scholarly journals Numerical study of spectral shaping in high energy Ho:YLF amplifiers

2016 ◽  
Vol 24 (9) ◽  
pp. 9905 ◽  
Author(s):  
Peter Kroetz ◽  
Axel Ruehl ◽  
Krishna Murari ◽  
Huseyin Cankaya ◽  
Franz X. Kärtner ◽  
...  
Keyword(s):  
Numerical Study ◽  
High Energy ◽  
Spectral Shaping

Numerical Study to Analyze the Effects of Hot/Cold Aisle Configurations on Heat Transfer Phenomenon in a Data Center

2013 ◽  
Author(s):  
Kamran Nazir ◽  
Naveed Durrani ◽  
Imran Akhtar ◽  
M. Saif Ullah Khalid
Keyword(s):  
Heat Transfer ◽  
Data Center ◽  
Data Centers ◽  
Cooling System ◽  
Numerical Study ◽  
High Energy ◽  
Research Area ◽  
Transfer Phenomenon ◽  
Heat Transfer Phenomenon ◽  
Active Research

Due to high energy demands of data centers and the energy crisis throughout the world, efficient heat transfer in a data center is an active research area. Until now major emphasis lies upon study of air flow rate and temperature profiles for different rack configurations and tile layouts. In current work, we consider different hot aisle (HA) and cold aisle (CA) configurations to study heat transfer phenomenon inside a data center. In raised floor data centers when rows of racks are parallel to each other, in a conventional cooling system, there are equal number of hot and cold aisles for odd number of rows of racks. For even number of rows of racks, whatever configuration of hot/cold aisles is adopted, number of cold aisles is either one greater or one less than number of hot aisles i.e. two cases are possible case A: n(CA) = n(HA) + 1 and case B: n(CA) = n(HA) − 1 where n(CA), n(HA) denotes number of cold and hot aisles respectively. We perform numerical simulations for two (case1) and four (case 2) racks data center. The assumption of constant pressure below plenum reduces the problem domain to above plenum area only. In order to see which configuration provides higher heat transfer across servers, we measure heat transfer across servers on the basis of temperature differences across racks, and in order to validate them, we find mass flow rates on rack outlet. On the basis of results obtained, we conclude that for even numbered rows of rack data center, using more cold aisles than hot aisles provide higher heat transfer across servers. These results provide guidance on the design and layout of a data center.

scholarly journals NUMERICAL STUDY OF THE GEOMETRIC INFLUENCE OF A FIN IN A CYLINDRICAL HEAT EXCHANGER FOR MELTING OF PCM

2019 ◽  
Vol 18 (1) ◽  
pp. 78
Author(s):  
F. C. Spengler ◽  
B. Oliveira ◽  
R. C. Oliveski ◽  
L. A. O. Rocha
Keyword(s):  
Heat Exchanger ◽  
Aspect Ratio ◽  
Phase Change ◽  
Latent Heat ◽  
Heat Storage ◽  
Numerical Study ◽  
Melting Process ◽  
High Energy ◽  
High Energy Density ◽  
Melting Time

The thermal heat storage it’s an effective way to suit the energy availability with the demand schedule. It can be stored in the means of sensible or latent heat, the latter applying a material denominated Phase Change Material (PCM), which is provided as organic compounds, hydrated salts, paraffins, among others. The latent heat storage systems offer several advantages, like the practically isothermal process of loading and unloading and the high energy density. However, the low thermal conductivity makes the cycle prolonged on these systems, restricting its applicability. Applying computational fluid dynamics, the behavior of the PCM melting process was studied in cylindrical cavities with horizontal and vertical fins, aiming the optimization of the fin geometry. In this way the fin area was kept constant, varying its aspect ratio. The numerical model was validated with results from the literature and it’s composed of the continuity, momentum and energy equations increased by the phase change model. Qualitative and quantitative results are presented, referring to mesh independence, contours of velocity, net fraction and temperature at different moments of the process. The results of the study indicate that the position of the fin in the heat exchanger influences the melting process, although the vertical fins have a faster total melting process, horizontal fins can reach larger partial liquid fractions in less time in the heat exchanger. Such as the position of the fin, the increase of its length propitiates the reduction of the melting time, evidencing the optimal aspect ratio.

