Packed Bed Region Research Articles

Experimental and numerical investigation of a latent heat thermal energy storage unit with ellipsoidal macro-encapsulation

This paper investigates ellipsoid-shaped macro-encapsulated phase change material (PCM) on a component scale. The selected PCM is a paraffin-based commercial material, namely ATP60; differential scanning calorimetry and transient plane source method are used to measure ATP60's thermo-physical properties. A 0.382 m3 latent heat thermal energy storage (LHTES) component has been built and experimentally characterized. The temperature measurement results indicate that a thermocline was retained in the packed bed region during charging/discharging processes. The experimental characterization shows that increasing the temperature difference between the heat transfer fluid (HTF) inlet temperature and phase-change temperature by 20 K can shorten the completion time of discharge by 65%, and increasing HTF inlet flowrate from 0.15 m3/h (Re = 77) to 0.5 m3/h (Re = 256) can shorten the completion time of charge by 51%. Furthermore, a one-dimensional packed bed model using source-based enthalpy method was developed and validated by comparison to experimental results, showing discrepancies in the accumulated storage capacity within 6.6% between simulation and experiment when the Reynolds number of the HTF inlet flow ranges between 90 and 922. Compared with a conventional capsule shaped in 69-mm-diameter and 750-mm-long cylinders, the ellipsoidal capsule shows 60% less completion time of discharge but 23% lower storage capacity. Overall, this work demonstrates a combined experimental and numerical characterization approach for applying novel macro-encapsulated PCM geometries for heating-oriented LHTES.

A two-fluid model simulation of an industrial moving grate waste incinerator

CFD modelling and simulation is an effective means of optimizing the design and operation of moving grate waste incinerators. Conventional approach models the grate combustion and the furnace combustion separately by using an in-bed/over-bed coupling procedure. In this paper, a comprehensive two-fluid reacting model that integrates the gas-solid grate incineration and the gas turbulent combustion in one scheme is developed for industrial incinerators. Realistic grate geometry and direct simultaneous coupling of the fuel bed and the freeboard gas phase are realized. According to different treatments of the solid phase, the whole incinerator is divided into three regions, namely the packed bed region, the fall region and the furnace region. The kinetic theory of granular flow (KTGF) is introduced to describe the rheological properties of waste particles, and the Ergun model is used for the gas-solid drag. Thermal conversion of wastes is characterized by the heterogeneous reactions of moisture evaporation, devolatilization, char-O2 combustion and the homogeneous reactions of hydrocarbons combustion. Distributions of temperatures and gas species are predicted and validated by measurements. Particle properties are calculated to reveal the grate incineration characteristics. Effects of waste throughput on the incineration are also investigated. Overall, the present model provides a new methodology of in-bed and over-bed integration for the moving grate incinerator simulation.

CFD Steady Model Applied to a Biomass Boiler Operating in Air Enrichment Conditions

A numerical model is proposed to perform CFD simulations of biomass boilers working in different operating conditions and analyse the results with low computational effort. The model is based on steady fluxes that represent the biomass thermal conversion stages through the conservation of mass, energy, and chemical species in the packed bed region. The conversion reactions are combined with heat and mass transfer submodels that release the combustion products to the gas flow. The gas flow is calculated through classical finite volume techniques to model the transport and reaction phenomena. The overall process is calculated in a steady state with a fast, efficient, and reasonably accurate method, which allows the results to converge without long computation times. The modelling is applied to the simulation of a 30 kW domestic boiler, and the results are compared with experimental tests with reasonably good results for such a simple model. The model is also applied to study the effect of air enrichment in boiler performance and gas emissions. The boiler operation is simulated using different oxygen concentrations that range from 21% to 90% in the feeding air, and parameters such as the heat transferred, fume temperatures, and emissions of CO, CO2, and NOx are analysed. The results show that with a moderated air enrichment of 40% oxygen, the energy performance can be increased by 8%, CO emissions are noticeably reduced, and NOx remains practically stable.

Quantifying the adsorption of flowing gas mixtures in porous materials by remote detection NMR

Traditional adsorption measurements are carried out at static conditions for a single gas component, and multi-component adsorption measurements are challenging and time-consuming. Here we introduce an efficient remote detection NMR method for in situ analysis of adsorption of flowing gas in mesoporous materials. We investigated adsorption of continuously flowing propane and propene gases as well as their mixture in packed beds of controlled pore glass and silica gel materials. Remote detection provided from 300 to 700 -fold sensitivity enhancement as compared to a direct experiment carried out by a large coil around the packed bed. The unique time-of-flight information obtained using this method was utilized in flow velocity determination, and the velocities were converted into amount of adsorbed gas. As the detection was performed outside the packed bed region, the spectra were not influenced by the porous materials. Because resonances of each gas component were well-resolved in the spectra, the amount of adsorption of each gas component could be determined from the same data, measured in a few minutes.

