Showing papers by "Iran University of Science and Technology published in 2022"

Numerical and experimental simulation of gas-liquid two-phase flow in 90-degree elbow

Abstract: In the present research, the effects of four 90-degree horizontal elbows with different curvature radii (17, 34, 51, and 68 cm) and an identical rectangular cross-section (20 * 34 mm) on a gas–liquid slug flow pattern have been studied experimentally and numerically. Gas and liquid superficial velocities in numerical and experimental parts were set in 2.5 m/s and 0.44 m/s, respectively. In the computational fluid dynamics section, the distribution of volume fraction, velocity, pressure, turbulence intensity, and swirling intensity parameters were investigated using the VoF model and the SST k-ω method. Experimental studies were conducted utilizing pressure data and signal processing tools to study the dominant frequency of slug flow alongside bandwidth distribution as well as the Shannon entropy. The results exhibited that although the dominant frequency of slug flow did not change after passing the 90-degree elbow, the frequency signal's bandwidth increased. In this regard, the application of Shannon entropy quantity revealed that the frequency distribution signal experienced a greater increase in bandwidth as the elbows’ curvature radius increases. The turbulent intensity of the elbows’ outlet reveals that by increasing the curvature radius, the flow field behaves smoother. Also, swirling intensity distribution shows that decreasing the elbow radius leads to increment in the swirling intensity.

Design and validation of simple bend beam specimen for covering the full range of I+II fracture modes

Abstract: Using short beam specimen containing an edge crack (perpendicular to the beam axis) and subjected to asymmetric three-point bend loading a new test configuration (called ASBB) was suggested for investigating the mixed mode I/II fracture. Despite the conventional beam specimen with high aspect ratio of length to width that is not able to produce mode II or dominantly mode II conditions, complete mode mixities were obtained using the proposed three-point bend asymmetric short beam specimen. The fracture parameters including modes I and II stress intensity factors and T-stress were determined numerically for this test specimen with different crack lengths and bottom rollers distances relative to the crack. The practical ability of the ASBB specimen was examined experimentally by conducting several mixed-mode I/II fracture tests on PMMA material. The critical stress intensity factors, the direction of fracture kinking and the path of fracture trajectory were investigated both experimentally and theoretically using MTS and GMTS criteria. The fracture toughness of PMMA tested with the ASBB specimen was increased by increasing the contribution of mode II component. The effects of beam length aspect ratio, crack type and loading type on the mixed mode fracture of cracked beam samples subjected to three-point bend loading were also examined.

Photocatalytic hydrogen generation using colloidal covalent organic polymers decorated bimetallic Au-Pd nanoalloy (COPs/Pd-Au)

Abstract: Photocatalytic H2 generation has been considered as an effective method for H2 generation, in which the cocatalysts play a critical role. Here, we report highly reactive nanocomposites composed of two-dimensional triazine-based covalent organic Polymers (COPs), Pd and Au nanocomponents which is designed to benefit from the alloying and visible light illumination effects as well as LSPR effect. Photocatalytic hydrogen production was achieved under low-cost visible light-driven. The COP/Pd-Au exhibited higher photocatalytic outstanding turnover frequency of 260.5 h − 1, which was 1.47 times of that under no light (177.3 h − 1). Additionally, it exhibits much advanced catalytic performance, which is 2.83-fold that of COP/Pd (91.98 h − 1) and 434.17-fold that of COP/Au (0.60 h − 1), under the similar reaction conditions. The great photocatalytic activity for COP/Pd-Au was also ascribed to the strong interface between Pd-Au NPs and COPs, and the preparation of single hollow construction of Pd-Au alloy with porous nature that presented active sites for hydrogen production.

Oxygen and nitrogen enriched pectin-derived micro-meso porous carbon for CO₂ uptake

Abstract: Oxygen and nitrogen enriched micro-meso porous carbon powders have been prepared from pectin and melamine as oxygen and nitrogen containing organic precursors, respectively. The synthesis process has been performed following a solvothermal approach in an alkaline solution during which Pluronic F127 was added to the solution as the soft template. Following the solvothermal treatment, the carbonization process has been performed at 700, 850 and 950 °C. The synthesized porous carbons have been characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption isotherms and Fourier transform infrared spectroscopy (FTIR). The surface area of 499.5 m2 g-1, total pore volume of 0.35 cm3 g-1, and a high nitrogen and oxygen content of 9.3 and 29.1 wt% are displayed for the fine sample. The optimal porous carbon had CO2 adsorption of up to 3.1 mmol g-1 at 273 K at 1 bar owing to abundant basic nitrogen-containing functionalities and the valuable micro-meso porous structure. Despite the absence of any reagent and also having a relatively moderate specific surface area, compared to similar materials, a very high ratio of adsorption capacity to specific surface area (6.2 μmol m-2) was observed. The Elovich kinetic model was found to be the best and the physisorption process was reported.