Numerical Study of Water Droplet Heat Removal and Dynamics During its Impact Onto the Micro-Pillar Array at Elevated Temperature

2018 ◽  
Author(s):  
Beni Mehrdad Shahmohammadi ◽  
Shangzhen Xie ◽  
Jiyun Zhao
Keyword(s):  
Heat Transfer ◽  
Level Set Method ◽  
Level Set ◽  
Solid Surface ◽  
Water Droplet ◽  
Heat Removal ◽  
Spray Cooling ◽  
Optimal Size ◽  
Droplet Dynamics ◽  
Micro Pillars

The spray cooling and heat removal efficiency is one of the important aspect of nuclear thermalhydraulics and safety, especially for passive containment cooling after severe accidents. In order to design and optimize these systems effectively, computer modelling of the underlying mechanism of the liquid drop interaction with the hot solid surface would be necessary. Therefore, completeness, accuracy and reliability of the models that are being used in such sensitive areas are vital to the society and environment. Furthermore, the current powerful computer resources need to be fully exploited, so that the precision and the accuracy of the obtained computational results would be further enhanced. Nowadays, Volume-Of-Fluid (VOF) method is widely used in simulating the droplet dynamics, however these models provide estimations that are different in certain extents compare to the experimental results. In present work, we have used the level-set method to study the droplet dynamics and heat removal when the water droplet impact on the surface with different morphologies. The developed model which is based on the finite element method (FEM) has been benchmarked with previously performed experiments regarding the droplet bouncing on a flat hydrophobic surface; these estimations were in a good agreement with the previously published results. Moreover, hot solid surfaces with presence of micro-pillar has been considered to perform sensitivity study for different sizes of the micro-pillars and water droplets. In addition, it has been found that the heat transfer and droplet dynamic behavior would significantly vary in scenarios when the micro-pillars are presents in compare to a flat solid surface; it is observed that a better droplet spreading can be obtained with optimal size of micro-pillars that are present underneath of the droplet axial trajectory. The present study and the model would add valuable information to the field of heat transfer in aspect of spray cooling by investigating the feasibility of using the level-set method for a better estimation of fluid and heat transfer related results.

Investigation of droplet behaviors for spray cooling using level set method

2018 ◽  
Vol 113 ◽  
pp. 162-170 ◽  
Author(s):  
Mehrdad Shahmohammadi Beni ◽  
Jiyun Zhao ◽  
K.N. Yu
Keyword(s):  
Level Set Method ◽  
Level Set ◽  
Spray Cooling

Direct Numerical Simulation of Heat Transfer in Spray Cooling Through 3D Multiphase Flow Modeling Using Parallel Computing

2009 ◽  
Vol 131 (12) ◽  
Author(s):  
Suranjan Sarkar ◽  
R. Panneer Selvam
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Parallel Computing ◽  
Phase Change ◽  
Power Electronics ◽  
Vapor Bubble ◽  
Heat Removal ◽  
Spray Cooling ◽  
Hot Surface ◽  
Liquid Vapor

Thermal management issues have become a major bottleneck for further miniaturization and increased power consumption of electronics. Power electronics require more increasing use of high heat flux cooling technologies. Spray cooling with phase change has the advantage of large amount of heat transfer from the hot surface of many power electronics. Spray cooling is a complex phenomenon due to the interaction of liquid, vapor, and phase change at small length scale. A good understanding of the underlying physics and the heat removal process in spray cooling through numerical modeling is needed to design efficient spray cooling system. A computational fluid dynamics based 3D multiphase model for spray cooling is developed here in parallel computing environment using multigrid conjugate gradient solver. This model considers the effect of surface tension, gravity, phase change, and viscosity. The level set method is used to capture the movement of the liquid-vapor interface. The governing equations are solved using finite difference method. Spray cooling is studied using this model, where a vapor bubble is growing in a thin liquid film on a hot surface and a droplet is impacting on the thin film. The symmetry boundary condition considered on four sides of the domain effectively represents a large spray made up of multiple equally sized droplets and bubbles and their interaction. Studies have also been performed for different wall superheats in the absence of vapor bubble to compare the effect of two-phase heat transfer compared to single-phase in spray cooling. The computed interface, temperature, and heat flux distributions at different times over the domain are visualized for better understanding of the heat removal mechanism.

