Showing papers in "Transactions of The Korean Society of Mechanical Engineers B in 2006"

The Characteristics of the Particle Position Along an Optical Axis in Particle Holography

Abstract: Particle diagnostics involving three-dimensional distributions are important topics in many engineering fields. The holographic particle velocimetry system is a promising optical tool for measuring three-dimensional particle velocities. One of the inherent limitations of particle holography is the very long depth of field of particle images, which causes considerable difficulty in the determination of particle positions along the optical axis. In this study, diffused illumination holography was adopted as a tool for analysing the characteristics of particles. The prerequisites for a more precise determination of the velocities of particles are a profound understanding of image properties and of the focusing parameter used to determine the particle position along an optical axis. For this purpose, the characteristics of speckles and particle images were investigated with respect to variations in hologram aperture and particle position along the optical axis. Based on our findings, we introduced three auto-focusing parameters corresponding to the sizes of particles, namely, correlation coefficient, sharpness index and depth intensity, to determine the focal plane of a particle along the optical axis. To investigate the suitability of these parameters, the plane image of a dot array screen containing different dot sizes was recorded and the positions of each dot along the optical axis were evaluated. In addition, the effect of particle distance from the holographic film was examined by changing the distance between the screen and the holographic film. All measurement results verified that the evaluated positions throughout the suggested auto-focusing parameters remain within acceptable error ranges. These research results may provide fundamental information for the development of a holographic velocimetry system based on automatic image processing.

A Numerical Study on the Characteristics of Flow Field, Temperature and Concentration Distribution According to Changing the Shape of Separation Plate of Kitchen Hood System

Abstract: This study aims deriving analysis the flow characteristic of kitchen hood system with using 3D numerical analysis method and improving the system to expel pollutes more efficiently. To understand the flow characteristics of four models, this study only focuses on velocity field, temperature field, and concentration field varying with followings whether separation plate is set or not and the shapes of separation plates. The quantityofair,speedofexhaustfanandtemperatureand concentrationofheatingsourceareconcerned asconstantvalues.Thethreemodelshaving different shapes have one exhaust port and the model which has the vent at the closest position to where pollutes are generated is discovered to be the most efficient model. Compare to the initial model (having no separation plate), it was 1.4‐1.9% more efficient at temperature distribution and 9.4‐11.9% more at CO2 concentration distribution. Published by Elsevier B.V.

Numerical Simulation in the IC Engine Lubricating Gerotor Oil Pump

Abstract: Numerical simulations were conducted on the gerotor type oil pump. Three oil pump models having different port and groove shape were considered. Firstly, two original models (baseline & variant.1 model) were simulated in order to validate the accuracy of the simulation results and to better understand the flow characteristics in the pump. It was found that the cavitation phenomenon as well as the teeth tip leakage is most important parameter on the pump performance. Based on the simulation results of the original models, final model (variant.2 model) which has improved port shape and pressure relief valve is suggested to enhance pump performance and to reduce driving torque. The volumetric efficiency and the hydraulic torque of the Variant.2 model is improved 4% and reduced 6.1% each at 2000RPM in experiment

Optimal Design of High Temperature Vacuum Furnace Using Thermal Analysis Database

Abstract: Optimization study has been carried out to design an energy efficient, high temperature vacuum furnace which satisfies users` design requirements First of all, the transient temperature distribution and the uniform temperature zone results have been compared with the steady state results to validate the feasibility of using steady state solution when constructing the thermal analysis DB In order to check the accuracy, the interpolated results using thermal analysis DB have been compared with the computational and the experimental results In this study, total heat flux is selected as the objective function, and the geometry parameters of vacuum furnace including the thickness of insulator, the heat zone sizes and the interval between heater and insulator are the design variables The Uniform temperature zone sizes and the wall temperature are imposed as the design constraints With negligible computational cost a high temperature vacuum furnace which has reduction in total heat flux is designed using thermal analysis DB

An Experimental Study on the Thermal Performance Measurement of Vertical Borehole Heat Exchanger(BHE)

Abstract: Knowledge of ground thermal properties is most important for the proper design of large BHE(borehole heat exchanger) systems. Thermal response tests with mobile measurement devices were first introduced in Sweden and USA in 1995. Thermal response tests have so far been used primarily for in insitu determination of design data for BHE systems, but also for evaluation of grout material, heat exchanger types and ground water effects. The main purpose has been to determine insitu values of effective ground thermal conductivity, including the effect of ground-water flow and natural convection in the boreholes. Test rig is set up on a small trailer, and contains a circulation pump, a heater, temperature sensors and a data logger for recording the temperature data. A constant heat power is injected into the borehole through the pipe system of test rig and the resulting temperature change in the borehole is recorded. The recorded temperature data are analysed with a line-source model, which gives the effective insitu values of rock thermal conductivity and borehole thermal resistance.

