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Records with Keyword: Fluid Dynamics
Effects of Geometric Parameters on the Physical Mechanisms of Supersonic Fluidic Oscillators
Yongjun Sang, Yong Shan, Han Lei, Xiaoming Tan, Jingzhou Zhang
March 28, 2023 (v1)
Keywords: delay time, Fluid Dynamics, oscillation period, supersonic oscillator
This paper considers supersonic oscillators, in which the widths of the power nozzle and throat are the significant geometric parameters in characterizing the different internal flow characteristics. Supersonic fluidic oscillators with different power nozzle and throat widths are studied through time-dependent numerical computations. Two characteristic parameters, namely the delay time for the initiation of oscillation t0 and the oscillation period T, are selected to describe the physical mechanisms of the various oscillators. The Mach numbers and streamlines at different times are also used to investigate the flow characteristics. The results show that, when the power nozzle exit width is much smaller than the inlet width of the mixing chamber, the delay time decreases as the throat width increases. Changing the throat width of the oscillator does not significantly affect the delay time t0 when the power nozzle exit width is equal to the inlet width of the mixing chamber. The oscillat... [more]
Effect of Cell Size on the Performance and Temperature Distribution of Molten Carbonate Fuel Cells
Jae-Hyeong Yu, Chang-Whan Lee
March 23, 2023 (v1)
Keywords: Fluid Dynamics, molten carbonate fuel cell, size effect, stack
Molten carbonate fuel cells (MCFCs) are high-operating-temperature fuel cells with high efficiency and fuel diversity. Electrochemical reactions in MCFCs are exothermic. As the size of the fuel cells increases, the amount of the heat from the fuel cells and the temperature of the fuel cells increase. In this work, we investigated the relationship between the fuel cell stack size and performance by applying computational fluid dynamics (CFD). Three flow types, namely co-flow, cross-flow, and counter-flow, were studied. We found that when the size of the fuel cells increased beyond a certain value, the size of the fuel cell no longer affected the cell performance. The maximum fuel cell temperature converged as the size of the fuel cell increased. The temperature and current density distribution with respect to the size showed a very similar distribution. The converged maximum temperature of the fuel cells depended on the gas flow condition. The maximum temperature of the fuel cell decrea... [more]
Study on Flow Characteristics and Mass Transfer Mechanism of Kettle Taylor Flow Reactor
Li Ye, Tengfei Wan, Xiaohui Xie, Lin Hu
March 1, 2023 (v1)
Keywords: Fluid Dynamics, mass transfer mechanism, numerical simulation, reactor, Taylor vortex
A scheme of a gas−liquid mixed jet is designed by installing gas distributor at the bottom of a stirred tank reactor to generate Taylor vortex. The eddy flow characteristics and mass transfer mechanism in the reactor are analyzed by numerical simulation and experiment. The results show that the evolution law of Taylor vortex in a stirred tank reactor with a rotating Reynolds number is similar to that in a conventional Taylor reactor. The Taylor vortex generated in the stirred tank reactor creates a partial plug flow region in the original complete mixing flow pattern, which reduces back mixing, the plug flow area expands with the increase of rotating Reynolds number. Under the condition of a critical rotating Reynolds number (Recr), the gas phase homogeneity of the reactor is increased by 28% and the dissolved oxygen rate is increased by about 5 times, which effectively improves the flow condition in the reactor and strengthens the mass transfer efficiency between the gas and liquid. T... [more]
The Structure of Permafrost in Northern West Siberia: Geophysical Evidence
Natalya Misyurkeeva, Igor Buddo, Ivan Shelokhov, Alexander Smirnov, Alexey Nezhdanov, Yury Agafonov
March 1, 2023 (v1)
Keywords: Arctic, cryopeg, electromagnetic surveys, Fluid Dynamics, frost mound, fuels, gas hydrates, northern West Siberia, permafrost, resistivity, shallow transient electromagnetic (sTEM) soundings, talik
The permafrost of Arctic West Siberia stores extremely rich resources of hydrocarbon fuels that remain a key energy source and an important element of the global economy. A large amount of natural gas in permafrost is bound in gas hydrates which may become an alternative fuel of the future. Shallow subsurface in the permafrost area of northern West Siberia has been studied by transient electromagnetic (TEM) soundings to estimate the permafrost thickness and to detect faults as channels for fluids and heaving features as possible indicators of gas hydrate accumulations. The shallow transient electromagnetic (sTEM) surveys were conducted in discontinuous and continuous permafrost at two sites in northern West Siberia (the northeastern Yamal Peninsula and the southern Gydan Peninsula), with a focus on the vicinities of lakes and cryogenic landforms (frost mounds). The sTEM method resolves well the heterogeneous permafrost structure, with faults, numerous unfrozen zones (taliks), and frost... [more]
Developing a Grey Forecasting Model for the Air Flowing across the Parallel Plate Duct
Alok Dhaundiyal
February 27, 2023 (v1)
Keywords: air heater, draught, Fluid Dynamics, heat analysis, numerical technique
