Showing papers in "Transactions of The Korean Society of Mechanical Engineers B in 2008"
TL;DR: In this article, a correlation based transition model was applied to predict aerodynamic performance of the NREL (National Renewable Energy Laboratory) Phase Ⅳ wind turbine rotor for a range of wind speed, including low speed shaft torque, power, root bending moment, and aerodynamic coefficients of 2D airfoil.
Abstract: Despite of the laminar-turbulent transition region co-exist with fully turbulence region around the leading edge of an airfoil, still lots of researchers apply to fully turbulence models to predict aerodynamic characteristics. It is well known that fully turbulent model such as standard k-model couldn't predict the complex stall and the separation behavior on an airfoil accurately, it usually leads to over prediction of the aerodynamic characteristics such as lift and drag forces. So, we apply correlation based transition model to predict aerodynamic performance of the NREL (National Renewable Energy Laboratory) Phase Ⅳ wind turbine. And also, compare the computed results from transition model with experimental measurement and fully turbulence results. Results are presented for a range of wind speed, for a NREL Phase Ⅳ wind turbine rotor. Low speed shaft torque, power, root bending moment, aerodynamic coefficients of 2D airfoil and several flow field figures results included in this study. As a result, the low speed shaft torque predicted by transitional turbulence model is very good agree with the experimental measurement in whole operating conditions but fully turbulent model(k- e) over predict the shaft torque after 7m/s. Root bending moment is also good agreement between the prediction and experiments for most of the operating conditions, especially with the transition model.
13 citations
TL;DR: Oxy-fuel combustion is a reliable way for the reduction of pollutants, the higher combustion efficiency and the separation of carbon dioxide as discussed by the authors, and a review of recent research trends and the prospects of oxyfuel combustion are presented.
Abstract: Oxy-fuel combustion is a reliable way for the reduction of pollutants, the higher combustion efficiency and the separation of carbon dioxide. The review of recent research trends and the prospects of oxy-fuel combustion were presented. The difference in characteristics among oxy-fuel combustion, conventional air combustion, oxy-fuel combustion with flue gas recirculation (FGR) technique was investigated. Recent experiments of oxy-fuel combustion with/without FGR were surveyed in various ways which are optimized burner design, flame characteristics, the soot emission, the radiation effect, the NOx reduction and the corrosion of combustor. Numerical simulation is more important in oxy-fuel combustion because flame temperature is so high that conventional measurement devices have a restricted application. Equilibrium and non-equilibrium chemical reaction mechanisms for oxy-fuel combustion were investigated. Combustion models suitable for the numerical simulation of non-premixed oxy-fuel flame were surveyed.
10 citations
8 citations
TL;DR: In this paper, the authors investigate the characteristics of an autothermal reformer at various operating conditions, including full combustion, steam reformulation, water-gas shift, and direct steam reforming.
Abstract: The objective of this paper is to investigate characteristics of an autothermal reformer at various operating conditions. Numerical method has been used, and simulation model has been developed for the analysis. Pseudo-homogeneous model is incorporated because the reactor is filled with catalysts of a packed-bed type. Dominant chemical reactions are Full Combustion reaction, Steam Reforming(SR) reaction, Water-Gas Shift(WGS) reaction, and Direct Steam Reforming(DSR) reaction. Simulation results are compared with experimental results for code validation. Operating parameters of the autothermal reformer are inlet temperature, Oxygen to Carbon Ratio(OCR), Steam to Carbon Ratio(SCR), and Gas Hourly Space Velocity(GHSV). Temperature at the reactor center, fuel conversion, species at the reformer outlet, and reforming efficiency are shown as simulation results. SR reaction rate is improved by increased inlet temperature. Reforming efficiency and fuel conversion reached the maximum at 0.7 of OCR. SR reaction and WGS reaction are activated as SCR increases. When GHSV is increased, reforming efficiency increases but pressure drop from the increased GHSV may decrease the system efficiency.