Design of An Axial Flow Fan with Shape Optimization

Abstract: This paper presents the response surface optimization method using three-dimensional Wavier-Stokes analysis to optimize the blade shape of an axial flow fan. Reynolds-averaged Wavier-Stokes equations with turbulence model are discretized with finite volume approximations using the unstructured grid. Regression analysis is used for generating response surface, and it is validated by ANOVA and t-statistics. Four geometric variables, i.e., sweep and lean angles at mean and tip respectively were employed to improve the efficiency. The computational results are compared with experimental data and the comparisons show generally good agreements. As a main result of the optimization, the total efficiency was successfully improved. Also, detailed effects of sweep and lean on the axial flow fan are discussed.

Experimental Study on Manufacturing of Insulation Vacuum Glazing and Measurement of the Thermal Conductance

Abstract: Window is a critical component in the design of energy-efficient buildings. To minimize the heat loss, insulation performance of the glazing has to be improved. Manufacturing of vacuum glazing has been motivated by the possibility of making windows of very good thermal insulation properties for such applications. It is made by maintaining vacuum in the gap between two glass panes. Pillars are placed between them to withstand the atmospheric pressure. Edge covers are applied to reduce conduction through the edge. Accurate measurements have been made of the radiative heat transfer, the pillar conduction and the gas conduction using a guarded hot plate apparatus. Vacuum glazing is found to have low thermal conductance roughly below . Among the heat transfer modes of residual gas conduction, conduction through support pillar and the radiative heat transfer between the glass panes, the last one is the most dominant to the overall thermal conductance. Vacuum glazing using very low emittance AI-coated glass has an overall thermal conductance of about .

A Numerical Study on Combustion-Stability Rating of Impinging-Jet Injector Using Air-Injection Technique

Abstract: Combustion stability rating of jet injector is conducted numerically using air-injection technique in a model chamber, where air is supplied to oxidizer and fuel manifolds of the model five-element injector head. A sample F(fuel)-O(oxidizer)-O-F impinging-jet injector is adopted. In this technique, we can simulate mixing process of streams flowing through oxidizer and fuel orifices under cold-flow condition without chemical reaction. The model chamber was designed based on the methodologies proposed in the previous work regarding geometrical dimensions and operating conditions. From numerical data, unstable regions can be identified and they are compared with those from air-injection acoustic and hot-fire tests. The present stability boundaries are in a good agreement with experimental results. The proposed numerical method can be applied cost-effectively to stability rating of jet injectors when mixing of fuel and oxidizer jets is the dominant process in instability triggering.

Effect of Blade Tip Geometry on Heat Transfer Coefficients on Gas Turbine Blade Tips and Near Tip Regions

Abstract: Detailed heat transfer coefficient distributions an two. types of gas turbine blade tip, plane tip and squealer tip, were measured using a hue-detection base transient liquid crystals technique.. The heat transfer coefficients an the shroud and near tip regions of the pressure and suction sides af the blade were also. measured. The heat transfer measurements were taken at the three different tip gap clearances af 1.0%, 1.5%, and 2.5% of blade span. Results shaw the overall heat transfer coefficients on the tip and shroud with squealer tip blade were lower than those with plane tip blade. By using squealer tip, however, the reductions af heat transfer coefficients near the tip regions of the pressure and suction sides were nat remarkable.