The focus of this work is on developing a nonlinear grey model for the laminar flow regime of carrier fluid across the flat plate collector. The trust region reflective algorithm was used to solve the nonlinear laminar flow problem and handle the sparse matrix. The stream function, dimensionless velocity, gradients of velocity components, carrier fluid temperature, and the absorber plate temperature were estimated for a flat plate collector operated with and without a circular chimney. Similarly, the same technique was adopted to determine a model for heat transfer across the absorber plate. The numerically obtained solution was also compared with the parameters obtained through the instrumental measurement. The relative tolerance was kept at 10−5 for the white and grey box solutions. The developed model was noticed to have a smaller deviation than the conventional analytical model to predict the experimental values. The slip condition was observed for the proposed scheme. The uncertai... [more]
Influence of Macroscopic Wall Structures on the Fluid Flow and Heat Transfer in Fixed Bed Reactors with Small Tube to Particle Diameter Ratio
Thomas Eppinger, Nico Jurtz, Matthias Kraume
February 23, 2023 (v1)
Keywords: CFD-DEM simulation, fixed bed reactor, Fluid Dynamics, heat transfer, wall structure
Fixed bed reactors are widely used in the chemical, nuclear and process industry. Due to the solid particle arrangement and its resulting non-homogeneous radial void fraction distribution, the heat transfer of this reactor type is inhibited, especially for fixed bed reactors with a small tube to particle diameter ratio. This work shows that, based on three-dimensional particle-resolved discrete element method (DEM) computational fluid dynamics (CFD) simulations, it is possible to reduce the maldistribution of mono-dispersed spherical particles near the reactor wall by the use of macroscopic wall structures. As a result, the lateral convection is significantly increased leading to a better radial heat transfer. This is investigated for different macroscopic wall structures, different air flow rates (Reynolds number Re = 16 ...16,000) and a variation of tube to particle diameter ratios (2.8, 4.8, 6.8, 8.8). An increase of the radial velocity of up to 40%, a reduction of the thermal entry... [more]
Heat Transfer and Hydrodynamics in Stirred Tanks with Liquid-Solid Flow Studied by CFD−DEM Method
Xiaotong Luo, Jiachuan Yu, Bo Wang, Jingtao Wang
February 23, 2023 (v1)
Keywords: CFD–DEM coupling method, Fluid Dynamics, heat transfer, liquid-solid stirred tanks
The heat transfer and hydrodynamics of particle flows in stirred tanks are investigated numerically in this paper by using a coupled CFD−DEM method combined with a standard k-e turbulence model. Particle−fluid and particle−particle interactions, and heat transfer processes are considered in this model. The numerical method is validated by comparing the calculated results of our model to experimental results of the thermal convection of gas-particle flows in a fluidized bed published in the literature. This coupling model of computational fluid dynamics and discrete element (CFD−DEM) method, which could calculate the particle behaviors and individual particle temperature clearly, has been applied for the first time to the study of liquid-solid flows in stirred tanks with convective heat transfers. This paper reports the effect of particles on the temperature field in stirred tanks. The effects on the multiphase flow convective heat transfer of stirred tanks without and with baffles as w... [more]
Bioink Temperature Influence on Shear Stress, Pressure and Velocity Using Computational Simulation
J. Carlos Gómez-Blanco, Enrique Mancha-Sánchez, Alfonso C. Marcos, Manuel Matamoros, Antonio Díaz-Parralejo, J. Blas Pagador
November 9, 2020 (v1)
Keywords: bioprinting, bioprinting material, commercial bioink, computational simulation, Fluid Dynamics, level-set, temperature
Bioinks are usually cell-laden hydrogels widely studied in bioprinting performing experimental tests to tune their rheological properties, thus increasing research time and development costs. Computational Fluids Dynamics (CFD) is a powerful tool that can minimize iterations and costs simulating the material behavior using parametric changes in rheological properties under testing. Additionally, most bioinks have specific functionalities and their properties might widely change with temperature. Therefore, commercial bioinks are an excellent way to standardize bioprinting process, but they are not analyzed in detail. Therefore, the objective of this work is to study how three temperatures of the Cellink Bioink influence shear stress pressure and velocity through computational simulation. A comparison of three conical nozzles (20, 22, and 25G) for each temperature has been performed. The results show that shear stress, pressure, and velocity vary in negligible ranges for all combination... [more]
Compartment Model of Mixing in a Bubble Trap and Its Impact on Chromatographic Separations
Jürgen Beck, William Heymann, Eric von Lieres, Rainer Hahn
October 26, 2020 (v1)
Keywords: extra-column dispersion, Fluid Dynamics, mechanistic modelling, peak broadening, preparative chromatography
Chromatography equipment includes hold-up volumes that are external to the packed bed and usually not considered in the development of chromatography models. These volumes can substantially contribute to band-broadening in the system and deteriorate the predicted performance. We selected a bubble trap of a pilot scale chromatography system as an example for a hold-up volume with a non-standard mixing behavior. In a worst-case scenario, the bubble trap is not properly flushed before elution, thus causing the significant band-broadening of the elution peak. We showed that the mixing of buffers with different densities in the bubble trap device can be accurately modeled using a simple compartment model. The model was calibrated at a wide range of flow rates and salt concentrations. The simulations were performed using the open-source software CADET, and all scripts and data are published with this manuscript. The results illustrate the importance of including external holdup volumes in ch... [more]
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