• International Journal of Air-Conditioning and Refrigeration
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• v.17 no.4
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• pp.129-134
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• 2009

The objectives of this paper are to study the effects of thermal and geometric conditions on the performance of indoor heat exchangers with R-410A for Gas Engine Driven Heat Pump (GHP) application and to find the optimum design conditions of indoor heat exchangers by parametric analysis for the key parameters. The key parameters are number of tube row, number of tube pipe, fin pitch and transverse tube pitch. In the air side, moisture out of the humid air condenses on the fin surface while the refrigerant (R-410A) boils inside the smooth tube. Therefore this study uses Log Mean Enthalpy Difference (LMHD) method to analyze the heat transfer from the humid air to the refrigerant. This study determines the heat exchanger size, air side/refrigerant side pressure drop and overall heat transfer coefficient. Optimum design conditions for the key parameters are also determined by the parametric analysis. The results show that number of rows and pipes, fin pitch have significant effect on the heat exchanger size. It is also found that the tube length of the louver fin is $17{\sim}30%$ shorter than that of the plate fin.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.4
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• pp.179-185
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• 2008

The purpose of this paper is to propose a systematic method on the weld pitch design of a vehicle sub-frame considering the fatigue life of spot welding points. The input data, which perform the fatigue analysis on the spot welding nuggets, are obtained by both the dynamic analysis of the multi-body vehicle model passing through the virtual proving ground of a typical Belgian road and the quasi-static analysis with the finite element model of the vehicle sub-frame. By utilizing the life cycle data obtained from the fatigue analysis, the welding points to perform the pitch change are determined. The sensitivity analysis on the fatigue life of the welding points is carried out by using the three-level orthogonal array design, and through the results of the sensitivity analysis, the best combination on the welding pitch is determined. This study shows that as compared with the baseline design, the sub-frame redesigned by the proposed technique improves the fatigue life about 7 percent while reducing the number of welding points about 19 percent.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.297-302
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• 1997

Linear displacement accuracy is one of the most important factors that determine machine tool accuracy. The laser interferometer has been usually recommended for the measurement of linear displacement accuracy. In this paper, microcomputer aided measurement and compensation system has been developed forthe pitch error in a CNC machine tool. For accurate pitch error calculation, the analysis code for the pitch error has been also implemented according to the international standards(ISO). The PC based automatic compensation system for the pitch error is also implemented. A new algorithm for calculating optimum value for pitch error compensation is proposed, minimizing the deviation at each target points. The development system has been applied to a practical CNC maching center and the performance has been demonstrated.

• Journal of KSNVE
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• v.10 no.5
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• pp.873-879
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• 2000

Experimental investigation was conducted to study the effects of pitch angle maximum camber on the performance and noise of an axial-flow fan used in outdoor-unit of air -conditioner. For this study the axial-flow fan whose pitch angle can be varied was made and the Specific sound Pressure Level and other coefficients were measured using the anechoic fan tester. It is found that pitch angle affects more severly than the maximum camber on the fan performance. On the while the maximum camber affects much on the specific sound power level. Present results show that it is important to choose the optimum pitch angle and maximum camber to design the high-performance and low-noise axial-flow fan and specific noise measured in the anechoic fan tester can be sued effectively for the design of low-noise fan.

• Korean Chemical Engineering Research
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• v.45 no.3
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• pp.269-276
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• 2007

$TiO_2$-containing pitch fibers were prepared and various stabilization variables were investigated by characterizations of the fibers and behaviors of $TiO_2$ particles in the optimum stabilization conditions. When pitch fiber was stabilized by air at the optimum condition, the fiber weight increased as an increase of the stabilization temperature and a decrease of $TiO_2$ concentration. The carbonization yield was 71~82 wt.%, showing a decrease of the yield with the $TiO_2$ increase caused by the catalytic activity of $TiO_2$ to combustion. During the stabilization, newly developed carbonyl and carboxyl groups were introduced on the fiber surface and cross-linking reactions were progressed resulting the thermosetting property, which was verified by the replacement of hydrogen with oxygen. Pore size of the activated carbon fiber was increased by an increase in $TiO_2$ concentration. In the considerations of the aggregation behaviors of the $TiO_2$ particles, the optimum stabilization conditions of 0.5 wt.% $TiO_2$ containing petroleum-based pitch fiber were suggested as $280^{\circ}C$, 3 hr.