8 citations
TL;DR: In this article, the performance experiments for a microchannel printed circuit heat exchanger (PCHE) of high performance and high efficiency on the two technologies of micro photo-etching and diffusion bonding were performed.
Abstract: The performance experiments for a microchannel printed circuit heat exchanger (PCHE) of high-performance and high-efficiency on the two technologies of micro photo-etching and diffusion bonding were performed in this study. The microchannel PCHE were experimentally investigated for Reynolds number in ranges of 100 700 under various flow conditions in the hot side and the cold side. The inlet temperatures of the hot side were conducted in range of while that of the cold-side were fixed at . In the flow pattern, the counter flow was provided 6.8% and 10 15% higher average heat transfer rate and heat transfer performance than the parallel flow, respectively. The average heat transfer rate, heat transfer performance and pressure drop increases with increasing Reynolds number in all the experiment. The increasing of inlet temperature in the experiment range has not an effect on the heat transfer performance while the pressure drop decrease slightly with that of inlet temperature. The experimental correlations to the heat transfer coefficient and pressure drop factor as a function of the Reynolds number have been suggested for the microchannel PCHE.
7 citations
TL;DR: In this article, the working principles of experimental system for convective heat transfer coefficient around a heated fine wire in cross flow of nanofluids and its application example to three samples of nano lubrication oils are explained in detail.
Abstract: Recent researches on nanofluids have mainly focused on the increase of thermal conductivity of nanofluids under static condition. The ultimate goal of using nanofluids, however, is to enhance the heat transfer performance under fluid flow. So it has been highly necessary to devise a simple and accurate measuring apparatus which effectively compares the heat transfer capability between the base and nanofluids. Though the convective heat transfer coefficient is not the complete index for the heat transfer capability, it might be one of useful indications of heat transfer enhancement. In this article, the working principles of experimental system for convective heat transfer coefficient around a heated fine wire in cross flow of nanofluids and its application example to three samples of nano lubrication oils are explained in detail.
7 citations
TL;DR: In this article, extensive CFD simulations on the steam-methane reforming process were conducted to study the performance of four reaction models, i.e. three Arrhenius-type models and a user-defined function (UDF) model.
Abstract: Hydrogen is considered as a fuel of the future for its renewability and environmental compatibility. The reforming of hydrocarbon fuels is currently the most important source of hydrogen, which is expected to continue for next several decades. In this study, extensive CFD simulations on the steam-methane reforming process were conducted to study the performance of four reaction models, i.e. three Arrhenius-type models and a user-defined function (UDF) model. The accuracies of different reaction models for various operating temperatures and steam carbon ratios (SCRs) were evaluated by comparing their CFD results with zero-dimensional intrinsic model of Xu and Froment. It was found that the UDF model generally produced more accurate results than Arrhenius-type models. However, it was also shown that Arrhenius-type models could be made sufficiently accurate by choosing appropriate reaction coefficients, and thus could also be useful for the simulation of the steam-methane reforming process.
6 citations
TL;DR: In this paper, a numerical simulation of brushless DC motor is performed to elucidate thermo-flow characteristics in winding and bearing with heat generation, and the design parameters such as the inlet location, geometry and bearing groove threshold angle have been selected in the present simulation.
Abstract: A numerical simulation of brushless DC motor is performed to elucidate thermo-flow characteristics in winding and bearing with heat generation. Rotation of rotor and blades drives influx of ambient air into the rotor inlet. Recirculation zone exists in the tiny interfaces between windings. The flow separation causes poor cooling performance in bearing part and therefore the redesign of the bearing groove is required. The design parameters such as the inlet location, geometry and bearing groove threshold angle have been selected in the present simulation. As the inlet location moves inward in the radial direction, total incoming flow rate and heat transfer rate are increased. Total incoming flow rate is increased with increasing the inlet inner length. The effect of the bearing groove threshold angle on the thermal performance is less than that of other design parameters.
