Transport phenomena and evolution mechanism of the melt pool during a laser based metal melting process

2021 ◽  
pp. 1-36
Author(s):  
Qingfei Bian ◽  
Ke Tian ◽  
Kong Ling ◽  
Yitung Chen ◽  
Min Zeng ◽  
...  
Keyword(s):  
Numerical Study ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Melting Process ◽  
Numerical Results ◽  
Interface Morphology ◽  
Momentum Exchange ◽  
Interface Capturing ◽  
Melt Pool ◽  
Metal Melting

Abstract This article presents a fully three-dimensional numerical study on the process of melt pool evolution. In order to overcome the simplifications used in many existing studies, an enthalpy method is developed for the phase change, and an accurate interface capturing method, i.e., the coupled volume-of-fluid and level set (VOSET) method, is employed to track the moving gas-liquid interface. Meanwhile, corresponding experimental studies are carried out for the purpose of validation. The obtained numerical results show the formed interface morphology during the process of melt pool with its typical sizes and are quantitatively consistent with those data measured in experiments. Based on the numerical results, the thermodynamic phenomena, induced by the interaction between heat and momentum exchange, occurring in the formation of melt pool are presented and discussed. Mechanisms of the melt pool evolution revealed in the present study provide a useful guidance for better controlling the process of additive manufacturing.

Numerical study of asymmetric and axisymmetric thermal jet with entropy generation concept

2021 ◽  
Vol 15 (1) ◽  
pp. 7628-7636
Author(s):  
D. Belakhal ◽  
Kouider Rahmani ◽  
Amel Elkaroui Elkaroui ◽  
Syrine Ben Haj Ayech ◽  
Nejla Mahjoub Saïd ◽  
...  
Keyword(s):  
Entropy Generation ◽  
Numerical Study ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Variable Density ◽  
Current Investigation ◽  
Numerical Resolution ◽  
Different Temperatures ◽  
Density Ratios ◽  
The Impact

In the current investigation, numerical study of a thermal jet of asymmetric (rectangular and elliptical) and axisymmetric (circular) geometry was investigated with variable density to verify the impact of the ratio of density and geometry on the generation of entropy. The central jet was brought to different temperatures (194, 293 and 2110 K) to obtain density ratios (0.66, 1 and 7.2) identical to a mixture jet ((Air-CO2), (Air-Air) and (Air-He)), respectively. Solving the three-dimensional numerical resolution of the Navier Stocks for turbulent flow permanent enclosed on the turbulence model K-εstandard was made. The results acquired are compared with that carried out in previous experimental studies, where it was concluded that, the axisymmetric (circular) geometry increases the entropy generation.

Fluid Flow and Lateral Fluid Dispersion in Bounded Granular Beds

2002 ◽  
Author(s):  
Azita Soleymani ◽  
Eveliina Takasuo ◽  
Piroz Zamankhan ◽  
William Polashenski
Keyword(s):  
Reynolds Number ◽  
Porous Media ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Numerical Study ◽  
Fluid Velocity ◽  
Three Dimensional ◽  
Numerical Results ◽  
Transition To Turbulence ◽  
Wide Range

Results are presented from a numerical study examining the flow of a viscous, incompressible fluid through random packing of nonoverlapping spheres at moderate Reynolds numbers (based on pore permeability and interstitial fluid velocity), spanning a wide range of flow conditions for porous media. By using a laminar model including inertial terms and assuming rough walls, numerical solutions of the Navier-Stokes equations in three-dimensional porous packed beds resulted in dimensionless pressure drops in excellent agreement with those reported in a previous study (Fand et al., 1987). This observation suggests that no transition to turbulence could occur in the range of Reynolds number studied. For flows in the Forchheimer regime, numerical results are presented of the lateral dispersivity of solute continuously injected into a three-dimensional bounded granular bed at moderate Peclet numbers. Lateral fluid dispersion coefficients are calculated by comparing the concentration profiles obtained from numerical and analytical methods. Comparing the present numerical results with data available in the literature, no evidence has been found to support the speculations by others for a transition from laminar to turbulent regimes in porous media at a critical Reynolds number.

scholarly journals Numerical Study of Fluid Flow and Heat Transfer Characteristics in Solid and Perforated Finned Heat Sinks Utilizing a Piezoelectric Fan

2019 ◽  
Vol 25 (7) ◽  
pp. 83-103
Author(s):  
Ayser Shamil Salman ◽  
Mohammed A. Nima
Keyword(s):  
Heat Transfer ◽  
Stokes Equations ◽  
Numerical Study ◽  
Air Flow ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Heat Sinks ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow Generator

