Outlet Size Research Articles

Designing experiments for estimating an appropriate outlet size for a silo type problem

Jam formation is a problem that may occur when granular material is discharged by gravity from a silo. The estimation of the minimum outlet size, which guarantees that the time to the next jamming event is long enough, can be crucial in the industry. The time is modeled by an exponential distribution with two unknown parameters, and this goal translates to precise estimation of a nonlinear transformation of the parameters. We obtain c-optimum experimental designs with that purpose, applying the graphic Elfving method. Because the optimal experimental designs depend on the nominal values of the parameters, we conduct a sensitivity analysis on our dataset. Finally, a simulation study checks the performance of the approximations, first with the Fisher Information matrix, then with the linearization of the function to be estimated. The results are useful for experimenting in a laboratory and then translating the results to a real scenario. From the application we develop a general methodology for estimating a one-dimensional transformation of the parameters of a nonlinear model.

The development of sand erosion induced by shield-tunnel joint leakage

Sand erosion induced by shield-tunnel joint leakage is one of the most frequent catastrophes, causing ground collapses and tunnel failures. In this paper, a self-designed test device that considers differences in water head, burial depth and leaky joint characteristics was used to investigate sand erosion and void development. The experimental results show that the development of sand erosion has obvious temporal and spatial evolution characteristics. In the temporal dimension, sand erosion development can be divided into four stages: vertical erosion, cavity formation, coarse-particle skeleton distribution (CPSR) and steady seepage. In the spatial dimension, it can be divided into three regions: the stable zone, slip surface and eroded zone shape. It is found that the erosion zone can be described by a rotating ellipsoid and the scope of the erosion zone increases with increasing water head, whereas the influence of the burial depth is not significant. The influence of the invert leakage on the volume flow rate is also determined to be larger than that of the vault leakage and the volume flow rate rapidly increases when the size of the leaky joint exceeds the critical outlet size. Finally, a theoretical model based on the test results is proposed to predict the volumetric flow rate of sand erosion.

Effect of particle shape on packing fraction and velocity profiles at outlet of a silo

Many studies on how the particle shape affects the discharge flow mainly focus on discharge rates and avalanche statistics. In this study, the effect of the particle shape on the packing fraction and velocities of particles in the silo discharge flow are investigated by using the discrete element method. The time-averaged packing fraction and velocity profiles through the aperture are systematically measured for superelliptical particles with different blockinesses. Increasing the particle blockiness is found to increase resistance to flow and reduce the flow rate. At an identical outlet size, larger particle blockiness leads to lower velocity and packing fraction at the outlet. The packing fraction profiles display evidently the self-similar feature that can be appropriately adjusted by fractional power law. The velocity profiles for particles with different shapes obey a uniform self-similar law that is in accord with previous experimental results, which is compatible with the hypothesis of free fall arch. To further investigate the origin of flow behaviors, the packing fraction and velocity field in the region above the orifice are computed. Based on these observations, the flow rate of superelliptical particles is calculated and in agreement with the simulated data.

Parametric study of cavity on the performance of a hydrogen-fueled micro planar combustor for thermophotovoltaic applications

In order to obtain high energy output power and energy conversion efficiency for micro-thermophotovoltaic system, a hydrogen-fueled micro planar combustor with cavity is designed in this work. Numerical investigations on the performance of micro-cylindrical combustors with and without cavity are executed under different cavity length, outlet size and solid wall materials. Results show that the micro planar combustor with cavity can obtain a higher and more uniform outer wall temperature comparing with the micro planar combustor without cavity. With the reduction of cavity length and outlet size, the energy output and energy conversion efficiency of MTPV is much higher, while the pressure loss becomes larger. Thus, the optimal dimensionless cavity length and outlet size is 3/9 and 5/7 × 1/3, respectively. Furthermore, with the optimal cavity length and outlet size, nickel is used as the solid wall material for higher energy conversion efficiency of MTPV system, which increases to 3.86% at the inlet velocity of 5 m/s. As a result, the micro planar combustor with cavity is more suitable in MTPV system for higher energy output and energy conversion efficiency.

