Role of physical and chemical properties of single and multicomponent liquid fuels on spray processes, flame stability, and emissions, The

2019 Fall.Includes bibliographical references.Ensuring reliable and clean combustion performance of IC engines, such as liquid-fueled gas turbines, is associated to our understanding of the impact of fuel composition and properties, as well as the processes that the liquid fuel experiences, e.g., atomization, vaporization, turbulent mixing, and chemical kinetics, on the combustion efficiency, stability, and emissions. This understanding is a key prerequisite to the development of fuel surrogates and the deployment of alternative jet fuels. Most of the surrogate formulation activities, especially with regard to aviation fuels, have targeted only the gas-phase behavior of the real fuels, often neglecting properties responsible for atomization, vaporization, and fuel/air mixing (i.e., physical properties). In addition, much research has been done to understand the flame stability (e.g., lean blowout limit and flame liftoff height) of gaseous and pre-vaporized fuels. Thus, the optimization of the fuels and the liquid fueled combustion devices, e.g., gas turbines, requires the consideration of the two-phase process and the coupling between the complex physical and chemical processes. This will improve the understanding of the mechanisms that controls flame lean blowout limit and liftoff height of liquid fuels. Therefore, an appropriate surrogates will be formulated and a faster processes to certify the alternative fuels will be achieved. In this work, the flame stability in spray burner, quantified by flame lean blowout liftoff height, for different single, binary, alternative, and conventional fuels were experimentally measured. The flame behavior from the spray burner was compared to the results which was done using gaseous flame platform, e.g., counterflow flame burner, to clearly demonstrate the significant importance of two-phase spray processes (i.e., atomization, vaporization, and turbulent mixing) on flame stability. It was found that the atomization process, which can lead to the variation of the droplet size and distribution, has significant impact on flame stability. This is because any change in the droplet size can enhance/diminish the vaporization and mixing processes, and therefore influence the clean and efficient energy conversion process. In addition, the sensitivity of the fuels properties on flame stability was evaluated to provide an explanation for why certain fuel properties govern flame stability, such as lean blowout and liftoff height. Thus, flame stability mechanisms can be developed. A number of approaches were used in this work to address these issues, such as multiple linear regression analysis, and previously developed correlations. The results indicate the importance of the atomization process (i.e. droplet size) on the vaporization rate and suggest that the liquid fuel fraction entering the flame plays a dominant role in controlling lean blowout limits. Thus, the large droplet and less volatile fuel was the most resistance fuel to flame blowout. The differences in liftoff height was shown to be a result of two-phase flame speed, which accounts for both pre-vaporized fuel reactivity defined by laminar flame speed (SL) and time scales associated with droplet evaporation. The influence of the physical and chemical properties of different jet fuels on spray process and thus on emissions is also investigated. This is done by measuring soot formation using Laser-Induced Incandescence (LII). The trends in spray flame soot formation are compared to the gas-phase Yield Sooting Index (YSI). Results indicate differences in planar soot distributions amongst the fuels and suggest a significant influence of the atomization and the vaporization processes on mixing and the soot formation

Heat transfer and pressure drop in turbulent nanofluid flow in a pin-fin heat sink : fin and nanoparticles shape effects

In this paper, the turbulent flow of a nanofluid in a channel is simulated in the presence of a pinfin heatsink. Pin fins have different shapes, including hexagonal, circular, square, and triangular that are considered in two different arrangements. Constant heat flux is applied to the heatsink from its bottom due to the operation of an electronic chip. The nanoparticles suspended in water are alumina, which are in different shapes such as blades, bricks, cylinders, and plates. Their shape effect is investigated. The nanofluid enters the channel at a constant velocity in the range of 1–3 m/s and a constant volume percentage of 2%, and exits after cooling the pin-fin heatsink. The standard k-ε turbulence model is used to model turbulent flow, and the SIMPLEC method is employed to linearize the equations. The variables include fin type, fin arrangement, nanoparticle shape, and nanofluid velocity. Their effect on the maximum and average heatsink temperature and pressure drop (ΔP) is studied. The results show that increasing the velocity leads to a reduction in heatsink temperature, and the use of brick-shaped nanoparticles and circular fin results in the best cooling performance. Also, the use of circular fin and brick nanoparticles requires less ΔP than other cases.The Deanship of Scientific Research (DSR) at King Abdulaziz University, Jeddah.https://http//www.elsevier.com/locate/csiteam2022Mechanical and Aeronautical Engineerin

