Bed Design Research Articles

Long-time coarse-grained CFD-DEM simulation of residence time distribution of polydisperse particles in a continuously operated multiple-chamber fluidized bed

Residence time distribution of particles is a critical parameter for proper design of gas-solid fluidized beds, especially in many non-catalytic solid conversion processes where it is highly desirable to match the residence time of a particle and its complete conversion time to achieve the synchronized conversion of particles of different sizes. However, the requisite of considering particle polydispersity and the long residence time of particles required by reaction kinetics together pose a great challenge to the computational fluid dynamics study of such systems. To this end, a GPU-based, massively parallel coarse-grained CFD-DEM method-the EMMS-DPM method (Lu et al., 2014) was extended to simulate the residence time distribution of polydisperse particles in a continuously operated multiple-chamber fluidized bed with a calculation of physical time of up to one hour. It was shown that the experimentally measured pressure drop of the bed or the solid holdup can be predicted reasonably well by the ad hoc drag models of non-spherical and polydisperse particles proposed in present study; the residence time distribution of particles of whole system can also be predicted correctly; and finally, the ratio of the mean residence time of coarse particles to that of fine particles is about three, which is insufficient to achieve the synchronized conversion of particles of different sizes according to an ideally theoretical analysis, great effort is needed to get a better match between the residence time and the compete conversion time of particles.

Progressive Latin Hypercube sampling-based robust design optimisation (PLHS-RDO)

ABSTRACT The main purpose of this paper is to present a novel Robust Design Optimisation (RDO) strategy based on an efficient Uncertainty Analysis (UA) approach. To this end, a Progressive Latin Hypercube Sampling (PLHS) method was developed to derive the minimum samples for UA. The required sample size is calculated based on the convergence of the UA results. Therefore, UA is achieved by a variable sample size Design of Experiments (DOE). This systematic approach leads to an efficient, adaptive and fast framework for RDO. The proposed algorithm performance was validated by some numerical simulations methods on a benchmark function. In conclusion, the proposed methodology was utilised to the design of a hydrazine catalyst bed as a case study. The results of applied RDO in catalyst bed design parameters and also the corresponding value of objective functions demonstrates the performance of the developed framework in space applications.

A novel high-temperature (>700 °C), volumetric receiver with a packed bed of transparent and absorbing spheres

The concentrated solar power industry requires high-temperature receivers to push towards advanced power cycles. However, as the outlet temperature of a receiver increases, radiation losses (which are ∝T4) become dominant. In addition, at high temperatures, not many liquid working fluids are suitable. To address these issues, this research proposes an innovative, robust design of a gas-phase cavity receiver which utilises semi-transparent spheres as a volumetric absorption medium. The motivation behind this design is to break the long-standing outlet temperature versus efficiency trade-off by maximising the “volumetric effect” (i.e. obtaining a higher outlet fluid temperature than the receiver’s surface temperature). A range of designs were compared (i.e. packed beds of semi-transparent and high-transparency quartz spheres against an opaque bed of ceramic spheres). This study is important because it determines how the volumetric effect modifies the overall receiver efficiency via a holistic metric (proposed herein) which accounts for the optical, thermal, and pumping power efficiencies. Through a detailed ray-tracing analysis and a comprehensive thermal circuit model, this study reveals that a semi-transparent quartz packed bed receiver can have an overall receiver efficiency of around 80% at outlet temperatures above 700 °C. Most significantly, the best proposed design achieved a high value for the elusive volumetric effect (e.g. a maximum index value of 1.45). Based upon these results, the authors can conclude that these packed bed designs represent a promising new pathway towards reliable and cost-effective high-temperature and high-efficiency receivers which can be implemented into advanced, high-temperature power cycles.

Application of the best-estimate model calibration and prediction through experimental data assimilation methodology to the tests performed on a helium cooled First Wall Mock-up

Abstract Experiments are under progress at the Karlsruhe Institute of Technology (KIT) as part of the general strategy for the development of the DEMO Helium Cooled Pebble Bed (HCPB) design. These experiments are part of the program on the qualification of components and on the validation of system codes. In 2018, thermal-hydraulic investigations have been performed looking into the transient response of a helium-cooled blanket First Wall Mock-Up under Loss Of Flow Accident (LOFA) conditions. The results obtained through these investigations captured the quick temperature rise on the surfaces exposed to heat loads (such as those coming from the plasma), and provided a robust set of data for the validation of system codes such as RELAP5-3D. Then, the present work describes the validation activities performed on the RELAP5-3D code. This validation was performed employing also a Best-Estimate methodology called “Best-Estimate Model Calibration and Prediction through Experimental Data Assimilation methodology”. In a previous work, the same methodology was used to calibrate a RELAP5-3D model of the HELOKA-HP electrical heater under normal operation. In this regard, the present work marks the first application of this methodology to fast transients in the field of fusion reactors.