Experimental Study on Heat Transfer of Pressurized Spray Cooling on the Heated Plate by Using 45° Full Cone Nozzles

2014 ◽  
Vol 535 ◽  
pp. 32-36 ◽  
Author(s):  
Peng Jiang ◽  
Qian Wang ◽  
I. Sabariman ◽  
Eckehard Specht
Keyword(s):  
Heat Transfer ◽  
Heat Removal ◽  
Infrared Camera ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Spray Cooling ◽  
Material Surface ◽  
Transient Temperature ◽  
Heated Plate ◽  
Water Spray Cooling

Water spray cooling is widely used in many industrial processes to control heat removal from a hot material surface. In this work, pressurized spray nozzle was applied to break film boiling immediately once the quenching process is started. For this purpose, a circular disc made of non-ferrous metals is heated to approximately 850 °C and sprayed on one side by hydraulic nozzle and the temperature distribution with respect to time and space is measured by using Infrared camera. On the other side, the measured surface was coated with graphite paint in order to achieve a high emissivity. By this IR thermography, transient temperature measurement can be carried out within the window of 320 × 80 pixels. The heat transfer was analyzed through 1D method. In this method, the temperature difference between both sides neglected. The local heat transfer can then be calculated from a simple differential energy balance.

scholarly journals Numerical Development of Heat Transfer Coefficient Correlation for Spray Cooling in Continuous Casting

2020 ◽  
Vol 7 ◽  
Author(s):  
Haibo Ma ◽  
Armin Silaen ◽  
Chenn Zhou
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Continuous Casting ◽  
Transfer Coefficient ◽  
High Performance ◽  
Dynamic Control ◽  
Heat Removal ◽  
Spray Cooling ◽  
Operating Conditions ◽  
Graphic User Interface

The desire to remain competitive and continuously produce high quality and high strength steel at the maximum production rate in continuous casting requires dynamic control over the spray cooling rate. Efficient and uniform heat removal without cracking or deforming the slab during spray cooling is critical. The challenge is to obtain accurate Heat Transfer Coefficient (HTC) on the slab surface as boundary condition for solidification calculations. Experiment based HTC correlations are limited to handful operating conditions and they might fail when changes occur. The current study presents a numerical model for spray cooling featuring the simulation of atomization and droplet impingement heat transfer in continuous casting. With the aid of high-performance computer, parametric studies were performed and the results were converted into mathematically simple HTC correlations as a function of essential operating parameters. Finally, a Graphic User Interface (GUI) was developed to facilitate future applications of the correlations. The HTC prediction is stored in the versatile comma-separated values (csv) format and it can be directly applied to solidification calculations. The proposed numerical methodology should benefit the steel industry by expediting the development process of HTC correlations and can further improve the accuracy of the existing casting control systems.

Imaging Measurements in Nano-Particle Enhanced Spray Cooling

2010 ◽  
Author(s):  
J. Torres ◽  
A. Perdones ◽  
A. Garcia ◽  
F. J. Diez
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Speed ◽  
Heated Surface ◽  
Heat Removal ◽  
Thermal Control ◽  
Spray Cooling ◽  
Nano Particles ◽  
Copper Block ◽  
Alumina Oxide

Thermal control is a major constraint in spacecraft development as increased demand on electronics performance requires large heat dissipation from smaller surfaces which has led to increased challenges for thermal control. Spray cooling has a great amount of application in industrial processes as a heat removal method. It is thought to be the future in thermal management systems in space because of its capability for ‘close’ and accurate control of heat removal. Spray cooling is based on phase change heat transfer generating high heat transfer rates for low superheats. This last term is used to describe the difference in temperature between the heated surface and the cooling fluid. When the temperature of the surface to be cooled rises above the saturation temperature of the fluid splashed to the surface, a phase change occurs at the solid liquid interface during the boiling regime. However, the most interesting phase (regime) is the nucleating boiling where the critical heat flux, CHF, is reached. The CHF is then achieved due to the vapor generation is such as great that the liquid cannot still be in contact with the surface. Thus the heat is transferred through the vapor if there is not enough cold fluid. The thermal conductivity of vapor is lower and so the efficient of the cooling process. This turns out in a decrease on heat flux. Nowadays it is being taken more into account nanofluids as a technique capable of enhancing heat transfer. Nanofluids, a mix of nano-size particles in a base fluid, have been found to have a very high thermal conductivity as compared to the base fluid. In You et al., 2003; Kim et al., 2004a; Moreno et al., 2005 water was used with various Al2O3 particle concentration in a flat plate nucleate pool boiling system. They came across with no change in the heat transfer coefficient but a dramatic enhancement in CHF. They also found that high concentrations can degrade nucleate boiling. The aim of this project is study the effects of spray cooling with suspended nano-particles as an enhanced method for heat transfer removal. The working fluid was water with different concentrations of alumina-oxide particles added. The alumina oxide particles were supplied by Nanophase Technologies (Nano Tek® Alumina Oxide AL-01000-003-025) which had a mean diameter of 60 nm. Three different concentrations were used and the following: .5 g/L, 1 g/L, 2 g/L. Since clumping of particles can affect the heat transfer properties of the droplets, the solution was placed on inside an ultrasonic bath and left there for at least 24 hrs and immediately used in the experiments. Two nozzles were used in this experiment to study a wide range of sauter diameter of droplets. The experiment was carried out using three experimental techniques which looked into different characteristics of spray cooling. In the first mode, the fluid was sprayed onto a copper block heater surface while it was imaged with a high speed camera and synchronized with a high speed Nd-YAG laser. 9 thermocouples were positioned inside the copper block heater, as seen on Figure 1, to measure critical heat flux, while a camera was used to record different impact properties and the influence of nano-particles. Some of these properties were pool buildup size, spread, and duration of pool. For the second imaging technique, the spray on the heated surface was also considered to be an impinging jet, so to visualize the flow of this jet and how the heated surface affected it, PIV (Particle Image Velocimetry) was used in the study. A third imaging technique was used to study the droplet behavior when in contact with a heated surface. A transparent glass heater made of aluminum silicate glass and coated with an ITO (indium tin oxide) film was used as the heater. The size of the drops had an average diameter of 2.38 mm. When compared to the copper block study, this method allows images to be taken from directly below the clear glass heater. Furthermore, these images allow for a clear edge detection of drops as they spread on the surface and what characteristics they develop when the droplets have different concentrations of nanoparticles, as seen on Figure 2. The experiment used a pulsed laser to provide the background illumination. This project is a continuing research project.

