Rectangular Bed Research Articles

Drying strategies of spent coffee grounds using refractance window method

The objective of this study was to evaluate, during the drying of spent coffee grounds, the application of pretreatments with ethanol and the application of ultrasound assisting the refractive window (RW) drying, and to compare with convective drying by hot air (AC). The effect on the kinetics parameters of the Fick and Page models were evaluated, as well as on the content of total phenolics and antioxidant capacity. For AC drying, samples of spent ground coffee were prepared in the form of fixed rectangular beds 0.7 cm high, which were placed on polyester sheets and pretreated up to 10 times sprayed with ethanol, then dried by AC at 80 °C and 0.8 m/s. For RW drying, the samples prepared in the same way as for AC were used. For this case, the application of ethanol as pretreatment and the use of ultrasound during process were tested. As results, regardless of the conditions applied, drying by RW was up to 50 % faster, evidenced in the highest values of effective diffusivity (from the Fick model) and the kinetic parameter (from the Page model). Regarding the treatments applied and their effect on the drying kinetics, any treatment had a significant effect on AC drying. On the contrary, the strategies applied in RW drying had significant effects, both the application of pretreatment with ethanol as well as the application of ultrasound assisting the process accelerated the drying kinetics. However, the treatment with ethanol and RW drying was the one that best preserved the phenolic compounds and the antioxidant capacity in the samples. Therefore, these strategies could be a good option to improve RW drying by accelerating the process and preserving the bioactive compounds in the spent coffee grounds for subsequent utilization.

Cavity, pinning and air lock in both rectangular and radial cross-flow moving beds with a gas-solid baffle

In a cross-flow moving bed, the gas-solid cross-flow pattern facilitates the high gas process capacity for a relatively low pressure drop, while the appearance of the abnormal phenomena of cavity, pinning and air lock reduces the bed operating flexibility. A new structural optimization of a gas-solid baffle is proposed. Relevant equations for evaluating these three phenomena are theoretically derived or summarized in the original bed and the bed with a gas-solid baffle. Based on experimental and theoretical data, with the proposed structural optimization, the cavity and pinning are weakened in rectangular and radial beds and the air lock can be easily controlled by increasing the height and diameter of the feed tube. The preferred location of the gas-solid baffle is the middle position (x/L = 0.5) of the rectangular bed and/or the position (r-r1)/(r2-r1) < 0.5 of the radial bed with different gas superficial velocities, particle diameters and bed voidages.

Inter-particle fluid flow visualisation of larger packed beds pertaining to heap leaching using X-ray computed tomography imaging

X-ray computed tomography (XCT) is a non-destructive 3-D imaging technique that permits visualisation of the internal structure within a sample, avoiding the stereological error found in conventional two-dimensional (2-D) image analysis. Its small-scale variant, in the present manuscript, referred to as X-ray micro-computed tomography (XMT) but more commonly referred to as µCT, has been widely studied for the characterisation of mineral particle beds, with a common focus in recent years being heap leaching applications. Several technical and computational factors have however limited the size of the configurations and samples studied with this methodology and thus CT flow path visualisation studies on packed beds larger than a few centimetres are uncommon in the literature. The methodology is also rarely used for fluid flow path identification, with other non-invasive alternatives being preferred. To remediate, the authors used a large medical XCT scanner to image a 266 * 200 * 100 mm3 rectangular bed configuration filled with non-porous 8 mm glass beads and porous 16–20 mm rock particles. The fluid flow was for its part imaged through the addition of Gastrografin®, a common medical contrast agent. Using Thermo Fisher Scientific's Avizo software, 3-D images of the beds, the liquid flows, as well as the pore networks were constructed and their parameters were computed. Validation experiments were also carried through ultraviolet (UV) fluorescence imaging using sodium fluorescein dye addition. By comparing the computed results of sphericity and equivalent diameter to the known values and the computed flow images to the UV fluorescence results, the authors conclude that their methodology is of adequate accuracy for further developments towards comprehensive analyses of unsaturated heap flow behaviour.

