• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.136-141
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• 2010

This study describes effects of width contraction in vaneless diffuser on the performance of centrifugal compressors using commercial CFD code. Numerical analysis for three different diffusers such as Parallel, half contraction, and full contraction was performed. The results show that the performance of the centrifugal compressor is improved through the use of the diffusers with width parallel in high flow rate. The width contraction of diffusers is influenced static pressure rises. Comparison with the experimental data shows agreement.

• Korean Journal of Microbiology
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• v.28 no.3
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• pp.278-282
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• 1990

Diffusion and partition of progesterone into the polyacrylamide gel was examined. Diffusion coefficient of progesterone decreased down to an asymptotic value as the concentration of the organic solvents in the diffusing medium increased. However the partition coefficient diminished steadily. Crosslinking density in the gel didn't affected the diffusion coefficient considerably but lowered the partition coefficient due to the contraction of pore volume of the gel. Progesterone showed higher diffusion coefficient as well as partition coefficient in the polyurethane than in the polyacrylamide gel, which seems to be ascribed to the difference in hydrophobicity, pore volume and pore size of the polymer matrix.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09b
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• pp.1281-1282
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• 2005

• Progress in Superconductivity and Cryogenics
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• v.14 no.4
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• pp.24-27
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• 2012

The measurement of the coefficient of thermal expansion (CTE) of polypropylene laminated paper (PPLP) as electric insulating material is important for its practical superconducting device application. The thermal strain induced to HTS tapes and its insulating material during cooling from room temperature might largely affect the critical current ($I_c$) of HTS tapes. In this study, the thermal contraction of PPLP material was measured during cooling from 300 K to 77 K using double extensometers. Initially, the CTE of a brass tape was measured and it was compared with a reference data. It was found that the measured thermal expansion data of the brass material approaches that of the reference one. Based on the results, it was then confirmed that the measurement technique could be applied to thin and flexible samples. Therefore, the same measurement procedure was applied to PPLP material using double extensometers. As a result, the linear CTE of the PPLP at 77 K has been measured to be ${\sim}15.3{\times}10^{-6}/K$. Also, it was found that the thermal contraction characteristics of PPLP was dominated by polypropylene on the cross direction (higher thermal contraction) while it was dominated by Kraft paper on the machine direction (lower thermal contraction). Overall, this measurement procedure could be adopted for the determination of CTE of flexible materials such as PPLP.

• Journal of the Earthquake Engineering Society of Korea
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• v.27 no.4
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• pp.181-186
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• 2023

In this study, considering the expansion/contraction behavior of the upper structure at all times and the abnormal behavior of the receiving friction elements that allow horizontal movement during earthquakes, a port receiving test body simulating the protrusion of the friction elements was created and the modulus performance was evaluated. In order to confirm the influence of the friction element's projection, the friction element's degree of separation was divided into four stages, and the shear behavior of the test specimen and the friction coefficient were confirmed. As a result of the experiment, it was found that the friction load increases as the protrusion degree of the friction element increases. On the other hand, as the degree of protrusion of the coefficient of friction increases, the coefficient of friction also increases. It was confirmed that damage to the friction elements during use increases the coefficient of friction, hinders smooth expansion and contraction of the upper structure, and causes stress concentration at the fixed-end support.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.4
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• pp.342-350
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• 1992

An experimental investigation of the stenosis effects on the pressure drop and flow change in the internal flow is presented. Stainless steel tubes of small diameter(3.175mm, 3.4mm) are used for the test section of the flow loop. Percent contraction ranges from 35% to 83% and the stenosis length ratio (L/d) is varied from 2.8 to 8. Water and aqueous glycerol solutions are used for Newtonian fluids and polymer solutions of Separan AP-273 (500 wppm, 1000 wppm) for non-Newtonian fluids. Pressure loss coefficients of non-Newtonian fluids decrease just as those of Newtonian fluids. The loss coefficients of Newtonian and non-Newtonian fluids increase as the percent contraction increases and the loss coefficients of non-Newtonian fluids are larger than those of Newtonian fluids for the same stenosed tube. The loss coefficient increases as the stenosis length ratio increases.

• Korean Journal of Materials Research
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• v.13 no.3
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• pp.137-143
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• 2003

The air gap between the metal and mold, formed by shrinkage during solidification, causes surface and subsurface cracks in the continuous casting process. Molten crack on the surface might also occur due to improper heat transfer between them. In order to compensate the air gap in mold design, the thermal contraction is an essential factor. In this study, the thermal contraction and expansion behaviors were examined from the ($\alpha$ and pearlite)/${\gamma}$ to ${\gamma}$/$\delta$ transformations in continuous casting steels by the commercial dilatometer and the self- assembled dilatometer with laser distance measurement. It was found that the thermal contraction and expansion behaviors were very dependant on the phase transformation of the ${\gamma}$/$\delta$ as well as ($\alpha$ and pearlite)/${\gamma}$. The sudden volume change from $\delta$ to ${\gamma}$ which might cause cracks in the continuous casting process, was observed on cooling just below the melting temperature by the self-assembled dilatometer.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.10
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• pp.2407-2417
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• 1993

Thermal deformations and stresses due to temperature changes are the serious problems in cryogenic structures such as the torque tube in a superconducting generator, In this paper, the equations of thermal expansion coefficients expressed only by material properties and winding angles are derived for the filament wound composite tubes. The experimental results of thermal contraction of CFRP tubes are compared with those from theoretical approach. Composite tubes with optimally regulated thermal expansion coefficient are designed on the basis of the study for the torque tube in the superconducting generator with temperature distributions varying from 300K to 4.2 K. The filament winding angle of composites resisting thermal stresses properly is sought by the finite element method using layered shell elements. The results show that the composite tubes designed for the requirements in cryogenic environments can effectively cope with the thermal stress problem.

• Korean Journal of Mathematics
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• v.22 no.4
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• pp.633-644
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• 2014

We get one theorem that there exists a unique solution for the fourth order semilinear elliptic Dirichlet boundary value problem when the number 0 and the coefficient of the semilinear part belong to the same open interval made by two successive eigenvalues of the fourth order elliptic eigenvalue problem. We prove this result by the contraction mapping principle. We also get another theorem that there exist at least two solutions when there exist n eigenvalues of the fourth order elliptic eigenvalue problem between the coefficient of the semilinear part and the number 0. We prove this result by the critical point theory and the variation of linking method.

• Journal of the Korean Applied Science and Technology
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• v.16 no.4
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• pp.287-291
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• 1999

Plasma polymerization of Perfluoropropene(PFP) was carried out in a tubular type reactor. The Plasma was generated by coupling inductively under the fixed discharge power of 25W and the pressure of 100, 140, and 200 mTorr of radio frequency generator. PFP plasma polymerization thin films were deposited in acrylic yams. For 1 hours, the acrylic yams treated and untreated by PFP plasma were immersed in boiling water. Then the reduction of contraction coefficient of acrylic yams were measured respectively. As a result of this experiment, untreated acrylic yams were reduced around 23%, while treated yams were contracted about 18-2%.