• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.21 no.5
• /
• pp.713-723
• /
• 1997

Performance and heat transfer characteristics of an air conditioning system filled with hydro- carbon refrigerants are experimentally investigated. Single component hydrocarbon refrigerants (propane, isobutane, butane and propylene) and binary mixtures of propane/isobutane and propane/butane are considered as working fluids in the air conditioning system. Performances of each refrigerant are obtained at several compressor speeds and temperature levels of secondary heat transfer fluids. The cooling capacity and the coefficient of performance are obtained as test results. Heat transfer data of selected refrigerants are achieved from overall conductance measurement. Average heat transfer coefficients at different mass fluxes are shown and they are also displayed for different heat capacities of the system. Experimental results show that some hydrocarbon refrigerants have better characteristics than R22.

• Journal of the Korean Ceramic Society
• /
• v.40 no.11
• /
• pp.1127-1131
• /
• 2003

Phosphate glasses known for low melting temperature glasses in electrical parts has been recently used in wide area with modification of thermal properties using alkali oxides. It is our purpose to find a correlation between thermal expansion coefficient, glass transition temperature and melting temperature through investigating thermal properties in P$_2$O$\sub$5/-SnO-ZnO-SiO$_2$/B$_2$O$_3$. As a result, the product of thermal expansion coefficient and the glass transition temperature in the glasses is found to be a constant value would be a unique value for knowing one of thermal properties.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.6B
• /
• pp.633-639
• /
• 2006

The validity of the existing formulas for the estimation of reflection coefficient of waves due to perforated wall is investigated using the result of hydraulic experiments conducted with perforated walls of various thickness. The result shows that, when the wall is thick, the energy loss coefficient is reduced to 62% of the value evaluated using the existing formula for sharp-crested orifice. The result also shows that the length of inertia resistance increases linearly as the thickness of the wall increases. The width of chamber to achieve the minimum reflection of waves decreases as the length of inertia resistance increases. Thus, the result found in the present study can be usful for the design of perforated wall.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2000.10a
• /
• pp.196-199
• /
• 2000

In this paper, we have designed a low-noise amplifier for the down-converter to apply the K-band Mu-kung-hwa satellite downconvertion. We have designed on three-stage to satisfy the property of low-noise amplifier for the down-converter required at least 30dB gain. The simulaition results for the designed three-stage Low-noise amplifier are measured that 33dB, gain and 0.93dB, noise-figure From 19.200 to 20.200, and The experiment results of the fabric are measured that 25dB, gain and 1.5dB, noise-figure. Since Input reflection coefficient and otput resection coefficient are -25dB and -28dB, respectively, and VSWR is lower than 1.5, this amplifier can be used as a low-noise amplifier for the down-converter to apply the K-band Mu-kung-hwa satellite downconvertion.

• Journal of Industrial Technology
• /
• v.28 no.B
• /
• pp.81-89
• /
• 2008

This paper is results of investigating the dominant factors influencing to coefficient of consolidation in horizontal direction of Korean marine clays and their correlations through literature review. From the results of analyzing data obtained from field tests such as piezocone penetration and dilatometer tests as well as laboratory tests, coefficient of consolidation in the horizontal direction was found to increase with increase of stiffness index of soil while it decreases with the increase of dissipation time of pore pressure developed during field tests. In general, the coefficient of consolidation in the horizontal direction tends to increase with increase of undrained shear strength and preconsolidation pressure although correlation between them are relatively low. Friction ratio has a high correlation with coefficient of consolidation in the horizontal direction in case of friction ratio being greater than 1.0. For methods of estimating coefficient of consolidation in the horizontal direction with different testing device, values obtained from methods of P2-logt and DMT-A with dilatometer were quite similar to values from piezocone penetration test. Consistency of soil is quite proportional to coefficient of consolidation in the horizontal direction. Clear correlation between coefficients of consolidation in the horizontal and the vertical directions could not be found. coefficient of consolidation in the horizontal direction estimated from the results of field test tends to be 1.13~3.11 times greater than that obtained from laboratory tests.

