Yong Shuai

Numerical Study of Radiation Characteristics in a Dish Solar Collector System

This paper aims at predicting radiation characteristics of the solar collector system by the Monte Carlo method with respect to the corresponding optical properties. Several probability models were introduced to analyze the effects of sunshape and surface roughness. Directional characteristics of radiative flux in the focal region and flux distribution of the cavity receiver were considered. An equivalent radiation flux method is presented for designing the shape of the cavity receiver. Based on the relative numerical simulation results, a new shape cavity receiver called “upside-down tear drop” is proposed to meet an almost uniform radiation flux field. Radiation effects due to multiple reflections and thermal emission in the cavity are parametrized by using the radiative exchange factor. The calculation results can be a valuable reference for the design and assemblage of the dish solar collector system. DOI: 10.1115/1.2840570

A new multi-function global particle swarm optimization

Display Omitted We introduced the concept of the population density.We proposed a method of measuring the search capability of the PSO.We proposed a new search strategy to get the global convergence of the PSO improved. In this paper, we introduce the concept of population density in PSO, and accordingly, we discuss the relationship between the search capability of PSO and the population density. From related numerical experiments, we find that the search capability of PSO becomes saturated when the population density exceeds a certain value. Accordingly, we propose a strategy that divides the particles into two parts for different functions. Thus, we propose an approach called multi-function global particle swarm optimization (MFPSO) on the basis of this strategy. Further, we carry out a series of numerical experiments to verify that MFPSO has high global convergence capability, high convergence speed, and highly reliable performance when it is used to solve complex problems.

Optical coherent thermal emission by excitation of magnetic polariton in multilayer nanoshell trimer.

A theoretical demonstration is given of coherent thermal emission via the visible region by exciting magnetic polaritons in isolated metal-dielectric-metal multilayer nanoshells and the collective behavior in a trimer comprising multilayer nanoshells. The dipolar metallic core induces magnetic polaritons in the dielectric shell creating a large enhancement of the emissivity, whose mechanism is different from that of film-coupled metamaterials. The coupling effect of the magnetic polaritons and the electric/magnetic modes of symmetric nanoparticle trimers is discussed to understand the collective behavior in self-assembled nanoparticle clusters with potential solar energy utilizations. The concept of hybridization is employed to understand the collective magnetic polaritons of a multilayer nanoshell trimer. The fundamental understanding gained herein opens up new ways to explore, control, and tailor spectral absorptance, thus facilitating rational design of novel self-assembled nanoclusters for energy harvesting.

Manipulating intrinsic behaviors of graphene by substituting alkaline earth metal atoms in its structure

In this paper, the structural, electronic, magnetic and optical properties of alkaline earth metal (AEM) atom-doped monolayer graphene are investigated using first-principles calculations. It is found that, Be, Mg and Ca atom substituted graphene structures exhibit half metallic behavior with 0.00 μB, 1.86 μB, and 4.00 μB magnetic moments, respectively. While, Sr and Ba atom-doped graphene structures display indirect band gap semiconductor behavior with 3.16 μB and 0.46 μB magnetic moments, respectively. All the impurity atoms are tightly bonded with graphene, having significant formation energy and the direction of charge transfer is from AEM atoms to the graphene. Upon analyzing density of states plots we found that the s and p orbitals of impurity atoms give rise to magnetic moments in graphene complexes. The optical properties for pure graphene and AEM atom-doped graphene complexes have been calculated within the random phase approximation (RPA) approach. The absorption coefficient and reflectivity plots for doped graphene complexes are calculated and compared to the results obtained for pure graphene. A significant change in optical properties specifically in the absorption spectrum of graphene is obtained after AEM atom substitution. It is found that AEM atom substitution into graphene produces an increase in the absorption spectrum in the energy range of 0 to 3 eV and a reduction in absorption peaks at a 14 eV energy level. In addition, a third minimum absorption peak appears in the energy interval of 7 to 11 eV, which is not present in the absorption spectrum of pure graphene. A significant red shift in absorption towards the visible range of radiation is also obtained. An increase in reflectivity peak in the low energy region is observed after AEM atom substitution into graphene. We believe that our results are suitable for further experimental exploration and useful for graphene based spintronic and optoelectronic devices.

Multi-focused microlens array optimization and light field imaging study based on Monte Carlo method

Plenoptic cameras are used for capturing flames in studies of high-temperature phenomena. However, simulations of plenoptic camera models can be used prior to the experiment improve experimental efficiency and reduce cost. In this work, microlens arrays, which are based on the established light field camera model, are optimized into a hexagonal structure with three types of microlenses. With this improved plenoptic camera model, light field imaging of static objects and flame are simulated using the calibrated parameters of the Raytrix camera (R29). The optimized models improve the image resolution, imaging screen utilization, and shooting range of depth of field.

