Rise Height Research Articles

Climate change modulates the stratospheric volcanic sulfate aerosol lifecycle and radiative forcing from tropical eruptions

Explosive volcanic eruptions affect climate, but how climate change affects the stratospheric volcanic sulfate aerosol lifecycle and radiative forcing remains unexplored. We combine an eruptive column model with an aerosol-climate model to show that the stratospheric aerosol optical depth perturbation from frequent moderate-magnitude tropical eruptions (e.g. Nabro 2011) will be reduced by 75% in a high-end warming scenario compared to today, a consequence of future tropopause height rise and unchanged eruptive column height. In contrast, global-mean radiative forcing, stratospheric warming and surface cooling from infrequent large-magnitude tropical eruptions (e.g. Mt. Pinatubo 1991) will be exacerbated by 30%, 52 and 15% in the future, respectively. These changes are driven by an aerosol size decrease, mainly caused by the acceleration of the Brewer-Dobson circulation, and an increase in eruptive column height. Quantifying changes in both eruptive column dynamics and aerosol lifecycle is therefore key to assessing the climate response to future eruptions.

Gas-lift enhanced natural circulation of alkali and heavy liquid metals for passive cooling of nuclear reactors

Gas-lift enhanced natural circulation of alkali and heavy liquid metals is a desirable option for passive cooling of advanced large, small, and micro nuclear reactors, accelerator driven systems, thermal solar plants, and experimental facilities and test loops. The injected inert gas into the riser or the chimney above the reactor core needs to be in the bubbly flow regime for best performance. Gas-heavy liquid metals flow maps are developed based on a well-established theoretical knowledge and the reported experimental data for various test loops. In addition, a thermal-hydraulics model for enhanced natural circulation of heavy liquid metals is developed and validated using the reported experimental data for LBE-N2 and LBE-Ar flow loops. The developed and validated thermal-hydraulics model and two-phase flow maps are used to parametrically investigate natural circulation enhancement of liquid sodium, molten lead, and liquid LBE in a representative loop with Ar gas injection. For enhanced natural circulation of alkali and heavy liquids metals of Na, Pb and LBE, the determined average gas void fraction in the bubbly flow regime is < 0.2. The rates of natural circulation of liquid sodium, molten lead, and liquid LBE increase with increased riser height and/or the gas injection rate for operating in the bubbly flow regime. For the same riser height and gas average void fraction, the natural circulation rates of molten Pb and LBE are similar but much higher than that of liquid sodium. However, liquid sodium has a much higher heat capacity for operating at higher fission power density in or lower temperature rise across the reactor core.

Pedestrian single file movement on stairway: Investigating the impact of stair configuration on pedestrian ascent and descent fundamental diagram

Due to the individuals’ interactions with the physical environment, pedestrian walking on various stair-facilities may present different features. Performing controlled pedestrian experiments have been regarded as a reliable data provision approach in this field. With this method, a series of pedestrian single-file experiments on specific stair configurations has been organized. Based on the individual’s trajectories information extracted from eight well-structured stair scenarios, this study investigates a range of questions concerning the effects of stair geometry on pedestrian locomotion properties. This including the influence of stair tread depth, riser height and stair slope as well as pedestrian dynamics on micro and macro levels. Our analysis indicated that there is a unified behavioral mechanism between pedestrian single-file movement on horizontal plane and stairs, i.e., the two regimes of speed-headway relationship. Besides, our analysis displayed those pedestrian characteristics, i.e., free movement speed and free movement headway varies as a result of different stair configurations. Therefore, we developed a linear regression model that predicts the free walking speed based on tread depth and riser height of the stair. Our results also indicated the significant effect of stair gradient on pedestrian density-specific flow relation on stairs by the microscope fundamental diagram method. We found the data point of density-specific flow for pedestrians almost has the same shape despite their walking in different facilities. The data and findings could contribute to the design of large buildings or stations, upgrade and enhance microscope pedestrian simulation models to provide more reality outputs of the human walking on stairs.

