• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.4
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• pp.187-194
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• 2015

This paper describes the PI controller design based on a practical transfer function model for centrifugal water chillers. The rotational speed of a compressor and the opening angle of an electronic expansion valve were simultaneously regulated as manipulated variables to maintain temperature reference and to ensure high efficiency of the chiller. The COP according to the change in each variable was investigated by performing some static experiments, and it was reflected in the PI controller design to accomplish the high efficiency control. Especially, the practical transfer function model of the chiller was built based on the dynamic experimental data considering the strong inherent non-linearity and complexity of the chiller system. The validity of the designed PI controller was proven by some experimental results using the test facility and the results were also compared to the conventional evaporating pressure control results.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.4
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• pp.700-707
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• 2013

Owing to high oil prices and environmental issues, the automobile industry has conducted considerable research and made large investments to manufacture a high-efficiency automobiles. In the case of automobile wheels in which a lightweight material is used to increase the fuel efficiency a mold is used to increase the production efficiency; however, the use of the molding method for this purpose is very expensive. Therefore an automobile wheel consists of two parts. In this study a two-piece automobile wheel is manufactured by the friction stir welding(FSW) of Al6061-T6 to reduce the manufacturing cost and process complexity. The FSW welding tool geometry and rotational speed, and the feed rate are key factors that significantly affect the weld strength. Therefore tensile tests were conducted on specimens produced using various welding conditions, and the optimal FSW welding conditions were applied to manufacture aluminum wheels. To ensure reliability, prototype aluminum wheels were manufactured and their mechanical reliability and safety were evaluated using a durability test, fatigue durability test, and impact test. Through this study, aluminum wheel production was made possible using the FSW method.

• KSTLE International Journal
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• v.8 no.1
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• pp.11-15
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• 2007

The mechanical face seal has been tested in Korea Aerospace Research Institute (KARl) for turbopump applications. In the turbopump under current development, the mechanical face seal is installed between fuel pump and turbine to prevent a mixture of fuel and combustion gas. Generally the mechanical face seal in turbopump is exposed to severe environment because of great rotational speed, high temperature of combustion gas and high level of pressure difference. Thus a series of tests were performed to guarantee the reliability of mechanical face seal by means of simulating the practical operating conditions. The tests were conducted up to 20,000 rpm with pressure difference of 800 kPa and temperature of 620 K In addition several carbon materials for mechanical face seal were conducted to the tests to compare the life time. During the tests, the performance against leakage was monitored and the carbon wear was also measured to estimate the life of a mechanical face seal The results show that the leakage flow rates of mechanical face seal is ignorable compared to an overall flow rate of fuel pump. The carbon material which has the finest wear resistance was found during the tests. Lastly no critical failure of mechanical face seal was found during the tests and the reliability of mechanical face seal for turbopump was successfully proved.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.10
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• pp.1011-1016
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• 2015

Gas piping systems in power plants and factories are always influenced by the mechanical vibrations of rotational machines such as pumps, blowers, and compressors. Unusual vibrations in a gas piping system influence possible leakages of liquids or gases, which can lead to large explosive accidents. Real-time measurements of unusual vibrations in piping systems in situ prohibit them from being possible leakages owing to the repeated fatigue of vibrations. In this paper, a non-contact 3-dimensional measurement system that can detect the vibrations of a solid body and monitor its vibrational modes is introduced. To detect the displacements of a body, a stereoscopic camera system is used, through which the major vibration types of solid bodies (such as X-axis-major, Y-axis-major, and Z-axis-major vibrations) can be monitored. In order to judge the vibration types, an artificial neural network is used. The measurement system consists of a host computer, stereoscopic camera system (two-camera system, high-speed high-resolution camera), and a measurement target. Through practical application on a flat plate, the measured data from the non-contact measurement system showed good agreement with those from the original vibration mode produced by an accelerator.

