Huajun Chen

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.

Research on the Transport and Deposition of Nanoparticles in a Rotating Curved Pipe

A finite-volume code and the SIMPLE scheme are used to study the transport and deposition of nanoparticles in a rotating curved pipe for different angular velocities, Dean numbers, and Schmidt numbers. The results show that when the Schmidt number is small, the nanoparticle distributions are mostly determined by the axial velocity. When the Schmidt number is many orders of magnitude larger than 1, the secondary flow will dominate the nanoparticle distribution. When the pipe corotates, the distribution of nanoparticle mass fraction is similar to that for the stationary case. There is a “hot spot” deposition region near the outside edge of bend. When the pipe counter-rotates, the Coriolis force pushes the region with high value of nanoparticle mass fraction toward inside edge of the bend. The hot spot deposition region appears inside the edge. The particle deposition over the whole edge of the bend becomes uniform as the Dean number increases. The corotation of pipe makes the particle deposition efficiency ...

Viscoelastic flow in rotating curved pipes

Fully developed viscoelastic flows in rotating curved pipes with circular cross section are investigated theoretically and numerically employing the Oldroyd-B fluid model. Based on Dean’s approximation, a perturbation solution up to the secondary order is obtained. The governing equations are also solved numerically by the finite volume method. The theoretical and numerical solutions agree with each other very well. The results indicate that the rotation, as well as the curvature and elasticity, plays an important role in affecting the friction factor, the secondary flow pattern and intensity. The co-rotation enhances effects of curvature and elasticity on the secondary flow. For the counter-rotation, there is a critical rotational number RΩ′, which can make the effect of rotation counteract the effect of curvature and elasticity. Complicated flow behaviors are found at this value. For the relative creeping flow, RΩ′ can be estimated according to the expression RΩ′=−4Weδ. Effects of curvature and elastici...

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

Oxidation companied by scale removal: initial and asymptotical kinetics

The general kinetics of oxidation companied by scale removal such as scale dissociation, volatilization, erosion, or mass transfer corrosion is analyzed by employing a dimensionless Tedmons equation. Analytical expressions suitable for analyzing and fitting the oxide thickness/weight changes at early stages and long-term operations are presented. The scale of the time, oxide thickness and mass gain are specified. In addition, a perturbation solution showing the effects of the parabolic oxidation and the linear scale removal, and the combined effects of both terms are obtained. The limitation of the perturbation solution is determined. The proposed model is also applied to interpret the experimental results of steel exposed in the liquid lead-bismuth eutectic. The results show that the present model is valid for analyzing experimental results and for predicting long-term behaviors.

Nanoparticle Transport and Coagulation in Bends of Circular Cross Section via a New Moment Method

Abstract Transport of nanoparticles and coagulation is simulated with the combination of CFD in a circular bend. The Taylor-expansion moment method (TEMOM) is employed to study dynamics of nanoparticles with Brownian motion, based on the flow field from numerical simulation. A fully developed flow pattern in the present simulation is compared with previous numerical results for validating the model and computational code. It is found that for the simulated particulate flow system, the particle mass concentration, number concentration, particle polydispersity, mean particle diameter and geometric standard deviation over cross-section increase with time. The distribution of particle mass concentration at different time is independent of the initial particle size. More particles are concentrated at outer edge of the bend. Coagulation plays more important role at initial stage than that in the subsequent period. The increase of Reynolds number and initial particle size leads to the increase of particle number concentration. The particle polydispersity, mean particle diameter and geometric standard deviation increase with decreasing Reynolds number and initial particle size.

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