• 한국세라믹학회지
• /
• 제50권6호
• /
• pp.410-415
• /
• 2013

$ZrB_2$-SiC ceramics are fabricated via hot pressing with different ratios of submicron or nano-sized SiC in a $ZrB_2$-20 vol%SiC system, in order to examine the effect of the SiC size ratio on the microstructures and physical properties, such as thermal conductivity, hardness, and flexural strength, of $ZrB_2$-SiC ceramics. Five different $ZrB_2$-SiC ceramics ($ZrB_2$-20 vol%[(1-x)SiC + xnanoSiC] where x = 0.0, 0.2, 0.5, 0.8, 1.0) are prepared in this study. The mean SiC particle sizes in the sintered bodies are highly dependent on the ratio of nano-sized SiC. The thermal conductivities of the $ZrB_2$-SiC ceramics increase with the ratio of nano-sized SiC, which is consistent with the percolation behavior. In addition, the $ZrB_2$-SiC ceramics with smaller mean SiC particle sizes exhibit enhanced mechanical properties, such as hardness and flexural strength, which can be explained using the Hall-Petch relation.

• Journal of Mechanical Science and Technology
• /
• 제16권3호
• /
• pp.354-362
• /
• 2002

In this paper, the heat transfer characteristics of a self-oscillating heat pipe are experimentally investigated for the effect of various working fluid fill charge ratios and heat loads. The characteristics of temperature oscillations of the working fluid are also analysed based on chaotic dynamics. The heat pipe is composed of a heating section, a cooling section and an adiabatic section, and has a 0.002m internal diameter, a 0.34m length in each turn and consists of 19 turns. The heating and the cooling portion of each turn has a length of 70mm. A series of experiments was carried out to measure the temperature distributions and the pressure variations of the heat pipe. Furthermore, heat transfer performance, effective thermal conductivity, boiling heat transfer and condensation heat transfer coefficients are calculated for various operating conditions. Experimental results show the efficacy of this type of heat pipe.

• 대한기계학회논문집B
• /
• 제24권3호
• /
• pp.346-353
• /
• 2000

In this paper, heat transfer characteristics of a loop type capillary heat pipe were experimentally investigated for the effect of several fill charge ratios of working fluid and heat loads. This type of heat pipe consists of a heating section, a cooling section and an adiabatic section. The heat pipe used has a 0.002m internal diameter, a 0.34m length in one turn and consists of 19 turns. Heating and cooling sections each have a length of 70mm. Experiments were performed to measure the temperature distributions and the pressure variation of the heat pipe. Heat transfer performance, effective thermal conductivity, boiling heat transfer and condensation heat transfer coefficients were calculated for various operating conditions of heat pipe and it was found that heat transfer characteristics of this type heat pipe were very excellent. As shown by this experimental study, this type of heat pipe operates by oscillatory flow caused by pressure and temperature oscillations.

• Structural Engineering and Mechanics
• /
• 제64권3호
• /
• pp.339-346
• /
• 2017

Slabs prevent harmful effects of fire that may occur in any floor. However, it is necessary to protect the slabs from fire. Insulation materials may be appropriate to protect reinforced concrete (RC) slab from elevated temperature. In the present study, a model has been developed in artificial neural network (ANN) to predict the moment capacity ($M_r$) of RC slabs exposed to fire with insulation material. 672 data were obtained for ANN model through author's prepared program. Input layer in model consisted of seven input parameters; such as effective depth (d), ratio of d'/d, thermal conductivity coefficient ($k_{insulation}$), insulation materials thickness ($L_{insulation}$), reinforcement area ($A_{st}$), fire exposure time ($t_{\exp}$), and concrete compressive strength ($f_c$). The predicted $M_r$ by ANN was consistent with the obtained $M_r$ by author. It is proposed to ease computational complexity in determining $M_r$ using ANN. The effects of using insulation material on the moment capacity in RC slabs were also investigated. Insulating material with low thermal conductivity has been found to be more effective for durability to high temperature.

