• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.82-90
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• 2017

The aim of this work is to develop a new computational program to determine the effect of using the gas of propulsion of combustion chamber at high temperature on the shape of the two-dimensional Minimum Length Nozzle giving a uniform and parallel flow at the exit section using the method of characteristics. The selected gases are $H_2$, $O_2$, $N_2$, CO, $CO_2$, $H_2O$, $NH_3$, $CH_4$ and air. All design parameters depend on the stagnation temperature, the exit Mach number and the used gas. The specific heat at constant pressure varies with the temperature and the selected gas. The gas is still considered as perfect. It is calorically imperfect and thermally perfect below the threshold of dissociation of molecules. A error calculation between the parameters of different gases with air is done in this case for purposes of comparison. Endless forms of nozzles may be found based on the choise of $T_0$, $M_E$ and the selected gas. For nozzles delivering same exit Mach number with the same stagnation temperature, we can choose the right gas for aerospace manufacturing rockets, missiles and supersonic aircraft and for supersonic blowers as needed in settings conception.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.5
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• pp.58-66
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• 2011

A 2-loop waste heat recovery system with Rankine steam cycles for the improvement of fuel efficiency of gasoline vehicles has been investigated. A high temperature loop(HT loop) is a system to recover the waste heat from the exhaust gas, a low temperature loop(LT loop) is for heat recovery from the engine coolant cold relatively. This paper has dealt with a layout of a LT loop system, the review of the working fluids, and the design of the cycle. The design point and the target heat recovery of the LT boiler, a core part of a LT loop, has been presented and analytically investigated. Considering the characteristics of the cycle, the basic concept of the LT boiler has been determined as a shell-and tube type counterflow heat exchanger, the performance characteristics for various design parameters were investigated.

• Journal of the Korea Institute of Building Construction
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• v.12 no.4
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• pp.451-459
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• 2012

At the Korea Land and Housing Corporation(LH), concretes with high design strength of 50 MPa and 80 MPa that are composed only of ordinary Portland cement, blast furnace slag, and fly ash are developed. To determine whether the developed high strength concretes have the same properties when they are produced in batch plant(B/P) condition in the ready mixed concrete plant, and as existing high strength concretes, field tests are performed and material properties are evaluated. To investigate the material properties of the high strength concretes before and after pumping, compressive strength, flowability, air content, hydration temperature, pumping and compactability are evaluated. In field tests, before and after pumping, flowability satisfied the relevant criteria. In terms of air content, while it was slightly decreased after pumping, it satisfied the requirements. Hydration temperature criteria were satisfied, and compactability was excellent as well. The study found that the developed ternary high strength concretes have the same properties as existing high strength concretes. They can also be useful for the construction of high-rise buildings, as they are economical.

• Journal of Energy Engineering
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• v.22 no.2
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• pp.226-236
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• 2013

The heat distribution and internal flow from the efficiency of actual reformer and specification variation, using the computer simulation and experiment about the steam methane reforming reaction which uses the high temperature reformer. Reaction model from steam refoemer uses the steam response model developed by Xu & Froment.As result we supposed the chemical react Steam Reforming(SR), Water Gas Shift(WGS), and Direct Steam Reforming(DSR) from the inner high temperature reformer dominates the response has dissimilar response. According to result of steam methane reforming reaction exam using high temperature reformer, we figured out when Steam Carbon Ratio(SCR) increase, number of hydrogen yield increases but methane decreases. When comparing and examining between design with one inlet and two inlet, result came out one inlet design is more outstanding at thermal distribution and internal flow, hydrogen yield in one inlet design than two inlet design.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1358-1362
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• 2005

The Ni-base superalloy GTD-111DS was designed in the 1970s and is widely used as the material of the first stage blade under a severe combination of temperature and pressure in gas turbines. But because GTD-111DS is distributed in the shape of blade and blade has a unique figure and many cooling channels, it is hard to manufacture the test specimen. In this reason, there are little data on the microstructure and mechanical properties of the alloy. Therefore through the microstructure analysis, present paper observed that the shape of $\gamma{'}$ did not change even if aging time was increased but the amount and volume of the deposition of secondary $\gamma{'}\;rose\;and\;secondary\;\gamma{'}\;grew\;among\;primary\;\gamma{'}$. Also, by tensile test for different temperature, there was difference between yield strength and tensile strength in room temperature on heat treatment and extracting region but the more increasing temperature, the more decreasing difference between yield strength and tensile strength.

