Now showing items 1-20 of 2479

    • Oil Spill Risk Analysis For The NEOM Shoreline

      Mittal, HVR; Hammoud, Mohamad Abed ElRahman; Carrasco, Ana K.; Hoteit, Ibrahim; Knio, Omar (2023-09-21) [Preprint]
      A risk analysis is conducted considering an array of release sources located around the NEOM shoreline. The sources are selected close to the coast and in neighboring regions of high marine traffic. The evolution of oil spills released by these sources is simulated using the MOHID model, driven by validated, high-resolution met-ocean fields of the Red Sea. For each source, simulations are conducted over a 4-week period, starting from first, tenth and twentieth days of each month, covering five consecutive years. A total of 48 simulations are thus conducted for each source location, adequately reflecting the variability of met-ocean conditions in the region. The risk associated with each source is described in terms of amount of oil beached, and by the elapsed time required for the spilled oil to reach the NEOM coast, extending from the Gulf of Aqaba in the North to Duba in the South. To further characterize the impact of individual sources, a finer analysis is performed by segmenting the NEOM shoreline, based on important coastal development and installation sites. For each subregion, source and release event considered, a histogram of the amount of volume beached is generated, also classifying individual events in terms of the corresponding arrival times. In addition, for each subregion considered, an inverse analysis is conducted to identify regions of dependence of the cumulative risk, estimated using the collection of all sources and events considered. The transport of oil around the NEOM shorelines is promoted by chaotic circulations and northwest winds in summer, and a dominant cyclonic eddy in winter. Hence, spills originating from release sources located close to the NEOM shorelines are characterized by large monthly variations in arrival times, ranging from less than a week to more than two weeks. Similarly, large variations in the volume fraction of beached oil, ranging from less then 50\% to more than 80\% are reported. The results of this study provide key information regarding the location of dominant oil spill risk sources, the severity of the potential release events, as well as the time frames within which mitigation actions may need to deployed.
    • Enhanced linearity through high-order antisymmetric vibration for MEMS DC power sensor

      zou, xuecui; Jaber, Nizar; Bu Khamsin, Abdullah; Yaqoob, Usman; Salama, Khaled N.; Fariborzi, Hossein (Applied Physics Letters, AIP Publishing, 2023-09-13) [Article]
      We present an electric power meter that capitalizes on the interaction of electrothermal strain and mechanical vibration in a micro-electro-mechanical systems (MEMS) beam undergoing the antisymmetric mode of vibration. This is achieved by using a resonant bridge driven with an electrothermal modulation technique. The change in electrical power is monitored through the alteration in the mechanical stiffness of the structure, which is tracked electrostatically. The observed deflection profile of the beam under the influence of electrothermal effects shows that the deflection geometry due to buckling exhibits similar trends as the first symmetric vibrational mode, in contrast to the antisymmetric mode. Therefore, we compare two distinct vibrational modes, converting the compressive thermal stress generated by the input electrical power via Joule heating into a shift in the resonance frequency. By employing antisymmetric vibrational mode, the output of our device is consistently monotonic to the input electrical power, even when the microbeam is experiencing buckling deflections. In addition, the sensing operation based on antisymmetric modes yields only a 1.5% nonlinear error in the response curve, which is ten times lower than that of symmetric modes. The observed deformation shape of the resonator agrees with the results obtained from multi-physics finite simulations. Finally, this approach has the potential to be extended to other frequency-shift-based sensors, allowing for higher linearity.
    • Downscaling using CDAnet under Observational and Model Noises: The Rayleigh-Benard Paradigm