Study on Basic Characteristics of Natural Gas Autothermal Reformer for Fuel Cell Applications

Abstract: Hydrogen production using current fueling facilities is essential for near-term applications of fuel cells. A preliminary process for developing a natural gas autothermal reforming (ATR) reactor for fuel cells is presented in this paper. A experimental reactor for methane ATR was constructed and used for characterization of Jin reactor. Temperature profiles of the reactor were observed, and reformed gas compositions were analyzed to evaluate efficiency, conversion and reaction heat with varying amounts of at selected furnace temperature and . The amount of showed strong offsets on reactor temperature, efficiency and conversion indicating that is a crucial operation condition. Operation conditions which result in thermal neutrality of ATR reactor system were determined for two cases of an ATR system based on the estimation of enthalpy difference between reactants of assumed inlet temperatures and the products from experimental results. The determined conditions for thermally neutral operations could be used for guidelines to design reformers and for determining the operation parameters of a self sustaining ATR reactor.

Aerodynamic Characteristics and Shape Optimization of Airfoils in WIG Craft Considered Ground Effect

Abstract: Shape optimization of airfoil in WIG craft has been performed by considering the ground effect. The WIG craft should satisfy various aerodynamic characteristics such as lift, lift to drag ratio, and static height stability. However, they show a strong trade-off phenomenon so that it is difficult to satisfy aerodynamic properties simultaneously. Optimization is carried out through the multi-objective genetic algorithm. A multi-objective optimization means that each objective is considered separately instead of weighting. Due to the trade-off, pareto sets and non-dominated solutions can be obtained instead of the unique solution. NACA0015 airfoil is considered as a baseline model, shapes of airfoil are parameterized and rebuilt with four-Bezier curves. There are eighteen design variables and three objective functions. The range of design variables and their resolutions are two primary keys for the successful optimization. By two preliminary optimizations, the variation can be reduced effectively. After thirty evolutions, the non-dominated pareto individuals of twenty seven are obtained. Pareto sets are all the set of possible and excellent solution across the design space. At any selections of the pareto set, these are no better solutions in all design space.

Structure Design and Experimental Appraisal of the Drag Force Type Vertical Axis Wind Turbine

Abstract: Experiments were conducted to estimate the performance of drag force type vertical axis wind turbine with an opening-shutting rotor. It was operated by the difference in drag force generated on both sides of the blades. The rotational speed was measured by a tachometer in a wind tunnel and the tunnel wind speed was measured by using a pilot-static tube and a micro manometer. The performance test for a prototype was accomplished by calculating power, power coefficient, torque coefficient from the measurement of torque and rpm by a dynamometer controller. Various design parameters, such as the number of blades(B), blade aspect ratio(W/R), angle of blades and drag coefficient acting on a blade, were considered for optimal conditions. At the experiment of miniature model, maximum efficiency was found at N

On the Problem of Using Mixing Index Based on the Concentration Dispersion

Abstract: In this study, the problem of using the mixing index as a measure of the mixing performance for a certain flow field has been discussed. The flow model subjected to this study is the two-dimensional unsteady lid-driven cavity flow. The transport equation for the concentration within the cavity was solved by using the finite volume method where the convective terms are discretized with the central difference scheme. It was shown that both the concentration dispersion and the mixing index depend highly on the initial distribution of the concentration, and therefore the mixing index obtained from the concentration dispersion equation loses its universal applicability.

Study on Soot Primary Particle Size Measurement in Ethylene Diffusion Flame by Time-Resolved Laser-Induced Incandescence

Abstract: Recently there is an increasing interest in particulate matter emission because of new emission regulations, health awareness and environmental problems. It requires to improve particulate measurement techniques as well as to reduce soot emissions from combustion systems. As mentioned above, it is demanded that reduction techniques together with measurement techniques of exhausted particulate matters in combustion systems such as vehicles. However, measurement techniques of particulate matters should be prior to reduction techniques of that because it is able to know an increase and a decrease of exhausted particulate matters when measured particulate matters. Therefore, in this study, we report the measurement of soot primary-particle size using time-resolved laser induced incandescence (TIRE-LII) technique in laminar ethylene diffusion flame. As an optical method, laser induced incandescence is one of well known methods to get information for spatial and temporal soot volume fraction and soot primary particle size. Furthermore, TIRE-LII is able to measure soot primary particle size that is decided to solve the decay ate of signal S and S at two detection time. In laminar ethylene diffusion flame, visual flame height is 40 mm from burner tip and measurement points are height of 15, 20, 27.5, 30 mm above burner tip along radial direction. As increasing the height of the flame from burne. tip, primary particle size was increased to HAB(Height Above Burner tip)

Surface Temperature Measurement in Microscale with Temperature Sensitive Fluorescence