6 citations
6 citations
TL;DR: In this paper, the authors presented the dynamic analysis of energy consumption for the large hospital building by heat resistance-capacitance method, and the system simulation of water storage air source heat pump is additionally performed by changing sizes and locations of the hospital building.
Abstract: In Korea, air source heat pump system is less efficient than conventional heat source facilities, because the air temperature in winter season is so low that COP of air source heat pump system drops below 3.0. Therefore, the study on the application of heat pump heating and cooling systems is crucial for the efficient popularization of heat pump. In this work, we present the dynamic analysis of energy consumption for the large hospital building by heat resistance-capacitance method. The system simulation of water storage air source heat pump is additionally performed by changing sizes and locations of the hospital building. The computed results show that energy cost of water storage air source heat pump is low, so it is more economical than absorption chiller & heater.
5 citations
TL;DR: In this article, a PIV (Particle Image Velocimetry) was applied to measure in-cylinder velocity field during intake stroke and the results showed that the intake flow component passing through valve area near the cylinder wall is not negligible in helical port engine with wide valve angle contrary to conventional one.
Abstract: This paper is the first of 2 companion papers which investigate in-cylinder swirl generation characteristics in helical port engine with wide valve angle. Two wide valve-angle engines, which are same ones and have slightly different rig swirl number, were used to compare the characteristics of cylinder-flow. One intake port is deactivated to induce swirl flow. A PIV (Particle Image Velocimetry) was applied to measure in-cylinder velocity field during intake stroke. The results show that the intake flow component passing through valve area near the cylinder wall is not negligible in helical port engine with wide valve angle contrary to conventional one. The effect of this velocity component on in-cylinder increases as the swirl ratio rises and intake process progresses. Consequently, this component interferes the formation of in-cylinder swirl flow resulting in lower actual swirl.
TL;DR: In this paper, the second order response surface method (RSM) was used to get optimum thermal design for enhancing heat transfer in a square channel with bleed flow, and the response surfaces of two design variables were constructed in cases with and without bleed flow.
Abstract: In the present study, the second order response surface method (RSM) is carried out to get optimum thermal design for enhancing heat transfer in a square channel with bleed flow. The RSM is used as an optimization technique. To calculate the heat transfer, RNG k-epsilon model and enhanced wall function are used. To design optimum rib turbulators, two design variables such as attack angle of rib (α) and rib pitch-to-rib height ratio ( p/e ) are optimized. In these analyses, the channel inlet Reynolds number was fixed at 10,000 in both non-bleeding and bleeding cases. The response surfaces of two design variables are constructed in cases with and without bleed flow. As a result, the optimum (or highest) heat transfer values are almost the same in ranges of two cases with and without bleed flow. However, the friction losses in the case with bleed flow are lower than those without bleed flow. 기호설명 BR Hole : 각 유출홀 당 유출유량 비, d : 유출홀 직경 (mm) D h : 유로수력직경 (mm) e
TL;DR: In this article, the effects of tube inclination on pool boiling heat transfer have been studied for the saturated water at atmospheric pressure, and seven inclination angles varying from the horizontal to the vertical and two tube diameters(25.4 and 30.0 mm) are tested.
Abstract: Effects of tube inclination on pool boiling heat transfer have been studied for the saturated water at atmospheric pressure. For the analysis, seven inclination angles varying from the horizontal to the vertical and two tube diameters(25.4 and 30.0 mm) are tested. According to the results, inclination angles result in much change on heat transfer. For the same wall superheat(about ) the ratio between two heat fluxes for the inclined and the vertical has the value of more than five when the tube diameter is 25.4mm. As the inclination angle is increasing from the horizontal to the vertical direction heat transfer is gradually increasing because of the increase in liquid agitation. However the detailed tendency depends on the ratio between the tube length and the diameter.
TL;DR: In this paper, the authors presented a numerical procedure to optimize the shape of cylindrical cooling hole to enhance film cooling effectiveness using RBNN method with Reynolds-averaged Navier-Stokes analysis with shear stress transport turbulent model.