• Journal of the Korean Ceramic Society
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• v.50 no.6
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• pp.533-538
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• 2013

Silicon carbide (SiC) materials are typical ceramic materials with a wide range of uses due to their high hardness and strength and oxidation resistance. In particular, due to the corrosion resistance of the material against acids and bases including the chemical resistance against ionic gases such as plasma, the application of SiC has been expanded to extreme environments. In the SiC deposition process, where chemical vapor deposition (CVD) technology is used, the reactions between the raw gases containing Si and C sources occur from gas phase to solid phases; thus, the merit of the CVD technology is that it can provide high purity SiC in relatively low temperatures in comparison with other fabrication methods. However, the product yield rarely reaches 50% due to the difficulty in performing uniform and dense deposition. In this study, using a computational fluid dynamics (CFD) simulation, the gas velocity inside the reactor and the concentration change in the gas phase during the SiC CVD manufacturing process are calculated with respect to the gas velocity and rotational speed of the stage where the deposition articles are located.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.6
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• pp.146-151
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• 2011

Wax spin coating is a part of several wafer handling processes in the silicon wafer polishing station. It is important to ensure the wax layer free of contamination to achieve the high degree of planarization on wafers after wafer polishing. Three-dimensional air flow characteristics in a wax spin coater are numerically investigated using computational fluid dynamics techniques. When the bottom of the wax spin coater is closed, there exists a significant recirculation zone over the rotating ceramic block. This recirculation zone can be the source of wax layer contamination at any rotational speed and should be avoided to maintain high wafer polishing quality. Thus, four air suction ducts are installed at the bottom of the wax spin coater in order to control the air flow pattern over the ceramic block. Present computational results show that the air suction from the bottom is quite an effective method to remove or minimize the recirculation zone over the ceramic block and the wax coating layer.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.3
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• pp.199-205
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• 2014

We propose a new variant of lateral shearing interferometer with a tunable laser source that enables 3D surface profile measurements of freeform optics with high speed, high vertical resolution, large departure, and large field-of-view. We have verified the proposed technique by comparing our measurement result with that of an existing technique and measuring a representative sample of freeform optics. Moreover, we propose a new algorithm that is able to compensate the rotational inaccuracy.

• Journal of Welding and Joining
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• v.30 no.4
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• pp.38-43
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• 2012

Using a fiber laser heat source, an oil pressure sensor was fabricated to measure the pressure in commercial vehicles. A stepping motor was used for the rotational and translational motion in the diaphragms and hardware joining. Laser welding process algorism including shielding gas control and vision system was integrated by using LabVIEW software for the high quality welding and in-line monitoring purpose. For the maximum flexibility in pressure transmission to the pressure sensor, thin sheet metal diaphragm, $25{\sim}50{\mu}m$(SUS-316L), was used and the diaphragms were optimally designed with FEM analysis. The welded samples were cross-sectioned the observation showed that the maximum depth ratio was more than seven times of diaphragms. The maximum welding speed was measured to be as high as 50in/mm by the developed automation mechanism. The fabricated prototypes were tested for the proof pressure, spring constant and sealing. The FEM results of spring constant measurement was as accurate as up to 80% of the design value and the sensor was safely operated up to the nominal pressure of 10bars.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.1
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• pp.57-65
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• 2021

With the increased utilization of CAM programs, end-mill processing is most commonly used for machining and metal processing. In particular, hole or shaft machining has high assembly precision, which inevitably leads to high utilization of end mills. However, the analysis of quality characteristics according to the process conditions of end mills is not performed systematically at the site, causing poor quality and productivity. The most influential factor of quality is the runout of the end mill. In this paper, the number of turns of the end mill, number of tool blades, cutting direction, and artificial runout volume were determined to identify the correlation between the epicenter, cylindricality, and surface roughness. Two types of end mills, three levels of runout, three levels of rotational speed, and two cutting directions were considered and 36 rounds of hole processing were conducted. For the analysis of shape characteristics according to the set process variables, the experimental planning method was applied to the measured specimen and the processing characteristics were analyzed according to the runout of the end mill through correlation analysis.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.4
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• pp.500-509
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• 2015

The numerical simulation of two-dimensional moving blade row interactions is conducted by CFD means to investigate the interactions between the front and rear propeller in a stratospheric airship contra-rotating open propeller configuration caused by different rotational speeds. The rotational speed is a main factor to affect the propeller Reynolds number which impact the aerodynamic performance of blade rows significantly. This effect works until the Reynolds number reaches a high enough value beyond which the coefficients become independent. Additionally, the interference on the blade row has been revealed by the investigation. The front blade row moves in the induced-velocity field generated by the rear blade row and the aerodynamic coefficients are influenced when the rear blade row has fast RPMs. The rear blade row moving behind the front one is affected directly by the wake and eddies generated by the front blade row. The aerodynamic coefficients reduce when the front blade row has slow RPMs while increase when the front blade row moves faster than itself. But overall, the interference on the front blade row due to the rear blade row is slight and the interference on the rear blade row due to the front blade row is much more significant.