• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.7
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• pp.492-507
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• 2010

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2009. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) Research trends of thermal and fluid engineering have been surveyed as groups of general thermal and fluid flow, fluid machinery and piping, and new and renewable energy. Various topics were covered in the field of general thermal and fluid flow such as an expander, a capillary tube, the flow of micro-channel water blocks, the friction and anti-wear characteristics of nano oils with mixtures of refrigerant oils, etc. Research issues mainly focused on the design of micro-pumps and fans, the heat resistance reliability of axial smoke exhaust fans, and hood systems in the field of fluid machinery and piping. Studies on ground water sources were executed concerning two well type geothermal heat pumps and multi-heat pumps in the field of new and renewable energy. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics and industrial heat exchangers. Researches on heat transfer characteristics included the heat transfer in thermoelectric cooling systems, refrigerants, evaporators, dryers, desiccant rotors. In the area of industrial heat exchangers, researches on high temperature ceramic heat exchangers, plate heat exchangers, frosting on fins of heat exchangers were performed. (3) In the field of refrigeration, papers were presented on alternative refrigerants, system improvements, and the utilization of various energy sources. Refrigeration systems with alternative refrigerants such as hydrocarbons, mixed refrigerants, and $CO_2$ were studied. Efforts to improve the performance of refrigeration systems were made applying various ideas of suction line heat exchangers, subcooling bypass lines and gas injection systems. Studies on heat pump systems using unutilized energy sources such as river water, underground water, and waste heat were also reported. (4) Research trend in the field of mechanical building facilities has been found to be mainly focused on field applications rather than performance improvements. In the area of cogeneration systems, papers on energy and economic analysis, LCC analysis and cost estimating were reported. Studies on ventilation and heat recovery systems introduced the effect on fire and smoke control, and energy reduction. Papers on district cooling and heating systems dealt with design capacity evaluation, application plan and field application. Also, the maintenance and management of building service equipments were presented for HVAC systems. (5) In the field of architectural environment, various studies were carried to improve indoor air quality and to analyze the heat load characteristics of buildings by energy simulation. These studies helped to understand the physics related to building load characteristics and to improve the quality of architectural environment where human beings reside in.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.7
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• pp.380-394
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• 2015

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2014. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) The research works on the thermal and fluid engineering have been reviewed as groups of heat and mass transfer, cooling and heating, and air-conditioning, the flow inside building rooms, and smoke control on fire. Research issues dealing with duct and pipe were reduced, but flows inside building rooms, and smoke controls were newly added in thermal and fluid engineering research area. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics, pool boiling and condensing heat transfer and industrial heat exchangers. Researches on heat transfer characteristics included the results for thermal contact resistance measurement of metal interface, a fan coil with an oval-type heat exchanger, fouling characteristics of plate heat exchangers, effect of rib pitch in a two wall divergent channel, semi-empirical analysis in vertical mesoscale tubes, an integrated drying machine, microscale surface wrinkles, brazed plate heat exchangers, numerical analysis in printed circuit heat exchanger. In the area of pool boiling and condensing, non-uniform air flow, PCM applied thermal storage wall system, a new wavy cylindrical shape capsule, and HFC32/HFC152a mixtures on enhanced tubes, were actively studied. In the area of industrial heat exchangers, researches on solar water storage tank, effective design on the inserting part of refrigerator door gasket, impact of different boundary conditions in generating g-function, various construction of SCW type ground heat exchanger and a heat pump for closed cooling water heat recovery were performed. (3) In the field of refrigeration, various studies were carried out in the categories of refrigeration cycle, alternative refrigeration and modelling and controls including energy recoveries from industrial boilers and vehicles, improvement of dehumidification systems, novel defrost systems, fault diagnosis and optimum controls for heat pump systems. It is particularly notable that a substantial number of studies were dedicated for the development of air-conditioning and power recovery systems for electric vehicles in this year. (4) In building mechanical system research fields, seventeen studies were reported for achieving effective design of the mechanical systems, and also for maximizing the energy efficiency of buildings. The topics of the studies included energy performance, HVAC system, ventilation, and renewable energies, piping in the buildings. Proposed designs, performance performance tests using numerical methods and experiments provide useful information and key data which can improve the energy efficiency of the buildings. (5) The field of architectural environment was mostly focused on indoor environment and building energy. The main researches of indoor environment were related to the evaluation of work noise in tunnel construction and the simulation and development of a light-shelf system. The subjects of building energy were worked on the energy saving of office building applied with window blind and phase change material(PCM), a method of existing building energy simulation using energy audit data, the estimation of thermal consumption unit of apartment building and its case studies, dynamic window performance, a writing method of energy consumption report and energy estimation of apartment building using district heating system. The remained studies were related to the improvement of architectural engineering education system for plant engineering industry, estimating cooling and heating degree days for variable base temperature, a prediction method of underground temperature, the comfort control algorithm of car air conditioner, the smoke control performance evaluation of high-rise building, evaluation of thermal energy systems of bio safety laboratory and a development of measuring device of solar heat gain coefficient of fenestration system.

