluded for the evaporating droplets. For both evaporating and freezing droplets, after the shift in flow direction, natural convection dominates the flow. In the end of the freezing process, conduction seems to be the only contributing factor for the flow.

A Natural Convection Fin with a Solution-Determined Nonmonotonically Varying Heat Transfer Coefficient

1981 ◽  
Vol 103 (2) ◽  
pp. 218-225 ◽  
Author(s):  
E. M. Sparrow ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Transfer Coefficient ◽  
First Principles ◽  
Numerical Solutions ◽  
Flow Direction ◽  
Operating Conditions ◽  
Fluid Temperature ◽  
Wide Range

A conjugate conduction-convection analysis has been made for a vertical plate fin which exchanges heat with its fluid environment by natural convection. The analysis is based on a first-principles approach whereby the heat conduction equation for the fin is solved simultaneously with the conservation equations for mass, momentum, and energy in the fluid boundary layer adjacent to the fin. The natural convection heat transfer coefficient is not specified in advance but is one of the results of the numerical solutions. For a wide range of operating conditions, the local heat transfer coefficients were found not to decrease monotonically in the flow direction, as is usual. Rather, the coefficient decreased at first, attained a minimum, and then increased with increasing downstream distance. This behavior was attributed to an enhanced buoyancy resulting from an increase in the wall-to-fluid temperature difference along the streamwise direction. To supplement the first-principles analysis, results were also obtained from a simple adaptation of the conventional fin model.

Natural Convection Liquid Cooling of a Substrate-Mounted Protrusion in a Square Enclosure: A Parametric Study

1992 ◽  
Vol 114 (2) ◽  
pp. 401-409 ◽  
Author(s):  
S. B. Sathe ◽  
Y. Joshi
Keyword(s):  
Natural Convection ◽  
Boundary Conditions ◽  
Flow Behavior ◽  
Air Cooling ◽  
Square Enclosure ◽  
Simple Boundary ◽  
Wide Range ◽  
Solid Region ◽  
Rayleigh Numbers ◽  
Thermal Conductivities

The coupled conduction and natural convection transport from a substrate-mounted heat generating protrusion in a liquid-filled square enclosure is numerically examined. The governing steady two-dimensional equations are solved using a finite-difference method for a wide range of Rayleigh numbers, protrusion thermal conductivities and widths, substrate heights, and enclosure boundary conditions. The results presented apply to liquids with 10≤Pr≤1000. It was established that in many situations it may be inappropriate to specify simple boundary conditions on the solid surface and decouple the conduction within the substrate or the protrusion. Higher Rayleigh numbers, protrusion thermal conductivities, and widths enhanced cooling. A variation in the substrate height did not affect the maximum protrusion temperature; however, the flow behavior was considerably altered. An empirical correlation for the maximum protrusion temperature was developed for a wide range of parametric values. The enclosure thermal boundary conditions changed the heat transfer in the solid region to only a small extent. Immersion cooling in common dielectric liquids was shown to be advantageous over air cooling only if the thermal conductivity of the protrusion was larger than that of the liquid.

Rapid Experimentation in Complex Internal Flow Passages Using SLA and MRV

2003 ◽  
Author(s):  
Christopher J. Elkins ◽  
John K. Eaton ◽  
Ryan B. Wicker
Keyword(s):  
Vector Fields ◽  
Rectangular Cross Section ◽  
Flow Direction ◽  
Flow Behavior ◽  
Internal Flow ◽  
Separated Flow ◽  
Secondary Flows ◽  
Internal Cooling ◽  
Iterative Design ◽  
Cooling Passage