Study on the Flow Characteristics of Desulfurization Ash Fine Particles in a Circulating Fluidized Bed

In view of the current status of catalytic cracking flue gas treatment, it is necessary to study the flow environment of desulfurization ash particles, which are a type of Geldart C particle, in a circulating fluidized bed (CFB) for semi-dry flue gas desulphurization using CFB technology. This study investigated the flow characteristics of desulphurization ash particles in a riser with an inner diameter of 70 mm and a height of 12.6 m, at a gas velocity of 4–7 m/s and a solids circulation rate of 15–45 kg/m2·s. The solids holdup in the axial distribution is relatively high near the bottom of the riser, and gradually decreases as the riser height increases, with a stable value from the middle to the top of the riser. In the radial distribution, the solids holdup of desulfurization ash particles is low in the center and high in the wall region. Within the above operating conditions, the solids holdup ranges from 0.008 to 0.025. The particle-based Archimedes number has a linear relationship with the solids holdup at all operating conditions.

Computational Analysis of the Hydrodynamic Behavior for Different Air Distributor Designs of Fluidized Bed Gasifier

Fluidized bed gasification has proven to be an appropriate technique for converting various biomass feedstocks into helpful energy. Air distributor plate design is one of the critical factors affecting the thermochemical conversion performance of fluidized bed gasifiers. The present study is proposed to investigate the mixing pattern and pressure drop across different configurations of air distributors using a two-fluid model (TFM) of finite volume method-based solver ANSYS FLUENT. The pressure drop across the bed and mixing pattern have been investigated through qualitative and quantitative analysis of CFD results using three diverse distributor plate designs: perforated plate, 90° slotted plate, and 45° swirling slotted plate. The pressure drop by employing the perforated distributor plate reveals the highest pressure drop due to the smallest open area ratio. However, the pressure drop in the case of 90° slotted plate is found to be 7% and 4% lesser than perforated and 45° slotted plate respectively due to a smaller velocity head developed through the wider open area of the straight slotted plates. The distributor design configuration having a 45° slotted plate exhibits considerable pressure drop compared to the 90° slotted plate due to the longer path length of the slot. Numerical pressure drop results across the bed with different types of distributor plates prove reasonable agreement with the experimental results available in the literature. Mixing behavior in perforated distributor plates exhibits lower portion solid volume fraction of around 0.58. However, it falls rapidly as go up the riser (7.7% of column height); 90° slotted plate shows bottom region solid volume fraction of around 0.5. In addition, it exhibits an even broader range of sand volume fraction and column height (13.46% of column height). Finally, the 45° distributor plate reveals the highest range of volume fraction through the riser height (17.3% of column height), indicating the better mixing characteristics of the fluidized zone.

Experimental investigation on wettability and capillary performance of ultrasonic modified grooved aluminum wicks

The grooved wick has a promising potential in the field of ultra-thin flat heat pipes, and the porous structure can improve the capillary performance of grooved wicks significantly. In this paper, an environmentally friendly method, named as ultrasonic modification, was developed to fabricate porous microstructures on grooved aluminum wick. The effects of ultrasonic modification times on the morphology, wettability and capillary performance of the porous grooved wick were investigated. The results indicate that appropriate ultrasonic modification times can realize an excellent distribution of porous microstructures throughout the groove surface. After ultrasonic modification, the modified surface became hydrophobic since the porous microstructures were covered with a low-surface-energy coating. However, in case of aluminum heat pipes with acetone as working liquid, the wettability and capillary performance of the modified grooved wick can still be enhanced significantly. The maximum capillary rise height and the capillary performance parameter of the modified grooved wicks were increased for a factor of 3 and an order of magnitude, respectively. This study provides a new idea for the fabrication of porous aluminum wicks, which is beneficial to promote the development of ultra-flat aluminum heat pipes.

Modelling of a Capillary Rise Height of Biochar by Modified Lucas–Washburn Equation

Modelling of a Capillary Rise Height of Biochar by Modified Lucas–Washburn Equation

Optimization Steel ingot Mould’ Riser Height Based on Solidification Simulation

Solidification process of 13.5t P91 steel ingot with different riser heights were simulated by software and predicted the distribution of shrinkage cavity. The simulation results showed the shrinkage cavity in the precedent ingots is much deeper. The simulation results is agreement well with experiment results. Therefore, the riser height was designed by solidifation simulation and verified by experiments and the results showed that optimized riser height can eliminate shrikage cavity and improve the quality of steel ingot.

