• Journal of the Korean Ceramic Society
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• v.22 no.6
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• pp.9-14
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• 1985

When the barium titanate is Synthesized in Solid-solid reaction the abnormal expansion occurs at about 110$0^{\circ}C$. The mixture was made of corresponding to the theoretical composition of barium titanate. The mixture was fired at various temperature from 90$0^{\circ}C$ to 130$0^{\circ}C$, After that the specimen was tested closely with XDR dilatometer and SEM. The results indicate that 1, The activation energy of barium titanate formation was 42 Kcal/mole. 2, Thermal expansion up to to 90$0^{\circ}C$ was mainly caused by $CO_2$ whereas it was mainly caused by the formation of the secondary phase above 100$0^{\circ}C$. 3. Thermal expansion was not influenced by the forming pressure up to 1000kg/$cm^2$ but it was largely influenced bythe forming pressure above 200kg/$cm^2$.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.2
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• pp.163-171
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• 2006

In order to control multi-zone temperatures, a multi-type air-conditioning system may be used. In this study, control algorithms for the compressor and the electronic expansion valve of a multi-type air-conditioning system were developed by using fuzzy logics. The compressor control algorithm was composed of a compressor pressure setpoint algorithm, a compressor pressure setpoint reset algorithm, and a compressor frequency setpoint algorithm. The electronic expansion valve control algorithm was composed of an indoor temperature control algorithm, and a superheat control algorithm. These algorithms were applied to a multi-type air-conditioning system. Test showed good results for the control of a multi-type air-conditioning system.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.675-680
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• 2006

Capacities of a tandem-type air-conditioner may be modulated by turning on and off of multiple compressors, and adjusting the position of a electronic expansion valve. In this study, control algorithms for compressors and a electronic expansion valve were developed by using fuzzy logics. The pressure control algorithm was also developed for the safe operation of compressors. There algorithms were implemented in a test lab and proved to be effective for the control of indoor air temperature and superheat temperature,

• Journal of the Korean Geosynthetics Society
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• v.17 no.1
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• pp.55-64
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• 2018

The purpose of this study is to evaluate the suitability of emergency underground cavity restoration method filling cavity with expansive material based on numerical analysis. For the numerical analysis, experiments were conducted to evaluate properties of expansive material. Based on the measured expansion pressure of the expansive material from the experiment, behavior of underground cavity restoration with various cavity dimensions (variation of height and width of rectangular-shape cavity) was numerically assessed. As a result of analysis, the vertical displacements of the top and bottom of cavity were significantly influenced by the cavity width and lateral displacements of cavity sides were highly dependent on cavity height. These vertical and lateral displacements were increased with increasing expansion pressure of expansive material. Also, when the expansion pressure was applied, the vertical displacement of the upper surface layer of the road was less dependent on cavity height, and was greatly influenced by cavity width.

• Transactions of Materials Processing
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• v.18 no.7
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• pp.565-571
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• 2009

This paper is concerned with the analysis on the surface stress profiles of perfectly plastic material in backward extrusion process. Due to heavy surface expansion appeared usually in the backward extrusion process, the tribological conditions along the interface between the material and the punch land are very severe. In the present study, the analyses have focused to reveal the surface conditions at the contact boundary for various punch shapes in terms of surface expansion, contact pressure, and relative movement between punch and workpiece which consists of sliding velocity and distance, respectively. Punch geometries adopted in the analysis include concave, hemispherical, pointed and ICFG recommended shapes. Extensive simulation has been conducted by applying the rigid-plastic finite element method to the backward extrusion process under different punch geometries. The simulation results are summarized in terms of surface expansion, contact pressure, sliding velocity and sliding distance at different reduction in height, deformation patterns, and load-stroke relationship, respectively.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.7
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• pp.553-559
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• 2012

