1,721,046 research outputs found
Morphology estimation from normal stress measurements for dilute immiscible polymer blends
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Soil Destabilization Induced by Water Wetting Treatments Simulating Rain Infiltration Processes, Studied via Rheology and Granulometry
No full textA soil depleted of its organic carbon content is typically destabilized, i.e., its capacity to maintain its microstructure intact under various stress conditions weakens, and consequently, landslides and mudflows can be triggered and propagated more easily. In a previous work, we showed with a rheological analysis that the removal of the sole water-soluble organic carbon “destabilized” the slurry very similarly to what occurs with the removal of the vast majority of soil organic carbon. In principle, the water-soluble organic carbon can be dissolved by rainfall, during which water can infiltrate the soil, eventually leaving it either by percolation or evaporation. These two processes are mimicked here with two different soil water wetting procedures. The stability of the treated (wetted) soils is studied with rheological and granulometric experiments. The former run on concentrated suspensions, while the latter run on very diluted ones. Despite this, the results agreed very well, indicating that the two wetting procedures induce the same destabilization of the soil which behaves as the one depleted by the whole water-soluble organic carbon. Our results concluded that a soil destabilized by a wetting procedure, i.e., by a rainfall event, will be more prone to trigger a landslide that will propagate more swiftly and will stop with more difficulties
Methane/hydrogen blends in controlled auto ignition engines with EGR: Evaluation of NOx emissions
Full text linkGaseous fuel utilisation reduces pollutant emissions and makes energy systems less dependent from oil. Their carbon content is low, which means a reduction in CO2 emissions per unit of energy in comparison with liquid fossil fuels. The use of biogases (BG) and/or natural gas (NG) in internal combustion engines (ICE) is very attractive. To increase the efficiency of NG engines hydrogen can be added to natural gas, and innovative BG containing hydrogen can be conveniently used. Hydrogen has a high combustion speed, providing a reduction of the combustion duration when mixed with methane. Consequently higher temperatures are attained in the combustion chamber and thus engines fuelled with NG/H2 blends increase the NOx emissions. NG and BG are generally adopted as fuel in positive ignition ICEs; however they are also suitable for fuelling Controlled Auto Ignition (CAI) engines. The authors investigated combustion in CAI ICE by means of numerical simulations. Starting with pure CH4, the fuel was subsequently enriched with H2, comparing engine performance and exhaust emissions. CAI systems are indirectly controlled with varying air-fuel ratio, boost pressure and charge temperature. Charge temperature depends on the residual gas content, which has an impact on the combustion process as the burning mixture composition consequently changes. The authors investigated the effect of exhaust gas recirculation on the in-cylinder gas temperature and reaction mechanism, with main focus on NOx emissions. Hydrogen addition reduces the intake temperature requirement for the autoignition, which means less EGR. Hydrogen enriched fuels also require lower boost pressure than CH4 to deliver the reference imep while engine efficiency does not change significantly between tested fuels. Hydrogen also helps in reducing NOx emissions due to lower boost pressure and EGR rates
Drop shape dynamics of a Newtonian drop in a non-Newtonian matrix during transient and steady shear flow
No full textTransient and steady deformation of a single Newtonian drop immersed in a non-Newtonian matrix subjected to a homogeneous shear flow is investigated microscopically. Two model Boger fluids have been used as non-Newtonian matrices. The three-dimensional drop shape is completely determined as observations from both the velocity-vorticity and velocity-velocity gradient plane are available. Start-up and relaxation are investigated varying both the capillary number and the elasticity of the matrix fluid, while the viscosity ratio is kept constant. The extensive data set demonstrates that matrix elasticity reduces the steady drop deformation and promotes droplet orientation, can induce a drop deformation overshoot in the start-up experiments and slows down the relaxation phenomena. The experimental results have been compared with predictions of a phenomenological model
The role of the water soluble organic carbon of soils on the stability of natural slurries
No full textConcentrated non-Brownian suspensions under oscillatory shear flow: Dependence on the applied strain and frequency
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