Numerical study is adapted to combine between piezoelectric fan as a turbulent air flow generator and perforated finned heat sinks. A single piezoelectric fan with different tip amplitudes placed eccentrically at the duct entrance. The problem of solid and perforated finned heat sinks is solved and analyzed numerically by using Ansys 17.2 fluent, and solving three dimensional energy and Navier–Stokes equations that set with RNG based k−ε scalable wall function turbulent model. Finite volume algorithm is used to solve both phases of solid and fluid. Calculations are done for three values of piezoelectric fan amplitudes 25 mm, 30 mm, and 40 mm, respectively. Results of this numerical study are compared with previous both numerical and experimental studies and give a good agreement. Numerical solution is invoked to explain the behavior of air flow and temperature distribution for two types of circular axial and lateral perforations. For each type, all the results are compared with an identical solid finned heat sink. Perforations show a remarkable enhanced in the heat transfer characteristics. The results achieved enhancement in the heat transfer coefficient about 12% in axial perforation and 25% in the lateral perforation at the maximum fan amplitude.  

scholarly journals Three-dimensional numerical study of thermal exchanges in different geometry sections of mini-channels using three different nanoparticles

10.30544/455 ◽  
2020 ◽  
Vol 26 (1) ◽  
pp. 103-119
Author(s):  
Kamel Chadi ◽  
Nourredine Belghar ◽  
Belhi Guerira ◽  
Aissam Messaoudi
Keyword(s):  
Reynolds Number ◽  
Volume Fraction ◽  
Numerical Study ◽  
Three Dimensional ◽  
Numerical Results ◽  
Junction Temperature ◽  
Ansys Fluent ◽  
Cooling Fluid ◽  
Mini Channels ◽  
Exchange Surface

In the present work, we have studied the thermal exchanges of different geometry sections of mini-channels of a cooler numerically. Particularly, we have chosen a mini channels cooler copper for cooling an electronic chip IGBT. In our simulation of three-dimensional (3D), we have compared the numerical results for the different forms of the proposed mini-channels and the three different types of nano-fluids by using the Cu-water, the Ag-water, and the Diamond-water with a volume fraction of 0.02%. The numerical results are obtained by choosing a Reynolds number (Re) between 100 and 900 and considering that the flow regime is stationary. The simulation was performed using commercial software, ANSYS-Fluent 15.0. The results obtained show that the increase of the exchange surface between the walls of the mini channels and the cooling fluid makes increases the heat exchange coefficient and the improvement of the maximum junction temperature of the electronic chip IGBT with the increase of the Reynolds number. The choice of nanoparticles has considerable effects on improving the heat transfer and the maximum junction temperature of the chip IGBT.

Numerical Study of Nozzle Design on Cadmium Quenching Process in Thermochemical Splitting of Water

2009 ◽  
Author(s):  
Jianhu Nie ◽  
Yitung Chen ◽  
Bunsen Wong ◽  
Lloyd C. Brown
Keyword(s):  
Heat Transfer ◽  
Hydrogen Production ◽  
Gas Flow ◽  
Numerical Study ◽  
Three Dimensional ◽  
Maximum Velocity ◽  
Numerical Results ◽  
Nozzle Design ◽  
Flow And Heat Transfer ◽  
Quenching Process

Three-dimensional liquid-gas flow with condensation during cadmium quenching process for hydrogen production was numerically simulated in order to effectively guide the design of solar decomposer and vapor quencher. The mixture model was selected for modeling the multiphase flow, and the two-equation RNG k-ε model was used to model the turbulent flow and heat transfer. Numerical results including velocity, temperature, pressure, and mole fraction distributions were obtained for different nozzle designs. Numerical results showed that flow is relatively low in the decomposer and close to the bottom and the top inlets. The maximum velocity develops in the region near the entrance of the quenching nozzle as the nozzle angle is small. As the nozzle angle is large, the maximum velocity appears in the exit tube. Temperature, pressure and cadmium vapor distributions are also directly affected by the nozzle angle.

Axisymmetric Inertial Oscillations in Transient Rotating Flows in a Cylinder

1997 ◽  
Vol 119 (2) ◽  
pp. 390-396
Author(s):  
Jae Won Kim ◽  
Jae Min Hyun
Keyword(s):  
Large Time ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Numerical Study ◽  
Experimental Studies ◽  
Numerical Results ◽  
Navier Stokes ◽  
Inertial Oscillations ◽  
Time Duration ◽  
Navier Stokes Equations

A numerical study is made of axisymmetric inertial oscillations in a fluid-filled cylinder. The entire cylinder undergoes a spin-up process from rest with an impulsively started rotation rate Ω(t) = Ω0 + εω cos(ωt). Numerical solutions are obtained to the axisymmetric, time-dependent Navier-Stokes equations. Identification of the inertial oscillations is made by inspecting the evolution of the pressure difference between two pre-set points on the central axis, Cp. In the limit of large time, the inertial frequency thus determined is in close agreement with the results of the classical inviscid theory for solid-body rotation. As in previous experimental studies, the t* − (Ω0/ω) plots are constructed for inertial oscillations, where t* indicates the time duration until the maximum Cp is detected. These detailed numerical results are in broad agreement with the prior experimental data. Flow intensifications under the resonance conditions are illustrated based on the numerical results. Depictions are made of the increase in the amplitude of oscillating part of the total angular momentum under the resonance conditions. Also, the patterns of t* − (Ω0/ω) curves are displayed for different inertial frequency modes.