Filtration characteristics with parameter variation for dust removal from syngas

BackgroundGranular bed filter technology is a newly emerging field, and the science is in its infancy. There is a lack of background information on these consistencies. This study provides new insights into clean processing, which is useful in hot gas cleanup technology. MethodsWe employed a moving granular bed filter, which is evaluated in two separate performance studies: (1) optimization of particle removal efficiency and bed pressure drop under different movement velocities of silica sand; and (2) high temperature model simulation conducted dust and Silica sand flow rates and superficial velocity. Besides, this evaluated the filter system's dynamic characteristics by measuring variations in the outlet concentration and size distribution of dust particulates. Significant findingsThe results indicated that the filtered dust in the silica sand considerably affected the dust via inertial impaction and diffusion. With higher movement velocity of silica sand, the higher specific resistance coefficient of k1 and k2 caused better performance of collection mechanism, thereby enhancing the removal efficiency. Consequently, this study observations indicated that at a high movement velocity of silica sand, the gas velocity favors dust attachment on the silica sand particle surface, facilitating dust removal.The purpose of this study is to investigate the efficiency of moving granular bed filter (MGBF) in high-temperature environment under different operation conditions. The effects of the test temperature and movement velocities of silica sand on the dust size distribution and removal efficiency were studied; further, an experimental system comprising a high-temperature environment of 600 °C was established for a filter system. The removal efficiency was enhanced at a test temperature of 25 °C when considering a gas velocity of 500 mm/s and a movement velocity of silica sand of 1.95 mm/s. The test results showed that an improvement in the movement velocity of silica sand decreased the temperature of the bed, increasing the removal efficiency. Furthermore, this study could be used in different high-temperature filter systems for gas cleanup.

A parabola-shaped free-fall arch in silos with centric and eccentric outlets

In this paper we report experimental results on the geometric characteristics of free-fall arch (FFA) inside two types of silos with outlets at different locations. A parabola-shaped FFA structure is discovered in the exit hole located close to the vertical wall of the silo. By comparing the height and width of FFA and the vector velocity of particles on the arch in the two types of silos, the direct reason for the larger mass discharge rate in the eccentric silo is revealed. In addition, we found that the vertical velocity of particles on FFA is positively correlated with the mass discharge rate. This highlights a surprising and unrecognized fact that the traditional calculation of mass discharge rate cannot ignore the velocity of particles on FFA, especially when the mass discharge rate is high. Measurement results of free-fall arch in silos. • A parabola-shaped FFA is observed in eccentric silo. • The maximum height of FFA in eccentric silo is higher. • The height and width of FFA in eccentric silo were positively correlated with MDR. • The vertical velocity of beads on arch increases with the increase of outlet size.

Prediction of size distribution in dairy cream homogenization

The size distribution of fat globules in homogenized concentrated dairy cream has been measured in High-Pressure Homogenizers ( HPH ), working at 80 °C and various operating pressures. For each pressure, the outlet size distribution is found to be self-similar to the inlet distribution, and can be accurately predicted dividing each class diameter of the inlet distribution by a single proportionality factor, which can be interpreted using a simplified deformation model of the fat globules as elongated filaments. The evolution of the factor with the operating pressure is consistent with a scaling analysis of the average shear rate in the HPH as well as with the value predicted from numerical simulations of the flow in the HPH , supporting the physical interpretation of the fragmentation model. • Homogenized fat globules size distribution in cream can be deduced from the entry size distribution with a single parameter. • A simple viscous shear dominated breakup model is proposed to interpret this result. • The breakup model parameter can be explicitely related to the HPH pressure.

A Numerical Analysis of the Leakage Characteristics of an Embankment Dam Slope With Internal Erosion

Leakage is a common defect of embankment dam slopes, and is usually accompanied by internal erosion. This study establishes a mathematical two-phase seepage coupling model that explicitly considers the effects of internal erosion. With the help of finite element software COMSOL Multiphysics®, we use this model to study the characteristics of fluid seepage, the fraction of leakage volume that is made up of migrated fine particles (migrated fine particles volume fraction), porosity, permeability, and displacement in the leakage process of a three-dimensional embankment dam slope, as well as to study the influence of the water level and leakage outlet size on the aforementioned features. Our results show that water seepage velocity gradually increases with time, especially at the downstream leakage outlet. Therefore, the erosion and migration of fine particles occur primarily at the downstream leakage outlet, resulting in a significant increase in the migrated fine particles volume fraction, porosity, and permeability. In addition, the maximum migrated fine particles volume fraction, the maximum porosity, and the maximum permeability in the slope increase nonlinearly with time. Curves for maximum displacement with a strength reduction factor can be divided into three stages: the early stable stage, the midterm nonlinear growth stage (creeping state), and the later rapid growth stage (instability state). We also find that the rise of the water level promotes the erosion and migration of fine particles on the slope and that the maximum migrated fine particles volume fraction and the maximum porosity increase with the water level. The values of the strength reduction factor for the creeping state decrease as the water level rises. Furthermore, the larger the size of the downstream leakage outlet, the larger the maximum migrated fine particles volume fraction and maximum porosity. However, the relationship between maximum displacement and strength reduction factor is nearly unaffected by the size of the leakage outlet.

