Three Dimensional Computational Study for Spiral Dry Gas Seal with Constant Groove Depth and Different Tapered Grooves

AbstractThe three dimensional simulation for dry gas seal with constant depth spiral grooves and with different taper grooves is done using ANSYS FLUENT CFD code. Grid independence study and code validation are done with experimental work. The fluid state effect on the gas seal internal flow and performance is studied. The laminar and turbulent flow with RNG K-ɛ turbulence model and LES is examined for the same geometrical and operating conditions. The influence of film thickness for constant depth groove gas seal is simulated for 2, 3 and 4μm film. The effect of different rotational speeds on gas seal performance is examined for 0, 2500, 5000, 7500 and 10380rpm. Three taper spiral grooves are studied each with three different angles, including taper grooves in the radial, circumferential and combined radial-circumferential directions. The laminar flow simulation for the dry gas seal agree well with the experimental results more than the turbulent flow simulation which overestimate the pressure distribution inside the seal. The results indicate that as the rotational speed increases the seal open force and leakage increase. The use of tapered type spiral groove causes a reduction in the seal open force and the leakage rate. Increasing the angle of radial taper groove reduces the temperature distribution inside the gas film. The reduction in seal open force and leakage rate is higher when the combined radial-circumferential taper is more than radial and circumferential taper used

TiO2 nanotubes with ultrathin walls for enhanced water splitting

We demonstrate, for the first time, the synthesis of titania nanotubes with ultrathin (3–5 nm) wall thickness. As revealed by the incident photon-to-current collection efficiency (IPCE) and electrochemical impedance spectroscopy measurements, the ultrathin walls, less than the charge carrier diffusion length, were essential to ensure fast and efficient charge carrier collection.Qatar National Research Fund, a member of Qatar Foundation NPRP Grant no. 6-569-1-11

On the aero acoustic and internal flows structure in a centrifugal compressor with hub side cavity operating at off design condition

This paper covers the characterization of the acoustic noise and the unsteady flow field of a high speed centrifugal compressor NASA CC3. In order to accurately predict the noise, all analyses are carried out through the use of Large Eddy Simulation and Ffowcs Williams–Hawkings model for noise prediction. The relative effect of hub cavity on flow characteristics and sound levels is investigated, for a compressor stage with a total pressure ratio equal to 4, working from surge to near choke condition. In comparison with the experimental results from literature, the predicted compressor performance and flow field are predicted well, some trends seen in experiments are captured. The hub cavity flow effect on the compressor aero acoustic generated noise is shown in the paper. The unsteady static pressure and sound pressure levels are compared not only at different location but also for design and off design operating points. The internal flow results inside the hub cavity are presented at surge, design and near choke points. The conclusion is that the cavity effect of the centrifugal compressor cannot be ignored in the numerical prediction of aerodynamic generated noise. The impeller back plate of the rotor experiences a strong pressure fluctuation, which is maxima at the impeller outer radius for all operating point, but higher pressure values at the surge point.This publication was made possible by NPRP grant No. 4-651-2-242 from the Qatar National Research Fund (a member of Qatar Foundation)

Centrifugal Compressor Spiral Dry Gas Seal Simulation Working at Reverse Rotation

Unidirectional dry gas seal may experiences reverse rotation when equipped in a centrifugal compressor. This paper describes how the reverse rotation effects on the spiral unidirectional dry gas seal performance and pressure distribution inside the gas film, also an investigation of using a different herringbone shape grooves configurations has been done using ANSYS FLUENT 14.5 CFD simulation. The influence of decreasing rotational speed to the static condition and rotate in the reverse direction on internal flow and gas seal performance is examined from 10800 to -10380rpm. The results indicate that the internal pressure distribution inside the gas seal in reverse rotation is decreased and the open force consequently decreased by 4%. The modification on the same seal is done to enhance its performance at reverse rotation condition. The herringbone spiral grooves is used with different configuration, the new configurations are examined in the forward and reverse rotation direction. The analysis for the pressure distribution is done and its effect on the seal performance is examined. Seal performance is compared with standard one for all geometrical and operating conditions. At high forward rotational speed 10380rpm, the pressure at the end of the spiral groove is about 11.4% higher than the inlet pressure at the seal outer diameter, while at reverse rotation, the pressure is not increased in radial direction. The open force corresponding to reverse rotation increased with a value 1.5kN for both the 100 overlap and 50% forward overlap seal faces, but using seal face with 50% backward overlap failed to enhance the open force at reversal condition.This publication was made possible by NPRP grant No. 4-651-2-242 from the Qatar National Research Fund (a member of Qatar Foundation)