Abstract: This study presents a numerical procedure to optimize the shape of cylindrical cooling hole to enhance film-cooling effectiveness. The RBNN method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer with shear stress transport turbulent model. The hole length-to-diameter ratio and injection angle are chosen as design variables and film-cooling effectiveness is considered as objective function which is to be maximized. Twelve training points are obtained by Latin Hypercube Sampling for two design variables. In the sensitivity analysis, it is found that the objective function is more sensitive to the injection angle of hole than the hole length-to diameter ratio. Optimum shape gives considerable increase in film-cooling effectiveness.
TL;DR: In this paper, the authors investigated the flow characteristics around a series of rectangular bodies placed in a deep turbulent boundary layer, and measured the surface pressure distribution around the bodies such as the suction pressure in the leading edge when the flow is normal, which is responsible for producing extreme suction pressures on the roof.
Abstract: We investigate the flow characteristics around a series of rectangular bodies (40 d ×80 w ×80 h , 80 d ×80 w ×80 h and 160 d ×80 w ×80 h ) placed in a deep turbulent boundary layer. The study is aiming to understand the surface pressure distribution around the bodies such as the suction pressure in the leading edge, when the flow is normal, which is responsible for producing extreme suction pressures on the roof. The experiment includes wind tunnel work by using HWA (Hot-Wire anemometry) and pressure transducers. The experiments are carried out at three different Reynolds numbers, based on the velocity U at the body height h , of 2.4×10 4 , 4.6×10 4 and 6.7×10 4 , and large enough that the mean flow is effectively Reynolds number independent. The results include the measurements of the growth of the turbulent boundary layer in the wind tunnel and the surface pressure around the bodies. 기호설명 U h : 육면체 높이에서 측정된 유속(m/s) Re h : 레이놀즈(Re) 수 uw : 경계층 전단응력 k : 폰 카르만 상수(=0.41)
TL;DR: In this article, shape optimizations of transonic compressor blade were performed to enhance the performance of Transonic compressor blades by using the Latin hypercube sampling of design of experiments and the weighted average surrogate model with the help of a gradient based optimization algorithm.
Abstract: The main purpose of the present study is to perform shape optimizations of transonic compressor blade in order to enhance its performance. In this study, the Latin hypercube sampling of design of experiments and the weighted average surrogate model with the help of a gradient based optimization algorithm are used within design space by the lower and upper limits of each design variable and for finding optimum designs, respectively. 3-D Reynolds-averaged Navier-Stokes solver is used to evaluate the objective functions of adiabatic efficiency and pressure ratio. Six variables from lean and airfoil thickness profile are selected as design variables. The results show that the adiabatic efficiency is enhanced by 1.43% by efficiency optimization while the pressure ratio is increased very small, and pressure ratio is increased by 0.24% by pressure ratio optimization.
TL;DR: In this paper, the performance of a gas turbine in the integrated gasification combined cycle (IGCC) plant is analyzed considering its integration with the air separation unit (ASU), and the influence of the degree of integration (split of air supplies to ASU from the auxiliary compressor and the gas turbine compressor) on the system performance is investigated.
Abstract: Integrated gasification combined cycle (IGCC) is an environment friendly method of using coal. Several commercial IGCC plants have been built worldwide during the past decade, and a domestic development project has also been launched recently. Operation and performance characteristics of a gas turbine in the IGCC plant deviates from those of original gas turbines due to several factors such as increased amount of fuel supply and integration with other components. In this study, performance of a gas turbine in the IGCC plant is analyzed considering its integration with the air separation unit (ASU). Influence of the degree of integration (split of air supplies to ASU from the auxiliary compressor and the gas turbine compressor) on the system performance is investigated. In addition, effect of modulating nitrogen return flow from the gasifier to the gas turbine on the operating characteristics of the gas turbine is examined. † 인하대학교 기계공학부 E-mail : kts@inha.ac.kr TEL : (032)876-7308 FAX : (032)876-7308 * 인하대학교 대학원 ** 서울대학교 기계항공공학부 *** 한국전력연구원
TL;DR: In this article, an experimental study was carried out in a small-scale furnace to investigate the performance, such as NOx emission, enhancement of heat transfer, uniformity of temperature, and etc., of oscillating combustion applied in a radiant tube burner system for heat treatment furnace.