Simulation of Spray Cooling on Hot Steel Slabs in Continuous Casting

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Haibo Ma ◽  
Armin A. Silaen ◽  
Chenn Q. Zhou
Keyword(s):  
Heat Transfer ◽  
Continuous Casting ◽  
Current Model ◽  
Radiation Heat Transfer ◽  
Heat Removal ◽  
Spray Cooling ◽  
Linear Instability ◽  
Standoff Distance ◽  
Droplet Distribution ◽  
Steel Slabs

Abstract Continuous casting is an important process to solidify molten steel. Efficient and uniform heat removal by water spray without cracking or deforming steel slabs is a major challenge during continuous casting. With the aid of computational fluid dynamics (CFD), the current study presents a numerical model of spray cooling for process understanding and improvement. The Eulerian–Lagrangian approach is utilized to track the movement of water droplets that are injected from a hydraulic nozzle. The initial droplet size is predicted by the linear instability sheet atomization (LISA) model and the droplet distribution satisfies the Rosin-Rammler distribution. Droplet-slab impingement is modeled by the wall jet model and the associated heat transfer accounts for both heat conduction and radiation. Heat transfer coefficient (HTC) on slab surface is validated against a hot-plate benchmark experiment and shows good agreement. The significance of spray standoff distance and spray direction on heat transfer is also investigated. The results indicate the existence of the critical standoff distance beyond which the cooling effect becomes negligible. Spray direction plays an important role in determining the heat transfer rate as well, and insufficient cooling is observed when droplets are sprayed against gravity. Additional 10% to 15% of water will compensate for such low heat transfer. The current study should benefit the steel industry by providing fundamental insights into the process. The current model can also be applied to other types of spray nozzles and can further improve the efficiency of future simulations.

The Cooling Performance of Mixed Convection in a Ventilated Enclosure With Different Ports Configurations

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Hayder A. Dhahad ◽  
Gazy F. Al-Sumaily ◽  
Laith J. Habeeb ◽  
Mark C. Thompson
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Cooling System ◽  
Heat Removal ◽  
Reynolds Numbers ◽  
Optimal Size ◽  
Maximum Heat ◽  
Left Wall ◽  
Square Enclosure ◽  
Over The Top

Abstract Mixed convection heat transfer in a vertically oriented air-cooled square enclosure is simulated numerically using the finite volume method. The vertical left wall being heated and all others are considered insulated. The effects of six opposite and staggered inlet/outlet openings' locations over the top and bottom walls are investigated, with different sizes of the opening height (0.05 ≤d/H≤ 0.3). The objective is to figure out the better size and location of inlet and outlet to acquire more efficient cooling system in the enclosure by maximizing the heat removal rate. This is conducted over ranges of the governing parameters, which are the Richardson number (0 ≤Ri≤ 30) and the Reynolds number (50 ≤Re≤ 250). The results show that the level of heat transfer enhancement increases with increasing the opening height, with an optimal size of d/H = 0.25 for obtaining maximum heat removal, for all Richardson and Reynolds numbers. The results also indicate that the higher heat dissipation occurs when the cold air is injected vertically near the hot wall and exits the enclosure from the opposite or staggered outlet, for all Richardson and Reynolds numbers.

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