Investigating the potential of using glass foam for an EMAS material to mitigate aircraft overrun accidents

ABSTRACT An aircraft overrun occurs when an aircraft is unable to stop within the runway design length. Commercial airports are required to have a 305 m (1000-ft) runway safety area (RSA) at each runway end to avail an aircraft adequate length for stoppage during an overrun. At airports where this space is unavailable, the Federal Aviation Administration (FAA) allows for an airport to use an Engineered Materials Arresting System (EMAS). An EMAS is positioned within the RSA and is comprised of an energy absorbing material that brings the aircraft to stoppage through drag forces developed at the tire-EMAS interface. EMAS are constructed using low-density 1.21 m × 1.21 m (4-ft × 4-ft) variable thickness cementitious blocks. The blocks are aligned adjacent to one another to form a rectangular EMAS bed within the RSA. This article presents the computer code, SGAS, developed by the author to predict aircraft stopping distance and behaviour of current aircraft types within an EMAS. The SGAS computer code is validated with results from the FAA ARRESTOR computer code. After validating the SGAS computer code, this article investigates the potential for using glass foam blocks as an alternative EMAS material.

Simulation of Three-dimensional Vibrated Fluidized Bed Dryer Using Distinct Element Method

The particle motion, temperature behavior, and drying rate of particle inside a vibrated fluidized bed dryer were numerically investigated in this work. In the simulation, the Distinct Element Method (DEM) based on the Newton’s second law of motion was used to solve the particle motion. The physical aspects of fluid motion and heat transfer were obtained by applying Computational Fluid Dynamics (CFD) technique. For the drying of particle, only the constant rate period was considered in order to save the computational time. Programming was developed in Standard-C language and using MATLAB to visualize the results. In the simulation, 2,000 particles with stiffness 800 N m-1 were simulated in a rectangular bed. The developed model was validated with an experimental result of Gupta et al. [1]. The program was then used to study the effect of superficial gas velocity (U0), frequency of vibration (f) and amplitude of vibration (a) in fluidized bed dryer. At low velocities and no vibration of bed, articles in the bed were not fluidized but smoothly circulated. Thus, the heat transfer occurred only near the orifice. When superficial gas velocity increased, the fluidization of the particles was observed. The fluidization and drying rate improved with increased in superficial velocity for both vibrated fluidized bed and stationary bed. With introducing of vibration, the fluidization behavior of the particle was improved. The particles in the bed were well mixed and also increased the drying rate. From the simulation results, increasing of frequency and amplitude could not significantly improve rate of drying.

Caracterização morfométrica e hidrológica da bacia hidrográfica formada pelos cursos hídricos da região central do município de Itabira (MG)

O processo de urbanização acarreta impactos hidrológicos e ambientais nos cursos hídricos, destacando-se a perda progressiva das potencialidades de seu uso, com consequências sobre a quantidade e a qualidade da água. Neste sentido este artigo objetivou a caracterização hidrológica e morfométrica da bacia hidrográfica formada pelos canais de drenagem das avenidas Carlos Drummond de Andrade, Carlos de Paula Andrade, Cristina Gazire e Prefeito Li Guerra, localizados na região central de Itabira (MG). Para tal, foi utilizada a pesquisa documental para análise do uso e ocupação do solo e realizados levantamentos em campo para identificação da geometria e vazão máxima dos canais. Com relação à análise morfométrica, o coeficiente de rugosidade e o índice de compacidade indicam que a bacia analisada é propensa a cheias. Verificou-se que a geometria dos canais varia de trapezoidal a seção mista (laterais com geometria retangular e leito triangular). Considerando a análise hidrológica, notou-se que a vazão máxima do canal da Avenida Prefeito Li Guerra, localizada na porção a jusante da bacia, não suporta a vazão de projeto obtida pelo método racional para um tempo de retorno de 50 anos. Assim, visando reduzir os impactos negativos relacionados às enchentes, sugere-se como medidas compensatórias a manutenção de áreas verdes, a regulação do uso do solo, poços de infiltração, valas de infiltração e a utilização de pavimentos permeáveis.