      Hammoud, Mohamad Abed ElRahman; Titi, Edriss S; Hoteit, Ibrahim; Knio, Omar (2023-09-13) [Preprint]
      Efficient downscaling of large ensembles of coarse-scale information is crucial in several applications, such as oceanic and atmospheric modeling. The determining form map is a theoretical lifting function from the low-resolution solution trajectories of an infinite-dimensional dissipative dynamical system to their corresponding fine-scale counterparts. Recently, Hammoud et al. (2022b) introduced CDAnet a physics-informed deep neural network as a surrogate of the determining form map for efficient downscaling. CDAnet was demonstrated to efficiently downscale noise-free coarse-scale data in a deterministic setting. Herein, the performance of well-trained CDAnet models is analyzed in a stochastic setting involving (i) observational noise, (ii) model noise, and (iii) a combination of observational and model noises. The analysis is performed employing the Rayleigh-Bénard convection paradigm, under three training conditions, namely, training with perfect, noisy, or downscaled data. The effects of observational and model noise on the CDAnet downscaled solutions are analyzed. Furthermore, the effects of the Rayleigh number and the spatial and temporal resolutions of the coarse-scale information on the downscaled fields are examined. The results suggest that the expected l 2 -error of CDAnet behaves quadratically in terms of the standard deviations of the observational and model noises. The results also suggest that CDAnet responds to uncertainties similar to CDA with an additional error overhead due to CDAnet being a surrogate model of the determining form map.
    • Shock Tube/Laser Absorption Measurements of the High-Temperature Spectra and Decomposition of Propyl Ethers.

      Adil, Mohammad; Farooq, Aamir (The journal of physical chemistry. A, 2023-09-10) [Article]
      This work presents measurements of temperature-dependent absorption spectra and thermal decomposition rates of propyl ethers, specifically di-n-propyl ether (DnPE) and diisopropyl ether (DiPE), which are two renewable fuel candidates. We employed a broadband rapid-tuning MIRcat-QT laser, operating in the scan/fixed-wavelength mode in combination with a shock tube. Spectral measurements were performed over the wavelength range of 8.4–11 μm (909.1–1190.5 cm–1), covering the strongest infrared absorption bands of the studied ethers, at temperatures of 559–853 K and pressure near 1 bar. These high-temperature spectra help in selecting the optimum wavelength for sensitive and selective measurements of the target ethers. Based on the criteria of high sensitivity, minimum interference, and insensitivity to temperature and pressure variations, we selected a wavelength of 1121.82 cm–1 for high-temperature diagnostics of DnPE and DiPE. Absorption cross sections at the selected wavelength of 1121.82 cm–1 were measured over 550–1500 K, and pressures ranging from 0.3–1.4 bar. This diagnostic was then applied to study the high-temperature pyrolysis of these ethers by measuring their time histories behind the reflected shock waves. Our experimentally measured overall decomposition rate coefficients for DnPE and DiPE are given as (unit of s–1) kDnPE = 1.25 × 1027 × T–3.483 × exp(−37620 K/T) and kDiPE = 5.26 × 1023 × T–2.857 × exp(−32360 K/T).
    • An updated functional-group-based approach to modeling the vacuum residue oil gasification kinetics

      Zhang, Xiaoyuan; Khandavilli, Muralikrishna; Gautam, Ribhu; AlAbbad, Mohammed A.; Li, Yang; Chatakonda, Obulesu; Kloosterman, Jeffrey W.; Middaugh, Joshua; Sarathy, Mani (Fuel, Elsevier BV, 2023-09-09) [Article]
      Gasification of heavy petroleum residues can convert low-value feedstock to hydrogen-rich syngas, which can further be used for power generation and/or chemical production. The present work proposed an updated functional-group-based approach (FGMech) to modeling the gasification of a vacuum residue oil (VRO), which is helpful for better understanding the detailed kinetics of the gasification and improving gasifier performance. Elemental, average molecular weight (AMW) and nuclear magnetic resonance (NMR) analyses were conducted experimentally to characterize VRO, including elemental composition, average molecular formula and the functional group distribution, which were further used for model construction. A lumped mechanism for VRO devolatilization was constructed based on the updated FGMech approach: stoichiometric parameters of stable gases, tars and char were obtained from experiments, while those of radicals were based on the multiple linear regression (MLR) correlations; thermodynamic and kinetic parameters were derived from Benson group additivity method and rate rules, respectively. A merged detailed model was adopted for describing the conversion of gases and tars, and a global model was used for char. To test the reliability of the present model approach, Orimulsion gasification experiments from literature were simulated using an integrated perfectly stirred reactor (PSR) and plug flow reactor (PFR) model. It shows that the present model can reasonably predict measured results under various equivalence ratios, and has better performance on the prediction of CH4 compared with most literature models. Based on model analyses, syngas comes from the conversion of C2H4, H2S, CH4 and char in different gasification stages. Benzene, toluene, naphthalene and 1-methylnaphthalene are initial tar species considered in the devolatilization of the VRO. They can undergo hydrogen abstraction acetylene addition (HACA) and C3H3/C5H5 addition reaction pathways to produce large PAHs.
    • Experimental estimation of turbulence modulation in droplet-laden two-phase jet