Fabrication and capillary performance of a novel composite wick for ultra-thin heat pipes

The rapid development of high-performance portable electronics requires ultra-thin heat pipes (UTHPs) with higher heat transfer capacity to meet their heat dissipation needs. Wick structure, the key component of a heat pipe, makes a decisive role in the heat transfer capacity of the heat pipe. However, since the wall thickness of UTHPs is typically < 0.1 mm, it is difficult to machine deep enough grooves on the shell to increase the permeability of the wicks like conventional heat pipes. Therefore, a novel composite wick structure with high permeability for UTHPs is proposed in this study. It is found that the wick with larger pores formed by parallel woven spiral meshes have higher permeability, resulting in more working fluid in the wick, which helps delay the drying out at the evaporation end of heat pipes. To further improve the capillary performance of wicks, the effect of thermal oxidation suitable for mass production on the capillary pumping performance of wicks is systematically studied for the first time. Compared with the single sintered wick, the capillary rise height after oxidation at 400 °C, 500 °C, 600 °C, and 700 °C for 150 min increased by about 32.2%, 19%, 19.5%, and 12.9%, respectively. Considering that the copper oxidation may limit the choice of working fluid for the heat pipe, the wicks are heated to 400 °C for reduction reaction for 1 h (with 95% N2+5% H2 gas). The results show that the capillary rise height of the wicks after oxidation at 400 °C, 500 °C, 600 °C, and 700 °C and reduction treatment is about 110%, 127%, 114%, and 91.4% of that of the single sintered wick, respectively. The experimental results show that the maximum heat load power of the UTVCs with 5 layers #200 mesh, single sintered composite wick and 500 °C oxidation–reduction wick are 16 W, 29 W and 38 W, respectively.

Wave Dissipation and Sediment Transport Patterns during Shoreface Nourishment towards Equilibrium

Implementing shoreface nourishment is an effective method to protect sandy beaches. A better understanding of the equilibrium mechanism of shoreface nourishments is necessary for coastal engineering designs and constructions. Two experiments on the beach profile equilibrium of the shoreface nourishment are carried out under mild wave conditions on the reflective and intermediate beach. It is observed that the shoreface nourishment increases local wave height and strengthens wave nonlinearity by its shallow water depth. The most intense wave breaking dissipation has been found on the crest of the shoreface nourishment, and the distribution of wave energy dissipation rate is more uniform on the quasi-equilibrium profile than that on the initial profile. A process-based numerical model is used to reproduce bed profile evolution successfully. On that basis, it is found that onshore bedload transport is the primary cause for the onshore migration of the shoreface nourishment. The magnitude of bedload transport decreases during the evolution of the shoreface nourishment towards equilibrium. The most intense sediment transport rate occurs over the shoreface nourishment or in front of the shoreline, depending on the ’lee effect’ of the nourishment. Furthermore, the effects of incident wave height, wave period, and sea-level rise on the equilibrium profile of the shoreface nourishment under mild wave conditions are analyzed.

A sustainable one-step pretreatment of cotton gray fabric with 18-crown-6 as phase transfer in supercritical carbon dioxide

With increasing awareness in environmental protection from the world, traditional pretreatment methods for textiles, which entail high costs and cause severe pollutions, can no longer meet the requirements of green and sustainable development in textile industry. Therefore, to explore a new pretreatment method to overcome those drawbacks is of great importance. In this work, green and environmentally friendly method was developed in supercritical carbon dioxide fluid to pretreat cotton gray fabric for removing various impurities with one step and one bath, by utilizing an 18-crown-6 phase transfer system. Various process parameters, such as the pH value of buffer solution, the dosage of phase transfer catalyst, hydrogen peroxide, buffer solution, and the system temperature, pressure, treatment duration, were investigated and optimized by employing the weight loss percent and the capillary rise height as assessment index. The obtained results show that the developed alkali-hydrogen peroxide one-step method involving the 18-crown-6 phase transfer system in supercritical carbon dioxide exhibits a good feasibility for the removal of various sizing agents and other impurities from cotton fabric, and a satisfactory pretreatment performance and efficiency were achieved. The pretreatment parameters showed an important and various effects on the pretreatment efficiency of cotton substrate during a phase transfer oxidative one-step process in supercritical carbon dioxide. Moreover, a phase transfer oxidative one-step process was also recommended for cotton gray fabric pretreatment in supercritical carbon dioxide, by achieving a fabric weight loss at 6.21% and a satisfactory capillary rise height at 8.0 cm under an optimized condition. Additionally, an oxidative one-step pretreatment mechanism by employing 18-crown-6 to phase transfer reactive species for cotton gray fabric in SCF-CO2 was further supposed.