Effect of flow pulsation on fluidization degree of gas-solid fluidized beds by using coupled CFD-DEM

In this paper, the effect of inlet flow type on fluidization of a gas-solid fluidized bed was studied by using numerical simulations. Gas-solid fluidized beds are widely used in processes such as heating, cooling, drying, granulation, mixing, segregating and coating. To simulate the gas-particle flows, the unresolved surface CFD‐DEM was used considering Eulerian–Lagrangian approach. The fluid phase was modeled by computational fluid dynamics (CFD) while the solid phase was solved by discrete element method (DEM), and the coupling between gas and solid phases was considered to be four-way. The uniform and pulsed flows were injected through three nozzles located at the bottom of a rectangular bed. Three types of pulsed flow were considered: sinusoidal, rectangular and relocating. The fluidized bed behavior was discussed in terms of minimum fluidization velocity (MFV), pressure drop, bubble formation, bed expansion, particles velocity and, gas-solid interaction and particle contact forces. The results of different simulations indicated that the minimum fluidization velocity of the beds fluidized by pulsed flows was decreased by up to 33%. The influence of the pulsation amplitude on the minimum fluidization velocity was more significant than that of the pulsation frequency. The bed expansion and particles average velocity were increased by the pulsed flows, while the pressure drop and interaction force were decreased. As the pulsation frequency increased, the pressure drop and gas-solid interaction force increased, although size of the bubbles and bed expansion decreased. It was also observed that in large vibration frequencies, the bubbles became more regular. In the sinusoidal flow, the velocity and contact force between the particles were initially increased by frequency and in larger frequencies they were decreased.

Bed configuration effects on the finned flat-tube adsorption heat exchanger performance: Numerical modeling and experimental validation

A three dimensional numerical scheme has been developed to examine geometrical configuration effects on the performance of a single bed adsorption chiller with a trapezoidal aluminum finned flat-tube heat exchanger (FFT HEx). A mathematical distributed model along with the linear driving force (LDF) model and Darcy’s law have been considered to take into account the effects of heat and both intra/inter-grain mass transfer resistances. The developed numerical scheme has also been validated experimentally by using a composite sorbent SWS-1L and water as a working pair. Additionally, rectangular beds with identical working conditions and bed dimensions as the tested trapezoidal beds have been examined in similar details to identify, which type of the fin geometry provides a superior performance. It was found that in this particular HEx, the heat transfer resistance is mainly influenced by both of the fin pitch and height, while the inter-grain mass transfer resistance is independently controlled by the bed length. This fact makes the role of the fin pitch and fin height almost interchangeable with respect to the cycle time and specific cooling power (SCP) especially in rectangular beds. However, the coefficient of performance (COP) is more influenced by the fin height than the fin pitch. In addition, higher SCP can be achieved at smaller bed dimensions at the expense of lower COP. Moreover, it was found that using rectangular bed is more appropriate, since its SCP is either the same or higher than its corresponding trapezoidal bed especially at shorter bed lengths, while COP remains almost the same for both bed types in all considered ranges of bed dimensions. Finally, a bed designing procedure has been proposed for proper designing of effective adsorption HExs based on the performed parametric studies.

How many holes is too many? A prototype tool for estimating mosquito entry risk into damaged bed nets

BackgroundInsecticide-treated bed nets (ITNs) have played an integral role in malaria reduction but how insecticide depletion and accumulating physical damage affect ITN performance is poorly understood. More accurate methods are needed to assess damage to bed nets so that they can be designed, deployed and replaced optimally.MethodsVideo recordings of female Anopheles gambiae in near approach (1–½ cm) to occupied untreated rectangular bed nets in a laboratory study were used to quantify the amount of mosquito activity (appearances over time) around different parts of the net, the per-appearance probability of a mosquito coming close to holes of different sizes (hole encounter) and the per-encounter probability of mosquitoes passing through holes of different sizes (hole passage).ResultsAppearance frequency on different parts of the net reflected previously reported patterns: the area of the net under greatest mosquito pressure was the roof, followed by the bottom 30 cm of the sides, followed by the 30 cm area immediately above this, followed by the upper two-thirds of the sides. The ratio of activity in these areas was (respectively) 250:33:5:1. Per-appearance probability of hole encounter on all parts of the net was strongly predicted by a factor combining hole perimeter and area. Per-encounter probability of hole passage, in turn, was strongly predicted by hole width. For a given width, there was a 20% greater risk of passage through holes on the roof than holes on the sides.DiscussionAppearance, encounter and passage predictors correspond to various mosquito behaviours that have previously been described and are combined into a prototype mosquito entry risk tool that predicts mosquito entry rates for nets with various amounts of damage. Scenarios that use the entry risk tool to test the recommendations of the WHOPES proportionate hole index (pHI) suggest that the pHI hole size categories and failure to account for hole location likely sometimes lead to incorrect conclusions about net serviceability that could be avoided by using an entry risk tool of the form presented here instead. Practical methods of collecting hole position, shape and size information for bed net assessments using the tool in the field are discussed and include using image analysis and on-line geometric analysis tools.