• Journal of the Korean Wood Science and Technology
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• v.36 no.3
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• pp.1-8
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• 2008

The lateral strength test of bending type was done to investigate the lateral capacity of the double bolt connection of domestic larix glulam according to bolt spacing. In the shear specimen, which is bolted connection in the inserted plate type, the hole of bolt was made, changing the diameter of bolt (12 mm and 16 mm), the number of bolt (single bolt : control and double bolt), the direction of bolt row (in parallel to grain : Type-A and in perpendicular to grain : Type-B) and the bolt spacing (Type-A : 4 d and 7 d and Type-B : 3 d and 5 d). Lateral capacity and failure mode of bolt connection were compared according to conditions. In prototype design (KBCS, 2000), the reduction factor of the allowable shear resistance that the bolt spacing is reduced was calculated. The results were as follows. 1) Bearing stress per bolt in the single and double bolt connection of Type-A was directly proportional to bolt diameter and bolt spacing. Bearing stress of Type-B decreased as bolt diameter was increased, and decreased by 2~10% when bolt diameter was increased. 2) In the single bolt connection and the double bolt connection of Type-A, the splitted failure was formed in the edge direction. When the bolt spacing was 3 d in Type-B, bolt was yielded more in the part of tension than in the part of compression, and the splitted failure started at the bolt in the part of tension. In the 5 d spacing specimen, the bolt in the part of tension was yielded similarly to bolt in the part of compression, and the splitted failure started in the part of compression. 3) In the prototype design, the reduction factor was calculated by non-dimensionizing the yielding load in the standard of bolt spacing (Type A : 7 d and Type B : 5 d). In 12 mm bolt connection, the reduction factor of bolt spacing 4 d (type-A) and single bolt connection was 0.87 and 0.55, respectively, and the reduction factor of bolt spacing 3 d (Type-B) and single bolt connection was 0.91 and 0.55, respectively. In 16 mm bolt connection, the reduction factor of bolt spacing 4 d (type-A) and single bolt connection was 0.96 and 0.76, respectively, and the reduction factor of bolt spacing 3 d (Type-B) and single bolt connection was 0.91 and 0.77, respectively.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5A
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• pp.557-564
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• 2009

In recent years, there have been numerous explosion-related accidents due to military and terrorist activities. Such incidents caused not only damages to structures but also human casualties, especially in urban areas. To protect structures and save human lives against explosion accidents, better understanding of the explosion effect on structures is needed. In an explosion, the blast overpressure is applied to concrete structures as an impulsive load of extremely short duration with very high pressure and heat. Generally, concrete is known to have a relatively high blast resistance compared to other construction materials. However, information and test results related to the blast experiment of internal and external have been limited due to military and national security reasons. Therefore, in this paper, to evaluate blast effect on reinforced have concrete structure and its protective performance, blast tests are carried out with $1.0m{\times}1.0m{\times}150mm$ reinforce concrete slab structure at the Agency for Defence Development. The standoff blast distance is 1.5 m and the preliminary tests consists with TNT 9 lbs and TNT 35 lbs and the main tests used ANFO 35 lbs. It is the first ever blast experiment for nonmilitary purposes domestically. In this paper, based on the basic experiment procedure and measurement details for acquiring structural behavior data, the blast experimental measurement system and procedure are established details. The procedure of blast experiments are based on the established measurement system which consists of sensor, signal conditioner, DAQ system, software. It can be used as basic research references for related research areas, which include protective design and effective behavior measurements of structure under blast loading.