A Lagrangian Stochastic Model of a Volcanic Eruption Column

AbstractWe present a Lagrangian stochastic model (LSM) of a volcanic plume in which the mean flow is provided by an integral plume model of the eruption column and fluctuations in the vertical velocity are modeled by a suitably constructed stochastic differential equation. This model is based on that of Bisignano and Devenish (2015, http://doi.org/10.1007/s10546-015-0055-3) with the mean flow provided by the integral plume model of Devenish (2013, http://doi.org/10.1016/j.jvolgeores.2013.02.015). The LSM is applied to the two eruptions considered by Costa et al. (2016, http://doi.org/10.1016/j.jvolgeores.2016.01.017) for the volcanic‐plume intercomparison study with no ambient wind and to the hypothetical cases with ambient wind considered by Aubry et al. (2019, http://doi.org/10.1029/2019GL083975). Vertical profiles of the mass concentration computed from the LSM are compared with equivalent results from large eddy simulations (LES). The LSM captures the order of magnitude of the LES mass concentrations and aspects of their profiles: for example, in contrast with a standard integral plume model, that is, without fluctuations, the mass concentration computed from the LSM decays (to zero) toward the top of the plume consistent with the LES plumes. In the lower part of the plume, we show that the presence of ash leads to a peak in the mass concentration at the level at which there is a transition from a negatively buoyant jet to a positively buoyant plume. A quantitative analysis of the cases with ambient wind shows generally good agreement between the LSM and the LES for a number of quantities including the maximum concentration, the level at which it occurs, the maximum rise height, and the total erupted mass.

Velocity and density measurements in forced fountains with negative buoyancy

In fluid mechanics, fountains take place when a source fluid is driven by its own momentum into a surrounding ambient fluid, and it is counterbalanced by buoyancy. These phenomena are largely encountered in nature and human activities. Despite the numerous studies on the subject, few experimental data are available about the internal structure of turbulent fountains. Here, we present a set of laboratory experiments with the aim to (i) get direct velocity and density measurements of fountains in a controlled environment and (ii) obtain insights about the basic physics of the phenomenon. The results concern the characteristics of the mean and turbulent flow: we report the analysis of the turbulent kinetic energy, the velocity skewness, and the Reynolds stresses, including a quadrant analysis of the fluctuating velocities. For some tests, the correlation between density and vertical velocity is investigated for both mean and fluctuating values. We have quantified the momentum transport, which is mainly out-downward at the nozzle axis with peaks at the mean rise height, where also maximum levels of the buoyancy and mass fluxes are present. The ability of acoustic Doppler current profilers to identify the rise height of the fountain and to measure the velocity field is also discussed.

Gating System Measuring of Sandcasting

Sandcasting is the oldest casting method and valuable however it has still some problems. This study discussed a mathematical approach in the gating system design. A gating system of a Connecting Road from cast iron was used as an object this study. This study measured fluid flow, a gating position in a mold, pouring, spur basin, pouring time, and riser. Solidification time affect volume and surface area, so in this study we adjusted the height of riser based of 1.2 up to 2 as riser diameter. Results of mathematic analysis show that pouring time was 3 sec, dimension of runner as 1.2 cm as High, 1.2 cm of Large, 2.06 of Pressure. The other dimensions were 2.9 cm of High spur, 5.5 cm of Pouring basin, 3.15 cm2 of large of spur with 7.56 cm3 as volume total, and weight total of gating system and riser 0.285 kg. The metal fluid was poured in a molding at 2.83 sec. Dimensions of gating were gotten the 0.42 cm2 from the first in gate and 0.63 cm2 for second in gate.