A first-principles study on alkaline earth metal atom substituted monolayer boron nitride (BN)

This paper presents first-principles density functional theory (DFT) calculations for the structural, electronic, magnetic and optical properties of monolayer boron nitride (BN) doped with different alkaline earth metal (AEM) atoms. We used two configurations for substituting AEM atoms in a BN layer. In the first case, nitrogen (N) was replaced with an AEM atom and in the second case, a boron (B) atom was replaced by AEM atoms. All the impurity atoms were tightly bonded to B and N atoms in the BN layer. When an AEM atom replaces an N atom, the B-AEM bond distance increases. On the other hand, when a B atom is replaced by an AEM atom, the N-AEM bond distance is decreased. It has been found that after AEM atom substitution in a BN layer, some surface states appear at the Fermi energy (EF) level, thereby making the BN layer a half metallic material. The appearance of surface states produces some interband transitions, which in turn introduces some new trends in the optical properties of the BN layer. Pure BN is a nonmagnetic material. However, AEM atom substitution in a BN layer induces finite magnetic moments, thereby introducing ferromagnetism in the BN layer. The values of the magnetic moments vary depending upon the type of impurity atom and the position of AEM atoms in the BN layer. The optical properties, specifically the absorption coefficient and reflectivity plots, of the AEM atom-doped BN structures were investigated using DFT with random phase approximation (RPA). A pure BN layer has zero absorption at an energy interval ranging from 0 to 4 eV. After AEM atom doping, a finite value of the absorption coefficient is obtained in the said energy interval. Similarly, a higher static reflectivity is achieved in a lower energy interval after AEM atom substitution in a BN layer. Our obtained results reveal that AEM atom substituted monolayer BN has potential applications in nanoelectronics, spintronics and optoelectronic devices.

Ray-Thermal-Structural Coupled Analysis of Parabolic Trough Solar Collector System

An effective approach to sustainable energy is the utilization of solar energy. The parabolic trough collector with central receiver is one of the most suitable systems for solar power generation. A type of concentrating solar collector that uses U-shaped troughs to concentrate sunlight onto a receiver tube, containing a working fluid such as water or oil, which is positioned along the focal line of the trough. Sometimes a transparent glass tube envelops the receiver tube to reduce heat loss. Parabolic troughs often use single-axis or dual-axis tracking. Temperatures at the receiver can reach 400°C. The heated working fluid may be used for medium temperature space or process heat, or to operate a steam turbine for power or electricity generation. As designed to operate with concentrated heat fluxes, the receiver will be subjected to the high thermal stresses which may cause the failure of receivers. The thermal stress of receiver or tube heat exchangers has drawn many researchers’ attention. Numerous studies have been carried out to investigate the temperature distributions and thermal stress fields of receiver or tube heat exchangers. A numerical analysis had been conducted by Chen [1] to study the effect on temperature distributions of using porous material for the receiver. Experiments were conducted by Fend [2] to research the temperature distributions on the volumetric receivers used two novel porous materials. A finite element analysis was conducted by Islamoglu [3] to study the temperature distribution and the thermal stress fields on the tube heat exchanger using the SiC material. To reduce the thermal stresses, Agrafiotis [4] employed porous monolithic multi-channeled SiC honeycombs as the material for an open volumetric receiver. Low cycle fatigue test of the receiver materials was conducted at different temperatures by Lata et al. [5], the results showed that the high nickel alloys had excellent thermo-mechanical properties compared to the austenitic stainless steel. Almanza and Flores [6, 7] proposed a bimetallic Cu-Fe type receiver, and the experimental test results showed that, when operated at low pressure, the bimetallic Cu-Fe type receiver had a lower thermal gradient and less thermal stress strain than the steel receiver. In Steven’s study [8], the receiver is divided into 16 sections, and the average solar radiation heat flux of each section is calculated. The average heat flux is used as boundary condition for each corresponding section in the thermal analysis model. This method is fairly straightforward and simple, but the deviations generated during the heat flux transformation process are enormous.

Nanoparticle-crystal towards an absorbing meta-coating

In this paper, a double layer nanoparticle-crystal has been proposed, which shown incident and polarization angle, substrate independences for spectral absorptivity. Such phenomenon originates from the near-field light redistribution and excitation of internal collective oscillating. This kind of nanoparticle-crystal can be made of various types of metal with similar optical responses. A three oscillators mode has been proposed in this paper to understand the shift between global and internal collective oscillating, and verify the physical picture demonstrated. That kind of near-field redistribution result in a prototype of novel meta-coating, and facilitates the large scale application of metamaterial.

Double Directions Nanoscale Range Finding Using Fano Resonance in Coupled Gratings

In this paper, a theoretical demonstration is given of nanoscale range finding by exciting Fano resonance in coupled gratings. Metallic ridges induce oscillation mode, whose interference with surface plasmon polartions generate narrow Fano resonance. The concept of hybridization is employed to understand the coupling effect of surface plasmon polartions and the oscillation due to metallic ridges. Fano behavior in this structure is captured by using the temporal coupled-mode theory. The gained fundamental understanding opens up new ways to control nanoscale spacing distances and tailor Fano resonance, thus facilitating rational design of nanosensors to improve the performance of nanomotion control systems.

Reliability of stray light calculation code using the Monte Carlo method

This paper mainly discusses the validity and the reliability of the stray light calculation code using the Monte Carlo method in an optical system. As a new method, the symmetrical test of radiation in two-dimensional media (STRTDM) is presented to verify the characteristics of pseudorandom numbers. The method can provide great flexibility and simplicity under various calculation conditions through iteratively comparing the performance of the pseudorandom number generators (PNGs) until a sufficiently good PNG is obtained. After a series of tests have been performed—including tests for the characteristics of a PNG, for the reliability of probability models, and for the summation reciprocity relationships of the radiative exchange factor—the results show the reliability of the stray light calculation code in this paper. Moreover, the Monte Carlo computer code is verified by comparing its predictions with previously published results for optical geometries similar to ours.