A detailed hydrothermal investigation of a helical micro double-tube heat exchanger for a wide range of helix pitch length

The present study was numerically inquired the heat transfer performance and fluid flow characteristic of a helical micro double-tube heat exchanger (HMDTHX) using the finite volume method. The tube length was considered to be constantly equal to 30 mm, and 12 different configurations were modeled by changing in turn number and pitch length (P) for Reynolds numbers of 50, 100, 150, and 200. The findings indicated that the heat transfer would enhance by applying any helix angle in the straight tube. However, it had an optimum point which varied by Reynolds number (Re). Rising Re caused overall heat transfer coefficient (OHTC), pressure drop, and pumping power augment for all cases. Increasing P in overall reduced OHTC, pressure drop, and pumping power which had different maximum points between P = 0.5 to 3. Maximum overall heat transfer coefficient (OHTC) enhancement was equal to 45% for Re = 200 and P = 2. Also, maximum effectiveness was 11.5% for P = 2 and Re = 200. Moreover, a 42% maximum increment was achieved for pressure drop, pumping power, and friction factor at Re = 200 and P = 2. Shear stress for Re = 100 to 200 showed that the values are almost the same for P = 0.5 and 1. Then by increasing P, the shear stress decreases. While, for Re = 50, a maximum is seen at P = 2. The temperature distribution was indicated that the maximum temperature of the straight tube and helical tube are the same, but the difference is in the average temperature, which was 3.2 K between straight and helical tubes. Finally, by investigating the velocity contour, it was determined that a secondary flow through the HMDTHX, affected by centrifugal force, was existed, enhancing the fluid flow turbulency and heat transfer rate

Effect of the COVID-19 Vaccine on the Menstrual Cycle among Females in Saudi Arabia

BACKGROUND: The number of reports of menstrual changes after COVID-19 vaccination in the Saudi population is still unknown. Therefore, this study aimed to assess the effect of the COVID-19 vaccine(Pfizer, AstraZeneca, and Moderna) on the menstrual cycle among females in Saudi Arabia. METHODS: This descriptive cross-sectional study was conducted in Saudi Arabia at Umm Al-Qura University (UQU) from August 2021 to February 2022. Data was collected through a previously validated online questionnaire. RESULTS: A total of 2338 participants who received the first dose of the COVID-19 vaccine participated in this study; 1606 (68.7%) of them received the second dose in addition to the first. The mean age of the study participants was 35.4±9.5 years. No significant associations were found between the type of COVID-19 vaccine and the impact on the menstrual cycle, either for the first or second dose (P-values > 0.05). A significant association was found only between the first dose vaccination day and the impact on the menstrual cycle in the second question of “After receiving the COVID-19 vaccine, your next period was” (P-value ≤ 0.05). Significant associations were found between the second dose vaccination day and the impact on the menstrual cycle in the first and second questions of “After receiving the COVID-19 vaccine, your next period was”, and “After receiving the first dose, your next period was," respectively (P-values ≤ 0.05). CONCLUSION: The study found a potential association between the COVID-19 vaccine and menstrual cycle irregularities, which could impact females' quality of life

Hydrothermal and entropy production analyses of magneto-cross nanoliquid under rectified Fourier viewpoint: A robust approach to industrial applications

The present article has been groomed to explore the boundary-driven magnetized flow of cross nanoliquid over thin needle subject to auto catalysis chemical reactions. In addition to it, the effect of entropy optimization model is incorporated and transportation of heat under non-uniform heat source/sink, Cattaneo-Christov heat flux (rectified Fourier) viewpoint (CCHF), and non-linear thermal radiation is also taken into account. Furthermore, the Brownian and thermophoresis aspects of nanoliquid are invoked. The dimensionless governing equations are solved by apposite shooting scheme. The outcomes of the present study via demonstrated graphs and numerical benchmarks seem to indicate that controlled Sakiadis and Blausius flow pattern of cross nanofluids is attained due to incremented magnetic field strength. Temperature ratio parameter contributes the upgradation of thermal boundary layer thickness and homogenous reaction rate leads to the diminution of nanoparticles concentration. The relative values of needle velocity and the velocity of cross nanofluid are most important factor for the regulation of viscous drag force and rate of heat transportation. Augmented Weissenberg parameter and Reynolds number are the prime factor for the uplift of the flow field and the related layer thickness. Furthermore, the existence of CCHF could result in augmentation in Nusselt