• Korean Journal of Agricultural Science
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• v.13 no.1
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• pp.103-112
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• 1986

This study was carried out to prevent the entwining of rice straw on rotary shaft and blade where rice straw was spreaded on paddy field as an organic source before rotary tilling. The rotary tillage was conducted in the paddy field having the soil moisture contents of 30%, 39%, 59% in dry basis and spreaded rice straw (450kg/10a) of 30cm, 45cm, 90cm length with the edged curve angles of rotary blade of $30^{\circ}$, $40^{\circ}$, $50^{\circ}$, $55^{\circ}$ at Yuseung area. And the test were performed on the plot which has width of 30cm and 5cm length and the quantity of entwined rice straw was analized. The test results were summarized as the followings. 1. Entwining phenomenon of rice straw was decreased as the blade edged curve angle increased. The edged curve angle of rotary blade must be determind by considering the characteristics of soil cutting resistance, tilling torque and entwining phenomenon of rice straw. But according to the entwining phenomenon of rice straw only, the edged curve angle of rotary blade should be bigger than $55^{\circ}$ for design. 2. Amount of entwining rice straw was minimized when soil moisture contents was 30 percent (d. b.). It would be better that rotary tillage is performed when soil moisture contents is lower than 30 percent in dry basis. 3. Amount of entwining rice straw was minimized when the length of rice straw was 30cm with $55^{\circ}$ edged curve angle. Therefore, it would be better to chop rice straw as 30cm. 4. Entwining phenomenon of rice straw was decreased as the forward speed decreased. To decrease the entwining rice straw, rotary tillage should be done with forward fist gear (0.35m/s).

• Journal of The Korean Association For Science Education
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• v.37 no.1
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• pp.87-101
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• 2017

The analysis was carried out with meta-analysis on master's and doctoral dissertations, and academic journals that analyzed the effects of STEAM education between 2012 and 2015. From the total number of 75 dissertations and articles analyzed, 183 different effect sizes were calculated. The analysis was done to find out the kinds of differences that would be created according to the effect size of creativity, problem-solving ability, and researcher, target area, student division research design type, and level of schools. The total effect size of creativity scored 0.776, and demonstrated satisfaction in symmetry of funnel plot, with no publication biases. The fail-safe N scored 780, and since the number is smaller than 8,945, the results of this research has credibility. Furthermore, problem-solving ability shows intermediate level of effect size with a score of 0.584. It also showed satisfaction in symmetry with funnel plot, with no publication bias. With the different research methods of the sub-factors of creativity, fluency scored the highest with 0.929, flexibility with 0.881, originality with 0.838, sophistication with 0.653, abstractness with title 0.705, and resistance to termination, 0.527. This study finds its significance in the demonstration of average effect size of STEAM education through meta-analysis. According to research results, the effects of inclusive education could be determined, yet the specific effect cause or learning principles were difficult to find. It was found that the effects of STEAM education do not rise or fall depending on school age, and demonstrated differences in creativity according to the research methods or the researchers.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.231-240
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• 2017

Recently, there have been frequent occurrences of ground sink in the urban area, which have resulted in human and material damage and are accompanied by economic losses. This is caused by artificial factors such as soil loss, poor compaction, horizontal excavation due to the breakage of the aged sewage pipe, and lack of water proof at vertical excavation. The ground sink can be prevented by preliminary restoration and reinforcement through exploration, but it can be considered that it is not suitable for urgent restoration by the existing method. In this study, a model experiment was carried out to simulate the in-ground cavities caused by groundwater flow for developing non-excavation urgent restoration in underground cavity and the range of the relaxation zone was estimated by detecting the around the cavity using a relaxation zone detector. In addition, disturbance region and relaxation region were separated by injecting gypsum into cavity formed in simulated ground. The shape of the underground cavity due to the groundwater flow was similar to that of the failure mode III formed in the dense relative density ground due to water pipe breakage in the previous study. It was confirmed that the relaxed region detected using the relaxation zone detector is formed in an arch shape in the cavity top. The length ratio of the relaxation region to the disturbance region in the upper part of the cavity center is 2: 1, and it can be distinguished by the difference in the decrease of the shear resistance against the external force. In other words, it was confirmed that the secondary damage should not occur in consideration of the expandability of the material used as the injecting material in the pre-repair and reinforcement, and various ground deformation states will be additionally performed through additional experiments.

