Optimal Design Conditions Research Articles

Rigorous analysis of an electric-field-driven liquid crystal lens for 3D displays

We numerically analyzed the optical performance of an electric field driven liquid crystal (ELC) lens adopted for 3-dimensional liquid crystal displays (3D-LCDs) through rigorous ray tracing. For the calculation, we first obtain the director distribution profile of the liquid crystals by using the Erickson-Leslie motional equation; then, we calculate the transmission of light through the ELC lens by using the extended Jones matrix method. The simulation was carried out for a 9view 3D-LCD with a diagonal of 17.1 inches, where the ELC lens was slanted to achieve natural stereoscopic images. The results show that each view exists separately according to the viewing position at an optimum viewing distance of 80 cm. In addition, our simulation results provide a quantitative explanation for the ghost or blurred images between views observed from a 3D-LCD with an ELC lens. The numerical simulations are also shown to be in good agreement with the experimental results. The present simulation method is expected to provide optimum design conditions for obtaining natural 3D images by rigorously analyzing the optical functionalities of an ELC lens.

Dynamic behaviors of the crankshafts in single-cylinder and twin-cylinder rotary compressors

Refrigeration rotary compressors are widely used in air-conditioners. A rotary compressor has a special rotor-bearing system, since the elastic cantilevered crankshaft is under dynamic transverse forces on different planes. The large deformation of the crankshaft would affect the thickness of the oil film, wear the bearings down or even induce the rotor-to-stator rubs. It is considered as a non-linear fluid–structure interaction problem. To ensure the compressor operating well, the dynamic behaviors of both single-cylinder and twin-cylinder compressors' crankshafts at various speeds are analyzed. The influence of configuration of balancers on the reliability of rotor system is investigated for the further. Calculation results suggest that the vulnerable sections of crankshaft vary with the rotational speed. It is also found that 80% of the dynamic balance is the optimum design condition to reduce the transverse forces on crankshaft and the wear-out of journal bearings.

Efficiency assessment of air stripping packed towers for removal of VOCs (volatile organic compounds) from industrial and drinking waters

Packed column strippers are being used for removing VOCs (volatile organic compounds) contaminants from drinking and industrial waste waters. In order to evaluate the capability of packed towers for reducing the contaminant concentration to its permissible limits, a mathematical mass transfer model is developed. The model, which is based on resistances-in-series approach and considers liquid-vapor equilibria in terms of temperature-dependent Henry's constants, is successfully validated against several experimental data. The effects of key parameters, such as column pressure, temperature, gas-to-liquid flow rate and VOC inlet concentration, on the removal of different VOCs from waste waters and also on the required tower height are thoroughly considered. It is found that these parameters can have different impacts on the removal of different VOCs, and the required tower height is highly dependent on the VOC solubility and volatility. The optimum design and operating conditions of a packed tower are also determined for the maximum VOC removal and the minimum packing height.

적외선 열화상 카메라용 캘리브레이션 타겟 개발

Abstract Camera calibration is an indispensable process for improving measurement accuracy in industry fields such as machine vision. However, existing calibration cannot be applied to the calibration of mid-wave and long-wave infrared cameras. Recently, with the growing use of infrared thermal cameras that can measure defects from thermal properties, development of an applicable calibration target has become necessary. Thus, based on heat conduction analysis using finite element analysis, we developed a calibration target that can be used with both existing visible cameras and infrared thermal cameras, by implementing optimal design conditions, with consideration of factors such as thermal conductivity and emissivity, colors and materials. We performed comparative experiments on calibration target images from infrared thermal cameras and visible cameras. The results demonstrated the effectiveness of the proposed calibration target. Keywords: Thermography, Lens Distortion, Calibration, Visible Image Thermal Image[접수일: 2014. 5. 13, 수정일: 2014. 6. 20, 게재확정일: 2014. 6. 21] *한국표준과학연구원 삶의질측정표준본부 , **상명대학교 문화기술연구소, ***상명대학교 컴퓨터과학과, ✝Corresponding Author: Metrology for Quality of Life, Korea Research Institute of Standards and Science, Daejeon 305-340, Korea (E-mail: mychoi@kriss.re.kr)