Designing complex internal cooling passages is extremely difficult without detailed information about the flow behavior due to the presence of separated flow zones and strong secondary flows. This paper describes a new approach to designing internal flow passages called Rapid Iterative Design Using Experimentation (RIDUE). RIDUE utilizes rapid prototyping (RP) manufacturing to quickly build an accurate model of a complex internal flow passage and magnetic resonance velocimetry (MRV) to measure the full three dimensional velocity field. Because both techniques offer very fast turnaround, it is feasible to conduct iterative design with a cycle time of 1–2 days. RIDUE is demonstrated using a generic turbine blade internal cooling passage with four serpentine channels. Two channels have rectangular cross-section and two are square. In each channel, two of the four walls have ribs (also called turbulators) angled at 45 degrees to the main flow direction. Two models based on the generic geometry are studied, each with different turbulator cross-sections, one square and one rounded. Both models were built using a stereo lithography apparatus. MRV provided three-component velocity vectors for flow at a Reynolds number of 10,000 based on the hydraulic diameter of the first passage. Sample vector fields are presented to illustrate the detail with which the flow can be investigated. Although little difference is seen in the flows between the two models, it is demonstrated that through its use of RP processes and the MRV measurement technique, RIDUE is a viable technique for modern internal passage design.

Analysis of Melt Flows in an Electric Heating Furnace for Quartz Glass Synthesis

2018 ◽  
Author(s):  
Qianli Ma ◽  
Haisheng Fang ◽  
Chunli Shang ◽  
Zhongyi Liu ◽  
Jing Wang
Keyword(s):  
Natural Convection ◽  
Flow Field ◽  
Flow Pattern ◽  
Quartz Glass ◽  
Flow Behavior ◽  
Electric Heating ◽  
Heating Furnace ◽  
Rotating Speed ◽  
Wide Range ◽  
Bubble Transport

Flow patterns in molten quartz are highly related to the bubble transport and removal. Understanding the flow behavior in molten quartz is of great importance to the manufacture of high-purity quartz glass. In this paper, a numerical model is set up to simulate the flow field of molten quartz in a typical electric heating furnace. Natural convection and Marangoni convection are examined for their respective effects on the flow pattern of molten quartz. Different heater arrangements will change the flow field by varying temperature distributions. Top heating and bottom heating have the same vortex direction; while side heating induces an opposite direction to them. To improve the flow field in molten quartz, forced convection is introduced by crucible rotation. The influences of rotating speed of crucible on the flow field are studied in a wide range varying from 0 to 100 rad/s. With the increase of rotating speed, a reverse vortex to natural convection shows in molten quartz; and the velocity magnitude increase at a growing speed. To find out the optimal flow pattern for quartz glass manufacture, a qualitative analysis is presented on the reliance of bubble transport behavior on the convection modes. Based on the results, useful suggestions are provided towards increasing the bubble-free area of molten quartz and improving the quality of quartz glass.

scholarly journals Experimental study of the internal flow in freezing water droplets on a cold surface

2019 ◽  
Vol 60 (12) ◽  
Author(s):  
Linn Karlsson ◽  
Henrik Lycksam ◽  
Anna-Lena Ljung ◽  
Per Gren ◽  
T. Staffan Lundström
Keyword(s):  
Natural Convection ◽  
Internal Flow ◽  
Light Sheet ◽  
Initial Time ◽  
Freezing Time ◽  
Water Droplets ◽  
Cold Surface ◽  
Time Period ◽  
Image Velocimetry ◽  
Marangoni Effects

Abstract The study of a freezing droplet is interesting in areas, where the understanding of build up of ice is important, for example, on wind turbines, airplane wings and roads. In this work, the main focus is to study the internal motion inside freezing water droplets using particle image velocimetry and to reveal if mechanisms such as natural convection and Marangoni convection have a noticeable influence on the flow within the droplet. The flow has successfully been visualized and measured for the first 25% of the total freezing time of the droplet when the velocity in the water is the highest and when the characteristic vortices can be seen. After this initial time period, the high amount of ice in the droplet scatters the PIV light sheet too much and the images retrieved are not suitable for analysis. Initially, it can be seen that the Marangoni effects have a large impact on the internal flow, but after about 15% of the total freezing time, the flow turns indicating increased effects of natural convection on the flow. Shortly after this time, almost no internal flow can be seen. Graphic abstract

scholarly journals NATURAL CONVECTION IN RECTANGULAR CAVITIES WITH DIFFERENT ASPECT RATIOS

