scholarly journals Influence of a non-condensable gas on mixing of a melt with water in a stratified configuration

2021 ◽  
Vol 2088 (1) ◽  
pp. 012032
Author(s):  
V I Melikhov ◽  
O I Melikhov ◽  
S E Yakush ◽  
B Saleh ◽  
N A Borzdyi
Keyword(s):  
Axisymmetric Problem ◽  
Heat Removal ◽  
Water Jet ◽  
Spherically Symmetric ◽  
Gas Bubble ◽  
One Dimensional ◽  
Polytropic Process ◽  
Symmetric Approximation ◽  
The Impact ◽  
Rapid Drop

Abstract The influence of bubbles of hot non-condensable gas formed at the interface between the melt and water on the formation of a mixture of melt with water capable of producing steam explosions is considered. The dynamics of such a bubble in subcooled water is analyzed numerically in a one-dimensional spherically symmetric approximation. It is shown that with significant initial superheat of the bubble relative to the water, a rapid drop in pressure in the bubble occurs due to strong heat removal into the water. This leads to the collapse of the bubble and the appearance of an accompanying flow of water. The results obtained made it possible to approximately describe the stage of collapse of the bubble as the polytropic process and to determine its index. The axisymmetric problem of the impact of the water jet on the surface of a melt during collapse of a gas bubble near the interface between the melt and water is numerically investigated. In this case, the obtained polytropic process equation is used to determine the pressure in the bubble. It is found that the resulting impact on the melt is capable of knocking out melt droplets into the water to a height of several centimeters, which leads to the formation of a layer of water mixed with the melt droplets, which is capable of producing strong steam explosions.

Altitude Effects on the Performance of Small Radial Turbomachinery: Part I — Compressor Impellers

2016 ◽  
Author(s):  
Dries Verstraete ◽  
Kjersti Lunnan
Keyword(s):  
Reynolds Number ◽  
Performance Analysis ◽  
Rotational Speed ◽  
Pressure Ratio ◽  
Unmanned Aircraft ◽  
Good Match ◽  
One Dimensional ◽  
Design Changes ◽  
Current Article ◽  
The Impact

Small unmanned aircraft are currently limited to flight ceilings below 20,000 ft due to the lack of an appropriate propulsion system. One of the most critical technological hurdles for an increased flight ceiling of small platforms is the impact of reduced Reynolds number conditions at altitude on the performance of small radial turbomachinery. The current article investigates the influence of Reynolds number on the efficiency and pressure ratio of two small centrifugal compressor impellers using a one-dimensional meanline performance analysis code. The results show that the efficiency and pressure ratio of the 60 mm baseline compressor at the design rotational speed drops with 6–9% from sea-level to 70,000 ft. The impact on the smaller 20 mm compressor is slightly more pronounced and amounts to 6–10%. Off-design changes at low rotational speeds are significantly higher and can amount to up to 15%. Whereas existing correlations show a good match for the efficiency drop at the design rotational speed, they fail to predict efficiency changes with rotational speed. A modified version is therefore proposed.

Performance Modeling of Desiccant Wheels: 1 — Model Development

2008 ◽  
Author(s):  
Chaoqin Zhai ◽  
David H. Archer ◽  
John C. Fischer
Keyword(s):  
Model Development ◽  
Axial Direction ◽  
Performance Model ◽  
Design Parameters ◽  
Residual Water ◽  
One Dimensional ◽  
Operating Variables ◽  
Steady State Operation ◽  
Rotary Speed ◽  
The Impact

This paper presents the development of an equation based model to simulate the combined heat and mass transfer in the desiccant wheels. The performance model is one dimensional in the axial direction. It applies a lumped formulation in the thickness direction of the desiccant and the substrate. The boundary conditions of this problem represent the inlet outside/process and building exhaust/regeneration air conditions as well as the adiabatic condition of the two ends of the desiccant composite. The solutions of this model are iterated until the wheel reaches periodic steady state operation. The modeling results are obtained as the changes of the outside/process and building exhaust/regeneration air conditions along the wheel depth and the wheel rotation. This performance model relates the wheel’s design parameters, such as the wheel dimension, the channel size and the desiccant properties, and the wheel’s operating variables, such as the rotary speed and the regeneration air flowrate, to its operating performance. The impact of some practical issues, such as wheel purge, residual water in the desiccant and the wheel supporting structure, on the wheel performance has also been investigated.