Effect of Opening Size on the Development of Ventilation-limited Fire

There are many factors, that affect the development of indoor fire, such as the size of the fire source, the opening or space of the room, and the nature of the combustible materials. Among them, the space of the room, has a significant impact on the development of a ventilation-limited fire. In this paper, the Fire Dynamics Simulator (FDS) software is used to analyze, the risk of fire initiation in the restricted ventilated compartment, when the size of vertical ventilation space is different. Through, a combination of experimental design, numerical simulation, and theoretical analysis, the changes in the level of carbon monoxide, visibility, temperature, Heat Release Rate (HRR) and, the smoke exhaust efficiency of natural smoke at different opening sizes are observed. It is observed that, when the ratio of inlet and outlet area reaches 2:1, the natural smoke exhaust effect is the best, however, the increasing in the opening size has little significance on the smoke exhaust effect. The research on the influence of smoke outlet size, will helps in the development of the law regarding fire prevention, smoke exhaust design, and fire rescue work of a building.

Marine environment numerical simulation of morphological planning of land reclamation

Based on the evaluation criteria of the impact of different types of reclamation design on the natural environment of coastal waters, the environmental fluid dynamics model was used to simulate the seawater environment in 13 scenarios from three aspects: the shape of the artificial island, the size of inner lake outlet and the layout of the artificial island. The hydrodynamic force and water exchange capacity of these islands were quantitatively compared, and the effects of different artificial islands on the Marine environment were summarized. The planning morphology design guidelines are summarized in four aspects: (1) reduce the serrated steep slope shoreline, avoid forming semi-closed water, and increase the simple and smooth shoreline; (2) reduce the width of the lake mouth to increase the length of the lake; (3) choose a simple alignment parallel to the shore; (4) the design mainly focuses on the morphology of shoreline, followed by consideration of the lake mouth and artificial island arrangement.

Optimization of the Battery Pack Heat Dissipation Structure of a Battery-Type Loader

The development of a battery-type loader is an important research direction in the field of industrial mining equipment. In the energy system, the battery will inevitably encounter the problem of heat dissipation when using high-power electricity. In this study, we took the power battery pack of a 3 m3 battery-type underground loader as the research object. The influence of single factors, such as the position of the air outlet of the battery pack, the size of the air outlet, the width of the separator, and the reverse plate, on the heat dissipation characteristics of the battery pack were studied. Then, a prediction model between the structural parameters and temperature was established using a radial basis function (RBF) neural network. This prediction model was then used as an adaptation evaluation model for global optimization through the multiobjective particle swarm optimization (PSO) algorithm, using which the optimal combination of structural parameters was obtained. The maximum temperature of the battery pack after optimization was reduced by 22%, compared to that before optimization, and the average temperature was reduced by 12.5%. Overall, the heat dissipation effect significantly improved. The optimization results indicate that the method proposed in this paper is feasible for use in optimizing battery heat dissipation systems in electric vehicles, thus providing a reference for research related to battery pack heat dissipation.

Collisional regime during the discharge of a two-dimensional silo.

The present work reports an investigation into the collisional dynamics of particles in the vicinity of the outlet of a two-dimensional silo using molecular dynamics simulations. Most studies on this granular system focus in the bulk of the medium. In this region, contacts are permanent or long-lived, so continuous approximations are able to yield results for velocity distributions or mass flow. Close to the exit, however, the density of the medium decreases and contacts are instantaneous. Thus, the collisional nature of the dynamics becomes significant, warranting a dedicated investigation as carried out in this work. More interesting, the vicinity of the outlet is the region where the arches that block the flow for small apertures are formed. It is found that the transition from the clogging regime (at small apertures) to the continuous flow regime is smooth in collisional variables. Furthermore, the dynamics of particles as reflected by the distributions of the velocities is as well unaffected. This result implies that there is no critical outlet size that separates both regimes, as had been proposed in the literature. Instead, the results achieved support the alternative picture in which a clog is possible for any outlet size.