Influence of new adsorbents with isotherm Type V on performance of an adsorption heat pump

The working pair is one of the main influencing parameter on performance of an adsorption heat pump (AHP). Researchers started to synthesize different adsorbents in order to improve the adsorption rate. Even the adsorption rate could seem very well, the new adsorbent could not be suitable for an AHP for given conditions. In this context, the effect of new adsorbent materials with isotherm Type V on adsorption-desorption processes of an unconsolidated adsorbent bed works for refrigeration are investigated. The adsorbate is taken as water. Type V isotherm equations for each adsorbent are predicted and the influence on the performance is analyzed. The constants in the equation that simulate the isotherm shape are found. The average temperature/concentration in the rectangular bed during the adsorption/desorption processes are plotted for different novel adsorbents; FAM-Z01, FAM-Z02, MIL101@GO5, and NH2-MIL-125(Ti). The performed numerical solutions for the case which is taken into account for this paper (evaporator temperature and bed heating temperature are 2 °C and 77.5 °C) showed that, MIL101(Cr)@GO5 has the best Specific Cooling Power for the volume of the bed which is 21.13 kJ/kga but has worst COP as 1.20. FAM-Z01 has 53.85 kJ/h evaporator capacity where this value is the best for the case.

Validation procedure for numerical model of hydraulic inflatable dam under pulse load

Hydraulic inflatable dams are cylindrical dams, formed by load bearing rubberized fabrics, placed across streams to raise the upstream water level when inflated. During operation, they are exposed to the water flow and its static and dynamic characteristics. While the behavior of these structures under static load is well studied, the dynamic load is still under investigation. This is particularly emphasized when the water flow is in the form of wave causing pulse load. Such behavior is difficult to being studied analytically and usual method here is a numerical simulation. This article presents a validation procedure for a model for numerical simulation of a hydraulic inflatable dam under pulse load, caused by water wave. The used software is ANSYS CFX. The experimental equipment and experimental procedure are described for short, two-side fixed dam in a rectangular bed. Visual and numerical criterions are proposed in order to estimate the adequacy of the model.

Measurements of pressure drop and particle velocity in a pseudo 2-D rectangular bed with Geldart Group D particles

A small scale pseudo 2-D bed of dimension 0.075m×0.23m×1.22m was utilized to measure the pressure drop and velocity statistics of Geldart Group D nylon beads. The pressure drop was measured using a fast-response pressure transducer and the particle velocities were measured with high speed particle image velocimetry, with particle tracking, in a slugging flow regime for three different superficial gas velocities (2, 3 & 4 times the minimum fluidization velocity (Umf)). At superficial gas velocity of 3 Umf, the measured slugging frequency was about 2.5Hz, while at conditions close to 2 Umf and 4 Umf, the slugging frequency was about 1.5 and 1.7Hz. Additionally, at 3 Umf condition, the bed exhibited a much higher root mean square (RMS) of pressure drop fluctuations than those at 2 Umf and 4 Umf. The varying trend suggested an existence of a complicated regime change for these shallow bed measurements that had not been previously explored. The measurement of millions of individual particle velocities at the vicinity of the wall had enabled accurate measurement of higher order statistics including RMS, granular temperature, skewness, and kurtosis of particle velocity. The measured skewness and kurtosis of the velocity distribution indicated that the particle velocity distribution deviated substantially from a normal distribution as the intersection of walls of the rectangular bed was approached.

