• Advances in Energy Research
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• v.7 no.1
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• pp.1-19
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• 2020

Energy consumption of air-conditioning and refrigeration systems is responsible for about 25 to 30% of the energy demand especially in hot seasons. This equipment is mostly electricity dependent and their use in principle affects negatively the environment. Enhancing the energy efficiency of the existing equipment is important as one of the measures to reduce environment impacts. This paper reports the results of an experimental study to evaluate the impacts of the use electronic expansion valve and variable velocity compressor on the performance of vapor compression refrigeration system. The experimental rig is composed of two independent circuits one for the vapor compression system and the other is the secondary fluid system. The vapor compression system is composed of a forced air condenser unit, evaporator, hermetic compressor and expansion elements, while the secondary system has a pump for circulating the secondary fluid, and an air conditioning heat exchanger. The manufacturer's data was used to determine the optimal points of operation of the system and consequently tests were done to evaluate the influence of variation of the compressor velocity and the opening of the expansion device on the performance of the refrigeration system. A fuzzy logic model was developed to control the rotational velocity of the compressor and the thermal load. Fuzzy control model was made in LabVIEW software with the objective of improving the system performance, stability and energy saving. The results showed that the use of fuzzy logic as a form of control strategy resulted in a better energy efficiency.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.3827-3831
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• 2014

This paper aims to solve the problem deterioration of power fuses. The deterioration of a power fuse is a cause of failure misoperation by a normal current flowing reduplicatively to fuse the element. An extension survey of a load feature rerating power fuse examined the power fuse deterioration removal, the cause of the deterioration of the power fuse, the front-after, and the thermal variation of the inside transformer room electric power equipment. The transformer showed an average improvement of $6[^{\circ}C]$. The temperature of the electrical line showed $7{\sim}8[^{\circ}C]$ improvement. The static condenser and direct reactor was $2{\sim}3[^{\circ}C]$ high-state maintenance the temperature and equipment syntonization relationship. In the subject of study $0.5{\sim}1.0[^{\circ}C]$ stabilizing three phase power fuse temperature differential was. Suggestion in the transformer room environment power equipment between the cause temperature happen elimination to deterioration of power fuse and temperature rise control.

• International Journal of Highway Engineering
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• v.13 no.1
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• pp.239-249
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• 2011

The behavior of the fiber reinforced concrete (FRC) base under environmental loads was analyzed numerically as a fundamental study to develop a high structural and functional performance composite pavement system in which the base was formed using FRC and the asphalt or cement concrete surface was placed on it. A two-dimensional finite element model of the FRC base was developed and the sensitivity study was performed with the variables including slab thickness of base, thermal expansion coefficient, elastic modulus, and tensile and compressive strengths. The crack spacing and crack width were selected as representatives of the base behavior. The effects of the selected variables on the crack spacing and crack width were analyzed and the sensitive variables were determined. The results of this study could be useful to determine the optimal material properties of the FRC base for combining well with the surface materials.

• 한국태양에너지학회:학술대회논문집
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• 2009.04a
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• pp.91-96
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• 2009

First, the base model of multi-family residential buildings are selected, and then the $CO_2$ reduction building technologies that are applicable for multi-family residential buildings are induced by analyzing the examples and then an optimal plan for when the $CO_2$ reduction building technologies can be integrated and applied to the base model was formulated. In the results of converting the energy consumption and reduction amount from the building technologies into $CO_2$ emissions to analyze the distribution ratio compared to the entire $CO_2$ emissions; the heat recovery ventilator is 0.5%, the photovoltaic system is $1.9%{\sim}5.9%$, the solar hot water heating system is $6.3%{\sim}13.1%$ and the ge thermal heat-pump system is 39.0% when both heating and hot water heating are applied. An optimally integrated application method for the building technologies is in charge of heating and hot water heating through the geothermal source heat pump system and in charge of the electricity load through the photovoltaic system(45.2%).

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1328-1333
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• 2005

This paper presents the temperature-pressure characteristics of a new SMH actuator using a Peltier module. The SMH actuator is characterized by its small size, low weight, noiseless operation, and compliance similar to that of the human body. The simple SMH actuator, consisting of the plated hydrogen-absorbing alloys as a power source, Peltier elements as a heat source, and a cylinder with metal bellows as a functioning part has been developed. To improve the thermal conductivity of the hydrogen-absorbing alloy, an assembly of copper pipes has been used. It is well known that hydrogen-absorbing alloys can reversibly absorb and desorb a large amount of hydrogen, more than about 1000 times of their own volume. The hydrogen equilibrium pressure increases when hydrogen is desorbed by heating of the hydrogen-absorbing alloys, whereas by cooling the alloys, the hydrogen equilibrium pressure decreases and hydrogen is absorbed. The new special metal hydride (SMH) actuator uses the reversible reaction between the heat energy and mechanical energy of a hydrogen absorbing alloys. The desirable characteristics of SMH actuator, which makes it suitable for the uses in medical and rehabilitation applications, have been also studied. For this purpose, the characteristics of the new SMH actuator for different temperature, pressure, and external load were explored.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.18-21
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• 2009

