Helen Wu

Constant-Step-Stress Accelerated Life Test of White OLED Under Weibull Distribution Case

In order to acquire the life information of the white organic light-emitting diode (OLED), Weibull distribution function was applied to describe the life distribution, whereas the least square method was employed to estimate the shape and scale parameters. The accelerated life equation was determined, and the statistics and analysis on constant-stress and step-stress test data were performed using the software developed by the authors. The numerical results indicate that Weibull distribution and the inverse power law are both consistent with the employed assumptions and that the accurately calculated acceleration parameters enable a rapid estimation of the white OLED life.

A Study of Accelerated Life Test of White OLED Based on Maximum Likelihood Estimation Using Lognormal Distribution

In this paper, accelerated life tests of white organic light-emitting diodes (WOLEDs) are conducted to obtain failure data at normal operation conditions. The lognormal distribution function was applied to describe WOLED life distribution. Log mean and log standard deviation were determined by maximum likelihood estimation. The Kolmogorov-Smirnov test was performed, and the results further confirmed that WOLED life met the lognormal distribution. Numerical results indicated that WOLED life followed the lognormal distribution. It was also found that the acceleration model was consistent with inverse power law.

An improved modeling for life prediction of high-power white LED based on Weibull right approximation method

Abstract Aiming at precisely predicting the life of the high-power white light LED (HPWLED), a three-parameter Weibull function and the right approximation method were employed to establish the luminance degradation model. The lumen maintenance data collected according to the IES LM-80-08 lumen maintenance test standard were fitted with and without error corrections, and the pseudo failure time of each HPWLED sample was extrapolated. The statistical analysis on the failure time was achieved by using Weibull distribution, normal distribution, lognormal distribution and Akaike Information Criterion (AIC). Then the life information was acquired. The results indicate that Weibull right approximation luminance degradation model (WRALDM) accurately reflects the variation of the lumen law with time. The failure time is accurately obtained. The best life distributions before and after the error correction to the lumen maintenance data are identified, based on AIC, as Weibull distribution and lognormal distribution, respectively. It is further confirmed by comparing the widths of life confidence interval and the life provided by the IES TM-21-11 method that the HPWLED life using WRALDM has a better accuracy. The optimized model provides researchers and manufacturers with significant guidelines for the further development of life prediction methodology.

Lifetime Prediction of White OLED Based on MLE Under Lognormal Distribution

To predict the lifetime of a white organic light-emitting diode (OLED) and reduce test time and cost, we conducted two constant stress and one step stress accelerated lifetime tests to obtain the failure time data of samples, described the lifetime distribution of white OLED with the lognormal distribution function, estimated the log mean and log standard deviation by using maximum likelihood estimation (MLE), achieved statistics and analysis of lifetime data, and developed lifetime prediction software by ourselves. Numerical results shows that white OLED lifetime follows the lognormal distribution, that the acceleration model is consistent with inverse power law, and that the acceleration parameters, which are accurately calculated, make fast estimation of white OLED lifetime possible.

A Numerical Simulation of Diffusion Charging Effect on Collection Efficiency in Wire-Plate Electrostatic Precipitators

In this paper, a numerical simulation was carried out to analyze the effect of diffusion charging on collection efficiency of a wire-plate electrostatic precipitator (ESP). The gas flow field, the electric field, and the particle field with diffusion charging considered were included in the numerical model, which was implemented by using the commercial FLUENT software. Collection efficiency was calculated by using the Deutsch-Anderson equation, in which the parameters were provided from the numerical solutions. The simulated results indicate that the effect of diffusion charging on the wire-plate ESP particle collection increases with the decreasing particle diameter, as well as applied potential, particularly for PM10. Moreover, with the increasing applied potential, collection efficiency of PM10 is obviously improved, and the effect extent first increases and then decreases with particle size increasing, but also, the size range of particle, which is significantly affected by the diffusion charging, becomes smaller. As gas velocity becomes higher, the effect of diffusion charging on grade efficiency also becomes more obvious, and the affected range of particle size gets much larger, however, at the price of grade efficiency decreasing. Using collection efficiency as reference variable of judgment, instead of particle charge, may lead to a more accurate estimation of the aforementioned size range, which can provide a great help in the further analysis of fine particle collection.

PM2.5 removal performance of a wire-pipe ESP under multi-field coupling and applied magnetic field

In order to study PM2.5 removal performance under multi-field coupling and applied magnetic field, a mathematical model was proposed to analyze the interaction between fluid flow field, electro- magnetic field and particle dynamic field. The computational fluid dynamics method and FLUENT were employed to numerically simulate the PM2.5 removal performance in a Wire-pipe ESP. The effects of magnetic field on PM2.5 collection efficiency at different working voltages and gas velocities were discussed. The results indicate that the influence of applied magnetic field on PM2.5 collection in the wire-pipe ESP becomes more obvious with the increase of the particle diameter, and the increment of PM2.5 grade efficiency decreases with the increasing magnetic flux density in a certain range of particle diameters. Furthermore, the effect of magnetic field on PM2.5 collection increases with a decrease of working voltage or an increase of gas velocity, and PM2.5 collection efficiency declines at the same time. At a lower flue gas velocity, the impact of flue gas velocity on PM2.5 overall efficiency is more significant than that of applied magnetic field.