      Wu, Hao; Zhang, Zhenyu; Zhang, Fujun; Wu, Kun; Roberts, William L. (Physical Review Fluids, American Physical Society (APS), 2023-09-05) [Article]
      The effect of liquid droplets generated from air-assisted atomization on gas flow characteristics was studied experimentally. A phase/Doppler particle analyzer was used to measure velocity and size distributions of continuous and dispersed phases in the droplet-laden two-phase flow. A comparison of mean gas velocity with and without droplets indicates the expected influence of dispersed phase on the carrier phase, i.e., two-way coupling. The flow characterization result shows the presence of liquid droplets contributes to the increase of gas-phase flow velocity in the spray field. The effect of liquid droplets on gas-phase turbulence is manifested in three ways. First, the presence of droplets leads to the increase in fluctuation velocity of gas-phase flow. Subsequently, it is observed that the range of fluctuation velocities in the gas phase is expanded in two-phase flow compared with single-phase flow. In the region characterized by a steep velocity gradient, the initial gas fluctuation velocities in two-phase flow demonstrate a notable enhancement of 20% compared with single-phase flow. Furthermore, the presence of droplets induces axial stretching within the shear region of the gas phase, and this stretching effect is particularly pronounced in cases of higher fuel-injection durations, primarily due to the influence of droplet gravity. The data obtained from the analysis of velocity gradient and fluctuation velocity within the two-phase flow field reveal a distinct segmental linear relationship, deviating from previous findings reported in the literature and highlighting a deeper understanding of the underlying mechanisms in current two-phase flow systems.
    • Lagrangian Analysis of Droplet Dynamics Using Computational Singular Perturbation

      Angelilli, Lorenzo; Malpica Galassi, Riccardo; Ciottoli, Pietro Paolo; Hernandez, Francisco; Valorani, Mauro; Im, Hong G. (Elsevier BV, 2023-09-05) [Preprint]
      Computational singular perturbation (CSP) has been successfully used in the analysis of complex chemically reacting flows by systematically identifying the intrinsic timescales and slow invariant manifolds that capture the essential subprocesses driving the dynamics of the system. In this article, the analytical and computational framework is applied for the first time to analyze the Lagrangian droplets undergoing evaporation and dispersion in the surrounding gases. First, a rigorous mathematical formulation is derived to adapt the CSP tools into the droplet dynamics equations, including the formal definition of the tangential stretching rate (TSR) that represents the explosive/dissipative nature of the system. Canonical case studies are then conducted to demonstrate the utility of the CSP methodology in identifying various physical mechanisms driving the evolution of the system, such as the distinction of thermal-driven and mass-driven regimes. Various definitions of the importance indices are also examined to provide in-depth analysis of different subprocesses and their interactions in modifying the droplet dynamics.
    • Effects of Ammonia Substitution in the Fuel Stream and Exhaust Gas Recirculation on Extinction Limits of Non-premixed Methane– and Ethylene–Air Counterflow Flames

      Chu, Carson Noel; Scialabba, Gandolfo; Liu, Peng; Serrano-Bayona, Raul; Aydin, Faruk; Pitsch, Heinz; Roberts, William L. (Energy & Fuels, American Chemical Society (ACS), 2023-09-04) [Article]
      The global extinction limits of non-premixed nitrogen/ammonia-substituted methane– and ethylene–air counterflow flames were experimentally evaluated. In comparison to nitrogen substitution, ammonia substitution reduced the extinction strain rates more. Measurements of OH* chemiluminescence, of which the intensity correlates with extinction limits, suggest that ammonia substitution reduces OH* production. The effects of transport, thermal and chemical properties on flame extinction of the ammonia-substituted flames were assessed, and it was found that their lower extinction limits were due to reactions that consume radicals, which hinder the chain-branching reactions. To mimic the effect of exhaust gas recirculation on the extinction limits of ammonia-substituted flames, carbon dioxide was added to the oxidizer stream. Lower extinction limits were observed with carbon dioxide addition as a result of thermal and chemical effects. Carbon dioxide addition lowered flame temperatures and, like ammonia substitution, introduced reactions that consume radicals. Nitric oxide (NO) production was quantitatively analyzed by simulations. It was found that, for ammonia flames, NO production was promoted by ammonia oxidation with OH, whereas for carbon dioxide addition, NO production was suppressed by the reduction of OH production.
    • Mini Review of Ammonia for Power and Propulsion: Advances and Perspectives