Abstract: An experimental study was carried out in a small-scale furnace to investigate the performance, such as NOx emission, enhancement of heat transfer, uniformity of temperature, and etc., of oscillating combustion applied in radiant tube burner system for heat treatment furnace. A premixed type burner and a solenoid type oscillating control valve were designed and used. The fuel was used commercial LPG in this study and the fuel flow was oscillated by periodically opening and shutoff of the solenoid valve. From the tests, it was found that NOx emission, compared to no oscillation, could be reduced by 32% at 2.0 Hz. However, as oscillating frequency was increased, abatement of NOx emission was gradually reduced. At the high NOx abatement of 1.0 Hz, carbon monoxide was emitted above 10,000 ppm. Although rate of NOx abatement was low, oscillation condition of 2.5 Hz and duty ratio of 10-30% was recommended for low carbon monoxide emission. From the measurement of furnace heating time from 100 ℃ to 720 ℃, it was shown that heat transfer was increased by 11.5% at 2 Hz oscillating frequency. Temperature distribution of radiant tube surface was more uniform at 2 Hz oscillating frequency with drop of the peak temperature and rise of low temperature. From these results, it was confirmed that oscillating combustion was useful in radiant tube burner system.
TL;DR: Numerical solutions are presented for a first harmonic oscillatory flow using commercial software ADINA 8.4 and it is found that the fluid mechanical disturbances due to the constriction were highly sensitive with rate of stenosis and Reynolds number.
Abstract: In the present computational study, simple stenotic artery models using pulsatile flow condition were investigated. A 1 Hz non-reversing sinusoidal velocity for pulsatile flow was imposed at the flow inlet and the corresponding Womersley number based on the vessel radius is 2.75. The simple stenotic geometries have been used that consist of 25%, 50% and 75% semicircular constriction in a cylindrical tube. In this paper, numerical solutions are presented for a first harmonic oscillatory flow using commercial software ADINA 8.4. As stenosis and Reynolds number increase, the maximum wall shear stress(WSS) increases while the minimum WSS decreases. As the stenotic rate increases, the pressure drop at the throat severely decreases to collapse the artery and plaque. It is found that the fluid mechanical disturbances due to the constriction were highly sensitive with rate of stenosis and Reynolds number. When Reynolds number and stenosis increase, the larger recirculation region exists. In this recirculation region the possibility of plaque attachment is increasingly higher. The present results enhance our understanding of the hemodynamics of a stenotic artery.
TL;DR: In this article, the performance behavior of solid oxide fuel cell using H 2 and CO as fuels was investigated, and the power densities and impedance results showed a little variation as the ratio of H2 and CO changed.
Abstract: The performance behavior of solid oxide fuel cell using H 2 and CO as fuels was investigated. The power densities and impedance results showed a little variation as the ratio of H 2 and CO changed. However, when the pure CO was used as a fuel, area specific resistance (ASR), especially low frequency region, was increased. This might be due to carbon deposition on anode. The maximum power density was 60% lower using CO than using H 2 . Carbon deposition reduced after constant current was applied. The SOFC performance was recovered from the carbon deposition after applying constant current during 100h. 1. 서 론 연료전지는 내연기관을 대체할 수 있는 에너지 전환 장치로 각광을 받으며 많은 연구가 진행되고 있다. (1) 연료전지 종류 중 고체산화물 연료전지(Solid oxide fuel cell, SOFC)는 높은 전력밀도와 고효율의 장점 때문에 가정용 발전 시스템(RPG) 이나 분산 발전 시스템으로 활용할 목적으로 활발히 연구 중이다. (1,2) SOFC는 고온의 작동 온도로 인하여 전극의 활성도가 높기 때문에 귀금속 촉매를 사용하지 않아도 될 뿐만 아니라 수소, 일산화 탄소(CO) 및 메탄(CH 4 )같은 다양한 연료를 다양하게 사용할 수 있는 장점이 있다. (3~5)
TL;DR: In this paper, the characteristics of non-premixed oxy-fuel flame in a multi-jet burner were experimentally and numerically investigated, and the results of numerical simulation were compared with the measured results which are temperature profile and direct flame observation.