scholarly journals Numerical Study of the Dynamic Compaction Process considering the Phenomenon of Particle Breakage

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Xi Li ◽  
Jing Li ◽  
Xinyan Ma ◽  
Jidong Teng ◽  
Sheng Zhang
Keyword(s):  
Numerical Study ◽  
High Energy ◽  
Particle Breakage ◽  
Dynamic Compaction ◽  
Coarse Grained ◽  
Impact Stress ◽  
Logarithmic Curve ◽  
Before And After ◽  
Soil Foundation ◽  
Overlapping Method

Dynamic compaction (DC) is commonly used to strengthen the coarse grained soil foundation, where particle breakage of coarse soils is unavoidable under high-energy impacts. In this paper, a novel method of modeling DC progress was developed, which can realize particle breakage by impact stress. A particle failure criterion of critical stress is first employed. The “population balance” between particles before and after crushing is guaranteed by the overlapping method. The performance of the DC model is successfully validated against literature data. A series of DC tests were then carried out. The effect of particle breakage on key parameters of DC including crater depth and impact stress was discussed. Besides, it is observed that the relationship between breakage amount and tamping times can be expressed by a logarithmic curve. The present method will contribute to a better understanding of DC and benefit further research on the macro-micro mechanism of DC.

scholarly journals Numerical Predictions of a Swirl Combustor Using Complex Chemistry Fueled with Ammonia/Hydrogen Blends

Energies ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 288 ◽  
Author(s):  
Marco-Osvaldo Vigueras-Zuniga ◽  
Maria-Elena Tejeda-del-Cueto ◽  
José-Alejandro Vasquez-Santacruz ◽  
Agustín-Leobardo Herrera-May ◽  
Agustin Valera-Medina
Keyword(s):  
Boundary Conditions ◽  
High Pressures ◽  
Numerical Study ◽  
High Energy ◽  
Combustion Efficiency ◽  
Heat Losses ◽  
High Hydrogen ◽  
Numerical Predictions ◽  
Combustion Systems ◽  
Complex Chemistry

Ammonia, a chemical that contains high hydrogen quantities, has been presented as a candidate for the production of clean power generation and aerospace propulsion. Although ammonia can deliver more hydrogen per unit volume than liquid hydrogen itself, the use of ammonia in combustion systems comes with the detrimental production of nitrogen oxides, which are emissions that have up to 300 times the greenhouse potential of carbon dioxide. This factor, combined with the lower energy density of ammonia, makes new studies crucial to enable the use of the molecule through methods that reduce emissions whilst ensuring that enough power is produced to support high-energy intensive applications. Thus, this paper presents a numerical study based on the use of novel reaction models employed to characterize ammonia combustion systems. The models are used to obtain Reynolds Averaged Navier-Stokes (RANS) simulations via Star-CCM+ with complex chemistry of a 70%–30% (mol) ammonia–hydrogen blend that is currently under investigations elsewhere. A fixed equivalence ratio (1.2), medium swirl (0.8), and confined conditions are employed to determine the flame and species propagation at various operating atmospheres and temperature inlet values. The study is then expanded to high inlet temperatures, high pressures, and high flowrates at different confinement boundary conditions. The results denote how the production of NOx emissions remains stable and under 400 ppm, whilst higher concentrations of both hydrogen and unreacted ammonia are found in the flue gases under high power conditions. The reduction of heat losses (thus higher temperature boundary conditions) has a crucial impact on further destruction of ammonia post-flame, with a raise in hydrogen, water, and nitrogen through the system, thus presenting an opportunity of combustion efficiency improvement of this blend by reducing heat losses. Final discussions are presented as a method to raise power whilst employing ammonia for gas turbine systems.