The life of components under high thermal load is typically shorter than other components. The turbopump turbine of liquid rocket is operated under these environments like high temperature and high centrifugal dorce due to high rotating velocity during operating time. These conditions may often cause low-cycle fatigue problem in the turbopump turbine. First of all, to analyze heat stress, ABAQUS/CAE is used and Coffin-manson's equation is used to consider elasticity and plasticity strain. S.W.T's method is used to consider the mean stress effect, using strain history, low-cycle fatigue analysis is done for turbopump turbine which may have FCL(fracture critical location). In this paper, strain life method is applied to analyze low-cycle fatigue.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.3
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• pp.261-269
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• 2003

Steel bridges, which have been damaged by load and corrosion, need repair or strengthening. In general, before the repair welding procedure, cutting procedure carry out. Therefore, the investigating of the behavior of stress generated by cutting is so important for safety of structure. Residual stress produced by gas cutting was analyzed using 2D and 3D thermal elasto plastic FEM. According to the results, the magnitude of temperature was analyzed by 2D FEM is smaller than that was analyzed using the 3D FEM program at the start and end edge of flange. And the magnitude and distribution of residual stress of perpendicular to the cutting line was analyzed by the 2D FEM program was similar to that was analyzed by the 3D FEM program. Therefore, it is possible to predict of cutting stress by 2D and 3D FEM.

• The Journal of Advanced Prosthodontics
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• v.9 no.5
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• pp.328-334
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• 2017

PURPOSE. This study evaluated fracture resistance with regard to ferrule lengths and post reinforcement on endodontically treated mandibular premolars incorporating a prefabricated post and resin core. MATERIALS AND METHODS. One hundred extracted mandibular premolars were randomly divided into 5 groups (n=20): intact teeth (NR); endodontically treated teeth (ETT) without post (NP); ETT restored with a prefabricated post with ferrule lengths of either 0 mm (F0), 1 mm (F1), or 2 mm (F2). Prepared teeth were restored with metal crowns. A thermal cycling test was performed for 1,000 cycles. Loading was applied at an angle of 135 degrees to the axis of the tooth using a universal testing machine with a crosshead speed of 2.54 mm/min. Fracture loads were analyzed by one-way ANOVA and Tukey HSD test using a statistical program (${\alpha}=.05$). RESULTS. There were statistical differences in fracture loads among groups (P<.001). The fracture load of F2 ($237.7{\pm}83.4$) was significantly higher than those of NP ($155.6{\pm}74.3N$), F0 ($98.8{\pm}43.3N$), and F1 ($152.8{\pm}78.5N$) (P=.011, P<.001, and P=.008, respectively). CONCLUSION. Fracture resistance of ETT depends on the length of the ferrule, as shown by the significantly increased fracture resistance in the 2 mm ferrule group (F2) compared to the groups with shorter ferrule lengths (F0, F1) and without post (NP).

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.745-748
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• 2008

The past structures were just required bearing capacity to service load, serviceability, and resistance to corrosion. However this point of view has changed after 9.11 terrorism, capacities which can bear impact loading by explosion, and heat by fire happening at the same time, become to be important as a basic condition. The blast resistance capacity of structures is very important part against all over the world is intimidated by terrorism everyday in current point of time. The target of this research is a development of segmented composites and layered structures with high blast resistance using cementitious composites, concrete and FRP composites, which has high tensile strength and ductility, to apply in not only existing facilities but also new ones. Through the improvement of blast resistance, casualties and economic loss can be minimized, and it is possible to diminish the structure collapse and delay the time of structure collapse by thermal effect, impact loading, dynamic loading and high strain.

• Journal of the Korean Ceramic Society
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• v.52 no.6
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• pp.455-461
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• 2015

Porous ceramics with tailored pore size and shape are promising materials for the realization of a number of functional and structural properties. A novel method has been reported for the investigation of the role of SiC in the formation of $SiO_2$ foams by colloidal wet processing. Within a suitable pH range of 9.9 ~ 10.5 $SiO_2$, particles were partially hydrophobized using hexylamine as an amphiphile. Different mole ratios of the SiC solution were added to the surface modified $SiO_2$ suspension. The contact angle was found to be around $73^{\circ}$, with an adsorption free energy $6.8{\times}10^{-12}J$. The Laplace pressure of about 1.25 ~ 1.6 mPa was found to correspond to a wet foam stability of about 80 ~ 85%. The mechanical and thermal properties were analyzed for the sintered ceramics, with the highest compressive load observed at the mole ratio of 1:1.75. Hertzian indentations are used to evaluate the damage behavior under constrained loading conditions of $SiO_2$-SiC porous ceramics.