• Carbon letters
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• v.2 no.3_4
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• pp.182-191
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• 2001

Quinoline insoluble formed by the heat treatment was hot-pressed near its softening point. The green body was stabilized in the temperature range of $300{\sim}400^{\circ}C$ and subsequently carbonized below $1300^{\circ}C$ in an argon atmosphere. The behaviors of QI formation was examined with varying the heat treatment temperature and the lapse of time of the sample carbonized at various temperatures. And the mechanical property, corrosion resistance, and friction behavior were also measured optimum content of mesophase pitch ensured a dense structure and high $LC_{(002)}$ value, which resulted in high mechanical properties, good corrosion resistance, and low-stable friction behavior.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.2
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• pp.129-136
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• 2006

Optimal design of an air-to-liquid finned plate heat exchanger is considered theoretically in this study. Based on existing correlations for the pressure loss and the heat transfer in channel flows, the optimal configuration of the plate heat exchanger including the optimal plate pitch and the optimal fin pitch is obtained to maximize the heat transfer within the limit of the pressure drop for a given flow depth of the plate heat exchanger. It is found that the optimal fin pitch is about one ninth of the optimal plate pitch. In the optimal configuration, the flow and thermal condition in the channels is just at the boundary between the laminar developing and laminar fully developed states. It is also found when reducing the flow depth of plate heat exchangers for compactness, the heat transfer performance can be maintained exactly the same if the geometric parameters such as the plate thickness, plate pitch, fin thickness, and fin pitch are reduced proportional to the square root of the flow depth as long as the flow keeps laminar within the heat exchangers.

• Journal of Electrical Engineering and Technology
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• v.12 no.6
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• pp.2268-2277
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• 2017

As constantly increasing wind power penetrates power grid, wind power plants (WPPs) are exerting a direct influence on the traditional power system. Most of WPPs are using variable speed constant frequency (VSCF) wind turbines equipped with doubly fed induction generators (DFIGs) due to their high efficiency over other wind turbine generators (WTGs). Therefore, the analysis of DFIG has attracted considerable attention. Precisely measuring optimum reference speed is basis of utilized maximum wind power in electric power generation. If the measurement of wind speed can be easily taken, the reference of rotation speed can be easily calculated by known system's parameters. However, considering the varying wind speed at different locations of blade, the turbulence and tower shadow also increase the difficulty of its measurement. The aim of this study is to design fuzzy controllers to replace the wind speedometer to track the optimum generator speed based on the errors of generator output power and rotation speed in varying wind speed. Besides, this paper proposes the fuzzy adaptive PID control to replace traditional PID control under rated wind speed in variable-pitch wind turbine, which can detect and analyze important aspects, such as unforeseeable conditions, parameters delay and interference in the control process, and conducts online optimal adjustment of PID parameters to fulfill the requirement of variable pitch control system.

• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.6
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• pp.519-530
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• 2011

The screw conveyor system installed in EPB Shield TBM chamber was manufactured in small scale for pilot test to investigate the tunnel muck hauling system that could control the earth pressure and support face thrust force. In this experimental study, there were three different test conditions that include screw angles, screw pitch, and screw RPM. Through analysis on test results based on the muck hauling amount per unit time from screw conveyor, the optimum conditions of screw conveyor were proposed to be efficiently performed by the muck processing system. Finally, this study provided the meaningful results such as optimum screw angle, screw RPM, and screw pitch for anti-reverse flow of muck hauling.

• Journal of the Korean Ceramic Society
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• v.29 no.5
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• pp.396-402
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• 1992

Carbon solid was prepared from dormant mesophase pitch (DMPP) without using a binder and its properties were characterized. DMPP powder was stabilized with air or nitric acid in pretreatment stage so that it might not soften in later heat ttreatment stage. Optimum sintering properties were obtained from carbon powder with 2.36∼2.38 of C/H atomic ratio and 1.27∼1.40 of C/O atomic ration in air stabilization. In nitric acid stabilization, optimum sintering properties were obtained when 20∼40 vol.% of nitric acid solution was used. Compressive strength increased up to 1200$^{\circ}C$ of heat treatment temperature, and the highest compressive strength and bulk density of carbon solid from DMPP were 3000 kgf/㎤, respectively. The optical properties of carbon solid obtained was fine mosaic structure. Carbon solid after graphitization showed the properties of hard carbon due to stabilization and its shore hardness was 120.