Search

The impact of supercritical CO2 transient high-pressure fracturing on coal pore structure is studied here. This examination uses a CO2 fracturing test platform to obtained coal samples at fracturing pressures of 22.6, 26.7, and 30.6 MPa, and we investigated the effects of CO2 transient high-pressure impacts on the pore structure of the coal by means of low-temperature N2 adsorption experiments and CO2 adsorption experiments. The results demonstrate that the specific surface area of the coal samples increased by 60.4%, 200.7%, and 92.6%, and the cumulative total pore volume increased by 56%, 267%, and 77.8% under the pressure impacts of 22.6, 26.7, and 30.6 MPa, with a significant increase in the number of pores. The original pore morphology of coal can be changed by the supercritical CO2 transient high-pressure impact, and the creation of new pores across the whole pore diameter section can be catalyzed. The impact fracturing on the pore structure is mainly attributed to the impact of supercritical CO2 and extraction. The meso-pores and macro-pores of the coal are further expanded by the impact of supercritical CO2, while the micro-pores with chemical properties are primarily modified by the extraction. An impact pressure of 26.7 MPa has a more pronounced effect on the expansion of meso-pores and macro-pores, and its effect on micro-pores is less significant compared to that of the other two fracturing samples. Therefore, it is possible that a specific fracturing pressure can more effectively expand meso-pores and macro-pores while reducing the impact on micro-pores. [ABSTRACT FROM AUTHOR]

Due to the non-streamlined blunt body shape of the elevator car, intense aerodynamic loads and noise are generated in the annular space when the elevator operates at high speed in a narrow hoistway. This article uses large-eddy simulation and Curle acoustic theory to establish a numerical model of the wellbore flow field under different guiding shapes of the elevator car. First, the mechanism of action between the flow guide shape, vortex characteristics, and aerodynamic load was studied, and the influence of operating speed on aerodynamic load under different flow guide shapes was analyzed. Second, the distribution and spectral characteristics of noise in the annular space under different flow guide shapes were studied from the near field and far field scales. Finally, it can be concluded that increasing the guide surface can significantly reduce the pressure difference between the upper and lower parts of the car, weakening the separation of the tail airflow. The number of guide surfaces, installation position, and vertex offset significantly impact drag and lateral force, with the optimal reduction of 34.65% and 57.6%, respectively. The maximum sound source intensity of near-field noise is mainly concentrated at the arc transition in the upper part of the annular space, and the frequency is mainly concentrated in the range of 500–1000 Hz. The sound pressure level is linearly related to the logarithm of the longitudinal distance, and the noise attenuation speed becomes faster with the increase in the number of guiding surfaces. [ABSTRACT FROM AUTHOR]

The absolute response of the GE Amersham Typhoontm imaging plate scanner is studied in this paper. The sensitivity function of the scanner with different photomultiplier tube voltages was obtained by using a pre-calibrated Cu Kα x-ray tube. The results showed that the sensitivity function decreases exponentially with higher voltage and is also affected by the scanning pixel size. The spatial resolution and the fading effect of the imaging plate system on x rays were also investigated and compared with the previous scanner models. [ABSTRACT FROM AUTHOR]

A vibration-assisted polishing device (VAPD) composed of leaf-spring and right-circular flexure hinges is proposed with the aim of realizing vibration-assisted machining along elliptical trajectories. To design the structure, energy methods and the finite-element method are used to calculate the performance of the proposed VAPD. An improved bacterial foraging optimization algorithm is used to optimize the structural parameters. In addition, the performance of the VAPD is tested experimentally. The experimental results indicate that the maximum strokes of the two directional mechanisms operating along the Z1 and Z2 directions are 29.5 μm and 29.3 μm, respectively, and the maximum motion resolutions are 10.05 nm and 10.01 nm, respectively. The maximum working bandwidth is 1,879 Hz, and the device has a good step response. [ABSTRACT FROM AUTHOR]