An efficient eco advanced oxidation process for phenol mineralization using a 2D/3D nanocomposite photocatalyst and visible light irradiations

Nanocomposites (CNTi) with different mass ratios of carbon nitride (C3N4) and TiO2 nanoparticles were prepared hydrothermally. Different characterization techniques were used including X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), transmission electron spectroscopy (TEM) and Brunauer-Emmett-Teller (BET). UV-Vis DRS demonstrated that the CNTi nanocomposites exhibited absorption in the visible light range. A sun light-simulated photoexcitation source was used to study the kinetics of phenol degradation and its intermediates in presence of the as-prepared nanocomposite photocatalysts. These results were compared with studies when TiO2 nanoparticles were used in the presence and absence of H2O2 and/or O3. The photodegradation of phenol was evaluated spectrophotometrically and using the total organic carbon (TOC) measurements. It was observed that the photocatalytic activity of the CNTi nanocomposites was significantly higher than that of TiO2 nanoparticles. Additionally, spectrophotometry and TOC analyses confirmed that degraded phenol was completely mineralized to CO2 and H2O with the use of CNTi nanocomposites, which was not the case for TiO2 where several intermediates were formed. Furthermore, when H2O2 and O3 were simultaneously present, the 0.1% g-C3N4/TiO2 nanocomposite showed the highest phenol degradation rate and the degradation percentage was greater than 91.4% within 30 min. 1 2017 The Author(s).Scopu

Three Dimensional Computational Study for Spiral Dry Gas Seal with Constant Groove Depth and Different Tapered Grooves

The three dimensional simulation for dry gas seal with constant depth spiral grooves and with different taper grooves is done using ANSYS FLUENT CFD code. Grid independence study and code validation are done with experimental work. The fluid state effect on the gas seal internal flow and performance is studied. The laminar and turbulent flow with RNG K-ɛ turbulence model and LES is examined for the same geometrical and operating conditions. The influence of film thickness for constant depth groove gas seal is simulated for 2, 3 and 4μm film. The effect of different rotational speeds on gas seal performance is examined for 0, 2500, 5000, 7500 and 10380rpm. Three taper spiral grooves are studied each with three different angles, including taper grooves in the radial, circumferential and combined radial-circumferential directions. The laminar flow simulation for the dry gas seal agree well with the experimental results more than the turbulent flow simulation which overestimate the pressure distribution inside the seal. The results indicate that as the rotational speed increases the seal open force and leakage increase. The use of tapered type spiral groove causes a reduction in the seal open force and the leakage rate. Increasing the angle of radial taper groove reduces the temperature distribution inside the gas film. The reduction in seal open force and leakage rate is higher when the combined radial-circumferential taper is more than radial and circumferential taper used.This publication was made possible by NPRP grant No. 4-651-2-242 from the Qatar National Research Fund (a member of Qatar Foundation)

Optimization Of The Electronic And Optical Properties Of Tio2 For Clean Fuel Production

Among different crystal structures and morphologies of TiO2, vertically oriented anatase nanotube arrays show the highest activity for solar energy conversion. However, the long-standing bottleneck is the fact that TiO2 is a wide band gap semiconductor, limiting its activation to the deep-blue and ultraviolet spectral region that contains but a small fraction (5%) of the incident solar energy. Herein, density functional theory (DFT) has been used to compare between density of states of bulk and nanotube forms of TiO2 by using different concentrations of N atoms. The wave functions were described using two different techniques; linear combination of atomic orbital (LCAO) and plane wave. Our results showed a shift in the calculated bandgap for bulk TiO2 only for small concentrations of N atoms as dopant. For TiO2 nanotube, the bandgap decreases as the concentration of N atoms increases. The effect of the diameter of TiO2 nanotubes on their optical and structural properties has also been investigated and discussed in details. Our study presents a protocol to fine tune the optical, electronic and structural properties of TiO2 for energy conversion applications.qscienc