      Guiberti, Thibault; Pezzella, Giuseppe; Hayakawa, Akihiro; Sarathy, Mani (Energy & Fuels, American Chemical Society (ACS), 2023-09-01) [Article]
      Ammonia is a molecule that has been essential to human activities for centuries. It is widely used as a feedstock for fertilizers, industrial chemicals, and emissions after-treatment systems. The properties of ammonia have led to its interest as a carrier for hydrogen in energy applications. The combustion of ammonia for power and propulsion offers direct applications of this molecule in energy and transportation applications. However, there are significant challenges related to ammonia combustion, including low flammability and potentially high emissions. Blending of ammonia with hydrogen or hydrocarbons offers opportunities to improve combustibility. This mini review discusses challenges related to ammonia combustion and current state-of-the-art approaches to overcoming these challenges with research into chemical kinetics, laminar and turbulent flames, and engine and turbine systems. This paper seeks to introduce and summarize recent results on ammonia combustion by highlighting pertinent aspects of this rich and rapidly increasing body of information.
    • Synergistic effect of non-thermal plasma and CH4 addition on turbulent NH3/air premixed flames in a swirl combustor

      Kim, Gyeong Taek; Park, Jeong; Chung, Suk Ho; Yoo, Chun Sang (International Journal of Hydrogen Energy, Elsevier BV, 2023-09-01) [Article]
      The synergistic effect of non-thermal plasma (NTP) induced by a dielectric barrier discharge (DBD) and CH4 addition on turbulent swirl-stabilized NH3/air premixed flames in a laboratory-scale gas turbine combustor is experimentally investigated by varying the mixture equivalence ratio, φ, the mixt velocity, U0, and the mole fraction of CH4 in the fuel, Xf,CH4. It is found that the streamer intensity is significantly increased by adding CH4 to NH3/air flames compared with that by adding H2. This is because positive ions generated by CH4 addition play a critical role in generating streamers. Such streamers intensified by CH4 addition enhance the ammonia combustion more together with CH4, and hence, the lean blowout (LBO) limits of NH3/CH4/air flames are significantly extended compared with those without applying NTP. The maximum streamer intensity is found to be linearly proportional to φ⋅Xf,CH4⋅U0 in wide ranges of φ, Xf,CH4, and U0. NTP is also found to significantly reduce the amount of NOx and CO emissions simultaneously. All of the results suggest that NTP can be used more effectively with CH4 addition to stabilize turbulent premixed NH3/air flames and reduce NOx/CO emissions, which is attributed to their synergistic effect on the ammonia combustion.
    • Learning to Read Analog Gauges from Synthetic Data

      Leon-Alcazar, Juan; Alnumay, Yazeed; Zheng, Cheng; Trigui, Hassane Ahmed; Patel, Sahejad; Ghanem, Bernard (arXiv, 2023-08-28) [Preprint]
      Manually reading and logging gauge data is time inefficient, and the effort increases according to the number of gauges available. We present a computer vision pipeline that automates the reading of analog gauges. We propose a two-stage CNN pipeline that identifies the key structural components of an analog gauge and outputs an angular reading. To facilitate the training of our approach, a synthetic dataset is generated thus obtaining a set of realistic analog gauges with their corresponding annotation. To validate our proposal, an additional real-world dataset was collected with 4.813 manually curated images. When compared against state-of-the-art methodologies, our method shows a significant improvement of 4.55 in the average error, which is a 52% relative improvement.
    • Effects of Engine Speed on Prechamber-Assisted Combustion