2011 ◽  
Vol 10 (1-2) ◽  
pp. 44
Author(s):  
R. M. Nogueira ◽  
M. A. Martins ◽  
F. Ampessan
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Flow Behavior ◽  
Heated Wall ◽  
Flow Profile ◽  
Height Ratio ◽  
Dimensionless Variable ◽  
Aspect Ratios ◽  
Wide Range

Natural convection in closed cavities has been extensively studied in recent decades. This spontaneous method of heat transfer has a wide range of applications in engineering. In the present work, natural convection was numerically analyzed in a rectangular cavity heated on one of the sides and cooled on the opposite side. Temperatures of the heated wall and of the cooled wall were assumed to be constant. The objective of these studies was to determine the effects of the aspect ratio and the Rayleigh number on flow behavior and heat transfer in the cavity. In the simulations, the Rayleigh number drastically influenced the flow profile and heat transfer inside de cavity, as well as the thickness of the thermal boundary layer. It was also verified that the Nusselt number is strongly dependent on the L/D (Length/Height) ratio, and that this dimensionless variable increases with the increase of the W/L. The simulation of natural convection problems in the CFD Studio satisfactorily described the studied situations.

The Marangoni Convection Effect on Melt Pool Formation during Selective Laser Melting Process

2021 ◽  
Vol 412 ◽  
pp. 107-114
Author(s):  
Samia Aggoune ◽  
Farida Hamadi ◽  
Karim Kheloufi ◽  
Toufik Tamsaout ◽  
El-Hachemi Amara ◽  
...  
Keyword(s):  
Selective Laser Melting ◽  
Molten Pool ◽  
Marangoni Convection ◽  
Flow Behavior ◽  
Internal Flow ◽  
Melting Process ◽  
Heat Diffusion ◽  
Maximum Temperature ◽  
Laser Melting ◽  
Pool Shape

In order to predict the effect of the Marangoni convection and the morphology of melted stainless steel powder, during the selective laser melting (SLM) process, a transient three-dimensional numerical model is developed at the mesoscale. The evolution of the temperature and velocity fields’ is then studied. The initial powder bed distribution is obtained by the discrete element method (DEM) calculation, and the temperature distribution and the molten pool shape deformation are calculated and analyzed by the Ansys-Fluent commercial code. The molten pool shape is obtained by considering the influence of Marangoni convection on the internal flow behavior. The recoil force was not considered in our calculation. As main results, a slight deviation between the position of the maximum temperature of the molten pool and the center of the laser spot is observed. The direction of the heat diffusion is more likely to be horizontal and the flow centrifugal, which causes the melt track to be wide. Finally, the Marangoni convection is the main driver of the flow.

Effects of Swirl on Velocity-Field Uniformity in Disk Shape SOFC Channel Flow

2011 ◽  
Author(s):  
Kazumi Tsunoda ◽  
Kazuyuki Aminaka
Keyword(s):  
Swirling Flow ◽  
Flow Direction ◽  
Flow Behavior ◽  
Fluid Motion ◽  
Reynolds Numbers ◽  
Primary Role ◽  
Flow Uniformity ◽  
Centripetal Acceleration ◽  
Current Collectors ◽  
Wide Range

Swirling flow behavior between two parallel disk shape plates was experimentally investigated with the aid of a particle image velocimetry (PIV). The experiment was performed at low Reynolds numbers (Re < 100) to simulate the practical operation in a disk shape planar-type solid oxide fuel cell (SOFC). To improve flow uniformity, we designed a new channel with circle involute shape current collectors. In the new channel, a swirling flow was generated and its velocity in a core region was kept at nearly constant value toward the channel exit. This trend was observed regardless of flow rates, and hence flow uniformity was achieved over the wide range of Reynolds numbers. This is because a flow passage consisting of two adjacent involute shape current collectors functions as a constat-area channel due to the geometrical property of the circle involute. In order to understand the above mentioned flow behavior, a swirling fluid motion in the channel with the circle involute shape current collector was investigated by using steady state Euler’s equation of motion. We confirmed that the velocity component in the flow direction was dominant compared with that in the other direction and played primary role to maintain a swirling motion through the centripetal acceleration term.