Experimental Assessment of Roughness Changes in the Cutting Surface and Microhardness Changes of the Material S 355 J2 G3 after Being Cut by Non-Conventional Technologies

2011 ◽  
Vol 314-316 ◽  
pp. 1944-1947 ◽  
Author(s):  
Jozef Maščeník ◽  
Stefan Gaspar
Keyword(s):  
Mechanical Properties ◽  
Production Process ◽  
Laser Plasma ◽  
Manufacturing Process ◽  
Production Quality ◽  
Water Jet ◽  
Cutting Edge ◽  
Experimental Assessment ◽  
Cutting Surface ◽  
The Impact

Production of components, necessary for the construction of the machine resp. or device is a demanding manufacturing process. One of the possibilities of increasing efficiency and production quality is the introduction of unconventional technologies to the production process. Knowing the dependence of the impact of non-conventional technologies on the mechanical properties of products and their subsequent verification is an important aspect when designing and manufacturing them. The article deals with the impact of used unconventional technology, that means laser, plasma and water jet on the roughness of a cutting edge and microhardness of material S 355 J2 G3.

Analysis for the Effect of Inverter Ripple Current on Fuel Cell Operating Condition

2001 ◽  
Author(s):  
Randall S. Gemmen
Keyword(s):  
Boundary Condition ◽  
Fuel Cell ◽  
Mass Transport ◽  
Transient Behavior ◽  
Mechanical State ◽  
Dimensional Model ◽  
One Dimensional ◽  
Fuel Cell Stack ◽  
A Cell ◽  
The Impact

Abstract The effect of inverter ripple current on fuel cell stack performance and stack lifetime remains uncertain. This paper provides a first attempt to examine the impact of inverter load dynamics on the fuel cell. Since reactant utilization is known to impact the mechanical state of a fuel cell, it is suggested that the varying reactant conditions surrounding the cell govern, at least in part, the lifetime of the cells. This paper investigates these conditions through the use of a dynamic model for the bulk conditions within the stack, as well as a one-dimensional model for the detailed mass transport occurring within the electrode of a cell. These two independent modeling approaches help to verify their respective numerical procedures. In this work, the inverter load is imposed as a boundary condition to the models. Results show the transient behavior of the reactant concentrations within the stack, and of the mass diffusion within the electrode under inverter loads with frequencies between 30 Hz and 1250 Hz.

Experimental Analysis of Different Coolants Used in Plasma Cutting Operation for the Improved Electrode Life

2015 ◽  
Vol 719-720 ◽  
pp. 46-49 ◽  
Author(s):  
Ginka Ranga Janardhana ◽  
Mani Senthil Kumar ◽  
B. Dhanasekar
Keyword(s):  
Temperature Rise ◽  
Metal Cutting ◽  
Cooling System ◽  
Heat Removal ◽  
Plasma Cutting ◽  
Life Test ◽  
Flow Rates ◽  
Optimal Flow ◽  
Cutting Operation ◽  
The Impact

The plasma cutting technology has been emerged as a developing technology which finds tremendous potential in fabrication and metal cutting industries. Thus for the cutting operation, the electrode inside the plasma torch plays a vital role for the plasma arc generation. The temperature of the arc is very high and at the electrode is around 3500°C. The cutting torch requires proper cooling system in order to prevent the electrode from quick wear due to the existence of high thermal gradient. The presented work aimed to study the impact of three coolants propylene glycol, ethylene glycol and de-ionized water flow over the electrode life. The experimental setups were arranged to study the heat transfer capabilities of the three coolants for different flow values and aimed to achieve the optimal flow rates for the efficient heat removal. The electrode life test trials were conducted to measure the electrode life for the flow values of three coolants in the temperature rise test. The optimal flow rates arrived from temperature rise test and the electrode life measured from life test are compared for the three coolant cases considered.