      Palombi, Lucia; Sharma, Priybrat; Cenker, Emre; Magnotti, Gaetano (SAE International, 2023-08-28) [Conference Paper]
      Lean combustion technologies show promise for improving engine efficiency and reducing emissions. Among these technologies, prechamber-assisted combustion (PCC) is established as a reliable option for achieving lean or ultra-lean combustion. In this study, the effect of engine speed on PCC was investigated in a naturally aspirated heavy-duty optical engine: a comparison has been made between analytical performances and optical flame behavior. Bottom view natural flame luminosity (NFL) imaging was used to observe the combustion process. The prechamber was fueled with methane, while the main chamber was fueled with methanol. The engine speed was varied at 1000, 1100, and 1200 revolutions per minute (rpm). The combustion in the prechamber is not affected by changes in engine speed. However, the heat release rate (HRR) in the main chamber changed from two distinct stages with a faster first stage to more gradual and merged stages as the engine speed increased. NFL imaging revealed that lower mean piston speed allowed for longer free jet propagation inside the combustion chamber resulting in faster and stronger HRR stages. At higher speeds, the jet-piston interaction started earlier and was dispersed in radial directions, resulting in a relatively prolonged HRR. Finally, the study emphasizes the importance of prechamber jet and piston interaction in shaping HRR.
    • Oxidative desulfurization of fuel oil and molecular characterization of the sulfone compound distribution in the different extractants

      Fan, Jiyuan; Khan, Hassnain Abbas; Wang, Tairan; Ruiz-Martinez, Javier; Saxena, Saumitra; Emwas, Abdul-Hamid M.; Samaras, Vasileios G.; Roberts, William L. (Separation and Purification Technology, Elsevier BV, 2023-08-28) [Article]
      PMoA/G5 catalyst was synthesized, and its oxidative desulfurization (ODS) performance on model oil was studied. The catalyst and oxidation-extraction-adsorption system was used for the ODS of Arabian Extra light oil (AXL). Acetonitrile and methanol were chosen as different extractants for the extraction of sulfones (O2S and O2S4). The distribution of sulfone was first reported in detail at each of the three-stage extraction solvents at the molecular level analyzed by the Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), proton, and 13C nuclear magnetic resonance (1H NMR,13C NMR). The FT-ICR MS results show that the extracted proportion of macromolecular sulfone compounds increases with the extraction stages. Acetonitrile exhibited better selectivity than methanol for polyaromatic sulfone with a high carbon number for the O2S species with double bond equivalent (DBE) = 12–15 and O2S2 species with DBE = 11–16. The NMR results reveal that polyaromatics with naphthenic rings and a low carbon number (<30) can be easily extracted due to their high polarity. The excellent performance of the PMoA/G5 catalyst makes it a promising candidate in the ODS reaction, and the research results give guidelines for ODS technology.
    • Effects of n-decane substitution on structure and extinction limits of formic acid diffusion flames

      Alfazazi, Adamu; Li, Jiajun; Xu, Chaochen; Es-sebbar, Et-touhami; Zhang, Xiaoyuan; Abdullah, Marwan; Younes, Mourad; Sarathy, Mani; Dally, Bassam (Fuel, Elsevier BV, 2023-08-26) [Article]
      Formic acid (FA) is a low-carbon fuel that can be produced from renewable hydrogen (H2) and carbon dioxide (CO2). However, transitioning completely to low carbon fuels might be lengthy and challenging, so it makes sense to gradually introduce low carbon fuels into the energy sector in conjunction with existing fuels. One practical approach could be blending FA with existing fossil fuels, such as kerosene in aviation. This study investigates the behavior of flames comprising FA and its blends with n-decane. The extinction limits of pure FA and FA/n-decane mixtures were measured in a counterflow non-premixed laminar flame setup at various blending ratios. Additionally, the flame structure was studied by measuring temperature and species distribution using probe-based sampling. The results indicate that replacing FA with n-decane in the FA-N2 flame greatly enhances the flame's reactivity. Blending the fuels also led to a decrease in CO2 production in the flame, while increasing the flame temperature and the concentration of H2 and CO species. Experimental results were modeled using an updated FA and n-decane model. The kinetic model agrees with the experimental trends, but slightly overpredicts H2, CH4 species, and flame temperature. The kinetic model was also used to investigate the kinetic coupling between FA and n-decane in non-premixed laminar flames. Kinetic analyses indicate that HOCO and OCHO intermediates play a crucial role in pure FA flames by reacting with active radicals like H and OH to produce CO2 and CO, while in n-decane blended flames, fuel decomposition proceeds through two other pathways leading to H2 and H2O2.
    • Temperature-Dependent Kinetics of Ozone Production in Oxygen Discharges