A plate-fin heat exchanger is a type of heat exchanger widely used in air conditioners, and tubes and fins are tightly assembled by the mechanical expansion process of tubes. The tube expansion process deforms the grooves inside the tube, and the groove shapes also affect the adhesion between tubes and fins. In this study, the adhesion and heat transfer performance affected by the tube expansion of the non-uniform groove shape tube with different heights are investigated by both analysis and experiments. From the analysis method, it was shown that the contact pressure of non-uniform groove tube is higher than that of the uniform groove tube, and the most appropriate high groove number of the non-uniform groove tube is designed for the maximum contact pressure. From the experimental results, the decreasing rate of the condensation heat transfer coefficient is smaller in the non-uniform groove tube with different heights, compared to the conventional uniform groove tube. Also, the air-side heat transfer coefficient of the non-uniform groove tube with different heights is higher than that of the uniform groove tubes.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.8
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• pp.744-749
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• 2011

In this study, determination method of initial optimal nozzle expansion in pintle rocket was investigated. The initial optimal initial nozzle expansion was decided by maximizing the mass-averaged thrust coefficient that is calculated from thrust coefficient of minimum and maximum chamber pressure. The determination of initial optimal initial nozzle expansion was equivalent to that of the minimum propellant mass which was required for obtaining the desired mission performance. The highest pressure, thrust turndown ratio and total impulse ratio effected on the initial optimal nozzle expansion. Among them, total impulse ratio had great influence on the initial optimal nozzle expansion.

• Journal of Acupuncture Research
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• v.25 no.1
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• pp.121-130
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• 2008

Objectives : Cupping therapy is a stimulation therapy similar to acupuncture and moxibustion with effects that differ depending on the degree of stimulus. To make the strength of the skin objective in cupping therapy for this study, we measured negative pressure in the cupping jar and calculated the expansion rate of the skin. Subjects and Methods : In this study, we experimented with cupping therapy jars made for sale and used in clinics. We studied the pressure in the jars and the changes on the skin surface by measuring properties. We used commercial jars of four different volumes and diameters and tried to discover the properties on the size of the jar. Results : The results of experiment with the cupping therapy are as follows: 1. The lowest pressure in a jar was measured at $-600{\sim}610mmHg$, and the number of operating of vacuum pump for reaching lowest pressure was increased recording where the volume of the jar would be big, but the lowest pressure was not increased recording where the size of that would be big. 2. As the vacuum pump continued to operate, the pressure gradient in the jar got smaller which shows that the expansion rate of the skin was not linear. The pressure gradient shows different operational numbers on the vacuum pump near 0mmHg/operation unrelated to jar volume. 3. When negative pressure worked on the jar, air in the jar decreased. The percentage of air gradually reduced as the negative pressure acted in the jar. For example, the percentage of skin was 37-66% when the negative pressure, reatched -500mmHg. According to out results, different test areas generate different percentages of air in the jar, presumably related to skin elasticity. This phenomenon was most pronounced with the smallest jars. 4. At -500mmHg, the expansion rate of the skin was 1.57-1.9 on the abdomen, and $1.52{\sim}1.68$ on the back. The expansion rate of the skin appeared greater when the jar was relatively small, and it appeared smaller when the jar volume was relatively large relatively.

• Structural Engineering and Mechanics
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• v.75 no.1
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• pp.101-108
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• 2020

The present study intends to analyze damage in thin-walled steel cylinders undergoing constant internal pressure and thermal cycles through use of anisotropic continuum damage mechanics (CDM) model coupled with nonlinear kinematic hardening rule of Chaboche. Materials damage in each direction was defined based on plastic strain and its direction. Stress and strain distribution over wall-thickness was described based on the CDM model and the return mapping algorithm was employed based on the consistency condition. Plastic zone expansion across the wall thickness of cylinders was noticeably affected with change in internal pressure and temperature gradients. Expansion of plastic zone over wall-thickness at inner and outer surfaces and their boundaries demarking elastic and plastic regions was attributed to the magnitude of damage induced over thermomechanical cycles on the thin-walled samples tested at various pressure stresses.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.8
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• pp.567-573
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• 2008

The conventional refrigeration system is composed of a compressor, condenser, receiver, expansion valve or capillary tube, and an evaporator. The refrigeration system used in this study has additional expansion valve and evaporator along with an evaporation pressure regulator(EPR) at the exit side of the evaporator. The two evaporators can be operated at different temperatures according to the opening of the EPR. The experimental results obtained using the refrigeration system with parallel control of evaporation pressure are presented and the performance analysis of the refrigeration system with two evaporators is conducted.