Production and Characterization of Controlled Release Urea Using Biopolymer and Geopolymer as Coating Materials.

Synthetic polymers-based controlled release urea (CRU) leaves non-biodegradable coating shells when applied in soil. Several alternative green materials are used to produce CRU, but most of these studies have issues pertaining to nitrogen release longevity, process viability, and the ease of application of the finished product. In this study, we utilized tapioca starch, modified by polyvinyl alcohol and citric acid, as coating material to produce controlled release coated urea granules in a rotary fluidized bed equipment. Response surface methodology is employed for studying the interactive effect of process parameters on urea release characteristics. Statistical analysis indicates that the fluidizing air temperature and spray rate are the most influential among all five process parameters studied. The optimum values of fluidizing air temperature (80 °C), spray rate (0.13 mL/s), atomizing pressure (3.98 bar), process time (110 min), and spray temperature (70 °C) were evaluated by multi-objective optimization while using genetic algorithms in MATLAB®. Urea coated by modified-starch was double coated by a geopolymer to enhance the controlled release characteristics that produced promising results with respect to the longevity of nitrogen release from the final product. This study provides leads for the design of a fluidized bed for the scaled-up production of CRU.

Static and dynamic behavior of steel-reinforced epoxy granite CNC lathe bed using finite element analysis

Machine tools are used to manufacture components with desired size, shape, and surface finish. The accuracy of machining is influenced by stiffness, structural damping, and long-term dimensional stability of the machine tool structures. Components machined using such machines exhibit more dimensional variations because of the excessive vibration during machining at higher speeds. Compared to conventional materials like cast iron, stone-based polymer composites such as epoxy granite have been found to provide improved damping characteristics, by seven to ten folds, due to which they are being considered for machine tool structures as alternate materials. The stiffness of structures made of epoxy granite can be enhanced by reinforcing with structural steel. The current work highlights the design and analysis of different steel reinforcements in the lathe bed made of the epoxy granite composite to achieve equivalent stiffness to that of cast iron bed for improved static and dynamic performances of the CNC lathe. A finite element model of the existing the cast iron bed was developed to evaluate the static (torsional rigidity) and dynamic characteristics (natural frequency) and the results were validated using the experimental results. Then finite element models of five different steel reinforcement designs of the epoxy granite bed were developed, and their static and dynamic behaviors were compared with the cast iron bed through numerical simulation using finite element analysis. The proposed design (Design-5) of the epoxy granite bed is found to have an improvement in dynamic characteristics by 4–10% with improved stiffness and offers a mass reduction of 22% compared to the cast iron bed, hence it can be used for the manufacture of the CNC lathe bed and other machine tool structures for enhanced performance.

Подавление влияния инструментальных возмущений локально инвариантным масштабированием физической модели угловой стабилизации космического аппарата

The study introduces a method of ground conditions physical modeling of the spacecraft motion around a fixed axis. On a natural scale of parameters and variables, the dynamic modes under consideration can be implemented only with an extremely small amount of kinetic energy dissipation. The feasible minimum friction for a test bed of simple design significantly exceeds the required values. In current modes of economical limit cycles, the characteristics of the simulated process are distorted so much that the physical modeling test bed is unsuitable for practical use. The solution to this problem is usually sought by complicating the design of the test bed through the use of air or magnetic suspension. The paper proposes an innovative method of “invariant scaling”, based on the principle of dynamic similarity of self-oscillating processes. Its application makes it possible to drastically reduce the effect of friction on the characteristics of physically modeled modes during ground developmental testing of control algorithms. Computer modeling with the use of this method has confirmed its high efficiency. It has been shown analytically and numerically that the modeling accuracy can be radically improved. An example of reducing the modeling error by 200 times is given.