      Bang, Seunghwan; Snoeckx, Ramses; Cha, Min Suk (Plasma Chemistry and Plasma Processing, Springer Science and Business Media LLC, 2023-08-26) [Article]
      Ozone has been widely used for its disinfection properties ever since its efficient production was made possible by plasma discharges. To-date, many experimental and modeling studies have been—and still are—dedicated to further improve the O3 production efficiency. Early on, it became clear that heat has a detrimental effect. Hence, little attention has been paid to the temperature-dependence of the plasma chemistry. However, with the increased use of O2 as (co-)reactant for plasma-based processes at elevated temperatures, this becomes essential. Therefore, we developed a reaction mechanism to study the temperature-dependence of the O2/O3 (plasma) chemistry. Here, we present the experimental validation of this mechanism and an analysis of the different O3 production trends as a function of gas temperature (300–590 K) and discharge power (5–20 W). Through improving key ozone reactions and electron impact dissociation processes, our mechanism could well-predict all experimentally observed trends. Our analysis revealed the importance of the electronic excited states of O2 and how the temperature-dependence of the plasma-based O3 production is highly dependent on the discharge power. Therefore, we believe that this work can contribute to a better understanding of the underlying physicochemical mechanisms of any O2/O3-containing (plasma) process operating at elevated temperatures. Nevertheless, our work also revealed the need for more accurate and comprehensive data with respect to the production and consumption of the electronic excited states of O2.
    • Study of engine knocking combustion using simultaneous high-speed shadowgraph and natural flame luminosity imaging

      Tang, Qinglong; Shi, Hao; Uddeen, Kalim; Sharma, Priybrat; Yao, Mingfa; Turner, James W. G.; Magnotti, Gaetano (Applied Thermal Engineering, Elsevier BV, 2023-08-25) [Article]
      Engine knocking is a classical but significantly impactful combustion phenomenon that arouses unfailing research interests. An in-depth understanding of the knocking mechanism holds the key to the next-generation high-efficiency spark ignition engines adopting a high compression ratio. In this study, a novel 72 kHz imaging system of simultaneous shadowgraph and natural flame luminosity (NFL) was implemented on an optical engine. The key combustion parameters that affect the engine knock intensity were investigated based on the heat release analysis. The shadowgraph image velocimetry (SIV) was utilized to measure the in-cylinder flow field. The end gas autoignition process in the engine knocking combustion was studied under knock intensity as high as 18.1 bar. The results indicate that there is an “optimum” combustion phasing that produces the highest knock intensity. The cases with more end gas mass at knock onset, though having lower mean temperatures, generally produce higher knock intensity. The knock intensity can be significantly different under the same end gas mass and mean end gas temperature, possibly due to the different temperature gradients in the end gas. The simultaneous shadowgraph and NFL imaging succussed in differentiating the density variation zone in the end gas caused by the low-temperature heat release from the hot flame zone before auto-ignition. An intense density variation zone is witnessed around the center of the cylinder under higher engine knock intensity by the shadowgraph images, showing a dark region that oscillates together with the local pressure oscillations. The coupling among the local density variation, pressure oscillation, and NFL intensity oscillation is observed during the engine knocking combustion. The velocity distribution of the flow field indicates that the engine knocking combustion enhances the in-cylinder flow, which may cause more convective heat transfer loss and flow loss.
    • The Influence of Marangoni Flow, Curvature Driven Drainage, and Volatility on the Lifetime of Surface Bubbles

      Aladsani, Abdulrahman (2023-08-24) [Thesis]
      Advisor: Truscott, T. T.
      Committee members: Daniel, Dan; Hoteit, Hussein
      This study investigates the factors that affect the lifetime and popping location of surface bubbles. The experiment was conducted using three different liquids (water, Sodium Dodecyl Sulfate, and Decane) with varying bubble sizes, using three different needle sizes. Each setup was tested 50 times. For pure water bubbles, the foot of the bubble is the most critical location because it typically has the highest temperature gradient, which creates a localized Marangoni flow that thins the film and eventually leads to the bubble bursting at the foot. When SDS was added to water, the bubble lifetime increased significantly. This is because the Marangoni stresses were reduced, and the bubble film thinned mainly due to curvature-driven drainage flow. The lifetime of the SDS bubble had a positive correlation with increasing bubble size. For Decane bubbles, the volatility of the liquid plays a significant role in the lifetime and popping location of the bubble. When the Decane was heated to 40°C, the lifetime of the bubbles increased significantly from 0-20 seconds to 8-12 minutes. This is because the high volatility of the Decane caused rapid evaporation of the bubble cap at the interface, which cooled the surface of the liquid. This temperature difference creates a difference in surface tension, which causes the liquid to flow from the bulk liquid into the apex of the bubble, thickening the cap film until it cools down. Then, it pops from the top due to the curvature-driven drainage.
    • Droplet detachment force and its relation to Young-Dupre adhesion