scholarly journals Analysis and modeling of the effects of process parameters on specific cutting energy in abrasive water jet cutting

2018 ◽  
Vol 22 (Suppl. 5) ◽  
pp. 1459-1470 ◽  
Author(s):  
Predrag Jankovic ◽  
Milos Madic ◽  
Dusan Petkovic ◽  
Miroslav Radovanovic
Keyword(s):  
Mathematical Model ◽  
Process Parameters ◽  
Water Jet ◽  
Abrasive Water Jet ◽  
Specific Cutting Energy ◽  
Important Indicator ◽  
Cutting Energy ◽  
Water Jet Cutting ◽  
Abrasive Water Jet Cutting ◽  
The Impact

The problem of cutting difficult-to-machine materials used in the aerospace industry, aircraft industry, and automobile industry, led to the development and application one of today?s most attractive technology for contour cutting - abrasive water jet cutting. For the efficient use of abrasive water jet cutting, it is of great importance to analyze the impact of process parameters on performance indicators, such as cutting quality, productivity, and costs. But also, from the energy utilization point of view, it is very important to analyze the impact of these parameters on the specific cutting energy which represents the amount of energy spent on the removal of material in the unit time. Having this in mind, this study presents the experimental results of abrasive water jet cutting of aluminum alloy with the aim of creating a mathematical model for estimating specific cutting energy as an important indicator of the degree of utilization of the available energy in the cutting process. The mathematical model of the specific cutting energy is explicitly represented as a non-linear function of the process parameters, obtained by the artificial neural network.

scholarly journals Deciphering The Molecular Mechanism Of Water Boiling At Heterogeneous Interfaces

2021 ◽  
Author(s):  
Konstantinos Karalis ◽  
Dirk Zahn ◽  
Nikolaos Prasianakis ◽  
Bojan Niceno ◽  
Sergey V. Churakov
Keyword(s):  
Molecular Mechanism ◽  
Heat Removal ◽  
Nucleate Boiling ◽  
Surface Hydrophobicity ◽  
Bubble Nucleation ◽  
Geothermal Systems ◽  
Transition Path ◽  
Nucleation Sites ◽  
Dynamics Simulations ◽  
The Impact

Abstract Water boiling control evolution of natural geothermal systems is widely exploited in industrial processes due to the unique non-linear thermophysical behavior. Even though the properties of water both in the liquid and gas state have been extensively studied experimentally and by numerical simulations, there is still a fundamental knowledge gap in understanding the mechanism of the heterogeneous nucleate boiling controlling evaporation and condensation. In this study, the molecular mechanism of bubble nucleation at the hydrophilic and hydrophobic solid-water interface was determined by performing unbiased molecular dynamics simulations using the transition path sampling scheme. Analyzing the liquid to vapor transition path, the initiation of small void cavities (vapor bubbles nuclei) and their subsequent merging mechanism, leading to successively growing vacuum domains (vapor phase), has been elucidated. The molecular mechanism and the boiling nucleation sites' location are strongly dependent on the solid surface hydrophobicity and hydrophilicity. Then simulations reveal the impact of the surface functionality on the adsorbed thin water molecules film structuring and the location of high probability nucleation sites. Our findings provide molecular-scale insights into the computational aided design of new novel materials for more efficient heat removal and rationalizing the damage mechanisms.

scholarly journals A Short Note about the Impact Action of a Water Jet Stabilized by a Coaxial Air Stream in the Air and Underwater

Materials ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 5015
Author(s):  
Josef Poláček ◽  
Irena Marie Hlaváčová ◽  
Martin Tyč
Keyword(s):  
Near Field ◽  
Pure Water ◽  
Air Flow ◽  
Relevant Literature ◽  
Short Note ◽  
Original Method ◽  
Water Jet ◽  
Impact Action ◽  
Dual Action ◽  
The Impact