• Proceedings of the KIEE Conference
• /
• 2001.11a
• /
• pp.75-77
• /
• 2001

The mechanical and electrical properties of the pressureless annealed SiC-$TiB_2$ electro conductive ceramic composites were investigated as functions of the transition metal of $TiB_2$. The result of phase analysis for the SiC-$TiB_2$ composites by XRD revealed $\alpha$-SiC(6H). $TiB_2$, and YAG($Al_5Y_3O_{12}$) crystal phase. The relative density showed the lowest 84.8% for the SiC-$TiB_2$ composites added with 39vol.%$TiB_2$. Owing to crack deflection, crack bridging and YAG of fracture toughness mechanism, the fracture toughness showed the highest value of $7.8\;MPa{\cdot}m^{1/2}$ for composites added with 39vol.%$TiB_2$ under a pressureless annealing at room temperature. The electrical resistivity of the SiC-27vol.%$TiB_2$ composites was negative temperature coefficient resistance(NTCR), and the electrical resistivity of the besides SiC-27vol.%$TiB_2$ composites was all positive temperature coefficient resistance(PTCR) in the temperature range of $25^{\circ}C$ to $700^{\circ}C$.

• Journal of the Korean Ceramic Society
• /
• v.29 no.7
• /
• pp.533-538
• /
• 1992

Effect of Li2O.4B2O frit on the microstructural and thermal expansion behaviour of $\beta$-spodumene ceramics was investigated. With 4.0~8.0 wt.% frit addition, sintering temperature range was enlarged and densification was enhanced through liquid phase sintering. As the amount of frit addition was increased, thermal expansion coefficient was increased to 1.72$\times$10-6$^{\circ}C$-1 of its highest value, which indicated that the increment of thermal expansion coefficient due to the second phase was constrained.

• International Journal of Ocean System Engineering
• /
• v.3 no.1
• /
• pp.1-9
• /
• 2013

A design procedure for a ship with minimum resistance had been developed using a numerical optimization method called SQP (Sequential Quadratic Programming) combined with computational fluid dynamics (CFD) technique. The frictional resistance coefficient was estimated by the ITTC 1957 model-ship correlation line formula and the wave-making resistance coefficient was evaluated by the potential-flow panel method with the nonlinear free surface boundary conditions. The geometry of the hull surface was represented and modified by B-spline surface modeling technique during the optimization process. The Series 60 ($C_B$=0.60) hull was selected as a parent hull to obtain an optimized hull that produces minimum resistance. The models of the parent and optimized hull forms were tested at calm water condition in order to demonstrate the validity of the proposed methodolgy.

• Steel and Composite Structures
• /
• v.2 no.4
• /
• pp.247-258
• /
• 2002

The high-temperature material properties of steel are very important to the fire resistance analysis of high-strength bolt connections. This paper reports on the results of the experimental studies on the high-temperature properties of 20 MnTiB steel which is widely used in high-strength bolts, and the friction coefficient of 16Mn steel plates at elevated temperature which is a necessary parameter for bolted frictional connection analysis. The test data includes yield strength, limit strength, modulus of elasticity, elongation and expansion coefficient of 20MnTiB steel at elevated temperature, and the friction coefficients between two 16Mn steel plates under elevated temperatures and after cooling. Based on the data from the tests, the mathematical models for predicting the mechanical properties of 20MnTiB steel and friction coefficients of 16Mn steel plates have been established.

• Journal of the Korean Ceramic Society
• /
• v.29 no.8
• /
• pp.646-650
• /
• 1992

Effect of Li2O.4B2O3 frit addition on microstructural and thermal expansion behaviour of the $\beta$-spodumene ceramics made from kaolinite was investigated. With 2.0~4.0 wt% frit addition, the densification by liquid phase sintering caused low water absorption below 3% and enhancement of beding strength. As the amount of frit addition was increased, thermal expansion coefficient was increased to large scale, but in 2 wt% frit addition, its thermal expansion coefficient was constrained to 1.92$\times$10-6$^{\circ}C$-1.