Abstract: The characteristics of nonpremixed oxy-fuel flame in a multi-jet burner were experimentally and numerically investigated. The overall flow rate of fuel and oxygen was fixed, and the oxygen feeding ratio (OFR) was varied by 0.25, 0.5, and 0.75. The results of numerical simulation were compared with the measured results which are temperature profile and direct flame observation. The probability density function (PDF) model was applied accounting to the description between turbulence and chemistry, and standard k- e model was used for turbulent flow field. Equilibrium assumption is very reasonable due to fast chemistry of the oxy-fuel combustion. Thus, the equilibrium calculation based on Gibbs free energy minimization was guaranteed to generate the solution of the oxy-fuel combustion. The result was obtained by numerical simulation. The predicted radial temperature profiles were in good agreement with the measured results. The flame length was shorten and was intensified with the decrease of OFR because the mixture of fuel and oxidizer are fast mixed and burnt. The maximum temperature became lower as the OFR increased, as a consequence of large flame surface area.
TL;DR: In this paper, an analysis of the characteristics of flowfield around the Pitot-static probe was performed by using a Navier-Stokes CFD code and for the purpose of finding an optimal configuration, a technique based on the response surface method is applied to the problem with design parameters including shape of the nose section and cone angle.
Abstract: Accurate measurement of speed and altitude of flying vehicles in air data system remains a critical technical issue. A highly reliable Pitot-static probe is required to obtain air data such as total pressure and static pressure. In this study, an analysis of the characteristics of flowfield around the Pitot-static probe was performed by using a Navier-Stokes CFD code. In addition, for the purpose of finding an optimal configuration, a technique based on the response surface method is applied to the problem with design parameters including shape of the nose section and cone angle. It is shown that the optimal configuration fulfills the MIL specification in wider range of high angles of attack.
TL;DR: In this article, the flow characteristics of a ship's propulsion mechanism of Weis-Fogh type, in which a airfoil(NACA0010) moves reciprocally in a channel, were investigated by the PIV.
Abstract: The Flow characteristics of a ship's propulsion mechanism of Weis-Fogh type, in which a airfoil(NACA0010) moves reciprocally in a channel, were investigated by the PIV. Velocity vectors and velocity profiles around the operating and stationary wings were observed at opening angles of α=15° and 30°, velocity ratios of V/U=0.5~1.5 and Reynolds number of Re=0.52×104~1.0×104. As the results the fluid between wing and wall was inhaled in the opening stage and was jet in the closing stage. The wing in the translating stage accelerated the fluid in the channel. And the flow fields of this propulsion mechanism were unsteady and complex, but those were clarified by flow visualization using the PIV. 1. 서 론 소위 Weis-Fogh메커니즘 (1,2) 은 영국의 생물 학자 Weis-Fogh가 Encarsia formosa로 불리는 작은 벌의 정지비행을 관찰함에 의해 발견한 독특하고, 효율이 좋은 양력 발생기구이다. 이 메커니즘의 동작원리를 Fig. 1에 나타낸다. 이 벌은 몸통을 수직으로 유지한 채 날개를 수평면으로 회전운동 시킴에 의해 정지 비행을 행하고 있다. 먼저 날개가 몸통의 등쪽에서 앞전(Leading edge)을 중심으로 닫힌다. 그리고 날개는 뒷전(Trailing edge)을 맞닿은 상태에서 열려, 어느 일정한 열림각(여기서 열림각이란 Fig. 1의 두 번째 그림에서두 날개가 이루는 각의 1/2로 정의한다)을 유지하
TL;DR: A post-processing program based on the OOP(Object-Oriented Programming) concept has been developed for flow visualization of the flow analysis code (PowerCFD) using unstructured cell-centered method and user-friendly GUI has been built on the base of MFC.