Greenhouse Gas Emissions during Swine Manure Composting in a Rectangular Bed with Daily Turning

Abstract. Composting is an effective management practice for converting animal waste to a valuable soil amendment that has the potential to reduce pollution. Rectangular bed composting with daily turning is widely used in China, but gas emission from this method has not be reported. The goals of this study were to evaluate seasonal differences in greenhouse gas (GHG) emissions and the relative contributions of the GHGs from a commercial swine manure composting facility with daily turning. The compost mixture of swine manure and mushroom residues was turned and moved forward 2 m every day, and it took approximately 20 d to move the raw materials from the head side to the end side of the composting bed. The gases were sampled daily with the static chamber method, and gas concentrations were measured with a gas chromatograph. Compost and air temperatures were monitored. The compost was sampled every 3 d for nitrogen and carbon contents. Cumulative emissions in spring, summer, autumn, and winter were 14.1 ±4.0, 24.1 ±2.2, 10.5 ±0.8, and 11.9 ±3.4 kg CO2 m-2, respectively; 311 ±106, 482 ±44, 113 ±9, and 105 ±21 g CH4 m-2, respectively; and 2.1 ±0.3, 2.7 ±0.4, 0.5 ±0.2, and 1.3 ±0.4 g N2O m-2, respectively. Averaged over the four seasons, greenhouse gas flux was 12.38 ±8.90 g CH4 m-2 d-1 and 0.083 ±0.048 g N2O m-2 d-1. The reason for the lowest emission in autumn was unclear. Excluding CO2, methane contributed approximately 87.5% to 94.9% of the CO2e emissions, whereas N2O contributed the rest. Because the static chamber did not capture emissions during turning, it is recommended that more robust methods (such as dynamic plume or mega dynamic chamber) should be applied to measure the emissions for inventory studies. The high temperatures in the last few days indicated that composting was still ongoing and the duration should be increased.

Eulerian–Eulerian simulation of irregular particles in dense gas–solid fluidized beds

As an important and essential physical property, particle shape affects fluidization characteristics of dense gas–solid fluidized beds greatly. However, numerical studies of irregular particles in gas–solid fluidization, especially using Eulerian–Eulerian model, are relatively scarce, primarily due to the lack of an appropriate inter-phase drag model. To this end, a simple and effective drag model was proposed in this work to address the critical role of particle shape in determining the inter-phase drag force. This drag model features the usage of Ganser correlation and Ergun correlation, respectively, in dilute and dense solid concentration conditions. Moreover, particle sphericity is introduced as a concise shape descriptor, and can be calibrated by experimentally measured minimum fluidization velocity and the corresponding voidage. To verify the established numerical model, experimental study was also conducted in a lab-scale three-dimensional rectangular bed filled with irregular Geldart group B particles. Other two kinds of irregular bed materials from open literature were investigated as well to provide further validation. The predicted results using the proposed drag model are overall in relatively better quantitative agreement with the experimental data or available empirical correlations, in terms of both macro-scale and micro-scale behavior. In contrast, the numerical model with the drag force assuming perfectly spherical particles completely fails to reproduce the experimental hydrodynamics of the gas–solid fluidized bed. In addition, sensitivity analysis of the proposed drag model demonstrated its weak sensitivity to the minimum fluidization characteristics of particles. The sufficient comparison and analysis indicated that the proposed drag model together with the estimation method of particle sphericity is quite reasonable and convenient for Eulerian–Eulerian simulation of irregular particles behavior in lab-scale dense gas–solid fluidized beds.

Pinning and cavity in two types of cross-flow moving beds

The pinning, cavity and pressure drop were investigated in both trapezoidal and rectangular cross-flow moving beds via a large plexiglass cold model under different operating conditions. Experimental results indicate that the pinning appears before cavity. The critical pinning/cavity superficial gas velocities of the trapezoidal bed are considerably higher than those in the rectangular bed. Namely, the trapezoidal configuration improves the operating flexibility of the moving bed. On the other hand, it also shows that the dimensions of the pinning and cavity are both enlarged when the superficial gas velocity increases. However, the size variations of the pinning and cavity are not significant with the change of the particle mass flux. Besides, most gas passes through the bed in the horizontal direction. In the operating process, there is an undesirable phenomenon called channeling in the top of bed. Based on the force balance analysis as well as the experimental results, a mathematical model of pinning is proposed. The critical pressure drops and the pinning thicknesses can be predicted by using this model.

Momentum Conservative Schemes for Shallow Water Flows

AbstractWe discuss the implementation of the finite volume method on a staggered grid to solve the full shallow water equations with a conservative approximation for the advection term. Stelling &amp; Duinmeijer [15] noted that the advection approximation may be energy-head or momentum conservative, and if suitable which of these to implement depends upon the particular flow being considered. The momentum conservative scheme pursued here is shown to be suitable for 1D problems such as transcritical flow with a shock and dam break over a rectangular bed, and we also found that our simulation of dam break over a dry sloping bed is in good agreement with the exact solution. Further, the results obtained using the generalised momentum conservative approximation for 2D shallow water equations to simulate wave run up on a conical island are in good agreement with benchmark experimental data.

