scholarly journals Microscopic Imaging Spray Diagnostics under High Temperature Conditions: Application to Urea–Water Sprays

2019 ◽  
Vol 9 (20) ◽  
pp. 4403 ◽  
Author(s):  
Christian Lieber ◽  
Rainer Koch ◽  
Hans-Jörg Bauer
Keyword(s):  
High Temperature ◽  
Turbulent Flows ◽  
Gas Flow ◽  
Catalytic Reduction ◽  
Operating Conditions ◽  
Turbulent Dispersion ◽  
Temperature Conditions ◽  
Astigmatism Correction ◽  
Water Sprays ◽  
Set Up

The quantitative investigation of droplet laden turbulent flows at high temperature conditions is of great importance for numerous applications. In this study, an experiment was set up for investigation of evaporating urea–water sprays, which are relevant for the effective reduction of nitrogen oxide emissions of diesel engines using Selective Catalytic Reduction. A shadowgraphy setup is pushed to its limits in order to detect droplet diameters as small as 4 m and droplet velocities up to 250 m / s . In addition, the operating conditions of the gaseous flow of up to 873 K and 0 . 6 M Pa are an additional challenge. Due to the high temperature environment, image quality is prone to be compromised by Schlieren effects and astigmatism phenomena. A water-cooled window and an astigmatism correction device are installed in order to correct these problems. The results to be presented include characteristics of the turbulent gas flow as well as detailed spray characteristics at different positions downstream of the atomiser. It is demonstrated that the velocity of the gas can be approximated by the velocity of the smallest detectable droplets with sufficient accuracy. Furthermore, the statistical analysis of velocity fluctuations provides data for predicting the turbulent dispersion of the droplets.

A 3D Numerical Investigation on Droplets Distribution in a Wave-Plate Separator

2013 ◽  
Vol 842 ◽  
pp. 522-529
Author(s):  
Yong Lei Qu ◽  
Shi Bu ◽  
Bo Wan
Keyword(s):  
Gas Flow ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Geometrical Model ◽  
Turbulent Dispersion ◽  
Liquid Loading ◽  
Wave Plate ◽  
Gas Liquid Flow ◽  
Set Up ◽  
Plate Separator

The gas-liquid flow in a wave-plate separator is extremely complex due to its three-dimensional characteristic. Numerical simulation accomplished by former investigators using two-dimensional model may be appropriate for the iteration of pressure drop, but they were far from accurate in prediction of removal efficiency. To fill the gap, a three dimensional geometrical model of wave-plate separator is set up in this paper, RNG k-ε model is employed to compute the gas phase flow field, and the droplet trajectories were predicted applying the Lagrangian method. The turbulent dispersion of droplets were simulated by discrete random walk model. Using the assumption of a constant liquid loading of gas flow, simulation were accomplished for six different inlet velocities and two different droplet sizes. The influence pattern of gravity together with gas velocity on droplets distribution and the overall removal efficiencies were obtained.

scholarly journals Discussion on Water Condensation in Membrane Pores during CO2 Absorption at High Temperature

Membranes ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 407
Author(s):  
Zhe Phak Chan ◽  
Lin Li ◽  
Guodong Kang ◽  
Norfaizah Ab Manan ◽  
Yiming Cao ◽  
...  
Keyword(s):  
High Temperature ◽  
Gas Flow ◽  
Accumulation Rate ◽  
Co2 Absorption ◽  
Experimental Conditions ◽  
Knock Out ◽  
Membrane Pores ◽  
Water Condensation ◽  
Temperature Conditions ◽  
Membrane Wetting

Water condensation is a possible cause of membrane wetting in the operation of membrane contactors, especially under high-temperature conditions. In this study, water condensation in pores of polytetrafluoroethylene (PTFE) hollow fiber membranes was investigated during high-pressure CO2 absorption around 70 °C. It was found that the liquid accumulation rate in the treated gas knock-out drum was constant during continuous operation for 24 h when all experimental conditions were fixed, indicating a stable degree of membrane wetting. However, as the operating parameters were changed, the equilibrium vapor pressure of water within membrane pores could change, which may result in a condensation-conducive environment. Water condensation in membrane pores was detected and proven indirectly through the increase in liquid accumulation rate in the treated gas knock-out drum. The Hagen–Poiseuille equation was used to correlate the liquid accumulation rate with the degree of membrane wetting. The degree of membrane wetting increased significantly from 1.8 × 10−15 m3 to 3.9 × 10−15 m3 when the feed gas flow rate was reduced from 1.45 kg/h to 0.40 kg/h in this study due to water condensation in membrane pores. The results of this study provide insights into potential operational limitations of membrane contactor for CO2 absorption under high-temperature conditions.