Three-dimensional, transient, nonisothermal model of all-vanadium redox flow batteries

A three-dimensional (3-D), transient, nonisothermal model of all-vanadium redox flow batteries (VRFBs) is developed by rigorously accounting for the electrochemical reactions of four types of vanadium ions (V2+, V3+, VO2+, and VO2+) and the resulting mass and heat transport processes. Particular emphasis is placed on analyzing various heat generation mechanisms, including irreversible and reversible heat generation due to vanadium redox reactions and joule heating arising from the solid electrode and electrolyte ionic resistances. The 3-D model is validated against voltage evolution curves measured under charging and discharging processes. The model predictions compare well with the experimental data over a wide range of state of charge (SOCs), and further reveal key electrochemical and transport phenomena inside VRFBs through multidimensional contours of solid electrode/electrolyte potentials, species concentrations, and temperatures. This full 3-D comprehensive VRFB model can be applied to realistic multicell stacks to determine the optimal design and operating conditions.

Design and Analysis of a Combined Rankine Cycle for Waste Heat Recovery of a Coal Power Plant Using LNG Cryogenic Exergy

In this study, a combined Rankine cycle was modeled and optimized. This process consists of a coal combustion unit, a steam cycle, a CO2 capture process, a gas conditioning process, and a CO2 organic Rankine cycle (ORC). This process is able to extract additional power without consuming additional fossil fuel by integrating the CO2-ORC with the steam cycle and a liquefied natural gas (LNG) evaporation process. Unlike conventional ORC, the CO2-ORC utilizes the low grade waste heat only for super heating of working fluid, while the main evaporation process is achieved by seawater. The CO2 condensation process in the ORC takes place at a temperature lower than the ambient temperature by coupling with the LNG evaporation system as a cold sink. Furthermore, a fraction of liquefied CO2 is purged for the sequestration. Therefore, CO2 liquefaction can be achieved without an additional refrigeration cycle. This process not only produces more power with the same fuel consumption but also reduces CO2 removal energy. The gross power is increased from 42.21 to 90.54 MWe compared with the conventional power plant, and total CO2 removal energy is decreased about 9%. The optimum design and operating conditions were also obtained through parameter sensitivity analysis. The power reduction of the proposed process resulting due to the CO2 capture process installation was identified as 19.3%. However, the net power generation is about 73% higher than that of the conventional power cycle even without CO2 capture.

Dynamic Analysis and Experimental Research of Laser Cutting Machines

Vibration is one of the most important problems in laser cutting machine tool, which causes the manufacturing errors, also influences the machining accuracy of the parts. Modal analysis can calculate vibration type of structures. The paper presents how to use the powerful FEA software ANSYS to do the modal analysis on laser cutting machine tool and also studies the undamped free vibration on laser cutting machine tool. Finally, the test results and theoretical results were compared to verify the rationality of the modal, these provide theoretical base and conditions for dynamics analysis and optimal design.

Experimental study on the optimum design of the flow-path system for a low noise indoor package air-conditioner

This study was carried out with the Taguchi method to find the optimum design condition of an indoor package air-conditioner (PAC) to minimize noise of operation. The goal of this study is to identify the optimum set of the control factors forming the flow-path system of an indoor PAC. The sound of operation and the number of revolutions of the fan of an indoor PAC were measured according to an orthogonal array of L18(23×34) and used to find the smaller-the-better quality characteristic among the static characteristic analyses. As a result, the optimum condition of an indoor PAC for a low noise of operation is a set of 〈G1 A2 B1 C1 D1 E3 F1〉, with the judgment criterion of the optimum set based on the sound of operation, the number of revolutions and the cost of production. The sound performance of an indoor PAC operating under optimum conditions improved 1.8 dBA compared to that of the standard condition, and resulted in a reduction of about 45 RPM in the number of revolutions for the target flow-rate of 18.5 m3/min.