Promoting cycling activities in the State of Qatar: Challenges and potential treatments

In the last few decades, cycling has received an increased attention due to its health, social, and economical benefits. Many countries are adopting different policies to encourage cycling as a daily mode of transport. In this paper, the main barriers and motivators to cycling and their relation to demographic factors were investigated. In addition, main trip purposes of cycling and the effect of seasonal variation on trips duration were studied in the State of Qatar. Data was obtained through questionnaire by interviewing 272 respondents. Descriptive statistics and correlations were conducted to investigate the causal relationships. Most of the respondents reported that they cycle for exercise/leisure purpose. Due to weather conditions, cyclists are willing to cycle more in the winter season compared to summer for all trip purposes. Results also revealed a significant relation between different barriers/motivators and demographic factors such as gender, age and ethnicity. The results of this study could be beneficial to policymakers in identifying the main barriers and motivators for the public in order to promote cycling.Qatar University Student Grant [QUST-1-CENG-2022-384

Exploring Crowd Management and Evacuation Strategies using Microscopic Pedestrian Simulation: A Case Study of Souq Waqif

Safe egress plans are critical for crowd evacuation at touristic attractions, particularly during special events, as visitors are often unaware of their options. Identification of bottlenecks in the walking spaces are vital for the development of safe and efficient crowd management and evacuation plans. This paper aims to explore crowd management and evacuation strategies for pedestrian egress flow in Souq Waqif, which is a famous touristic attraction in Doha, under varying crowd demand conditions. PTV Viswalk pedestrian simulation tool was used to evaluate crowd evacuation strategies and identify potential bottlenecks during the egress of crowds. Several guided and unguided evacuation scenarios were developed to understand the egress patterns to the allocated assembly areas inside the Souq. The crowd demands and densities were estimated using publicly available data. Eight major locations were identified as the bottleneck during the simulation. Simulation outcomes highlighted that the current evacuation plans and assembly locations are inadequate in providing safe evacuation routes. However, guided scenarios reduced evacuation times considerably when compared to unguided scenarios, particularly when the demand is high. A sensitivity analysis was also conducted to identify the effect of variations in walking behavior parameters in the simulation model. Variations in the walking behavior parameters changed the evacuation times considerably. Thus, proper calibration of walking behavior parameters considering local conditions could improve simulation accuracy. This study helps to identify probable bottlenecks and their characteristics that could help policymakers to assess the effectiveness of evacuation plans and crowd management strategies for crowd safety

Autonomous vehicles between anticipation and apprehension: Investigations through safety and security perceptions

Due to the ongoing enormous infrastructural developments and car ownership culture in Qatar, it could be one of those countries to introduce Autonomous Vehicles (AV) technology at the early stages. Therefore, this study surveyed a number of residents at the State of Qatar to improve our understandings of their perceptions regarding overall safety of AV (General_safety), safety due to the fact that AV could eliminate human errors (Human_errors), safety due to the interactions between Human-Driven Vehicles (HDV) and AV (HDV-AV_interactions), performance in harsh environmental conditions, security, comfort level, travel time, congestion and operational costs. In addition, the study uncovered the relationships of public perceptions towards AV and some other contextual factors with the willingness to adopt it in the future. To study these relations, we relied on a Structural Equation Modeling. Overall, the results showed that respondents had higher and positive perceptions regarding “General_safety” and “Human_errors”, however, they were more concerned about “HDV-AV_interactions” and its security. In addition, individuals’ preference to shift to AV in the future was positively correlated with their perception level of “General_safety”, “Human_errors”, Comfort and Travel_time. Regarding ethnicity of the respondents, non-Arabs reported higher concerns regarding AV security, compared to Arabs. Furthermore, interestingly the results revealed that individuals having higher knowledge about AV technology had more concerns on “General_safety” and “HDV-AV_interactions”, while they had positive perceptions that AV could eliminate human errors. The findings from this study are anticipated to allow AV manufacturers and other relevant authorities to enhance public confidence towards AV technology by targeting different sub-groups through particular safety or security awareness campaigns.The Qatar–Japan Research Collaboration Application Award [M-QJRC-2020-8] from Qatar University. Open Access funding provided by the Qatar National Library