• Journal of the Korea Concrete Institute
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• v.26 no.4
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• pp.429-440
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• 2014

Since the World Trade Center and Pentagon attacks in 2001, terror, military attack, or man-made disaster caused impact, explosion, and fire accident have frequently occured on civil infrastructures. However, structural behavior researches on major Prestressed Concrete (PSC) infrastructures such as bridges, tunnels, Prestressed Concrete Containment Vessel (PCCVs), and LNG tanks under extreme loading are significantly lacking. Especially, researches on possible secondary fire scenarios after terror, bombing, collision of vehicles and vessels on concrete structures have not been performed domestically where most of the past researches related to extreme loadings on structures focused on an independent isolated extreme loading scenario. Due to the outcry of public concerns and anxiety of potential terrorist attacks on major infrastructures and structures, a study is urgently needed at this time. Therefore, in this study, the bi-directional prestressed concrete $1400{\times}1000{\times}300mm$ panels applied with 430 kN prestressing force using unbonded prestressing thread bars were experimentally evaluated under impact, fire, and impact-fire combined loadings. Due to test site restrictions, impact tests were performed with 14 kN impactor with drop heights of 10m and 3.5 m to evaluate impact resistance capacity. Also, fire and impact-fire combined loading were tested using RABT fire loading curve. The measured residual strength capacities of PSC and RC specimens applied with impact, fire, impact-fire combined loadings were compared with the residual strength capacity of undamaged PSC and RC specimens for evaluation. The study results can be used as basic research data for related research areas such as protective design and numerical simulation under extreme loading scenarios.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.1
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• pp.49-64
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• 2014

Seabed beneath and near the coastal structures may undergo large excess pore water pressure composed of oscillatory and residual components in the case of long durations of high wave loading. This excess pore water pressure may reduce effective stress and, consequently, the seabed may liquefy. If the liquefaction occurs in the seabed, the structure may sink, overturn, and eventually fail. Especially, the seabed liquefaction behavior beneath a gravity-based structure under wave loading should be evaluated and considered for design purpose. In this study, to evaluate the liquefaction potential on the seabed, numerical analysis was conducted using 2-dimensional numerical wave tank. The 2-dimensional numerical wave tank was expanded to account for irregular wave fields, and to calculate the dynamic wave pressure and water particle velocity acting on the seabed and the surface boundary of the structure. The simulation results of the wave pressure and the shear stress induced by water particle velocity were used as inputs to a FLIP(Finite element analysis LIquefaction Program). Then, the FLIP evaluated the time and spatial variations in excess pore water pressure, effective stress and liquefaction potential in the seabed. Additionally, the deformation of the seabed and the displacement of the structure as a function of time were quantitatively evaluated. From the analysis, when the shear stress was considered, the liquefaction at the seabed in front of the structure was identified. Since the liquefied seabed particles have no resistance force, scour can possibly occur on the seabed. Therefore, the strength decrease of the seabed at the front of the structure due to high wave loading for the longer period of time such as a storm can increase the structural motion and consequently influence the stability of the structure.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.4
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• pp.249-255
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• 2009

The performance of microbial fuel cell (MFC) can be affected by many factors including the rate of organic matter oxidation, the electron transfer to electrode by electrochemical bacteria, proton diffusion, the concentration of electron acceptor, the rate of electron acceptor reduction and internal resistance. the performance of MFC using oxygen as electron acceptor can be influenced by oxygen concentration as limit factors in cathode compartment. Many studies have been performed to enhance electricity production from MFC. The series or parallel stacked MFC connected several MFC units can use to increase voltages and currents produced from MFCs. In this study, a single MFC (S-MFC) and a stacked MFC (ST-MFC) using acetate as electron donor and oxygen as electron acceptor were used to investigate the influence of dissolved oxygen (DO) concentrations in cathode compartment on MFC performance. The power density (W/$m^3$) of S-MFC was in order DO 5 > 3 > 7 > 9 mg/L, the maximum power density (W/$m^3$) of S-MFC was 42 W/$m^3$ at DO 5 mg/L. The power density (W/$m^3$) of ST-MFC was in order DO 5 > 7 > 9 > 3 mg/L and the maximum power density (W/$m^3$) of STMFC was 20 W/$m^3$ at DO 5 mg/L. These results suggest that the DO concentration of cathode chamber should be considered as important limit factor of MFC operation and design for stacked MFC as well as single MFC. The results of ST-MFC operation showed the voltage decrease of some MFC units by salt formation on the surface of anode, resulting in decrease total voltage of ST-MFC. Therefore, connecting MFC units in parallel might be more appropriate way than series connections to enhance power production of stacked MFC.