Discharge Characteristics of Series Surface/Packed-Bed Discharge Reactor Diven by Bipolar Pulsed Power**supported by National Natural Science Foundation of China (No. 51177007), the Joint Funds of National Natural Science Foundation of China (No. U1462105), and Dalian University of Technology Fundamental Research Fund of China (No. DUT15RC(3)030)

The discharge characteristics of the series surface/packed-bed discharge (SSPBD) reactor driven by bipolar pulse power were systemically investigated in this study. In order to evaluate the advantages of the SSPBD reactor, it was compared with traditional surface discharge (SD) reactor and packed-bed discharge (PBD) reactor in terms of the discharge voltage, discharge current, and ozone formation. The SSPBD reactor exhibited a faster rising time and lower tail voltage than the SD and PBD reactors. The distribution of the active species generated in different discharge regions of the SSPBD reactor was analyzed by optical emission spectra and ozone analysis. It was found that the packed-bed discharge region (3.5 mg/L), rather than the surface discharge region (1.3 mg/L) in the SSPBD reactor played a more important role in ozone generation. The optical emission spectroscopy analysis indicated that more intense peaks of the active species (e.g. N2 and OI) in the optical emission spectra were observed in the packed-bed region.

Using crosslinkable diacetylene phospholipids to construct two-dimensional packed beds in supported lipid bilayer separation platforms

Separating and purifying cell membrane-associated biomolecules has been a challenge owing to their amphiphilic property. Taking these species out of their native lipid membrane environment usually results in biomolecule degradation. One of the new directions is to use supported lipid bilayer (SLB) platforms to separate the membrane species while they are protected in their native environment. Here we used a type of crosslinkable diacetylene phospholipids, diynePC (1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine), as a packed material to create a ‘two-dimensional (2D) packed bed’ in a SLB platform. After the diynePC SLB is exposed to UV light, some of the diynePC lipids in the SLB can crosslink and the non-crosslinked monomer lipids can be washed away, leaving a 2D porous solid matrix. We incorporated the lipid vesicle deposition method with a microfluidic device to pattern the location of the packed-bed region and the feed region with species to be separated in a SLB platform. Our atomic force microscopy result shows that the nano-scaled structure density of the ‘2D packed bed’ can be tuned by the UV dose applied to the diynePC membrane. When the model membrane biomolecules were forced to transport through the packed-bed region, their concentration front velocities were found to decrease linearly with the UV dose, indicating the successful creation of packed obstacles in these 2D lipid membrane separation platforms.

CFD modeling and experimental validation of sulfur trioxide decomposition in bayonet type heat exchanger and chemical decomposer for different packed bed designs

The growth of global energy demand during the 21st century, combined with the necessity to master greenhouse gas emissions has lead to the introduction of a new and universal energy carrier: hydrogen. The Department of Energy (DOE) Nuclear Hydrogen Initiative was investigating thermochemical cycles for hydrogen production using high-temperature heat exchangers. In this study a three-dimensional computational model of high-temperature heat exchanger and decomposer for decomposition of sulfur trioxide by the sulfur–iodine thermochemical water-splitting cycle with different packed bed designs has been done. The decomposer region of the bayonet heat exchanger also called as silicon carbide integrated decomposer (SID) is designed as the packed bed region. Cylindrical, spherical, cubical and hollow cylindrical pellets have been arranged inside the packed bed. The engineering design of the packed bed was very much influenced by the structure of the packing matrix, which was governed by the shape, dimension and the loading of the constituent particles. Staggered and regular packing methods are used for packing the pellets in the packed bed region. The numerical model is created using GAMBIT and fluid, thermal and chemical analyses were performed using FLUENT. The decomposition percentage of sulfur trioxide is found for the packed bed region with different pellets and the numerical results obtained is compared with the experimental results. A comparison is made for the decomposition percentage of SO3 for the packed bed approach and the porous media approach.

Numerical study of sulfur trioxide decomposition in bayonet type heat exchanger and chemical decomposer with porous media zone and different packed bed designs