White OLED Weibull Life Prediction Using Maximum Likelihood Estimation

A theoretical model using Weibull distribution and maximum likelihood estimation (MLE) was established to statistically analyze the test data, which were obtained by three groups of constant stress accelerated life tests. The life prediction software was applied to simplify the calculation and achieve organic light-emitting device (OLED) life estimation. The results indicate that the Weibull distribution is fit to describe white OLED life, and the precise accelerated parameter β is particularly useful to predict the white OLED life within a shorter time, which provides significant guidelines to help engineers make decisions in design and manufacturing strategy from the aspect of reliability life.

Three-dimensional numerical investigation of vortex-induced vibration of a rotating circular cylinder in uniform flow

The vortex-induced vibration (VIV) of an elastically mounted rotating circular cylinder vibrating in a uniform flow is studied numerically. The cylinder is allowed to vibrate only in the cross-flow direction. In the numerical simulations, the Reynolds number, the mass ratio, and the damping ratio are kept constants to 500, 11.5, and 0, respectively. Simulations are performed for rotation rates of α = 0, 0.5, and 1 and a range of reduced velocities from 1 to 13, which covers the entire lock-in regime. It is found that the lock-in regime of a rotating cylinder is wider than that of a non-rotating cylinder for α = 0, 0.5, and 1. The vortex shedding pattern of a rotating cylinder is found to be similar to that of a non-rotating cylinder. Next, simulations are performed for three typical reduced velocities inside the lock-in regime and a range of higher rotation rates from α = 1.5 to 3.5 to investigate the effect of the rotation rate on the suppression of VIV. It is found that the VIV is suppressed when the rotation rate exceeds a critical value, which is dependent on the reduced velocity. For a constant reduced velocity, the amplitude of the vibration is found to increase with increasing rotation rate until the latter reaches its critical value for VIV suppression, beyond which the vibration amplitude becomes extremely small. If the rotation rate is greater than its critical value, vortex shedding ceases and hairpin vortices are observed due to the rotation of the cylinder.The vortex-induced vibration (VIV) of an elastically mounted rotating circular cylinder vibrating in a uniform flow is studied numerically. The cylinder is allowed to vibrate only in the cross-flow direction. In the numerical simulations, the Reynolds number, the mass ratio, and the damping ratio are kept constants to 500, 11.5, and 0, respectively. Simulations are performed for rotation rates of α = 0, 0.5, and 1 and a range of reduced velocities from 1 to 13, which covers the entire lock-in regime. It is found that the lock-in regime of a rotating cylinder is wider than that of a non-rotating cylinder for α = 0, 0.5, and 1. The vortex shedding pattern of a rotating cylinder is found to be similar to that of a non-rotating cylinder. Next, simulations are performed for three typical reduced velocities inside the lock-in regime and a range of higher rotation rates from α = 1.5 to 3.5 to investigate the effect of the rotation rate on the suppression of VIV. It is found that the VIV is suppressed when the ro...

Numerical study on PM10 collection efficiency in a wire-cylinder electrostatic precipitator under multi-field coupling

The PM10 collection efficiency of a wire-cylinder electrostatic precipitator (ESP) was studied by means of a developed mathematical model, including the multi-field coupling between the gas flow field, the particle dynamic field and the electric field, and applying the Deutsch–Anderson Equation. The diffusion charging mechanism was considered due to the diameter range of PM10. The investigated variables were the applied potential, the gas velocity and the particle distribution. Numerical results indicate that the diffusion charging has significant influence on PM10 removal performance and the effect is more obvious with the decreasing diameter, and that the PM10 collection efficiency increases with the increasing applied potential and the increment of collection efficiency is more significant at lower voltage. Moreover, as the gas velocity at inlet decreases, collection efficiency of PM10 will increase. Finally, the overall efficiency increases with increasing the mean diameter of particle distribution. The research results can provide theoretical and technical references for the design of novel ESP aiming at economy and environment protection.

Tensile properties and fracture toughness of three rubber-modified epoxies

This paper investigates the tensile properties and fracture toughness of a liquid rubber-modified highly crosslinked epoxy cured using 4,4 diaminodiphenyl sulphone (DDS/LR). The results for DDS/LR epoxy in relation to rubber and matrix properties are also compared with those of rubber-modified lowly crosslinked epoxy systems, namely, liquid rubber-modified piperidine cured epoxy (Piperidine/LR) and core-shell-rubber modified piperidine cured epoxy (Piperidine/CSR). It was found that highly crosslinked DDS/LR epoxy has a higher tensile strength than that of either Piperidine/LR or Piperidine/CSR epoxy, while it shows only a moderate increase in the fracture toughness.