      Daniel, Dan; Koh, Xue Qi (Research Square Platform LLC, 2023-08-23) [Preprint]
      Droplets adhere to surfaces due to their surface tension γ and understanding the vertical force Fd required to detach the droplet is key to many technologies (e.g., inkjet printing, optimal paint formulations). Here, we predicted Fd on different surfaces by numerically solving the Young-Laplace equation. Our numerical results are consistent with previously reported results for a wide range of experimental conditions: droplets subjected to surface vs. body forces with |Fd| ranging from nano- to milli-newtons, droplet radii R ranging from tens of microns to several millimetres, and for various surfaces (micro-/nano-structured superhydrophobic vs. lubricated surfaces). Finally, we derive an analytic solution for Fd on highly hydrophobic surfaces and further show that for receding contact angle θr > 120◦, the normalized Fd/πR is equivalent to the Young-Dupre work of adhesion γ(1 + cos θr).
    • Linear stability of Poiseuille flow over a steady spanwise Stokes layer

      Massaro, Daniele; Martinelli, Fulvio; Schmid, Peter J.; Quadrio, Maurizio (arXiv, 2023-08-22) [Preprint]
      The temporal linear stability of plane Poiseuille flow modified by spanwise forcing applied at the walls is considered. The forcing consists of a stationary streamwise distribution of spanwise velocity that generates a steady transversal Stokes layer, known to reduce skin-friction drag in a turbulent flow with little energetic cost. A large numerical study is carried out, where the effects of both the physical and the discretization parameters are thoroughly explored, for three representative subcritical values of the Reynolds number Re. Results show that the spanwise Stokes layer significantly affects the linear stability of the system. For example, at Re=2000 the wall forcing is found to more than double the negative real part of the least-stable eigenvalue, and to decrease by nearly a factor of four the maximum transient growth of perturbation energy. These observations are Re-dependent and further improve at higher Re. Comments on the physical implications of the obtained results are provided, suggesting that spanwise forcing might be effective to obtain at the same time a delayed transition to turbulence and a reduced turbulent friction.
    • Numerical assessment of the performance and emissions of a compact Wankel rotary engine applied as a range extender on the BMW i3 model

      Vorraro, Giovanni; Turner, James W. G. (JSAE/SAE, 2023-08-22) [Conference Paper]
      Amongst all the hybrid-vehicles technologies and layouts, range-extended electric vehicles are the ones with the real prospect to reduce the emissions produced by the thermal machine when in driving conditions, while assuring an adequate range for the common user. The BMW i3 represents one of the most successful series hybrid electric vehicles, having been on the market since 2013. Given the complexities of a hybrid layout employing both thermal and electrical machines, the range extender must have compactness and lightweight characteristics in addition to a suitable power output for the vehicle. Usually, standard 4- stroke small-displacement engines are employed for this application, with the BMW i3 employing a 2- cylinder range extender. More interestingly, a Wankel rotary engine can provide the same amount of mechanical power by reducing the weight and the volume of nearly a third to the equivalent 4-stroke engine. In this study a numerical assessment of the Advanced Innovative Engineering UK (AIE UK) 225CS Wankel rotary engine as a range extender for the BMW i3 was carried out. A full vehicle model of the BMW i3 was built in Siemens Simcenter Amesim 2021.2 to evaluate the behaviour of the aforementioned engine as a range extender. The engine sub-model used was a Mean Value Engine Model (MVEM) set up by implementing the experimental data collected during previous experimental campaign while the BMW i3 chassis sub-model was characterised by using the publicly available data from an Argonne National Laboratory benchmarking project (vehicle weight, front surface, drag coefficient, tires dimensions, etc.). Finally the model was tested over the standard Worldwide harmonized Light vehicles Test Procedure (WLTP) driving cycle in both Charge Depleting and Charge Sustaining modes.