Yitung 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.

A Photoelectrochemical Model of Proton Exchange Water Electrolysis for Hydrogen Production

proton exchange membrane is proposed based on Butler-Volmer kinetics for electrodes and transport resistance in the polymer electrolyte. An equivalent electrical circuit analogy is proposed for the sequential kinetic and transport resistances. The model provides a relation between the applied terminal voltage of electrolysis cell and the current density in terms of Nernst potential, exchange current densities, and conductivity of polymer electrolyte. Effects of temperature on the voltage, power supply, and hydrogen production are examined with the developed model. Increasing temperature will reduce the required power supply and increase the hydrogen production. An increase of about 11% is achieved by varying the temperature from 30° C to 80° C. The required power supply decreases as the illumination intensity becomes greater. The power supply due to the cathode overpotential does not change too much with the illumination intensity. Effects of the illumination intensity can be observed as the current density is relatively small for the examined illumination intensities. DOI: 10.1115/1.2789722

The Parametric Study of an Innovative Offset Strip-Fin Heat Exchanger

Offset strip-fin heat exchangers have numerous applications throughout various industries because they can provide a large amount of heat transfer area in a small volume. The widespread use of the offset strip-fin design has ensured that there are numerous dimensional variations and shown that changes in dimensional parameters affect performance. It is then important to understand how the geometry of an offset strip-fin heat exchanger can affect its performance. Therefore, an investigation into the parametric effects on the global performance of an innovative high-temperature offset strip-fin heat exchanger was numerically performed in this study, where the numerical solution was obtained through a finite-volume method. Computations were carried out for each of the heat exchangers geometrical parameters: fin thickness (t), fin length (1), channel height (H), spanwise pitch (p x ), and the newly introduced gap parameter (g). Also, the effects of rounding the fins leading and trailing edges were investigated, while the heat exchangers volume, mass flow rates, and inlet temperatures were kept constant. The results are presented in the form of pressure drops and heat transfer rates, and the coefficient of performance parameter shows that fins with rounded leading and trailing edges outperform fins with rectangular edges.

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...

Oxygen Control Technique in Molten Lead and Lead-Bismuth Eutectic Systems

Abstract The key aspects of oxygen control technique used for steel corrosion mitigation in lead-alloy systems include the thermodynamic stability of protective oxides, oxygen concentration range, measurement and control methods, and oxide layer structures and transport properties. Practical conditions for oxygen control and the proper oxygen concentration ranges for typical nonisothermal liquid lead and lead-bismuth eutectic (LBE) systems are presented based on the available thermodynamic and solubility data. Theoretical expressions for the widely used oxygen sensor signals are obtained. The sensors are calibrated by comparing the experimental results from a nonisothermal LBE loop and the theoretical calculations. Analyses show that the fully turbulent flow leads to a nearly uniform oxygen concentration over the entire loop, and there is no significant delay of sensor response to a change of the operating condition. Under conditions of actively controlled oxygen in lead and LBE, the possible behaviors for oxidation, corrosion, and corrosion product precipitation are analyzed, providing the means to optimize corrosion control through oxide protection.

Design of a Compact Ceramic High-Temperature Heat Exchanger and Chemical Decomposer for Hydrogen Production

This article describes a compact silicon carbide ceramic, high-temperature heat exchanger for hydrogen production in the sulfur iodine thermochemical cycle, and in particular, to be used as the sulfuric acid decomposer. In this cycle, hot helium from a nuclear reactor is used to heat the SI (sulfuric acid) feed components (H2O, H2SO4, SO3) to obtain appropriate conditions for the SI decomposition reaction. The inner walls of the SI decomposer channels are coated with platinum to catalytically decompose sulfur trioxide into sulfur dioxide and oxygen. Hydrodynamic, thermal, and the sulfur trioxide decomposition reaction were coupled for numerical modeling. Thermal results of this analysis are exported to perform a probabilistic mechanical failure analysis. This article presents the approach used in modeling the chemical decomposition of sulfur trioxide. Stress analysis of the design is also presented. The second part of the article shows the results of parametric study of the baseline design (linear channels). Several alternate designs of the chemical decomposer channels are also explored. The current study summarizes the results of the parametric calculations whose objective is to maximize the sulfur trioxide decomposition by using various channel geometries within the decomposer. Based on these results, a discussion of the possibilities for improving the productivity of the design is also given.

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.

Calculation of Fluid Flow Distribution Inside a Compact Ceramic High Temperature Heat Exchanger and Chemical Decomposer

Numerical analysis of flow distribution inside a compact ceramic high temperature heat exchanger and chemical decomposer (thereafter, heat exchanger), which will be used for hydrogen production, wherein the sulfur iodine thermochemical cycle is performed. To validate the numerical model, experimental investigation of the heat exchanger is accomplished. The study of the flow distribution in the base line design heat exchanger shows that the design has large-flow maldistribution and the reverse flow may occur at poor inlet and outlet manifold configurations. To enhance uniformity of the flow rate distribution among the heat exchanger internal channels, several improved designs of the heat exchanger manifolds and supply channels are proposed. The proposed designs have a sufficiently uniform flow rate distribution among the internal channels, with an appropriate pressure drop.

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