Effect of tillage and crop establishment practices on performance of rice (Oryza sativa) under rice-wheat cropping system

A field experiment was conducted at Agricultural Research Farm, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh during Kharif season of 2018. The experiment consisted of six combinations of different tillage methods and crop establishment practices with four-time replicated under randomized block design. Zero tillage [direct seeded rice - wheat (Full CA; anchored residue of rice and wheat + mungbean residue retention)]showed significantly higher plant height, number of tillers m-2and chlorophyll content as compared to the other treatments, while the lowest values of these parameters were observed under conventional tillage (rice-wheat without residue). There was a steady rise in plant height and number of tillers with age of plant under all the treatments. The yield and its attributes were significantly higher under zero tillage [direct seeded rice - wheat (full CA; anchored residue of rice and wheat + mungbean residue retention)] followed by treatments zero tillage [direct seeded rice - wheat (full CA; anchored residue of rice and wheat)]. While, the poor yield was reported in conventional tillage (rice-wheat without residue). Zero tillage [direct seeded rice - wheat (full CA; anchored residue of rice and wheat + mungbean residue retention)] increased nutrient use efficiency in term of partial factor productivity of applied NPK in rice crop.

Effects of Tube Radius and Surface Tension on Capillary Rise Dynamics of Water/Butanol Mixtures

Capillary-driven action is an important phenomenon which aids the development of high-performance heat transfer devices, such as microscale heat pipes. This study examines the capillary rise dynamics of n-butanol/water mixture in a single vertical capillary tube with different radii (0.4, 0.6, and 0.85 mm). For liquids, distilled water, n-butanol, and their blends with varying concentrations of butanol (0.3, 0.5, and 0.7 wt.%) were used. The results show that the height and velocity of the capillary rise were dependent on the tube radius and liquid surface tension. The larger the radius and the higher the surface tension, the lower was the equilibrium height (he) and the velocity of rise. The process of capillary rise was segregated into three characteristic regions: purely inertial, inertial + viscous, and purely viscous regions. The early stages (purely inertial and inertial + viscous) represented the characteristic heights h1 and h2, which were dominant in the capillary rise process. There were linear correlations between the characteristic heights (h1, h2, and he), tube radius, and surface tension. Based on these correlations, a linear function was established between each of the three characteristic heights and the consolidated value of tube radius and surface tension (σL/2πr2).

Wetting Dynamics of a Lipid Monolayer.

Direct measurement and control of the dynamic wetting properties of a lipid-coated water-air interface over a wide range of surface tension variations have many important applications. However, the wetting dynamics of the interface near its partial-to-complete wetting transition has not been fully understood. Here, we report a systematic study of the wetting dynamics of a lipid-coated water-air interface around a thin glass fiber of diameter 1-5 μm and length 100-300 μm. The glass fiber is glued onto the front end of a rectangular cantilever to form a "long-needle" atomic-force-microscope probe. Three surface modifications are applied to the glass fiber to change its wetting properties from hydrophilic to hydrophobic. A monolayer of phospholipid dipalmitoylphosphatidylcholine (DPPC) is deposited on the water-air interface in a homemade Langmuir-Blodgett trough, and the surface tension γL of the DPPC-coated water-air interface is varied in the range of 2.5 ≲ γL ≲ 72 mN/m. From the measured hysteresis loop of the capillary force for the three coated fiber surfaces with varying γL, we observe a sharp transition from partial to complete wetting when γL is reduced to a critical value (γL)c. The obtained values of (γL)c are 27 ± 1 mN/m for a DPPC-coated fiber surface and 23 ± 1 mN/m for an trichloro(1H,1H,2H,2H-perfluorooctyl) silane (FTS)-coated surface. Below (γL)c, the contact angle θ0 of the liquid interface is found to be zero for both hydrophobic fiber surfaces and the corresponding spreading parameter S becomes positive. For the FTS-coated fiber surface, the height of capillary rise exhibits a jump when γL is reduced to (γL)c, which indicates that a rapidly advancing liquid film is formed on the fiber surface when the partial-to-complete wetting transition takes place. Our experiment thus establishes a quantitative method by which many other liquid interfaces coated with polymers, surfactants, and biomolecules (such as proteins and lipids) may be characterized dynamically.

Studies on an Alternative Method for Preparation and Fermentation of idlis Made from Proso Millet (Panicum miliaceum L.), Horsegram (Macrotyloma uniflorum (Lam) Verdc.) and Fenugreek (Trigonella foenum-graecum L.)