URBAN FACADE GEOMETRY ON OUTDOOR COMFORT CONDITIONS: A REVIEW

2020 ◽  
Vol 4 (1) ◽  
pp. 45
Author(s):  
Elahe Mirabi ◽  
Nasrollahi Nazanin
Keyword(s):  
Thermal Comfort ◽  
Urban Areas ◽  
Natural Ventilation ◽  
Flow Behavior ◽  
Air Flow ◽  
Urban Geometry ◽  
Wide Range ◽  
Low Energy Buildings ◽  
Outdoor Comfort ◽  
Solar Access

<p>Designing urban facades is considered as a major factor influencing issues<br />such as natural ventilation of buildings and urban areas, radiations in the<br />urban canyon for designing low-energy buildings, cooling demand for<br />buildings in urban area, and thermal comfort in urban streets. However, so<br />far, most studies on urban topics have been focused on flat facades<br />without details of urban layouts. Hence, the effect of urban facades with<br />details such as the balcony and corbelling on thermal comfort conditions<br />and air flow behavior are discussed in this literature review. <strong>Aim</strong>: This<br />study was carried out to investigate the effective factors of urban facades,<br />including the effects of building configuration, geometry and urban<br />canyon’s orientation. <strong>Methodology and Results</strong>: According to the results,<br />the air flow behavior is affected by a wide range of factors such as wind<br />conditions, urban geometry and wind direction. Urban façade geometry<br />can change outdoor air flow pattern, thermal comfort and solar access.<br /><strong>Conclusion, significance and impact study</strong>: In particular, the geometry of<br />the facade, such as indentation and protrusion, has a significant effect on<br />the air flow and thermal behavior in urban facades and can enhance<br />outdoor comfort conditions. Also, Alternation in façade geometry can<br />affect pedestrians' comfort and buildings energy demands.</p>

COVID-19 Outbreak Prediction with Machine Learning

2020 ◽  
Author(s):  
Sina Faizollahzadeh Ardabili ◽  
Amir Mosavi ◽  
Pedram Ghamisi ◽  
Filip Ferdinand ◽  
Annamaria R. Varkonyi-Koczy ◽  
...  
Keyword(s):  
Machine Learning ◽  
Prediction Models ◽  
Fuzzy Inference ◽  
Control Measures ◽  
Future Research ◽  
Complex Nature ◽  
Inference System ◽  
Wide Range ◽  
Standard Models ◽  
High Level

Several outbreak prediction models for COVID-19 are being used by officials around the world to make informed-decisions and enforce relevant control measures. Among the standard models for COVID-19 global pandemic prediction, simple epidemiological and statistical models have received more attention by authorities, and they are popular in the media. Due to a high level of uncertainty and lack of essential data, standard models have shown low accuracy for long-term prediction. Although the literature includes several attempts to address this issue, the essential generalization and robustness abilities of existing models needs to be improved. This paper presents a comparative analysis of machine learning and soft computing models to predict the COVID-19 outbreak as an alternative to SIR and SEIR models. Among a wide range of machine learning models investigated, two models showed promising results (i.e., multi-layered perceptron, MLP, and adaptive network-based fuzzy inference system, ANFIS). Based on the results reported here, and due to the highly complex nature of the COVID-19 outbreak and variation in its behavior from nation-to-nation, this study suggests machine learning as an effective tool to model the outbreak. This paper provides an initial benchmarking to demonstrate the potential of machine learning for future research. Paper further suggests that real novelty in outbreak prediction can be realized through integrating machine learning and SEIR models.

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