Structure, properties and oxidation resistance of prospective HfB2–SiC based ceramics

2020 ◽  
pp. 41-54
Author(s):  
Yu. S. Pogozhev ◽  
A. Yu. Potanin ◽  
S. I. Rupasov ◽  
E. A. Levashov ◽  
V. A. Volkova ◽  
...  
Keyword(s):  
Silicon Carbide ◽  
High Temperature ◽  
Oxidation Resistance ◽  
Hot Pressing ◽  
Plasma Torch ◽  
Gas Flow ◽  
Operating Conditions ◽  
Average Particle ◽  
Hafnium Diboride ◽  
Protective Oxide

The paper focuses on obtaining a heterophase powdered and sintered ceramics based on hafnium diboride and silicon carbide by combined self-propagating high-temperature synthesis (SHS) and hot pressing (HP). The structure of the synthesized SHS powder consists of hafnium diboride grains and agglomerated polyhedral 2–6 μm silicon carbide grains. The powders obtained had an average particle size of ~10 μm with a maximum value of 30 μm. Phase compositions were identical for the ceramics sintered by hot pressing and the synthesized powder. The resulting compact featured by a high degree of structural and chemical uniformity, porosity of 3.8 %, hardness of 19.8±0.4 GPa, strength of 597±59 MPa, and fracture toughness of 8.8±0.4 MPa·m1/2. Plasma torch testing (PTT) was carried out to determine the oxidation resistance under the influence of a high-enthalpy gas flow. The phase composition and surface microstructure of the compact after testing were investigated. The HP compact demonstrated an outstanding resistance to the high-temperature gas flow at 2150 °С and heat flow density of 5.6 MW/m2 for 300 s. A dense protective oxide layer 30–40 μm thick was formed on the surface of HfB2–SiC ceramics during the plasma torch testing. The layer consisted of a scaffold formed by HfO2 oxide grains with a space between them filled with SiO2–B2O3 amorphous borosilicate glass. The HfB2–SiC SHS composite powder was hot pressed to produce experimental samples of model bushings for the combustion chamber of a low thrust liquid rocket engine designed for PTT in the environment close to actual operating conditions.

scholarly journals Comparison of a One-Dimensional Model of a High-Temperature Solid-Oxide Electrolysis Stack With CFD and Experimental Results

2005 ◽  
Author(s):  
J. E. O’Brien ◽  
C. M. Stoots ◽  
J. Stephen Herring ◽  
G. L. Hawkes
Keyword(s):  
High Temperature ◽  
Gas Flow ◽  
Operating Conditions ◽  
Operating Voltage ◽  
Dimensional Model ◽  
One Dimensional ◽  
Constant Flow Rate ◽  
High Temperature Steam ◽  
The One ◽  
Increasing Temperature

A one-dimensional model has been developed to predict the thermal and electrochemical behavior of a high-temperature steam electrolysis stack. This electrolyzer model allows for the determination of the average Nernst potential, cell operating voltage, gas outlet temperatures, and electrolyzer efficiency for any specified inlet gas flow rates, current density, cell active area, and external heat loss or gain. The model includes a temperature-dependent area-specific resistance (ASR) that accounts for the significant increase in electrolyte ionic conductivity that occurs with increasing temperature. Model predictions are shown to compare favorably with results obtained from a fully 3-D computational fluid dynamics model. The one-dimensional model was also employed to demonstrate the expected trends in electrolyzer performance over a range of operating conditions including isothermal, adiabatic, constant steam utilization, constant flow rate, and the effects of operating temperature.

scholarly journals Predicting performance of a thermal shield of a spacecraft in a high-temperature gas flow

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Lyudmila Ivanovna Gracheva
Keyword(s):  
High Temperature ◽  
Gas Flow ◽  
Experimental Studies ◽  
Theory Of Elasticity ◽  
Operating Conditions ◽  
Stress Distributions ◽  
Thermal Shield ◽  
Predicting Performance ◽  
Temperature Heating ◽  
High Temperature Gas