Substrate Diffusion and Consumption in Rectangular Capillary-Tissue Bed

AbstractA diffusion equation can be used to estimate the oxygen concentration profiles for a highly-regular capillary bed of skeletal muscle. In reality, the capillaries may be arranged more or less randomly in normal tissues. The oxygen concentration, along with its time-wise distribution, may be uneven. Heterogeneity in the tissue bed is much more commonly considered. This article presents a mathematical analysis of the capillary-tissue exchange of substrate in microcirculation in rectangular regions where multiple capillaries are embedded with arbitrary characteristics. A matching technique is used to help solve the associated governing equations.

Investigation of segregation of large particles in a pressurized fluidized bed with a high velocity gas: A discrete particle simulation

A numerical study on mixing/segregation phenomena in a pressurized fluidized bed with large particles of Geldart D type of binary density but same diameter with high velocity gas was performed by the use of discrete particle simulation. Particle mixtures are composed of spherical particles with 2 mm diameter and 1 g/cm3 flotsam density and different jetsam densities of 1.25, 2 and 2.5 g/cm3 with jetsam volume fraction of 0.5. The particles are initially packed approaching perfect mixing state in a rectangular bed and then fluidized by gas uniformly injected at the bottom of the bed. Effect of increase of pressure and density ratio was investigated and mixing/segregation behavior is discussed in terms of flow patterns, solid concentration profile, height variation, pressure drop variation and mixing kinetics. The results show that increase of pressure causes a more vigorous and chaotic motion with more slugs and large bubbles. With increase of pressure, pressure drop and height of the bed increase and both of them fluctuate more with larger amplitude and shorter frequency. Mixing index also decreases with the increase of pressure, and thus solids' mixing diminishes. Effect of increase of density ratio is somehow like effect of increase of pressure in most cases but has a little difference in some cases.

Hydrodynamics of a fluidized bed co-combustor for tobacco waste and coal

The fluidization characteristics of binary mixtures containing tobacco stem (TS) and cation exchange resin (a substitute for coal) were studied in a rectangular bed with the cross-section area of 0.3×0.025m2. The presence of herbaceous biomass particles and their unique properties such as low density and high aspect ratio resulted in different fluidization behaviors. Three fluidization velocities, i.e. initial, minimum and full fluidization velocities, were observed as the TS mass fraction increased from 7% to 20%, and four hydrodynamic stages were experienced, including the static, segregation, transition and mixing stages, with increasing operational gas velocities. The results suggest that the operational gas velocity should be in the range of 2.0–5.0 times of the minimum fluidization velocity of the binary mixtures, and less than 7% TS mass fraction should be used in an existing bubbling fluidized bed. Higher TS fraction inclusion requires the introduction of central jet gas to improve the mixing effect.

Imaging a rectangular fluidised bed by electrical capacitance tomography: preliminary results

PurposeRectangular fluidised beds are commonly used in industry, e.g. circulating fluidised bed (CFB) boilers. Apparently, no one has tried to imagine rectangular fluidised beds by electrical capacitance tomography (ECT). The purpose of this paper is to design a rectangular ECT sensor to understand the behaviour of a rectangular CFB riser.Design/methodology/approachA rectangular sensor with eight electrodes is adopted to obtain the capacitance data. The sensitivity map is simulated to calculate the grey level of pixels for visualisation using the linear back‐projection algorithm.FindingsExperiments showed that the position of the objects in the riser can be obviously indicated and the central region of the object(s) has significantly higher grey level than other regions in the images using the rectangular ECT sensor.Research limitations/implicationsIt has a limitation in providing a higher resolution image.Practical implicationsThe results obtained by the rectangular ECT sensor show that it is promising to study the characteristics of flow non‐uniformity in the fast fluidisation regime of CFB.Originality/valueWithout using square and circular ECT sensors, this is the first time a rectangular ECT sensor has been developed to study the unique problems of the characteristics of flow non‐uniformity in a rectangular CFB riser.