A new original method, applying a coaxial protective airflow, was tested aiming to improve the pure water jet efficiency in surface layer removal or medium hard materials cutting or blasting. The dual action of the air flow is expected: the air co-flowing the water jet with approximately the same velocity should prevent the central jet from breaking up into tiny droplets in the near field, and simultaneously, it should support jet decomposition into big parts with enough destructive potential in the far-field. A brief survey of the relevant literature dealing with the water jet instability is presented, introducing four recognized breakup regimes. An original cutting head designed to generate a waterjet surrounded by protective coaxial air flow is introduced. The submitted device is supposed to operate within the first wind-induced regime. Two types of experiments, consisting of blasting limestone bricks placed either in the air or underwater, were realized. The depths of kerfs produced with different water pressures and air overpressures were evaluated. While no substantial positive effect was recognized in the air performance, the submerged blasting of the same material under similar conditions appeared to be promising.

scholarly journals Design and Simulation of Nozzle for Pure Water Jet Portable Cutting Tool

2019 ◽  
Vol 8 (12S2) ◽  
pp. 703-706
Keyword(s):  
Pressure Drop ◽  
Cross Sections ◽  
Pure Water ◽  
Water Jet ◽  
Element Analysis ◽  
Cutting Machine ◽  
Water Jet Cutting ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Through ◽  
The Impact

A pure water jet at subsonic speed provides an opportunity for application in cutting soft material with the advantage of not contaminating the workpiece. Inside the nozzle, water is flowing through various cross sections, which lead to pressure drop and loss of energy. This requires a nozzle with a design that causes minimum pressure drop. In this work, Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) were used to analyse the flow through five different nozzles. For each nozzle, the pressures of 10 MPa, 20 MPa and 30 MPa were applies at the inlet. For the inlet pressure of 10 MPa, the highest outlet velocity us 136.12 m/s at the pressure of 9.261 MPa. The impact pressure at stand distance of 0.5 mm and 1.0 mm were 8.26 MPa and 8.02 MPa, respectively. For this nozzle, the Factor of Safety for 10 MPa, 20 MPa and 30 MPa were 6.4, 3.2 and 2.961, respectively. The findings are relevant to the development of pure water jet cutting machine

scholarly journals Deciphering the molecular mechanism of water boiling at heterogeneous interfaces

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Konstantinos Karalis ◽  
Dirk Zahn ◽  
Nikolaos I. Prasianakis ◽  
Bojan Niceno ◽  
Sergey V. Churakov
Keyword(s):  
Molecular Mechanism ◽  
Heat Removal ◽  
Nucleate Boiling ◽  
Surface Hydrophobicity ◽  
Bubble Nucleation ◽  
Geothermal Systems ◽  
Transition Path ◽  
Nucleation Sites ◽  
Dynamics Simulations ◽  
The Impact

AbstractWater boiling control evolution of natural geothermal systems is widely exploited in industrial processes due to the unique non-linear thermophysical behavior. Even though the properties of water both in the liquid and gas state have been extensively studied experimentally and by numerical simulations, there is still a fundamental knowledge gap in understanding the mechanism of the heterogeneous nucleate boiling controlling evaporation and condensation. In this study, the molecular mechanism of bubble nucleation at the hydrophilic and hydrophobic solid–water interface was determined by performing unbiased molecular dynamics simulations using the transition path sampling scheme. Analyzing the liquid to vapor transition path, the initiation of small void cavities (vapor bubbles nuclei) and their subsequent merging mechanism, leading to successively growing vacuum domains (vapor phase), has been elucidated. The molecular mechanism and the boiling nucleation sites’ location are strongly dependent on the solid surface hydrophobicity and hydrophilicity. Then simulations reveal the impact of the surface functionality on the adsorbed thin water molecules film structuring and the location of high probability nucleation sites. Our findings provide molecular-scale insights into the computational aided design of new novel materials for more efficient heat removal and rationalizing the damage mechanisms.

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