Abstract: A post-processing program based on the OOP(Object-Oriented Programming) concept has been developed for flow visualization of the flow analysis code(PowerCFD) using unstructured cell-centered method. User-friendly GUI(GTaphic User Interface) has been built on the base of MFC(Microsoft Foundation Class). The program is organized as modules by classes including those based on VTK(Visualization ToolKit)-library, and these classes are made to function through inheritance and cooperation which is an important and valuable OOP concept. The major functions of this post-processor program are introduced and demonstrated, which include mesh plot, contour plot, vector plot, surface plots, cut plot, clip plot, xy-plot and streamline plot as well as view manipulation (translation, rotation, scaling etc).
TL;DR: In this paper, the influence of using syngas in a gas turbine, originally designed for natural gas fuel, on its performance was investigated by simulating off-design gas turbine operation.
Abstract: Integrated Gasification Combined Cycle (IGCC) power plant converts coal to syngas, which is mainly composed of hydrogen and carbon monoxide, by the gasification process and produces electric power by the gas and steam turbine combined cycle power plant. The purpose of this study is to investigate the influence of using syngas in a gas turbine, originally designed for natural gas fuel, on its performance. A commercial gas turbine is selected and variations of its performance characteristics due to adopting syngas is analyzed by simulating off-design gas turbine operation. Since the heating value of the syngas is lower, compared to natural gas, IGCC plants require much larger fuel flow rate. This increases the gas flow rate to the turbine and the pressure ratio, leading to far larger power output and higher thermal efficiency. Examination of using two different syngases reveals that the gas turbine performance varies much with the fuel composition.
TL;DR: In this paper, numerical analysis is applied to model Pt-catalyzed reaction in a micro-scale combustor fueled by butane, and the reaction constants of catalytic oxidation are determined from plug flow model with the experimental data.
Abstract: Numerical analysis is applied to model Pt-catalyzed reaction in a micro-scale combustor fueled by butane. The reaction constants of catalytic oxidation are determined from plug flow model with the experimental data. Orders of magnitude between the chemical reaction rate and the mass transfer rate are carefully compared to reveal which mechanism plays a dominant role in the total fuel conversion rate. For various conditions of fuel flow rate and surface temperature, the profiles of Sherwood number are investigated to study the characteristics of the mass transport phenomena in the micro-tube combustor. 기호설명 A : Pre-exponential factor A c : 연소기의 단면 면적 C B,b : 부탄의 혼합평균 몰 농도 C B,s : 촉매 표면에서의 부탄 몰 농도 c p : 비열 D B : 부탄의 2 성분 질량 확산 계수 d : 연소기의 수력 직경 E a : 활성화 에너지 Gz m : 물질 Graetz 수 h i : i 화학 종의 엔탈피 J i,r : i 화학 종의 반경 방향 질량 유속 성분 J i,z : i 화학 종의 축 방향 질량 유속 성분 k c : Specific reaction rate k m,b : 부탄의 물질 전달 계수 L : 연소기의 길이 p : 압력 Re : 레이놀즈 수 R u : 유니버설 가스 상수
TL;DR: In this paper, the thermal performance of a micro channel water block for computer CPU cooling was investigated experimentally, and the effects of liquid flow rate, micro channel width and height on the thermal performances of water block were investigated.