A Significant Solar Energy Note on Powell-Eyring Nanofluid with Thermal Jump Conditions: Implementing Cattaneo-Christov Heat Flux Model

PTSCs (parabolic trough solar collectors) are widely employed in solar-thermal applications to attain high temperatures. The purpose of this study is to determine how much entropy is created when Powell-Eyring nanofluid (P-ENF) flows across porous media on a horizontal plane under thermal jump circumstances. The flow in PTSC was generated by nonlinear surface stretching, thermal radiation, and Cattaneo-Christov heat flux, which was utilized to compute heat flux in the thermal boundary layer. Using a similarity transformation approach, partial differential equations were converted into ordinary differential equations with boundary constraints. Then, the boundary restrictions and partial differential equations were merged to form a single set of nonlinear ordinary differential equations. To obtain approximate solutions to ordinary differential equations, the Keller-Box approach is utilized. Nanofluids derived from silver- and copper-based engine oil (EO) has been employed as working fluids. The researchers observed that changing the permeability parameter reduced the Nusselt number while increasing the skin frictional coefficient. Total entropy variation was also calculated using the Brinkman number for flow rates with Reynolds number and viscosity changes. The key result is that thermal efficiency is inversely proportional to particular entropy production. For example, using Cu-EO nanofluid instead of Ag-EO nanofluid increased the heat transport rate efficiency to 15–36%

Numerical investigation to evaluate the effects of gravity and pressure on flame structure and soot formation of turbulent non-premixed methane-air flame

In this study, a turbulent non-premixed (diffusion) methane-air flame has been investigated computationally to analyze the influences of pressure and gravity on flame structure and sooting characteristics between 1 and 10 atm. The simulation has been conducted in a 2-D axisymmetric computational domain using the finite volume-based computational fluid dynamics (CFD) code. The interaction of turbulence and chemistry is modeled by considering the steady laminar flamelet model (SLFM) and the GRI Mech 3.0 chemical mechanism. The radiative heat transfer calculation is carried out by considering the discrete ordinate (DO) method and the weighted sum grey gas model (WSGGM). The semi-empirical Moss-Brookes model is considered to calculate soot. The impact of gravity on flame and sooting characteristics are evaluated by comparing the normal-gravity flames with the zero-gravity flames. The effect of soot and radiation on flame temperature is also examined. The results show a close agreement with the measurement when both soot and radiation are included in the numerical modeling. The rates of soot formation, surface growth, and oxidation increase with increased operating pressure, regardless of gravity. Zero-gravity flames have a higher soot volume fraction, a wider soot-containing zone, a higher CO mass fraction, and a lower flame temperature than normal-gravity flames while maintaining constant pressure. In normal-gravity flames, the CO mass fraction decreases with pressure, whereas it increases with pressure rise in flames of zero gravity. Flames of zero gravity appear taller and broader compared to the flames of normal-gravity for a fixed pressure. An increase in pressure significantly reduces the flame length and width in normal-gravity flames. However, the pressure elevation has little effect on the shape of a zero-gravity flame. The outcomes of the present study will assist in fully understanding the combustion and sooting characteristics of turbulent diffusion flames that will help design and develop high-efficiency, pollutant-free combustion devices and fire suppression systems for space application

<i>Khalas</i> date flavonoids inhibited cell viability, induced apoptosis and expression of the pro-autophagy LC3-B gene in human hepatocellular carcinoma cells (HepG2)

Autophagy is a protective mechanism important in human diseases as cancer. We evaluated the impact of khalas date extract (KDE) (20-60 mg/mL) on cell viability, morphological changes, DNA fragmentation and gene expression of LC3B-II associated with autophagosome on HepG2 cell line. The GC/MS identification of KDE showed its high content of flavonoids including quercetin, myricetin, kaempferol and catechol. KDE reduced cell viability of HepG2 with IC50 (31.52 mg/mL). Cells treated with KDE showed two band of DNA fragments at (30 and 40 mg) indicating that KDE induced DNA damage and apoptosis in HepG2. The analysis RT-PCR data showed a 0.2-fold increase in the expression of LC3-B in the cells treated with KDE versus control. We concluded that, KDE flavonoids such as quercetin, myricetin kaempferol exhibited anticancer properties manifested by inhibition of HepG2 cell viability and induction of apoptosis and upregulation of the pro-autophagy LC3-B gene. </p