scholarly journals Diffusion and radiation in magnetized collisionless plasmas with small-scale Whistler turbulence

2016 ◽  
Vol 82 (2) ◽  
Author(s):  
Brett D. Keenan ◽  
Mikhail V. Medvedev
Keyword(s):  
Numerical Study ◽  
High Energy ◽  
High Energy Density ◽  
Larmor Radius ◽  
Small Scale ◽  
Collisionless Plasmas ◽  
Correlation Scale ◽  
Scale Turbulence ◽  
Solar Plasmas ◽  
High Energy Density Plasmas

Magnetized high-energy-density plasmas can often have strong electromagnetic fluctuations whose correlation scale is smaller than the electron Larmor radius. Radiation from the electrons in such plasmas – which markedly differs from both synchrotron and cyclotron radiation – is tightly related to their energy and pitch-angle diffusion. In this paper, we present a comprehensive theoretical and numerical study of particle transport in cold, ‘small-scale’ Whistler-mode turbulence and its relation to the spectra of radiation simultaneously produced by these particles. We emphasize that this relation is a superb diagnostic tool of laboratory, astrophysical, interplanetary and solar plasmas with a mean magnetic field and strong small-scale turbulence.

Numerical study of head-on droplet collisions at high Weber numbers

2016 ◽  
Vol 789 ◽  
pp. 785-805 ◽  
Author(s):  
M. Liu ◽  
D. Bothe
Keyword(s):  
White Noise ◽  
Numerical Study ◽  
High Energy ◽  
Collision Dynamics ◽  
Noise Disturbance ◽  
Droplet Collisions ◽  
Long Time ◽  
Thin Lamella ◽  
Noise Disturbances ◽  
Good Agreement

Head-on collisions of binary water droplets at high Weber numbers are studied by means of direct numerical simulations (DNS). We modify the lamella stabilization method of Focke & Bothe (J. Non-Newtonian Fluid Mech., vol. 166 (14), 2011, pp. 799–810), which avoids the artificial rupture of the thin lamella arising in high-energy collisions, and validate it in the regime of high Weber numbers. The simulations are conducted with and without initial disturbances and the results are compared with the experimental work of Pan et al. (Phys. Rev. E, vol. 80 (3), 2009, 036301). The influence of initial white noise disturbance on the collision dynamics is identified and good agreement between the simulation results and the experimental results is obtained when the initial noise disturbances are properly exerted. In order to include the stochastic nature of the disturbance, we conduct several simulations with white noise disturbance of same strength and average the spectrum diagram for the unstably developing rim of the collision complex. We show that the magnification of rim perturbation can be predicted by Plateau–Rayleigh theory over a long time span.

scholarly journals Desalination of Agricultural Wastewater by Solar Adsorption System: A Numerical Study

2021 ◽  
Vol 10 (4) ◽  
pp. 901-910
Author(s):  
Jehan F AlRubaiea ◽  
Farkad A Latteiff ◽  
Jasim M Mahdi ◽  
Mohammed A Atiya ◽  
Hasan Sh Majdi
Keyword(s):  
Silica Gel ◽  
Numerical Study ◽  
High Energy ◽  
Water Desalination ◽  
Hot Water ◽  
Coefficient Of Performance ◽  
Cooling Power ◽  
Adsorption System ◽  
Factors Affecting ◽  
Usage Cost