Space Design of Rural Bed and Breakfast in the Context of Ecological Aesthetics

In China, with the continuous development of rural economy and the promotion of beautiful rural strategy, rural modern tourism has become the main trend in promoting the development of rural areas. As an important technology and main carrier to lead and develop rural modern tourism in the development process of rural modern tourism, the space design of rural bed and breakfast plays a vital role in rural modern tourism in China. In this paper, considering that the leading role of Chinese traditional aesthetics is very important for the development of the space design of rural bed and breakfast in China, the design idea is clarified according to the principle of beautiful space design and traditional aesthetic logic, and the development path of the construction of modern space design of rural bed and breakfast in the context of ecological aesthetics is put forward by fully combining the actual needs of the development of modern rural tourism in China, that is, the architectural connotation and practice with the characteristics of Chinese rural human history are combined on the basis of scientific and reasonable development of the space design of rural bed and breakfast, so that the villagers can establish a correct ecological outlook on nature and a leisure lifestyle in line with ecological aesthetics, aiming to provide reference for the development of modern space design of rural bed and breakfast in China.

Design of adsorption column for reclamation of methyldiethanolamine using homogeneous surface diffusion model

A predictive simulation model was applied to design a fixed-bed adsorber for studying the removal of Total Organic Acid (TOA) anions from lean Methyldiethanolamine (MDEA) solution using Calcium Alginate Bentonite (CAB) clay hybrid composite adsorbent. Unlike other conventional techniques typically used for packed bed design, the predictive Homogeneous Surface Diffusion Model (HSDM) does not require any test column breakthrough curves a priori. Mass transfer coefficients and isotherm model parameters are provided as input data to HSDM for simulating column breakthrough curves. Various isotherm models were fitted to batch equilibrium data for TOA adsorption on CAB composite adsorbent. Based on Akaike Information Criterion (AIC), Freundlich isotherm was selected and the model parameters were obtained by non-linear regression. Film transfer coefficients and surface diffusivities were determined using appropriate empirical correlations available in the literature. HSDM predictions were first validated using lab-scale column adsorption data generated at lower residence times. The effects of dimensionless numbers (Biot and Stanton) on breakthrough times were investigated using the dimensionless HSDM system and a suitable scale-up regime (Bi& ~& 1 and St& >& 10) was established wherein the sensitivity of mass transfer parameters would be minimal. Using similitude rules on key design parameters, a pilot-scale adsorption column was designed and breakthrough curves were generated using the validated HSDM. The appropriateness of the design technique was verified by comparing the estimated breakthrough data and column design parameters with conventional scale-up and kinetic approaches.

Effect of Multiple Liquid Inlets on Mass Transfer in Rotating Packed Beds

This study deals with optimalization of rotating packed bed design using computational fluid dynamics approach. Comparison of three variants of liquid distributor were performed on 2D geometry. Turbulence was modelled using unsteady RANS approach and volume of fluid technique were used to simulate gas-liquid interphase. Results were compared on basis of liquid holdup evaluation.

Sensitivity analysis based on Progressive LHS Applied to Hydrazine Catalyst Bed Design

Sensitivity analysis based on Progressive LHS Applied to Hydrazine Catalyst Bed Design

Analyzing hydriding performance in full-scale depleted uranium beds

In this study, the hydrogen absorption characteristics of depleted uranium (DU) are analyzed using a three-dimensional transient DU hydride model. The DU model is first validated using experimental data taken from a copper foam-based DU hydride bed, where it is found that the simulation results agree well with the experimental DU temperature evolution and hydriding time. Using the experimentally validated model, we then compare two DU bed designs: one designed to contain 1.86 kg of DU for a tritium capacity of 70 g and loaded with the copper foam to enhance the internal heat transfer during the exothermic hydrogen absorption process, and the other based on copper fins and 5.26 kg of DU to increase a hydrogen isotope (tritium and deuterium) capacity. The simulation results for full-scale DU beds reveal differences in the DU hydriding behavior of the two DU designs, information that is useful in the development of optimal bed design strategies to achieve optimal hydrogen charging performance.

Theoretical model of a fluidized bed solar reactor design with the aid of MCRT method and synthesis gas production