Wicking and evaporation of liquids in porous wicks: A simple analytical approach to optimization of wick design

Wicking and evaporation of volatile liquids in porous, cylindrical wicks is investigated where the goal is to model, using simple analytical expressions, the effects of variation in geometrical parameters of a wick, such as porosity, height and bead‐size, on the wicking and evaporation processes, and find optimum design conditions. An analytical sharp‐front flow model involving the single‐phase Darcy's law is combined with analytical expressions for the capillary suction pressure and wick permeability to yield a novel analytical approach for optimizing wick parameters. First, the optimum bead‐radius and porosity maximizing the wicking flow‐rate are estimated. Later, after combining the wicking model with evaporation from the wick‐top, the allowable ranges of bead‐radius, height and porosity for ensuring full saturation of the wick are calculated. The analytical results are demonstrated using some highly volatile alkanes in a polycarbonate sintered wick. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1930–1940, 2014

음이온 생성을 위한 표면 유전체장벽방전의 설계조건 연구

his paper describes a study of the design conditions of a planar surface dielectric barrier discharge (DBD) reactors for generating negative air ions. The capacity of negative air ion generated by the surface DBD reactor is affected by the shape, area ratio and the location of the discharge and induction electrodes of it. To study the optimal design conditions of DBD reactors, the electrodes printed on the substrate of a PCB board is utilized to conduct kind of experiments: the distance of the each electrode along with the X-Y axis, the area ratio of the discharge electrode to induction electrode, and the symmetrical and asymmetrical location of two electrodes. The ion generation capacity is inverse proportional to the gap increases along with X-Y axis. And the optimum ion concentration generated by the ionizer was inspected when the electrodes area ratio was 3 and 5 times of the symmetrical and asymmetrical experimental condition respectively.

Numerical optimization study to install air curtain in a subway tunnel by using design of experiment

Subways are a major mode of public transportation in metropolitan cities. A proper ventilation system is required to maintain indoor air quality in subway tunnels. Platform screen doors improve the platform environment but degrade air quality in subway tunnels. Trains transport fine particles from the tunnel into the platform. An air curtain installation in the subway tunnel permits traffic and reduces the transfer of bacteria and fine particles. The existing tunnel of Seoul subway was investigated by using computational fluid dynamics and design of experiment method for optimum air curtain installations. The flow field of the subway tunnel was computed by using ANSYS CFX software. Minitab software was used to generate the design process and to analyze the computational results. The computational domain of the existing tunnel included two natural ventilation shafts, one mechanical shaft, and the twin tracks. The height, width, and length of each track were 6, 4, and 400 m, respectively. The air curtain installation area was located between the natural and the mechanical ventilation shafts of Rrack 1. The design variables for the optimization study were the width, velocity, and installation location of the air curtain. The object function for optimization was mass flow rate at the natural ventilation shaft. The length of the air curtain was fixed at 4 m. The predicted mass flow rates were analyzed with the design variables by using the response surface method (RSM). The optimum values of the design variables, i.e., velocity, width, and installation location were 25 m/s, 0.2 m, and 5.8195 m, respectively. The maximum mass flow rate with the optimum design values was 114.4447 kg/s. The optimum values of the design variables were validated by computing the tunnel with the optimum values from RSM. The mass flow rate in the natural ventilation shaft 1 was 114.2 kg/s, as predicted. The optimization study can be helpful to set the optimum design conditions for the subway ventilation system.

