Hsuan-Tsung Hsieh

Computational Fluid Dynamics Modeling of Gas-Particle Flow Within a Solid-Particle Solar Receiver

A detailed three-dimensional computational fluid dynamics (CFD) analysis on gas-particle flow and heat transfer inside a solid-particle solar receiver, which utilizes free-falling particles for direct absorption of concentrated solar radiation, is presented. The two-way coupled Euler-Lagrange method is implemented and includes the exchange of heat and momentum between the gas phase and solid particles. A two-band discrete ordinate method is included to investigate radiation heat transfer within the particle cloud and between the cloud and the internal surfaces of the receiver. The direct illumination energy source that results from incident solar radiation was predicted by a solar load model using a solar ray-tracing algorithm. Two kinds of solid-particle receivers, each having a different exit condition for the solid particles, are modeled to evaluate the thermal performance of the receiver Parametric studies, where the particle size and mass flow rate are varied, are made to determine the optimal operating conditions. The results also include detailed information for the gas velocity, temperature, particle solid volume fraction, particle outlet temperature, and cavity efficiency.

CFD Modeling of Gas Particle Flow Within a Solid Particle Solar Receiver

A detailed three dimensional computational fluid dynamics (CFD) analysis on gas-particle flow and heat transfer inside a solid particle solar receiver, which utilizes free-falling particles for direct absorption of concentrated solar radiation, is presented. The two-way coupled Euler-Lagrange method is implemented and includes the exchange of heat and momentum between the gas phase and solid particles. A two band discrete ordinate method is included to investigate radiation heat transfer within the particle cloud and between the cloud and the internal surfaces of the receiver. The direct illumination energy source that results from incident solar radiation was predicted by a solar load model using a solar ray tracing algorithm. Two kinds of solid particle receivers, each having a different exit condition for the solid particles, are modeled to evaluate the thermal performance of the receiver. Parametric studies, where the particle size and mass flow rate are varied, are made to determine the optimal operating conditions. The results also include detailed information for the particle and gas velocity, temperature, particle solid volume fraction, and cavity efficiency.Copyright

Development of an object-oriented finite element program with adaptive mesh refinement for multi-physics applications

In this paper, an object-oriented framework for numerical analysis of multi-physics applications is presented. The framework is divided into several basic sets of classes that enable the code segments to be built according to the type of problem to be solved. Fortran 2003 was used in the development of this finite element program due to its advantages for scientific and engineering programming and its new object-oriented features. The program was developed with h-type adaptive mesh refinement, and it was tested for several classical cases involving heat transfer, fluid mechanics and structural mechanics. The test cases show that the adaptive mesh is refined only in the localization region where the feature gradient is relatively high. The overall mesh refinement and the h-adaptive mesh refinement were justified with respect to the computational accuracy and the CPU time cost. Both methods can improve the computational accuracy with the refinement of mesh. The overall mesh refinement causes the CPU time cost to greatly increase as the mesh is refined. However, the CPU time cost does not increase very much with the increase of the level of h-adaptive mesh refinement. The CPU time cost can be saved by up to 90%, especially for the simulated system with a large number of elements and nodes.

Numerical Investigation on Optimal Design of Solid Particle Solar Receiver

Solar thermo-chemical processes often require high temperatures that can be achieved by direct absorption of solar energy. The solid particle solar receiver can be used to heat ceramic particles that may serve as a heat transfer and storage medium or as a substrate on which chemical reaction may be performed directly. Using solid particles enclosed in a cavity to absorb concentrated solar radiation can provide efficient absorption of concentrated sunlight. In this work, different solid particle solar receiver designs have been investigated by using computation fluid dynamics (CFD) technique. The gas particle flow with the solid particle solar receiver was simulated by using two-way coupled Euler-Lagrange method. The direct illumination energy source that results from incident solar radiation was predicted by a solar load model using a solar ray tracing algorithm. The detailed information to guide the experiment, such as the particle and gas velocity, temperature, particle solid volume fraction, and cavity efficiency under different designs has been analyzed.Copyright

Theoretical Analysis on the Secondary Flow in a Rotating Helical Pipe With an Elliptical Cross Section

In the present study, the flow in a rotating helical pipe with an elliptical cross section is considered. The axes of the elliptical cross section are in arbitrary directions. Using the perturbation method, the Navier-Stokes equations in a rotating helical coordinate system are solved. The combined effects of rotation, torsion, and geometry on the characteristics of secondary flow and fluid particle trajectory are discussed, Some new and interesting conclusions are obtained, such as how the number of secondary flow cells and the secondary flow intensity depends on the ratio of the Coroilis force to the centrifugal force. The results show that the increase of torsion has the tendency to transfer the structure of secondary flow into a saddle flow, and that the incline angle a increases or decreases the secondary flow intensity depending on the resultant force between the Corilois force and centrifugal force.