Energy is one of the most critical inputs for the development and economic growth. The objective of this study is to investigate the possibilities of fulfilling such global market demands, even going so far as to provide for a more reliable power source that can extend its reach to rural and remote areas. Therefore, in this work, investigating the gasification of carbonaceous materials (biomass materials) was conducted to produce syngas in a theoretically modelled solar reactor (fluidized bed) design. The Monte Carlo ray tracing method was utilized to design an indirectly irradiated fluidized bed solar reactor. This solar reactor was used in the co-gasification process of 50% olive-pomace and 50% lignite mixture to investigate the performance of gasification with changing the H2O: fuel and O2: fuel ratios. Such a solar reactor model approves the ability to use solar energy as the primary heat source in gasification. Oxygen could be fed into a solar gasification reactor reliably to increase temperatures by combusting some of the used feedstock during the frequency of solar transients. The development of the stoichiometric equilibrium model for the co-gasification process was aimed to investigate the solar reactor performance where the addition of lignite to olive-pomace played a significant role in reducing tar formation and increasing the gasification temperature. Monte Carlo ray tracing method presented the absorbed fluxes over a 40 × 40 mm area centre of the tube where the peak flux and average heat flux were 592.4 and 162.5 kW/m2, respectively. Also, the results indicated that, the optimum H2O: fuel and O2: fuel ratios were 1.16 and 0.33, respectively. The change of H2O: fuel ratio has less effect than the change of O2: fuel ratio in the co-gasification process.

Particle-Scale Study of the Effect of Operating Conditions on Spout Deflection Behavior in a Flat-Bottomed Spout-Fluidized Bed

Spout deflection is a common instability phenomenon in spout fluidized beds The hydrodynamics of spout deflection under several key operating variables, including static bed height (H0), background velocity (Ubg) and reactor column width (W), is investigated by means of Computational Fluid Dynamic-Discrete Element Method (CFD-DEM) coupling approach. The results show that non-alternating spout deflection can be easily observed when the H0 is larger than 236 mm or the W is less than 0.14 m in this study. For alternating spout deflection, firstly, there is an upper limit for its amplitude because of self-locking phenomenon in the bottom corner. Large W promotes the regularity while the effect of H0 on regularity is neglectable. Thirdly, the main frequency of the alternating spout deflection reduces with increasing H0 and increasing Ubg, and finally stabilizes at 1.7 Hz. This study sheds light on the design, optimization and operation of spout fluidized beds.

Hydrodynamics and Particle Mixing Characteristics of a Ternary Mixture in a Gas-Solid Fluidized Bed

Gas-Solid Fluidized Beds are widely used in current industrial practices for their high efficiency in producing products of very high standards. The study of bed dynamics has become an important concern for the design of fluidized beds. Various parameters like pressure, temperature, gas velocity, mean residence time and solids composition affect the bed behavior. In this view, an experimental study was carried out to determine the influence of gas flow rate, mixing time, solids composition and bed height on mixing/segregation behaviour of the bed of particles. Since fluidized beds involving more than two solids are more frequently encountered in current industrial practices, the experiments were conducted using three solid sand particles of average sizes 231 μm, 335 μm, and 510 μm. Various mixing patterns were observed for different mixing times (10, 20 and 30 minutes), different gas flow rates (7.5, 12.5, 17.5, 22.5 and 27.5 LPM), and different solids ratio. Good mixing occurred at an optimum mixing time of 30 minutes and gas flow rates of 17.5 LPM and 22.5 LPM at all solids ratio. The components exhibited relatively better mixing at intermediate bed heights.

Comparative study of different storage bed designs of a solid-state hydrogen tank

Abstract This work discusses the influence of different metal hydride storage bed configurations. The objective was to design and optimize a solid-state hydrogen storage for a nonpolluting mobility. A study of the absorption and desorption dynamics of a loose powder bed was performed first, followed by three different storage bed configurations: compacted Ti-Mn alloy powder, alternated Ti-Mn alloy compacts with stainless steel fins and compacted [Ti-Mn alloy/Stainless steel] powder mixture. A numerical model was developed to simulate the heat transfer and the hydrogen absorption and desorption rates. The alternation and compact mixture configurations gave better heat transfer efficiencies, absorption and desorption rates and increased hydrogen storage densities. Indeed, an efficient heat transfer (between the tank and its surrounding fluid), a tailored porosity of the metal hydride storage bed and the addition of high thermal conductivity materials allowed the overall storage performance to be improved. Thus, the required time for loading/unloading hydrogen was reduced drastically. The alternation configuration would offer the additional advantage of a simple, inexpensive and efficient recycling procedure.

