scholarly journals Direct Numerical Simulation and Visualization of Subcooled Pool Boiling

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Tomoaki Kunugi ◽  
Yasuo Ose
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
High Speed ◽  
High Performance ◽  
High Spatial Resolution ◽  
Pool Boiling ◽  
Numerical Results ◽  
Condensation Model ◽  
High Performance Computers ◽  
Good Agreement

A direct numerical simulation of the boiling phenomena is one of the promising approaches in order to clarify their heat transfer characteristics and discuss the mechanism. During these decades, many DNS procedures have been developed according to the recent high performance computers and computational technologies. In this paper, the state of the art of direct numerical simulation of the pool boiling phenomena during mostly two decades is briefly summarized at first, and then the nonempirical boiling and condensation model proposed by the authors is introduced into the MARS (MultiInterface Advection and Reconstruction Solver developed by the authors). On the other hand, in order to clarify the boiling bubble behaviors under the subcooled conditions, the subcooled pool boiling experiments are also performed by using a high speed and high spatial resolution camera with a highly magnified telescope. Resulting from the numerical simulations of the subcooled pool boiling phenomena, the numerical results obtained by the MARS are validated by being compared to the experimental ones and the existing analytical solutions. The numerical results regarding the time evolution of the boiling bubble departure process under the subcooled conditions show a very good agreement with the experimental results. In conclusion, it can be said that the proposed nonempirical boiling and condensation model combined with the MARS has been validated.

Numerical Study on Bubble Departing Behavior From Heated Surface in Subcooled Pool Boiling

2011 ◽  
Author(s):  
Yasuo Ose ◽  
Zensaku Kawara ◽  
Tomoaki Kunugi
Keyword(s):  
Numerical Simulations ◽  
High Speed ◽  
Numerical Study ◽  
Heated Surface ◽  
Pool Boiling ◽  
Three Dimensional ◽  
Condensation Model ◽  
Departure Behavior ◽  
Shape Changes ◽  
Good Agreement

In this study, in order to clarify the heat transfer characteristics of the subcooled pool boiling and to discuss its mechanism, the boiling and condensation model for numerical simulation on subcooled boiling phenomena has been developed. In this paper, the three dimensional numerical simulations based on the MARS (Multi-interface Advection and Reconstruction Solver) with the boiling and condensation model which consisted of the improved phase-change model and the relaxation time based on the quasi-thermal equilibrium hypothesis have been conducted for the subcooled pool boiling phenomena especially regarding to the bubble departure behavior from the heated surface. The results of the numerical simulations were compared with the experimental data obtained by the high-speed camera (Phantom 7.1) with the Cassegrain optical system, and then the influence of the degree of subcooling for the bubble departing behaviors including their shape changes from the heated surface were numerically predicted. As the results, the numerical results of the bubble departing behavior from the heated surface showed in good agreement with the experimental observations quantitatively.

Turbulent dispersion in a non-homogeneous field

1999 ◽  
Vol 392 ◽  
pp. 45-71 ◽  
Author(s):  
ILIAS ILIOPOULOS ◽  
THOMAS J. HANRATTY
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Stochastic Model ◽  
Point Source ◽  
Time Scales ◽  
Langevin Equation ◽  
Turbulent Dispersion ◽  
Homogeneous Field ◽  
Fully Developed Flow ◽  
Good Agreement

Dispersion of fluid particles in non-homogeneous turbulence was studied for fully developed flow in a channel. A point source at a distance of 40 wall units from the wall is considered. Data obtained by carrying out experiments in a direct numerical simulation (DNS) are used to test a stochastic model which utilized a modified Langevin equation. All of the parameters, with the exception of the time scales, are obtained from Eulerian statistics. Good agreement is obtained by making simple assumptions about the spatial variation of the time scales.

On Direct Numerical Simulation of Turbulent Flows

2011 ◽  
Vol 64 (2) ◽  
Author(s):  
Giancarlo Alfonsi
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
High Performance Computing ◽  
Turbulent Flows ◽  
High Performance ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Turbulent Shear ◽  
Navier Stokes Equations ◽  
Performance Computing

The direct numerical simulation of turbulence (DNS) has become a method of outmost importance for the investigation of turbulence physics, and its relevance is constantly growing due to the increasing popularity of high-performance-computing techniques. In the present work, the DNS approach is discussed mainly with regard to turbulent shear flows of incompressible fluids with constant properties. A body of literature is reviewed, dealing with the numerical integration of the Navier-Stokes equations, results obtained from the simulations, and appropriate use of the numerical databases for a better understanding of turbulence physics. Overall, it appears that high-performance computing is the only way to advance in turbulence research through the front of the direct numerical simulation.

Direct numerical simulation of flow transition in high-speed boundary layers around airfoils

1997 ◽  
Author(s):  
Zhining Liu ◽  
Wei Zhao ◽  
Chaoqun Liu ◽  
Guohua Xiong ◽  
Zhining Liu ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Boundary Layers ◽  
High Speed ◽  
Flow Transition

Amorphous Silicon Ultra Thin Base Bipolar Phototransistor with High Performance (β=12, τx ≤30μs)

1985 ◽  
Vol 54 ◽  
Author(s):  
C. Y. Chang ◽  
B. S. Wu ◽  
Y. K. Fang ◽  
R. H. Lee
Keyword(s):  
Amorphous Silicon ◽  
High Speed ◽  
High Performance ◽  
Response Speed ◽  
High Gain ◽  
Bipolar Transistor ◽  
Current Gain ◽  
Flat Panel Display ◽  
Element Array ◽  
Good Agreement

ABSTRACTAn n+ /i/p /i/n amorphous silicon bipolar transistor has been successfully fabricated with a current gain of 12 and a response speed of 30 yS This new structure of bipolar transistor has a very thin base (200Å), therefore, high gain and high speed is obtainable. This device has a very promising applications as a flat panel display transistor and a phototransistor in photosensing element/array and photo coupler. Electrical and optical characteristics have been extensively investigated. Theoretical model and experimental results are plausibly in good agreement.Variation from the fundamental structure is also been developed, such as the Schottky emitter Al/i/p /i/n bipolar transistor.

scholarly journals Numerical Simulation of 980 nm-LD-Pumped Yb3+-Er3+-Tm3+-Codoped Fiber Amplifier for 1500 nm and 1600 nm Bands

2009 ◽  
Vol 2009 ◽  
pp. 1-8
Author(s):  
Chun Jiang
Keyword(s):  
Numerical Simulation ◽  
Theoretical Model ◽  
Pump Power ◽  
Fiber Length ◽  
Fiber Amplifier ◽  
Numerical Results ◽  
Experimental Result ◽  
Signal Wavelength ◽  
Gain Spectra ◽  
Good Agreement

The theoretical model of Yb3+-Er3+-Tm3+-codoped fiber amplifier pumped by 980 nm laser is proposed, and the rate and power propagation equations are numerically solved to analyze the dependences of the gains at 1500 nm and 1600 nm bands on the activator concentrations, fiber length, pump power, and signal wavelength. The numerical results show that our model is in good agreement with experimental result, and with pump power of 200 mW and fiber length varying from 0.15 to 1.5 m, the gains at the two bands may reach 10.0–20.0 dB when the codoping concentrations of Yb3+, Er3+, and Tm3+ are in the ranges 1.0–3.0×1025, 1.0–3.0×1024, and 1.0–3.0×1024 ions/m3, respectively. The fiber parameters may be optimized to flatten the gain spectra.

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