The Department of Energy (DOE) Nuclear Hydrogen Initiative was investigating thermochemical cycles for hydrogen production using high temperature heat exchangers. The present work was concerned with use of bayonet type heat exchanger as silicon carbide integrated decomposer (SID) which produces sulfuric acid decomposition product – sulfur dioxide. The product can be used within the sulfur–iodine thermochemical cycle and hybrid sulfur process. A two-dimensional axis-symmetric geometry of the bayonet heat exchanger has been created using GAMBIT software. Fluid, thermal and chemical reaction analyses were performed using FLUENT software. The working fluids in the model were sulfur trioxide, sulfur dioxide, oxygen and water vapor. Silicon carbide with 1 wt% of platinum was used as a catalyst for the chemical reaction. The form of pellets packing was simple cubical packing and porous media approach was used. The chemical reaction for the two-dimensional model was carried out in two cases (ways): (1) constant outer wall temperature and (2) by applying the measured values obtained from the thermocouples placed along the outer wall of the lab scale model of the bayonet heat exchanger in Sandia National Lab (SNL). The decomposition of sulfur trioxide for the two-dimensional model was calculated and the obtained results were compared with the experimental results. But, practically the flow of fluid between the pellets in the decomposer region of the bayonet heat exchanger may have many swirling and recirculation. Hence a further study on three-dimensional model of the decomposer with different arrangement of the pellets in the packed bed region was carried out. The chemical decomposition that occurred in packed bed was of the decomposer. The engineering design of the packed bed was very much influenced by the structure of the packing matrix, which was governed by the shape, dimension and the loading of the constituent particles. The investigations of different types of catalyst in the packed bed region and the decomposition of sulfur trioxide were calculated and the results obtained were consistent with the experimental results.

The development of a CFD model of a submerged arc furnace for phosphorus production

A computational fluid dynamics (CFD) based model of a submerged arc furnace for the production of phosphorus was developed. The model was constructed to investigate the influence of changing operating conditions on energy distribution within the burden and reaction characteristics such as the position of the solid–gas reaction zone. Two user-developed models generate a volumetric distribution of the mass sources and energy sinks within the packed bed region. Boundary conditions, initial values and material specifications are provided by industrial measurements, laboratory experiments and a combination of empirical and thermodynamical data. The results provide three-dimensional furnace characteristics of gas flow, energy distribution and chemical reactions that will give decision support for a predictive, Dynamic-CFD hybrid model [Scheepers, E., Yang, Y., Reuter, M., Adema, A., 2006. A dynamic-cfd hybrid model of a submerged arc furnace for phosphorus production. Minerals Engineering 19 (3), 309–317].

Effect of sugar consumption on ethanol fermentation in a tower fermentor packed with self-aggregating yeast

A strain of self-aggregatingSaccharomyces uvarum was cultivated in a 6-L tower fermentor for continuous ethanol fermentation. Large aggregates (2–3 mm) were formed and packed in the column. The height of this packed region depends on the sugar concentration. As sugar concentrations were reduced to below a critical value, most of the large aggregates disintegrated into smaller aggregates (0.1–0.2 mm). Above the packed bed region, small aggregates and small amount of large aggregates were fluidized and formed a well mixed region by the liquid medium and the produced carbon dioxide. A mathematical model of a plug flow with consideration of axial dispersion and a Continuous Stirred Tank Reactor (CSTR) in series is proposed to describe such fermentor. The concentration profile of sugar can be simulated by this model. The height of the packed bed region can then be estimated based on the predetermined critical sugar concentration. Final ethanol concentration and the productivity of such fermentor can also be predicted.

Thermal Control of Ceramic Breeder Blankets

AbstractThermal control is an important issue for ceramic breeder blankets since the breeder needs to operate within its temperature window for the tritium release and inventory to be acceptable. A thermal control region is applicable not only to situations where the coolant can be run at low temperature, such as for the International Thermonuclear Experimental Reactor (ITER) base blanket, but also to ITER test module and power reactor situations, where it would allow for ceramic breeder operation over a wide range of power densities in space and time. Four thermal control mechanisms applicable to ceramic breeder blanket designs are described: a helium gap, a beryllium sintered block region, a beryllium sintered block region with a metallic felt at the beryllium-cladding interface, and a beryllium packed-bed region. Key advantages and issues associated with each of these mechanisms are discussed. Experimental and modeling studies focusing on beryllium packed-bed thermal conductivity and wall conductance, ...

Thermal control of solide breeder blankets

An assessment of the thermal control mechanisms applicable to solid breeder blanket designs under ITER-like operating conditions is presented in this paper. Four cases are considered: a helium gap; a sintered block Be region; a sintered block Be region with a metallic felt at the Be-clad interface; and a Be packed bed region. For these cases, typical operating conditions are explored to determine the ranges of wall load which can be accomodated while maintaining the breeder within its allowable operating temperature window. The corresponding region thicknesses are calculated to help identify the practicality of each concept and the design tolerances.

Prediction of bed height in a self-aggregating yeast ethanol tower fermenter

A packed bed region and a mixed region were observed in an ethanol tower fermenter packed with flocs of self-aggregating yeast. Sizes of yeast flocs were 2–3 mm and 0.2–0.3 mm in diameter in the packed bed region and the mixed region, respectively. Three major factors were found to affect the height of the packed bed region significantly. They were dilution rate, nutrient limitation, and hydrodynamic limitation. An empirical method was proposed using these three factors to predict the height of the packed bed region in the fermenter.