Effects of Briquettes with Different Crack Structures on Propagation Characteristics of Ultrasonic Waves under Wetting Conditions

2020 ◽  
Author(s):  
Gang Wang ◽  
Jinzhou Li ◽  
Huaixing Li ◽  
Zhiyuan Liu ◽  
Yanpei Guo ◽  
...  
Keyword(s):  
Particle Size ◽  
Ultrasonic Velocity ◽  
Bituminous Coal ◽  
Ultrasonic Attenuation ◽  
Crack Size ◽  
Ultrasonic Waves ◽  
Ultrasonic Frequency ◽  
Propagation Characteristics ◽  
Sample Mass ◽  
Velocity Increase

Abstract In order to examine the effect of briquettes with different crack structures on ultrasonic characteristics under different wetting conditions, a series of ultrasonic testing are carried out on briquettes at different wetting heights and the ultrasonic characteristics in these coal samples are explored. The results show that ultrasonic amplitude is positively correlated with the emission voltage, whereas ultrasonic frequency is negatively correlated with the emission voltage. Changes in both are closely related to the particle size and density. The ultrasonic velocity is positively correlated with the wetting degree. Sample mass has the greatest effect on the ultrasonic velocity, followed by particle size, and pressure has the smallest effect. At dry stage, ultrasonic velocity in gas coal is less than that in bituminous coal. The opposite is true in the fully wet state. The influence of crack thickness on ultrasonic velocity gradually increases with the wetting degree increasing. At dry stage, the velocity gradually increases with the crack dip increasing, while as the wetting height increasing, magnitude of velocity increase gradually decreases with the dip increasing. The ultrasonic attenuation in the briquettes reduces with the emission voltage enhancing. The attenuation decreases with sample particle size, crack thickness and crack size decreasing and with sample mass, pressure and crack dip increasing. The ultrasonic attenuation shows a trend of increase before decrease with the wetting height increasing. The attenuation of ultrasonic wave increases with wave velocity increasing for intact samples and shows a trend of increase before decrease for cracked samples.

Ultrasonic Attenuation of Gas-Solid Flow Pneumatic Conveying Fly Ash

2013 ◽  
Vol 437 ◽  
pp. 335-338
Author(s):  
Guang Bin Duan ◽  
Hong Li Pan ◽  
Yong Wang ◽  
Zong Ming Liu
Keyword(s):  
Particle Size ◽  
Fly Ash ◽  
Volume Fraction ◽  
Ultrasonic Attenuation ◽  
Particle Volume Fraction ◽  
Ultrasonic Frequency ◽  
Pneumatic Conveying ◽  
Particle Volume ◽  
Attenuation Coefficients ◽  
Volume Fractions

In order to set solid particle phase distributed uniformly in the whole detection space， the McClements model and Bouguer -Lambert -Beer law model were applied to formulate the ultrasonic attenuation properties of gas-solid flow for pneumatic conveying fly ash. The theoretical relation between the ultrasonic attenuation coefficients and the flow parameters of gas/ solids two-phase flow was established. By numerical simulations, the alteration laws of the ultrasonic attenuation coefficients with particle volume fraction， ultrasonic frequency and particle size were analyzed. The results show that the higher the ultrasonic frequency was, the greater the attenuation coefficients were. The ultrasonic attenuation coefficients linearly increased with the increasing of the solid particles volume fraction. If some fixed frequency was chosen， the slopes of attenuation -volume fractions curves can be confirmed by just testing ultrasonic attenuation coefficients under two volume fractions. So that testing of particle volume fraction corresponding to arbitrarily ultrasonic attenuation coefficients can be achieved. If the fly ash particle sizes were in the domain of 10 -200 μm with the same volume fraction， the ultrasonic attenuation coefficients monotonically decreased with the increasing of the particle size. But if the fly ash particle size was higher than 200 μm， the ultrasonic attenuation coefficients were no longer sensitive to the solids particle size.