Modelling and experimental investigation of compact packed bed design of methanol steam reformer

A comprehensive mathematical model was developed to analyse methanol steam reforming in catalytic packed-bed tubular reactor. All the important aspects of reaction kinetics of main reactions and thermodynamic terms of heat and mass transfer were studied for commercially available CuO/ZnO/Al2O3 catalysts from Süd-Chemie. This numerical model was simulated using Engineering Equation Solver (EES). Through the set of organized simulation studies, the basic operational boundary conditions of operating temperature (573 K) with respect to complete conversion of methanol and optimum hydrogen generation, optimum S/C ratio (1.4) of methanol water mixture feed and operating capacity of one tubular reactor array were discovered. At temperatures near 573 K it was found that the reformate gas does not require any purification/filtration to be supplied to a HT-PEMFC as the CO concentration in reformate gas was low (below 30000 ppm). The simulation work for understanding the effect of different operating condition(s) on the reformer performance generated design of experiment for investigation of the efforts carried out to evaluate, build and demonstrate a 0.25 kWe equivalent methanol reformer for HT-PEM fuel cell system.The paper discusses few of the important aspects on the experimental investigation of effect of operating conditions on methanol steam reformer design with packed bed configuration for hydrogen production. The basic investigation included the analysis of effect of design and operating parameters on the methanol conversion and quality of reformate gas generation (amount of CO). The investigation also covers the analysis of heat and mass transfer along with chemical reaction and generation of species to achieve optimum process parameters and system efficiency. These investigations led to finalise, the operating parameters and basic design philosophy of the packed bed tubular methanol steam reformer for 5 kWe HT-PEMFC system application.

Control system design of multi-dimensional lumbar traction treatment bed

A multi-dimensional lumbar traction treatment bed is designed with two degrees of freedom, which can realize controllable traction treatment of lumbar through flexion, extension and rotation motion. Two linear actuators are used to provide motion. Building a mathematical model of the device by least squares identification. PID controller and Kalman filter constitute two groups of control modes: (i) speed control; (ii) position control. Using MATLAB to perform simulation experiments. The results show that the designed controller can achieve high control accuracy. The motion speed of lumbar platform is stable and the position of traction treatment set by user is approached exactly, which ensuring the security and stability of this device.

Micromechanical analysis of bubbles formed in fluidized beds operated with a continuous single jet

Advancement in the knowledge of bubble dynamics and properties can significantly aid to improve the design and operation of gas-solid fluidized beds. In this work, bubble properties in a single jet fluidized bed were studied by the combined approach of CFD and DEM. The results illustrated that the process of the continuous injection of a central air jet to the bed was successfully reproduced, with the formation of a series of bubbles which rise through the bed and burst at the bed top. During this process, the series of bubbles align vertically which show coalescence in three different levels of the bed. However, the coalescence patterns depend upon jet velocity and are fairly regular. The bubbles are categorized into two types: primary/leading bubbles and trailing bubbles. The size of primary bubbles keeps increasing with bed height while the size of trailing bubbles decreases since trailing bubbles coalesce with primary bubbles. Primary bubbles, although formed at different times, are of similar shape at different heights of the bed while trailing bubbles are generally elongated in shape. Trailing bubbles have a higher velocity than primary bubbles. The spatial analysis of pressure gradient, drag, and particle-fluid interaction force shows that the presence of bubbles leads to different particle flow zones where forces vary significantly. Moreover, the bubble passage can be delineated by the temporal variation of the particle-fluid interaction force.

A mixture of hydrogen peroxide and tetraglyme as a green energetic monopropellant

An effort is presented to seek a promising candidate for a green energetic monopropellant based on hydrogen peroxide. The novel premixed monopropellant is composed of 90 wt.% H2O2 as the oxidizer and tetraglyme (C10H22O5) as the fuel. Different mixture ratios were prepared by varying the weight percentage of the fuel in the mixture, and the mixtures were named HPM-08 (8 wt.% of fuel), HPM-12 (12 wt.% of fuel), and HPM-20 (20 wt.% of fuel). The theoretical performance of the mixtures was estimated, and their thermostability in air was evaluated via thermogravimetric analysis. A small-scale packed-bed catalytic reactor was utilized to assess the feasibility of the catalytic ignition of HPM-08 with a lanthanum-doped manganese oxide catalyst. Ground hot-firing tests were implemented with an engineering model monopropellant thruster on the scale of 10 N. The demonstrations of the thruster operation using HPM-08 and HPM-12 were successful, but an explosion was caused in the case of HPM-20. A technical speculation suggested that the explosion could be closely related to the phenomenon of detonation. In this study, the configuration of the catalyst bed was regarded as the principal factor in the triggering of detonation in the thruster module. The packed-bed-type catalyst bed containing millimeter-scale pellets may accelerate the phenomenon of deflagration-to-detonation transition, resulting from the rapid compressive heating process based on the superposition of the pressure waves. These results should be taken into account during the design of the catalyst bed in order to utilize particular types of this premixed monopropellant. In addition, a new ignition technique may be applied to prevent the explosion.