Abstract: The object of this paper is to study on the thermal performance of a micro channel water block for computer CPU cooling. The effects of liquid flow rate, micro channel width and height on the thermal performances of water block are investigated experimentally. The water block was fabricated Al and machined with a micro milling. The water block consisted of rectangular micro channels 0.5 to 0.9 mm width and 1.5 to 4.5 mm height. The experiments were conducted using deionized water, over a liquid flow rate ranging from 0.2 to 2.0 kg/min. The base temperature and thermal resistance decrease with increasing of liquid flow rate. The increase of a channel height is more effective on the thermal resistance than the decrease of a channel width. At the flow rate of 0.7 kg/min, input power of 100 W, the base temperature and thermal resistance of sample 6 is 33℃ and 0.13 ℃/W respectively. 기호설명 C p : 비열 [J/kg․℃] D h : 수력직경 [mm] H ch : 채널높이 [mm] I : 전류 [A]△ P : 압력강하 [kPa] Q : 열전달량 [W]
TL;DR: In this paper, the numerical study of land/channel flowfield optimizations is performed, using a multi-dimensional, multi-phase, non-isothermal PEFC model, and the numerical simulations reveal more uniform current density and HFR(High Frequency Resistance) distributions and thus better PEFC performance with a narrower land and channel width where the less severe oxygen depletion effect near the land region and more uniform contact resistance variation along the inplane direction are achieved.
Abstract: The performance and durability of Polymer Electrolyte Fuel Cells (PEFCs) are strongly influenced by the uniformity of current density, temperature, species distributions inside a cell In order to obtain uniform distributions in them, the optimal design of flowfield must be a key factor. In this paper, the numerical study of land/channel flowfield optimizations is performed, using a multi-dimensional, multi-phase, non-isothermal PEFC model. Numerical simulations reveal more uniform current density and HFR(High Frequency Resistance) distributions and thus better PEFC performance with narrower land/channel width where the less severe oxygen depletion effect near the land region and more uniform contact resistance variation along the in-plane direction are achieved. The present study elucidates detailed effects of land/channel width and assist in identifying optimal flow-field design strategies for the operation of PEFCs, * 회원, 인하대학교 기계공학부 E-mail : hcju@inha.ac.kr TEL : (032)860-7312 FAX :(032)868-1716
TL;DR: In this article, a welded plate heat exchanger with the plate of chevron embossing type was numerically analyzed by controlling mass flow rate, solution concentration, and inlet temperatures.
Abstract: Numerical analysis was carried out to examine the heat transfer and pressure drop characteristics of plate heat exchangers for absorption application using Computational Fluid Dynamics(CFD) technique. A commercial CFD software package, FLUENT was used to predict the characteristics of heat transfer, pressure drop and flow distribution within plate heat exchangers. In this paper, a welded plate heat exchanger with the plate of chevron embossing type was numerically analyzed by controlling mass flow rate, solution concentration, and inlet temperatures. The working fluid is H 2 O/LiBr solution with the LiBr concentration of 50-60% in mass. The numerical simulation shows reasonably good agreement with the experimental results. Also, the numerical results show that plate of the chevron shape gives better results than plate of the elliptical shape from the view points of heat transfer and pressure drop. These results provide a guideline to apply the welded PHE for the solution heat exchanger of absorption systems.기호설명 : 수력직경(m) : 패닝 마찰 계수 : 난류 강도 : 열전도율(W/m․K) : 질량유량(kg/s)
TL;DR: In this article, a heat recovery unit producing hot water was installed at the exhaust side of a 30 kW class microturbine and its performance characteristics following micro-turbines power variation was investigated.
Abstract: Recently, microturbines have received attention as a small-scale distributed power generator. Since the exhaust gas carries all of the heat release, the microturbine CHP (combined heat and power) system is relatively compact and easy to maintain. Generating hot water or steam is usual method of heat recovery from the microturbine. In this work, a heat recovery unit producing hot water was installed at the exhaust side of a 30 kW class microturbine and its performance characteristics following microturbine power variation was investigated. Heat recovery performance has been compared for different operating conditions such as constant hot water temperature and constant water flow rate. In particular, the influence of water flow rate and hot water temperature on the recovered heat was analyzed.