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Item Differential equation for the flow rate of discharging silos based on energy balance(2020-05) Darias, José Ramón; Madrid, Marcos A.; Pugnaloni, LuisSince the early work of Hagen in 1852 and Beverloo et al. in 1961, the flow rate of granular material discharging through a circular orifice from a silo has been described by means of dimensional analysis and experimental fits, and explained through the “free fall arch” model. Here, in contrast with the traditional approach, we derive a differential equation based on the energy balance of the system. This equation is consistent with the well known Beverloo rule thanks to a compensation of energy terms. Moreover, this new equation can be used to explore new conditions for silo discharges. In particular, we show how the effect of friction on the flow rate can be predicted. The theory is validated using discrete element method simulations.Item Stability and conductivity of proppant packs during flowback in unconventional reservoirs: a CFD–DEM simulation study(Elsevier B.V., 2021) Vega, Federico G.; Carlevaro, Manuel; Sánchez, Martín; Pugnaloni, LuisWe present simulations using a coupled Computational Fluid Dynamics–Discrete Element Method (CFD–DEM) approach for a slurry of millimeter-sized particles in water which is squeezed between two walls and then made flow out though a narrow aperture. The process is akin to the flowback stage in the near wellbore zone of a hydraulic-stimulated well for hydrocarbon recovery. We consider different wall roughness and investigate its effect on particle production, final distance between walls, spatial particle distribution between the walls, and fluid production rate. We have found that the final distribution of particles changes significantly with small variations in the roughnesses of the walls. This in turn leads to production flow rates that may vary up to 50%. Although the main driver of the production for unconventional wells is the propped fracture network, these results suggest that the roughness of the fracture walls seems to play an important role in the final conductivity and therefore in the ultimate recovery.Item Universal features of the stick-slip dynamics of an intruder moving through a confined granular medium(2022-04-21) Pugnaloni, Luis; Carlevaro, Manuel; Kozlowski, Ryan; Zheng, Hu; Kondic, Lou; Socolar, Joshua E. S.Experiments and simulations of an intruder dragged by a spring through a two-dimensional annulus of granular material exhibit robust force fluctuations. At low packing fractions (φ < φ0), the intruder clears an open channel. Above φ0, stick-slip dynamics develop, with an average energy release that is independent of the particle-particle and particle-base friction coefficients but does depend on the width W of the annulus and the diameter D of the intruder. A simple model predicts the dependence of φ0 on W and D, allowing for a data collapse for the average energy release as a function of φ/φ0. These results pose challenges for theories of mechanical failure in amorphous materials.Item On the use of magnetic particles to enhance the flow of vibrated grains through narrow apertures(2021-06-28) Carlevaro, Manuel; Kuperman, Marcelo N.; Bouzat, Sebastián; Pugnaloni, Luis; Madrid, Marcos A.The ow of grains through narrow apertures posses an extraordinary challenge: clogging. Strategies to alleviate the effect of clogging, such as the use of external vibration, are always part of the design of machinery for the handling of bulk materials. It has recently been shown that one way to reduce clogging is to use a small fraction of small particles as an additive. Besides, several works reported that self-repelling magnetic grains can ow through narrow apertures with little clogging, which suggest these are excellent candidates as \lubricating" additives for other granular materials. In this work, we study the effect of adding self-repelling magnetic particles to a sample of grains in two-dimensions. We find that, in contrast with intuition, the added magnetic grains not necessarily aid the ow of the original species.