The present study was undertaken to develop an alternative idli from proso millet with horse gram and fenugreek seeds. Two types of wet batters (Batter A &amp; Batter B) were prepared by soaking the ingredients proso millet, horse gram and fenugreek separately (in the ratio by weight 7:2:1) in excess water for 8 hours at room temperature (25±2ºC). In method A, the ingredients were soaked in excess water and whereas in method B, fenugreek was soaked in buttermilk. The soaked ingredients were ground separately with adequate amount of water using a grinder and mixed with the addition of 1% salt. The resulting batter was fermented for 10 hours at room temperature. The batter was analyzed for its microbial load (Total Plate Count, Lactobacillus and Yeast and Mold) and physico-chemical properties (height rise, pH and titratable acidity) by drawing aliquots at fixed intervals. Microbial analysis revealed maximum load at 6th hour of fermentation for TPC, LAB and Yeast growth. Suppressing activity of the organisms was seen after this stage and there was a sharp decline in microbial growth (LAB and Yeast). The pH and total titratable acidity ranged between 4.88-6.20 and 0.19–0.51% respectively. The nutritional analysis and sensorial acceptance of the idli formulated with both the batters were also studied. Both the idlis were found to have a two-fold increase in protein content and a 50% reduction in carbohydrate content when compared with the traditional rice idli. The sensory analysis was conducted with 100 untrained panelists and the results revealed that idli prepared from Batter A was preferred. A dry ready to cook idli mix was also formulated and was studied for the above said properties. The study highlights that proso millet, horse gram and fenugreek can be used as an effective alternative for preparation of idli.

Experimental study of horizontal heated buoyant jets in a linearly stratified ambience

Horizontal warm buoyant jets injecting into a linearly stratified ambience are common in lakes, estuaries, and oceans. Dynamic features and potential surface temperature signatures of heated buoyant jets are experimentally investigated using particle image velocimetry and an infrared camera. Results reveal that when heated jets are completely underwater, the flow evolution can be classified into the horizontal regime, ascending regime, and collapsing regime, respectively. The maximum rise height and the neutral height both increase linearly with the increasing jet length scale. Based on this relationship, an equation is developed to predict the surface impingement of a horizontal heated buoyant jet. If the surface impingement occurs, staggered vortexes and large meanders caused by mixing between the jet and the free surface are observed on the surface temperature maps. Furthermore, surface temperature fluctuation fields are decomposed using the Karhunen-Loeve method, the first four eigenmodes appear to capture the root mean square temperature fluctuations and the features correlated with the swirling vortexes. In the turbulent kinetic energy budget, mean-flow convection is found to be mainly balanced by turbulent transport. As the heated jet propagates downstream, more kinetic energy is transferred into potential energy rather than into turbulent energy.

The Contribution of Internal Variability to Asian Midlatitude Warming

AbstractThe tropospheric warming in the Northern Hemisphere (NH) midlatitudes has been an important factor in regulating weather and climate since the twentieth century. Apart from anthropogenic forcing leading to the midlatitude warming, this study investigates the possible contribution of internal variability to Asian midlatitude warming and its role in East Asian circulation changes in boreal summer, using four reanalysis datasets in the past century and a set of 1800-yr preindustrial control simulations of the Community Earth System Model version 1 large ensemble (CESM-LE). The surface and tropospheric warming in the Asian midlatitudes is associated with a strong upper-level geopotential height rise north of the Tibetan Plateau (TP). Linear trends of 200-hPa geopotential height (Z200) confirm a dipole of an anomalous high north of the TP and an anomalous low over the Iranian Plateau in 1958–2017. The leading internal circulation mode bears a striking resemblance to the Z200 trend in the past 60 and 111 years, indicating that the long-term trend may be partially of internal origin. The Asian midlatitude warming is also found in preindustrial simulations of CESM-LE, further suggesting that internal variability explains at least part of the temperature change in the Asian midlatitudes, which is in a chain of wave trains along the NH midlatitudes. The Asian warming decreases the meridional gradient of geopotential height, resulting in the weakening of westerly winds over the TP and the TP thermal forcing. Thus, it is essential to consider the role of internal variability in shaping East Asian surface temperature and East Asian summer monsoon changes in the past decades.