• Journal of the Korean Society of Safety
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• v.28 no.3
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• pp.18-22
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• 2013

The Co-base super heat resisting alloy ECY768 is employed in gas turbine because of its high temperature strength and oxidation resistance. The prediction of fatigue life for superalloy is important for improving the efficiency. In this paper, low cycle fatigue tests are performed as variables of total strain range and temperature. The relations between strain energy density and number of cycle to failure are examined in order to predict the low cycle fatigue life of ECY768 super alloy. The lives predicted by strain energy methods are found to coincide with experimental data and results obtained from the Coffin-Manson method. The fatigue lives is evaluated using predicted by Coffin-Manson method and strain energy methods is compared with the measured fatigue lives at different temperatures. The microstructure observing was performed for how affect able to low-cycle fatigue life by increasing the temperature.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.5 s.170
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• pp.103-112
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• 2005

This paper presents one-axis high precision scanning system and illustrates the design of modified $X-Y-{\theta}$ stage as a tracker using VCM and commercialized air bearings for it. The scanning system for 100nm resolution is composed of the 3-axis stage and one axis long stroke linear motor stage as a follower. In this study a previous proposed and presented structure of VCM for the fine stage is modified. The tracker has 3 DOF($X-Y-{\theta}$ motions by four VCM actuators which are located on the same plane. So 4 actuating forces are suggested and designed to create least pitch and roll motions. This article will show about the design especially about optimal design. The design focus of this fine stage is to have high acceleration to accomplish high throughput. The optimal design of maximizing acceleration is performed in restrained size. The most sensitive constraint of this optimal design is heat dissipation of coil. There are 5 design variables. Because the relationship between design variables and system parameters are quite complicated, it is very difficult to set design variables manually. Due to it, computer based optimal design procedure using MATLAB is used. Then, this paper also describes the procedures of selecting design variables for the optimal design and a mathematical formulation of the optimization problem. Based on the solution of the optimization problem, the final design of the stage is also presented. The results can be verified by MAXWELL. The designed stage has the acceleration of about 5 $m/s^{2}$ with 40kg total mass including wafer chuck and interferometer mirror. And the temperature of coil is increased $50^{\circ}C$. In addition, the tracker is controlled by high precision controller system with HP interferometer for it and linear scaler for the follower. At that time, the scanning system has high precision resolution about 5nm and scanning resolution about 40nm in 25mm/s constant speed

• Transactions of the Korean Society of Automotive Engineers
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• v.23 no.4
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• pp.388-395
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• 2015

The waste gate valve (WGV) for gasoline vehicles operate in a harsh high-temperature environment. Hence, WGVs are typically made of Inconel 713C, which is a type of Ni-based superalloy. Recently, the metal injection molding (MIM) process has attracted considerable attention for parts used under high-temperature conditions. In this study, an MIM analysis for the head and other parts of the WGV is conducted using a commercial CAE program Moldflow. Further, optimal manufacturing conditions are determined by analyzing flow characteristics at various injection times and locations. Moreover, to improve the accuracy of the analysis results, we compare the actual temperature of the mold during injection processing with that observed through the analysis. As the results, metal injection patterns of analysis are well in accord with these of short shot test. And the temperature variations of analysis is also very similar with those of feedstock when metal injection molding.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.2
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• pp.144-154
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• 1998

A functionally graded material is a nonhomogeneous material, which is composed of several different materials to maintain structural rigidity and endure high temperature loads. An analytical method is presenter to solve the unsteady heat conduction equation for nonhomogeneous materials. A one-dimensional infinite plate made of functionally graded material is considered. The approximate Green's function solution is derived and to be used to obtain the temperature distribution them the stress distributions may be obtained. The volume fraction, the porosity, the stress difference, and the stress ratio are the design parameters and are to be used to set up a systematic design procedure.

• Korean Journal of Human Ecology
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• v.18 no.2
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• pp.509-522
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• 2009

This is a basic study to improve air quality of school classrooms in winter time. The purposes are to check indoor thermal and air environment in school classrooms during winter and to analyze influencing factors on indoor environment. The measurements of students' physical elements with questionnaire surveys were carried out in a total of 6 classrooms. As a result, this research shows that the temperature of one classroom was below indoor thermal standard level, three classrooms had lack of heat, and two classrooms are heated much, which induce relatively low humidity. All of 6 classrooms had lack of ventilation, being high level of $CO_2$ concentration and 2 classrooms are in condition of high PM10 concentration. The majority of students(76%) answered that the cause of their 'heated space syndrome' is because of the lack of ventilation. Students' opening windows for ventilations is hardly carried out at normal times, except that indoor temperature is over standard. That is, we can suggest one of solutions, which is to enable students to operate heating and ventilating system by themselves according to students' physical condition.