Computational Study of 16 kWth Furnace Cofired Using Pulverized Bituminous Coal and Liquified Petroleum Gas Operated in Un-Staged and Air-Staged Conditions

2020 ◽  
Vol 143 (8) ◽  
Author(s):  
Nitesh Kumar Sahu ◽  
Mayank Kumar ◽  
Anupam Dewan
Keyword(s):  
Particle Size ◽  
Coal Particle ◽  
Bituminous Coal ◽  
Computational Study ◽  
Pearson Correlation ◽  
Turbulence Models ◽  
The Other ◽  
Test Facility ◽  
Measured Temperature ◽  
Inlet Swirl

Abstract This paper presents a computational study on air-fuel combustion of bituminous coal and liquified petroleum gas (LPG) in a 16 kWth test facility with a coflow-swirl burner. The performance of three turbulence models is investigated for the furnace operated under both air-staged and un-staged conditions by comparing their predictions with the reported measurements of temperature and species concentrations. This comparison shows that the shear stress transport (SST) k–ω model and SST k–ω model with low-Re correction predict the profiles of temperature and species concentrations reasonably well, but significantly underpredict the temperature in the furnace core at axial locations away from the burner. On the other hand, the transition SST k–ω model provides better overall congruency with the measured temperature and species concentrations when compared with the other turbulence models used, as indicated by relatively higher values of the Pearson correlation coefficient at locations away from the burner. The present high-fidelity computational model developed is also capable of accurately simulating the effect of coal particle size on the furnace environment, which is verified by the match between the computational predictions and the experimental results for two different sized coal samples. The model is also used to investigate the effect of coal particle size on the internal recirculation zone (IRZ) and the reattachment length (LR) for the same inlet swirl number (SN). A decrease of nearly 50% in the coal sample size results in the increase of LR and IRZ length by 20% and 82.6%, respectively.

NDE of Structural Ceramics

1986 ◽  
Author(s):  
Stanley J. Klima ◽  
Alex Vary
Keyword(s):  
Silicon Carbide ◽  
Silicon Nitride ◽  
Ultrasonic Velocity ◽  
Detection Probability ◽  
Ultrasonic Attenuation ◽  
Acoustic Microscopy ◽  
Modulus Of Rupture ◽  
Structural Ceramics ◽  
X Ray ◽  
Microscopy Techniques

Radiographic, ultrasonic, scanning laser acoustic microscopy (SLAM), and thermo-acoustic microscopy techniques were used to characterize silicon nitride and silicon carbide modulus-of-rupture test specimens in various stages of fabrication. Conventional and microfocus x-ray techniques were found capable of detecting minute high density inclusions in as-received powders, green compacts, and fully densified specimens. Significant density gradients in sintered bars were observed by radiography, ultrasonic velocity, and SLAM. Ultrasonic attenuation was found sensitive to microstructural variations due to grain and void morphology and distribution. SLAM was also capable of detecting voids, inclusions, and cracks in finished test bars. Consideration is given to the potential for applying thermo-acoustic microscopy techniques to green and densified ceramics. The detection probability statistics and some limitations of radiography and SLAM also are discussed.

Fuel Flexible Biomass Reburn Technology

2009 ◽  
Author(s):  
Guang Xu ◽  
Wei Zhou ◽  
Larry Swanson
Keyword(s):  
Particle Size ◽  
Bituminous Coal ◽  
Nox Reduction ◽  
Unburned Carbon ◽  
Gas Temperature ◽  
Mean Particle Size ◽  
High Volatility ◽  
Order Of Magnitude ◽  
Char Reactivity ◽  
Computational Fluid Dynamics Cfd

Biomass reburn is a low NOx alternative to cofiring that effectively uses the high volatility and high char reactivity of biomass for NOx reduction. In this paper, computational fluid dynamics (CFD) and thermal modeling, and a NOx prediction model were used to evaluate the impacts of sawdust/coal reburn on the performance of a 250 MW opposed-fired boiler burning bituminous coal as the primary fuel. The results showed that the reburn system maintained overall boiler performance with a 50 – 70 °F reduction in the furnace exit gas temperature. Predicted losses in thermal efficiency were caused by the lower biomass fuel heating value (similar to biomass cofiring) and increase in unburned carbon. The higher unburned carbon emissions were attributed to an order of magnitude larger biomass mean particle size relative to bituminous coal. Thus, LOI emissions can be improved significantly by reducing the biomass mean particle size. The NOx predictions showed that for reburn rates above about 19%, adding dry sawdust biomass to a coal reburn system can improve NOx reduction; i.e., using pure dry sawdust as reburn fuel at 30% of the total heat input can lead to NOx levels about 30% less than those for pure coal reburn under for similar firing conditions.

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