An Experimental and Numerical Study of a Micro-Synthetic Jet in a Shallow Cavity

2008 ◽  
Author(s):  
Alexander Sinclair ◽  
Victoria Timchenko ◽  
John Reizes ◽  
Gary Rosengarten ◽  
Eddie Leonardi
Keyword(s):  
Numerical Study ◽  
Experimental Studies ◽  
Maximum Velocity ◽  
Stokes Number ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Numerical Results ◽  
Transfer Rates ◽  
Micro Scale ◽  
Shallow Cavity

By disrupting laminar flow, micro-scale synthetic jets have the potential to significantly increase mixing and heat transfer rates in micro-devices. Due to the difficulty involved in performing measurements on the micro-scale, few experimental studies of micro-synthetic jets exist. In this paper we describe instantaneous velocity fields obtained by μPIV measurements in the vicinity of a synthetic jet orifice 24 μm in diameter issuing into a confined geometry. Numerical results for a synthetic jet operating under similar conditions have been used to help validate and clarify the experimental results. Comparisons between the experimental and numerical results during the expulsion phase of the actuator cycle for a synthetic jet with a Reynolds number (based on maximum velocity), Re = 239 and Stokes number, S = 9, indicate there is good agreement, thereby demonstrating that the μPIV technique can be used successfully for future studies. Experimental difficulties encountered are presented and methods of overcoming them discussed.

Behavior of Geocell-Reinforced Sand under a Vertical Load

2008 ◽  
Vol 2045 (1) ◽  
pp. 95-101 ◽  
Author(s):  
Jie Han ◽  
Xiaoming Yang ◽  
Dov Leshchinsky ◽  
Robert L. Parsons
Keyword(s):  
Bearing Capacity ◽  
Numerical Study ◽  
Three Dimensional ◽  
Numerical Results ◽  
Shear Stresses ◽  
Vertical Load ◽  
Reinforced Sand ◽  
Numerical Software ◽  
Load To Failure ◽  
Test Process

Geocells have a three-dimensional cellular structure, which can be used to stabilize foundations by increasing bearing capacity and reducing settlements. However, a considerable gap exists between the applications and the theories for the mechanisms of geocell-reinforced foundations. An experimental and numerical study on the behavior of geocell-reinforced sand under a vertical load is presented. A single geocell was filled with sand and subjected to a vertical load to failure. This test process was modeled by using the FLAC3D numerical software to investigate the mechanisms of geocell and sand interactions. Experimental and numerical results both demonstrated that the geocell increased the ultimate bearing capacity and the modulus of the sand. The numerical results include the distributions of displacements in the sand and geocell walls and the distributions of tensile stresses and shear stresses acting on the geocell walls. The numerical results for geocell-reinforced sand are compared to those for sand without geocell.

Numerical Study of Vortex Shedding From a Circular Cylinder in Linear Shear Flow

1999 ◽  
Vol 121 (2) ◽  
pp. 460-468 ◽  
Author(s):  
A. Mukhopadhyay ◽  
P. Venugopal ◽  
S. P. Vanka
Keyword(s):  
Circular Cylinder ◽  
Stokes Equations ◽  
Numerical Study ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Slip Condition ◽  
Navier Stokes ◽  
Finite Volume Scheme ◽  
Constant Frequency ◽  
Wall Boundary Conditions

A three-dimensional numerical simulation of linearly sheared flow past a circular cylinder has been performed for a shear parameter β of 0.02 and a mean Reynolds number of 131.5. A cylinder of 24 diameters span is considered. A second-order accurate finite volume scheme is used to integrate the unsteady Navier-Stokes equations. Present computations confirm both qualitatively and quantitatively, the aspects of cellular shedding as reported by several investigators through experimental studies. Up to five constant frequency cells of obliquely shedding vortices are observed. The nondimensional frequencies of these cells are observed to be lower than those given by parallel shedding correlations at the equivalent Reynolds numbers. It is also observed that the cell boundaries continuously move in time. Detailed distributions of vorticity and velocity components are presented to describe the flow. The influence of end-wall boundary conditions is studied by computing two cases, one with free-slip condition, and the other with no-slip condition on disks of radius of five cylinder diameters.

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