A fundamental understanding of the mechanism of material interaction with a medium is based on correspondence between experimental studies and actual operating conditions of a given model or a structure. We estimated performance of thermal shield structures based on computations brought about considering physical properties of materials obtained under conditions simulating re-entry of a spacecraft into the atmosphere.A thermal shield is considered of a layered type shell, made of fiber glass with phenol-phormaldehide matrix. Both elastic and thermo-physical characteristics are varied depending on the temperature change.A thermal-stressed state of a cylindrical shield subjected to action of a high-temperature gas flow, is defined based on solving a 3D problem simultaneously using equations of theory of elasticity, thermal conductivity, and numerical analysis. Results are given as dependencies of stress distributions through the thermal coating, taking into account such parameters of atmosphere in re-entry as temperature, heating rate, pressure of a gaseous medium.

Mixing Design for Air Agitated Rectangular Tanks

1980 ◽  
Vol 15 (1) ◽  
pp. 1-16
Author(s):  
W. Akhtar ◽  
G.P. Mathur ◽  
D.S. Dickey
Keyword(s):  
Convective Flow ◽  
Large Scale ◽  
Gas Flow ◽  
Liquid Velocity ◽  
Mixing Time ◽  
Waste Water Treatment ◽  
Operating Conditions ◽  
Turbulent Dispersion ◽  
Mixing Times ◽  
Tank Geometry

Abstract Design equations have been developed to estimate liquid velocities and mixing times in air agitated tanks. Determination of the gas rate necessary for adequate agitation in a given geometry is possible with this information. Air agitation offers benefits of increased dissolved oxygen and cost effective mixing for some waste water treatment applications. Empirical expressions for surface and bottom velocities, as a function of gas flow rate and tank geometry have been developed from laboratory measurements. Since neither statistical nor dimensional analysis of the laboratory results could prove conclusively the correct form of the velocity correlations, the different correlation forms were used to verify large scale velocity measurements. Only one of the three trial correlations correctly predicted large scale velocities. The importance of these velocity correlations is evident from experience with mechanical agitator design, which shows that liquid velocity is the appropriate design criterion for most similar applications. Mixing times were measured experimentally in the laboratory and studied with a mathematical model. The model was an unsteady state mass balance containing convective flow terms with turbulent dispersion super-imposed on the flow. The velocities for the convective flow terms were calculated from the empirical velocity correlations. Estimates of the turbulent dispersion coefficients were investigated experimentally. Because multiple velocity correlations and a computer model for mixing time are difficult to use when performing design calculations, empirical correlations for bulk velocity and mixing time were derived. Combined with a relationship for power input, the design correlations provide information necessary to determine operating conditions in large scale, air agitated tanks. The effects of tank geometry on air agitated design have been explored within a range of typical construction dimensions. Thus, the principal elements of a complete design approach to air agitated rectangular tanks are presented.

DISPERSED PHASE VELOCITY IN A HIGH-TEMPERATURE GAS FLOW

2019 ◽  
Vol 23 (4) ◽  
pp. 319-328
Author(s):  
Dmitry V. Nesterovich ◽  
Oleg G. Penyazkov ◽  
Yu. A. Stankevich ◽  
M. S. Tretyak ◽  
Vladimir V. Chuprasov ◽  
...  
Keyword(s):  
High Temperature ◽  
Phase Velocity ◽  
Gas Flow ◽  
Dispersed Phase ◽  
High Temperature Gas

Passive Auto-Focus Algorithm for Correcting Image Distortions Caused by Gas Flow in High-Temperature Measurements of Surface Phenomena

2012 ◽  
Vol 17 (4) ◽  
pp. 379-384 ◽  
Author(s):  
Krzysztof Strzecha ◽  
Tomasz Koszmider ◽  
Damian Zarębski ◽  
Wojciech Łobodziński
Keyword(s):  
High Temperature ◽  
Gas Flow ◽  
Temperature Measurements ◽  
Surface Phenomena ◽  
Auto Focus ◽  
High Temperature Measurements

Abstract In this paper, a case-study of the auto-focus algorithm for correcting image distortions caused by gas flow in high-temperature measurements of surface phenomena is presented. This article shows results of proposed algorithm and methods for increasing its accuracy.

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