Self-similarity of density and velocity profiles in a 2D hopper flow of elliptical particles: Discrete element simulation

Two-dimensional discharge flow of elliptical particles with different aspect ratios from a silo is investigated by using discrete element simulation. The measured flow rate of the particles is well fitted via Beverloo's law. The flow rate shows a monotonic decrease with increasing aspect ratio. The density and velocity profiles of particles at the outlet were systematically measured. At an identical outlet size, the speed of particles through the aperture decreases with increasing aspect ratio. The velocity profiles in all cases follow the same definite self-similar law and are in good agreement with the reported experimental results, thereby showing compatibility with the free fall arch postulation. The density profiles show obvious self-similar feature and can be fitted conveniently by using a fractional power law. Based on these observations and the results of the previous work, the flow rate for elliptical particles is calculated and is in agreement with the simulated results.

Effects of inlet-outlet positioning, muffler geometry, and baffle design on vehicle muffler performance for desired sound transmission loss

A systematic comparative examination of different single-chamber and double-chamber muffler geometries, comprised of various baffle geometry and size, number of chambers, and inlet-outlet positioning was conducted to determine the most suitable geometry for size-efficient mufflers which can meet size-limitations of automotive applications, confirming enhanced transmission loss (TL). First, we considered a reference model for validation of the simulation method. Then, we objectively studied the effects of circular and rectangular baffles of different sizes on the TL of single-chamber mufflers. Next, double- and single-chamber models were compared. Consequently, to better analyze the performance of the representative benchmark double-chamber muffler, the effects of different layouts of the outlet were studied and the corresponding TL was derived, while the inlet and baffle type and size were fixed. Finally, the effect of inlet layout, considering given outlet position, baffle type, and size, was studied on the noise control performance of the muffler. Results indicate that the 75% circular baffle has a wide frequency range and high TL of 58 dB, where the 75% rectangular plate baffle has a transmission loss of 67 dB. The double-chamber muffler has a wider frequency range and a higher TL of 78 dB compared to the single-chamber muffler. Moreover, changes in the inlet-outlet of the silencer significantly affect TL. As the inlet-outlet positioning of the silencer greatly contributes to the space constraints and packaging of the vehicle components, therefore, the variations of the inlet-outlet position of the silencer in the limited space available in vehicles need to be considered as an important design parameter, considering packaging limitations and noise control performance, which can significantly affect tailpipe radiated noise.

Influence of grain bidispersity on dense granular flow in a two-dimensional hopper

This work uses the discrete-element method to investigate bidisperse dense granular flow with large and small grains in a two-dimensional hopper. A half-circular dynamical force arch forms above the outlet, and the robustness of Beverloo's law is verified to describe the relationship between flow rate and outlet size. The bidisperse flow peaks when monodisperse flow of small grains is supplemented with a small fraction of large grains. The dense flow rate relates closely to the local flow characteristics of a key area. However, the interior packing structures (i.e., an ordered arrangement for monodisperse flow and a disordered arrangement for bidisperse flow) dominate the flow-pattern transition from mass flow to funnel flow. The earlier occurrence of the transition increases the grain velocity and therefore the flow rate. This discovery of interior flow rheology provides a plausible basis for constructing a general constitutive framework for dense granular flow.

Analysis of Turbulent Boundary Layer Jet Flow Pattern of TPS Standard Nozzle

The design of the standard nozzle affects the air mass flow calibration accuracy of TPS. The relationship between the outlet diameter and the jet flow pattern is studied by performing jet simulation simulation on the three outlet size standard nozzles under the same boundary conditions. Through the simulation results, it can be seen that the outlet diameter under a single variable determines the value and range of the jet Mach number, which will cause a huge change in the mixing zone of the turbulent boundary layer, which directly affects the turbulent kinetic energy and has a linear relationship with the mass flow rate.