Computational Fluid Dynamics Analysis on Underfloor Air Distribution (UFAD) System in BTLab

As an alternative to Conventional Air Distribution (CAD) systems, underfloor air distribution (UFAD) systems have been widely used in different country. Although many advantages of a well-designed UFAD system can be found, there is still a higher risk to designers and building owners due to a lack of objective information and standardized design guidelines. UFAD systems design have been influenced by increasing emphasis on indoor air quality (IAQ), energy conservation, environmental effects, safety, and economics. To investigate the performance of the UFAD system, a detailed 3-D computational fluid dynamics (CFD) analysis on the turbulent buoyancy flow and heat transfer inside the BTLab, which locates at University of Nevada, Las Vegas, has been made in this paper. The particular interest has been concentrated on the flow distribution through underfloor swirl diffuser. By CFD analysis with unstructured meshes associated with using parallel processing, the impact of different operating parameters on the air flow and temperature distribution has been studied in detail. Usefully information has been provided on the development of high energy efficiency with human comfort of UFAD systems.Copyright

Modeling of a Diffusion Controlling Oxidation Process with Scale Removal in Oxygen-Containing Liquid Flow

A diffusion controlling oxidation model, considering scale removal, is developed in an oxygen-containing liquid flow environment. Scale removal is implemented and the effect of the scale removal rate on the formation mechanism of the duplex oxide layer structure is analyzed in the model. The volume expansion effect caused by density difference is coupled with the weight gain during oxidation. A coordinate transform technique is employed to obtain the diffusion equations with advection term. The governing equations are non-dimensionalized and analogized with the Stefan problem and solved numerically by the finite difference method. The non-dimensional parameters are studied and the model is extended to an oxide growth model with duplex layer structure and noble elements. The model is benchmarked with previous results, and good agreement is obtained.Copyright

A Stochastic Model of Oxidation Mechanism on High Temperature Corrosion of Stainless Steel

To interpret the role of diffusion and reaction process, a cellular automaton model, which combines the surface growth and internal oxidation, was developed to explain the oxidation mechanism of stainless steels in high temperature corrosive liquid metal environment. In this model, three main processes, which include the corrosion of the substrate, the diffusion of iron species across the oxide layer and precipitation of iron on the oxide layer, are simulated. The diffusion process is simulated by random walk model. Mapping between present model and Wagner theory has been created. The gross features concerning the evolution of the involved process were founded.Copyright

Numerical Analysis of Natural Convection Induced Oxygen Transport in Liquid Lead Bismuth Eutectic

Liquid lead bismuth eutectic (LBE) is very corrosive to steels. To mitigate structural corrosion of LBE systems, active oxygen control technique is developed. To enhance the speed of oxygen transport in liquid LBE, natural convection has been proposed. This paper numerically analyzes the oxygen transport in a natural convection induced LBE enclosure. Different temperature boundary conditions are added to the container. Both laminar and turbulent LBE flows which are distinguished by strength of flow measured are analyzed. Three laminar cases: (a) heated from the bottom and cooled from the top of the container; (b) heated from the sidewalls and cooled from the top of the container; (c) one sidewall heated and the opposite wall cooled, and one fully turbulent case with one sidewall heated and the opposite sidewall cooled are chosen. Oxidization in near wall areas and formation of oxide layers on container surfaces are considered. In each case, the characteristic velocity and oxygen diffusion time are estimated, the change of oxygen distribution with time are obtained, and the bulk concentration of oxygen and the efficiency of oxide layer formation on different liquid-solid interfaces are calculated. To obtain more information of oxygen transportation and distribution, three-dimension analysis of the laminar flow is done. Based on the analysis, several conclusions are finally obtained.Copyright

Modeling Corrosion and Precipitation in Non-Isothermal LBE pipe/loop Systems

A previous kinetic model on corrosion and precipitation for a non-isothermal LBE pipe/loop system is improved by considering a turbulent core region and a laminar sub-layer, respectively. Exact solutions of the mass transfer equations in both core and boundary regions are obtained. Based on the present model, both of the local corrosion/precipitation rate and bulk concentration can be calculated. The present study shows that the effects of the axial temperature profile on the corrosion/precipitation rate and bulk concentration by applying this model to DELTA loop at the Los Alamos National Laboratory. Correlations for average Sherwood number at the highest isothermal temperature section for both open pipes and close loops are presented. In addition, the present solution can be extended to the more general cases of high Schmidt number mass transfer in the developed turbulent wall-bounded shear flows.