• 한국세라믹학회지
• /
• 제55권1호
• /
• pp.61-66
• /
• 2018

In this study, fabrication method of inorganic insulation were studied to reduce $CO_2$ from buildings. Main materials for inorganic insulation were used cement, blast furnace slag and aluminum powder as foaming agent. Mixing ratio of cement and slag was controlled and physical properties of inorganic insulation were analyzed. When inorganic insulation was fabricated using cement and slag, expanded slurries were not sunken and hardened normally. Pore size was 0.5 - 2 mm; mean pore size was about 1mm in inorganic insulation. Compressive strength of inorganic insulation increased with curing time and increased slightly with cement fineness. However, specific gravity decreased slightly with curing time; this phenomenon was caused by evaporation of adsorptive water. When inorganic insulation was dried at $60^{\circ}C$, compressive strength was higher than that of undried insulation. The highest compressive strength was found with a mixture of cement (50%) and slag (30%) in inorganic insulation. Compressive strength was 0.32 MPa, thermal conductivity was 0.043 W/mK and specific gravity was $0.12g/cm^3$.

• 한국지반공학회논문집
• /
• 제26권4호
• /
• pp.5-14
• /
• 2010

본 연구에서는 새로운 동상 억제제로서 폐타이어 파우더의 활용가능성을 검토하기 위해 폐타이어 분말 혼합토와 미혼합토를 대상으로 3년간 일본 토마코마이에서 야외실험 수행하였다. 야외실험 결과, 폐타이어 파우더를 20% 혼합함에 의해 현저한 동상억제 효과가 발생함을 확인하였으며, 관련 동상억제 효과를 동상량, 동상율, 열전도율, 투수성, segregation potential 이론 등을 중심으로 정량적으로 검토하였다.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
• /
• pp.775-780
• /
• 2002

Sandwich panel made by foamed styrene and ployuretane has been used generally in the construction area because of the high thermal conductivity and light weight but they occur harmful gases to both bodies and environments in the high temperature over $50^{\circ}C$. So, the purpose of this study is to investigate the physical properties of light-weight panel using the non-structural lightweight aggregate as a part of the substitution of foamed styrene and ployuretane. This paper dealt with the effect of the addition of polymer dispersion such as SBR, St/BA-1 and St/BA-2 having polymer-cement ratio as 5, 10, 15% and the filling ratio of continuous void as 50, 60% on the strength of polymer-modified sandwich panel core. From the results, we could know that the compressive and flexural strength of the sandwich panel core using non-structural lightweight aggregate and polymer dispersion such as SBR, St/BA-1 and St/BA-2 tended to be increased with an increase in the polymer-cement ratio and the filling ratio of continuous void.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.1394-1399
• /
• 2004

Recently solar energy is representative in the technology development and spread of alternative energy. Specially in condition of solar collectors, they have had very various shape. This paper reports experimental study about the application of Oscillating Capillary Tube Heat Pipe to flat-plate solar collector. In conclusion, overall temperature distribution of OCHP was investigated by charging ratio and inclination angle. Respective charging ratio is 15%, 20%, 40% and respective inclination angle is horizontal, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, perpendicular. As a result of experiment, charging ratio 20% heat pipe has shown the most uniform temperature distribution and also performance of heat transfer has been the best.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
• /
• pp.861-864
• /
• 2006

This study investigates the properties of light weight foamed concrete with variances in incorporating ratio of cement kiln dust(CKD). Test showed that an increase of CKD incorporating ratio decreased the fluidity of fresh concrete and increased the unit weight. A sinking depth of specimens incorporating CKD decreased, compared with that of control. As for the compressive strength, it firstly increased and then slightly decreased when incorporated CKD. Tensile strength values were similar to the values of compressive strength, but the ratio of comp. to tens. strength increased. Appearances density of specimens were all raged in KS and the thermal conductivity was also satisfied in KS; less than 0.05-0.160W/($m{\cdot}k$).

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2008년도 춘계학술대회 논문집
• /
• pp.178-181
• /
• 2008

Cylindrical stainless-steel/sodium heat pipe for a high-temperature application was manufactured and tested for transient and steady-state operations. The container material was made of stainless-steel 316, and the working fluid was sodium. Stainless-steel 316 mesh screen was inserted as a capillary structure. The working fluid fill charge ratio was approximately 64 $\sim$ 181% based on the pore space of the wick. The outer diameter of the heat pipe was 12.7 mm and the total length was 250 mm. The evaporator part was 150 mm and the condenser 80 mm. The performance test of the heat pipe has been conducted in the furnace with up to 800 W. The variation of the average heat transfer coefficient was investigated as a function of heat flux and vapor temperature. As input thermal load increased, it was showed that difference of temperatures in evaporator and condenser decreased and that operating section and heat transfer characteristics at the heat pipe increased.