Abstract: A technique for measuring surface temperature field in micro scale is newly proposed, which uses temperature-sensitive fluorescent (TSF) dye coated on the surface and is easily implemented with a fluorescence microscope and a CCD camera The TSF dye is chosen among mixtures of various chemical compositions including rhodamine B as the fluorescent dye to be most sensitive to temperature change In order to examine the effectiveness of this temperature measurement technique, numerical analysis and experiment on transient conduction heat transfer for two different substrate materials, i e, silicon and glass, are performed In the experiment, to accurately measure the temperature with high resolution temperature calibration curves were obtained with very fine spatial units The experimental results agree qualitatively well with the numerical data in the silicon and glass substrate cases so that the present temperature measurement method proves to be quite reliable In addition, it is noteworthy that the glass substrate is more appropriate to be used as thermally-insulating locally-heating heater in micro thermal devices This fact is identified in the temperature measuring experiment on the locally-heating heaters made on the wafer of silicon and glass substrates Accordingly, this technique is capable of accurate and non-intrusive high-resolution measurement of temperature field in microscale

Study of Operation Strategy for Hybrid PEM Fuel Cell and Supercapacitor

Abstract: PEMFC has several technical problems such as water management, long term stability and performance degradation as PEMFC has been studied not only to solve water management, but also to generate power in stable manner to system by using a hybrid system with auxiliary energy storage device The purpose of this study is to couple PEMFC with supercapacitor to make a hybrid system and to design and test control strategies for stable power generation in case of changing output power The polarization curve and dynamic behaviors while changing power were investigated to find out characteristics of PEMFC stack A DC/DC converter was fabricated in order to increase fuel cell and supercapacitor voltage and to charge supercapacitor We found that the operation strategy 2 was recommended to the system because of solving water management problem and increasing the dynamic behavior

Optimization of Blade Sweep of NASA Rotor 37

Abstract: The shape optimization of blade sweep in a transonic axial compressor rotor of NASA Rotor 37 has been performed using response surface method and the three-dimensional Wavier-Stokes analysis. Two shape variables of the rotor blade, which are used to define the rotor sweep, are introduced to increase the adiabatic efficiency of the compressor. Throughout the optimization, optimal shape having a backward sweep is obtained. Adiabatic efficiency, which is the objective function of the present optimization, is successfully increased. Separation line due to the interference between a shock and surface boundary layer on the blade suction surface is moved downstream for the optimized blade compared to the reference one. The increase in adiabatic efficiency for the optimized blade is caused by suppression of the separation due to a shock on the blade suction surface.

The PIV Measurements on the Respiratory Gas Flow in the Human Airway

Abstract: The mean and RMS velocity field of the respiratory gas flow in the human airway was studied experimentally by particle image velocimetry (PIV) Some researchers investigated the airflow for the mouth breathing case both experimentally and numerically But it is very rare to investigate the airflow of nose breathing in a whole airway due to its geometric complexity We established the procedure to create a transparent rectangular box containing a model of the human airway for PIV measurement by combination of the RP and the curing of clear silicone We extend this to make a whole airway including nasal cavities, larynx, trachea, and 2 generations of bronchi The CBC algorithm with window offset (64 64 to 32 32) is used for vector searching in PIV analysis The phase averaged mean and RMS velocity distributions in Sagittal and coronal planes are obtained for 7 phases in a respiratory period Some physiologic conjectures are obtained The main stream went through the backside of larynx and trachea in inspiration and the frontal side in expiration There exist vortical motions in inspiration, but no prominent one in expiration

The Effect of Karman Vortex for Mixing in a Micro-channel with an Oscillating Micro-stirrer

Abstract: In order to consider the effect of Karman vortex for mixing, mixing indices are calculated for 4 models of micro channel flows driven from the combinations of a circular cylinder and a oscillating stirrer. And their results are compared to that of a simple straight micro channel flow(model I). The mixing rate is improved 5.5 times by Karman vortex (model II) and 11.0 times by the stirrer(model III) respectively. In case of successive mixing by the cylinder and the stirrer(model IV), of shortening the channel length for the complete mixing as well as 1.37 times improvement of mixing efficiency then model III. And then, variation of mixing indices are much stable comparing with the others. Thus, it is found that the Karman vortex plays a good role as a pre-mixing method. The D2Q9 Lattice Boltzmann methods are used.