OPTIMIZATION OF DESIGN PARAMETERS OF A STIRLING GENERATOR FOR USE WITH A FLUIDIZED BED COMBUSTOR

This work investigates the possibility to place the head of a Stirling engine, more specifically the elements of the hot side heat exchanger, in direct contact with the sand of a Fluidized Bed Combustor. This choice is primarily suggested by the heat exchange coefficients between the multiphase fluidized bed medium and the surface of the heat exchanger, much larger than those attained when the heat exchanger is located in the stream of hot flue gases. Moreover, the mechanical action exerted by the fluidized solid particles substantially reduces the fouling usually caused by impurities in exhaust gases of a biomass combustion process. A mathematical model, which covers the fluidized bed and the Stirling engine, is developed and used to optimize design and operating conditions with specific attention to the Stirling hot side heat exchanger. It is shown that the choice to place the heat exchange in direct contact of the fluidized bed can lead to an improvement of performance in terms of efficiency and shaft power output.

Optimal sizing of a thermoelectric heat pump (THP) for heating energy-efficient buildings

This paper aims to determine the optimal design and operating conditions of an air-to-air thermoelectric heat pump (THP) composed of thermoelectric modules (TEMs) and two heat sinks, coupled to an energy-efficient building. We focus on the optimal number of TEMs and the optimal electrical current for three standard cases. The performance is quantified using two different coefficients of performance (COP) definitions: performance of THP only (COPHP) and performance of THP coupled to an energy-efficient building (COPu). These COP are also studied for both instantaneous and seasonal conditions. We show that for each coupling, a range of modules exists, with which the maximum performance of the THP can be approached, by simply adapting the electrical current for each condition. Finally, the seasonal performance COPHPs/COPus for the French city of Macon is estimated and compared for the three cases considered. The original sizing approach proposed here leads to a slight increase of the COPHPs/COPus (up to +4%), compared to the classical design based on instantaneous nominal conditions (norm). Moreover, we show that the optimal number of modules can be largely reduced (up to −39% for the cases considered) compare with nominal condition method.

A Design on Reduction Cogging Torque of Dual Generator Radial Flux Permanent Magnet Generator for Small Wind Turbine

In this paper, the design for an electromagnetic structure and reduction cogging torque of a dual generator structured RFPM generator, which is a combination of the inner- and outer-rotor types, has been proposed. We call this a dual generator radial flux permanent magnet generator. To reduce the cogging torque, firstly, stator tooth pairing was designed; secondly, stator displacement was designed and finally, stator tooth pairing and stator displacement were carried out simultaneously. We found the optimal design condition about stator tooth pairing angle combination and stator displacement angle for cogging torque minimization. As a result, a cogging was reduced by 93.3[%] by this study.

Removal of formaldehyde from overactivated‐carbon‐fiber‐loaded biological enzyme

To remove formaldehyde effectively, we used activated carbon fiber as a carrier to prepare the composite materials (biological enzyme/activated carbon fiber) by loading biological enzyme on its surface. A one‐factor‐at‐a‐time design and orthogonal design were used in the experimental design methods to optimize the biological enzyme based on soya protein. The experimental results indicate that the pH value was the most significant condition for optimizing the biological enzyme. The optimum orthogonal design conditions were proposed to be a reaction temperature of 80°C, a pH of 4, a reaction time of 6 h, and an amino nitrogen content of up to 5.4%. In addition, the morphologies of the composite materials were characterized with scanning electron microscopy, and the removal efficiency of formaldehyde was investigated with the acetyl acetone method. The results show that the formaldehyde removal efficiency was the best and the removal rate was 80% when the loading time was 8 h. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2619–2623, 2013

Optimal design and operation of polymer electrolyte membrane reactors for pure hydrogen production

Carbon monoxide (CO) in the hydrogen (H2) stream diminishes the performance of a low-temperature polymer electrolyte membrane (PEM) fuel cell. An on-board CO removal unit is essential in any fuel processor system to be developed for production of hydrogen with low CO concentration (<10ppm). Low process temperature (80°C or lower) and pressure are critical for such a gas clean-up unit. The existing gas clean-up units operate at high temperatures and pressures and often require on-board oxygen or air supply for CO oxidation. An attractive solution for on-board/site production of pure hydrogen is the electrochemical approach. This method removes the CO molecules in the synthetic gas stream after they have been adsorbed onto the catalyst surface in the anode side of a polymer electrolyte membrane reactor. In this process, some additional hydrogen is also produced through the water-gas shift reaction at the cathode side of the reactor offsetting the energy required to drive the electrolysis. In this study, through a parametric study, the optimal geometrical design and operation conditions of the CO removal reactor are determined with an attempt of maximizing the adsorption capacity and minimizing the catalyst consumption.