There are still areas around the world suffer from severe shortage of freshwater supplies. Desalination technologies are not widely used due to their high energy usage, cost, and environmental damaging effects. In this study, a mathematical model of single-bed adsorption desalination system using silica gel-water as working pair is developed and validated via earlier experiments. A very good match between the model predictions and the experimental results is recorded. The objective is to reveal the factors affecting the productivity of fresh water and cooling effect in the solar adsorption system. The proposed model is setup for solving within the commercially-available software (Engineering Equation Solver). It is implemented to solve the mass and heat balance equations for the adsorbent bed, condenser, and evaporator components. At a typical temperature of 89 °C and flow rate of 30 m3/sec for the hot water entering the bed, the following results are reported: (a) the specific daily water production of 1.89 m3 /ton of silica gel/ day, (b) coefficient of performance of 0.32, and (c) specific cooling power of 40.82 W/kg of silica gel. The concentration of salt (X) in the product (desalinated water) has been set with value of 0.5 gm/kg to be suitable for drinking and irrigation. The salt concentration in the evaporator is estimated to be 4.611 gm/kg during the overall adsorption process. The results from this study should be of wide interest for the field of solar water desalination and air-conditioning.

scholarly journals Numerical Study of Rock Fragmentation Process and Acoustic Emission by FDEM Based on Heterogeneous Model

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Qi Liu ◽  
Penghai Deng
Keyword(s):  
Acoustic Emission ◽  
Mechanical Response ◽  
Numerical Study ◽  
High Energy ◽  
Uniaxial Compression Test ◽  
Rock Damage ◽  
Heterogeneous Model ◽  
Damage And Fracture ◽  
Heterogeneous Rock ◽  
Rock Model

Rock has the characteristics of natural heterogeneity and discontinuity. Its failure phenomenon induced by external force involves complex processes, including the microcrack initiation, propagation, coalescence, and the macrocrack formation. In this study, the Weibull random distribution based on the rock microstructure characteristics is introduced into the combined finite-discrete element method (FDEM) to establish the heterogeneous rock model, and the mechanical response and damage evolution of rock samples in uniaxial compression test are simulated. The results show that FDEM simulation with loaded heterogeneous rock model can reflect the progressive development of rock damage, fracture, and acoustic emission (AE) activity in real rock well. Meanwhile, the statistical analysis indicates that the number and energy evolution of AE events with different fracture modes in the model are consistent with the macroscopic failure mode of rock. The change of b-value also agrees with the increasing trend of high-energy events in the loading process. This method provides a new tool for the analysis of rock damage and fracture evolution.

Performance analysis of multi-row vertical axis hydrokinetic turbine–straight blade cascaded (VAHT-SBC) turbines array

2019 ◽  
Vol 13 (3) ◽  
pp. 5665-5688
Author(s):  
E. Septyaningrum ◽  
R. Hantoro ◽  
I. K. A. P. Utama ◽  
J. Prananda ◽  
G. Nugroho ◽  
...  
Keyword(s):  
Numerical Study ◽  
Flow Direction ◽  
Vertical Axis ◽  
High Energy ◽  
Energy Concentration ◽  
Great Expectation ◽  
Array Configuration ◽  
Hydrokinetic Turbine ◽  
Array Performance ◽  
Rotational Direction

Due to its high energy concentration, hydrokinetic energy from tidal and rivers flow provides great expectation. One of the effective ways to meet the energy production target is to reduce the installation and maintenance effort arranging turbines in such configuration, known as hydrokinetic turbine array. The performance of array configuration is affected by turbine position and rotational direction. This research provides a comprehensive analysis of the effect of turbine rotational direction and position on the array performance. The experimental study and URANS simulation were carried out to gain deeper information. This previous study proposed 3 side-by-side configurations, i.e. Co-rotating” (Co), “counter-rotating-in” (CtI) and “counter-rotating-out” (CtO) and the current study proposed 2 multi-row configurations, i.e. 3T-A and 3T-B. The comprehensive information is provided. Both experimental and numerical study confirmed that the velocity superposition in the interaction zone gives the constructive effect on turbine performance. All site-by-site configurations is able to enhance farm effectiveness. Co configuration is recommended to install in the resource having unpredictable flow direction. However, the CtI is for canal or river since it has better performance. The study for multi-row configuration shows that the downstream turbine has performance decrement due to the bad effect of the upstream turbine wake.

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