Numerical analysis of the effects of different outlet sizes on pebble flows in HTR-10 pebble beds

The effects of outlet size on the flow characteristics in the pebble bed are studied by means of Discrete Element Method (DEM). Two ways of changing the outlet are considered: fixed hopper angle (‘D’ cases) and fixed hopper height (‘d’ cases). The pebble flow inside pebble beds shows the characteristics of mass flow in the upper part and funnel flow in the lower part, therefore, the changes in the flow pattern are studied first to find out the special transition region by critical time and critical height. Results show that the transition of flow pattern will occur earlier when the opening is smaller, and the critical height of transition increases with the decrease of outlet size for‘d’ cases. By contrast, there is almost no difference in the critical time and height in ‘D’ cases, indicating that the hopper angle is an important factor affecting the overall flow pattern rather than the hopper height.In the second part, from the perspective of core safety, the influences of outlet size on the retention, flow uniformity and velocity characteristics inside the core are analyzed.The increase of outlet size can improve both the retention and flow uniformity. Changing the outlet byadjusting the hopper anglehas a more significantinfluence on the flow performance. From the analysis of pebbles in different radial positions, it can be found that although pebbles in the middle region flow out slower when the opening is larger, it is opposite in terms of pebbles near the wall, where less retention is observed. Overall, a larger proportion of pebbles are in motion with relatively small but similar speed, showing a more uniform movement. Interestingly, simply changing the hopper height to adjust the opening has no effect on the flow of pebbles within 1d range from the wall.

Effect of inlet and outlet size, battery distance, and air inlet and outlet position on the cooling of a lithium-ion battery pack and utilizing outlet air of cooling system to heat an air handling unit

This paper evaluated the cooling of a plate li-ion pack of batteries (LIPB) with 12 battery cells using airflow. The LIPB is placed in a cooling chamber that is cooled by a forced flow of air passing through the battery cells. The impact of using the outlet air from 5 LIPBs of this type of battery for heating an air handling unit (AHU) is assessed. The variables include the input distance from the lower wall and the output distance from the upper wall, the input and output dimensions, as well as the distance between the battery packs, which are in the range of 0 to 1 meter, 0 to 0.8 m and 0 to 0.1 m, respectively. The amount of energy required for the residential unit in different months of the year for a cold and dry environment is estimated using the Carrier software. COMSOL Multiphysics software is also employed to simulate LIPB cooling. The heat transfer coefficient, the temperature of the batteries, the outlet temperature, and the pressure drop in the cooling system are determined by changing the size of the inlet and outlet of the airflow, the distance of the batteries from each other, and the change of the inlet and outlet location. The results reveal that an increment in the inlet airflow enhances the amount of pressure drop and heat transfer coefficient and reduces the value of battery cell temperature and outlet air temperature. As the distance between the batteries is enhanced, the pressure drop and air outlet temperature are intensified and the temperature of the battery cells is reduced. Also, it is observed that 10.3 kWh of the required heating energy of the building can be achieved from the outlet air from the cooling system of the batteries. Therefore, this system provides a maximum of 100% of heating energy in June and October and a minimum of 15% of the energy required for the house in October.

Characterization of the Clogging Transition in Vibrated Granular Media.

The existence of a transition from a clogged to an unclogged state has been recently proposed for the flow of macroscopic particles through bottlenecks in systems as diverse as colloidal suspensions, granular matter, or live beings. Here, we experimentally demonstrate that, for vibrated granular media, such a transition genuinely exists, and we characterize it as a function of the outlet size and vibration intensity. We confirm the suitability of the "flowing parameter" as the order parameter, and we find out that the rescaled maximum acceleration of the system should be replaced as the control parameter by a dimensionless velocity that can be seen as the square root of the ratio between kinetic and potential energy. In all the investigated scenarios, we observe that, for a critical value of this control parameter S_{c}, there seems to be a continuous transition to an unclogged state. The data can be rescaled with this critical value, which, as expected, decreases with the orifice size D. This leads to a phase diagram in the S-D plane in which clogging appears as a concave surface.

Granular internal dynamics in a silo discharged with a conveyor belt

The dynamics of granular media within a silo in which the grain velocities are controlled by a conveyor belt has been experimentally investigated. To this end, the building of coarse-grained field maps of different magnitudes has allowed a deep analysis of the flow properties as a function of two parameters: the orifice size and the belt velocity. First, the internal dynamics of the particles within the silo has been fully characterized by the solid fraction, the velocity of the particles and the kinetic stress. Then, the analysis of the vertical profiles of the same magnitude (plus the acceleration) has allowed connection of the internal dynamics with the flow rate. In particular, we show that the gamma parameter – which accounts for the integration of the normalized acceleration along the vertical direction – can successfully discriminate the kind of flow established within the silo (from the quasistatic regime to the free discharge) depending on the outlet size and belt velocity.