Computational fluid dynamics study of the optimal design and operating conditions of the segmentation ring used in parallel segmented flow columns

We report on a numerical study wherein we modeled the influence of the segmentation ring used in the recently introduced parallel segmented flow concept. The study reconfirms that the parallel segmented flow concept can indeed improve separation performance of radially heterogeneous beds. It was however also found that the segmentation ring in itself introduces significant flow disturbances. Depending on its thickness and the fraction of the total flow rate going through the central opening, the ring itself can constitute a loss in volumetric variance (σv2) in the order of a few up to a few tens of μl2. Although the ideal flow-split ring would be infinitely thin, it was found that halving the current 0.62mm ring thickness used in literature to 0.31mm would already eliminate most of its negative effect. At the inlet, the optimal central flow rate fraction for a 0.62mm as well as a 0.31mm wide ring in a 4.6mm I.D. column lies in the range of 0.25–0.4. At the outlet, the optimal range is 0.15–0.4.

Investigation of Choking and Combustion Products' Swirling Frequency Effects on Gas Turbine Compressor Blade Fractures

Premature fracture failure of blades occurred in four of a refinery's gas turbine compressors. In order to evaluate the probability of combustion instability's effects on failure of the blades; i.e., choking and chamber resonance problems, 3D models of the combustion chamber structure and combustion flow were studied with finite element and computation fluid dynamics codes, respectively. Comparison of results of combustion chamber natural frequencies with combustion swirl frequency showed that the chamber structure is not under resonance. In order to verify probability of choking, the combustion product flow's Mach number was studied. Results of the Mach number distribution showed that the flow is subsonic in the transition piece area but, due to existence of supersonic flow conditions near the swirl vanes it may become supersonic in some critical conditions. Thus, it is suggested to operators that, for avoiding choking probabilities, it is better that engine operation be maintained close to optimum design conditions. Results of simulations showed that the fracture of the blades is not due to combustion problems.

Charged particle energy analyzer based on a modified cylindrical mirror

A modified design of an electrostatic energy analyzer of the cylindrical mirror type is suggested. The outer electrode of the modified analyzer consists of three cylinders with equal radii and different potentials. The electron-optical properties of the analyzer are numerically simulated, and it is demonstrated that it may offer a much higher focusing quality than a conventional cylindrical mirror. Optimal design and operating conditions are found for which the spherical aberration decreases fivefold compared with the conventional mirror.

An analysis for a molten carbonate fuel cell of complex geometry using three-dimensional transport equations with electrochemical reactions

A three-dimensional (3D) analysis has been developed and applied to obtain performance characteristics of a molten carbonate fuel cell (MCFC) of complex geometry. The equations are solved to obtain the velocity, temperature, pressure, and concentration distributions in the cathode/anode channel. The channel with uniformly distributed trapezoidal supports, is approximated by an anisotropic porous medium, and the effective permeability and conductivity are obtained by separate three-dimensional finite volume method (FVM) calculations for a single periodic module. The current density distribution for a given cell voltage is calculated iteratively by coupling it to the local chemical reaction rate. Thus, the current–voltage relation can be successfully obtained. Here, the cell characteristics for various operating conditions are presented and discussed. The calculation is carried out by increasing the electric load until the fuel-depleted region appears on the electrode surface. This procedure is capable of predicting essential cell features and may be used in finding the optimal cell design and/or operating conditions.