• International Journal of High-Rise Buildings
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• v.8 no.1
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• pp.71-82
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• 2019

The purpose of this study is to evaluate the indoor air quality (IAQ) and energy benefits of a dedicated outdoor air system (DOAS) and compare them with a conventional variable air volume (VAV) system. The DOAS is a decoupled system that supplies only outdoor air, while reducing its consumption using an enthalpy wheel. The VAV system supplies air that is mixed outdoor and transferred indoor. The VAV has the issue of unbalanced ventilation in each room in multiple zones because it supplies mixing air. The DOAS does not have this problem because it supplies only outdoor air. That is, the DOAS is a 100% outdoor air system and the VAV is an air conditioning system. The transient simulations of carbon dioxide concentration and energy consumption were performed using a MATLAB program based on the thermal loads from the model predicted by the TRNSYS 18 program. The results indicated that when the air volume is large, such as in summer, the distribution of air is not appropriate in the VAV system. The DOAS however, supplies the outdoor air stably. Moreover, in terms of annual primary energy consumption, the DOAS consumed approximately 40% less energy than the VAV system.

• Structural Engineering and Mechanics
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• v.92 no.1
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• pp.89-97
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• 2024

Discarded cigarette butts in the environment have caused significant pollution. Therefore, providing solutions to address these environmental issues is of great importance. Concrete is known as one of the most widely used materials around the world. Hence, this study investigates the feasibility of using cigarette butts to product concrete. For this purpose, cellulose acetate fibers obtained from cigarette butt filters were added to silica fume concrete in 10 different volume ratios. Then, the mechanical properties of the concrete samples, including compressive strength, Brazilian tensile strength, and flexural tensile strength, were examined. Based on the results, adding fibers to silica fume concrete improved the mechanical properties of the concrete. Among the 10 mixing designs, adding 0.2% by volume of fibers to silica fume concrete yielded the highest compressive and tensile strengths. In other words, adding 0.2% by volume of fibers resulted in a 16% and 34% increase in compressive strength and a 70% and 38% increase in Brazilian tensile strength at 7 and 28 days, respectively, compared to the state without cellulose acetate fibers. Additionally, the flexural tensile stress capacity increased by 56%. Furthermore, the vertical deformation tolerance in beam specimens increased by 287%, and the energy absorption capacity of the concrete beam also significantly increased. Consequently, along with the significant improvement in the mechanical properties of concrete, this study proposes a new and practicalstrategy to addressthe environmental issues caused by waste cigarette butts.

• Journal of Mushroom
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• v.13 no.2
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• pp.139-144
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• 2015

This study was done the calculation formula for calculating the below item. That is the moisture content of the substrates raw materials, water content of the mixed substrates; the amount of media, dry weight, amount of liquid, bulk density in the bottle; dried materials volume, water volume, mixing ratio in a substrates mixing materials; water requirement amount, replenishment amount for water content control of the substrates and the total amount of substrates. And each was prepared in an Excel file for automatically calculated. The calculation of the Excel file will be able to take advantage for the mushroom growers; to make raw material costs, per bottle nutrient content and moisture content maintained throughout the year and new media composition. At this time we expect, while minimizing the quantity or deterioration in the daily ups and downs continued growing courses throughout the year contribute to stabilizing production.

• Journal of the Korean GEO-environmental Society
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• v.10 no.3
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• pp.5-12
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• 2009

This study presents static and dynamic strength of coal ashes collected from disposal site of power plant. Main compositions of coal ashes were bottom ashes. In order to evaluate static and dynamic characteristics of coal ash, NGI direct-simple shear tests, cyclic simple shear tests and direct shear tests were conducted. The strengths of coal ashes from those tests were compared to those of sands. Bottom ashes among coal ashes used for this study were classified as sand from the grain size distribution and show higher strength properties than the sands. For utilization of coal ashes in civil engineering project, mixing coal ashes with sandy soil using batch plant is inconvenient and the cost is higher than the spreading sand layer and coal layer alternately. In order to simulate both mixing type and layered type construction, sands and coal ashes were mixed with volume ratio 50:50 and prepared sand and coal ash layers alternately with the same volume ratio. From the tests mixed coal ashes-specimen shows slightly higher static and cyclic strength than the layered specimen at the same density. The higher strength seems due to the angular grain of bottom ashes. The cyclic stress ratio at liquefaction decreases rapidly as the number of cycle increases at mixed specimen than that of layered specimen.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.4
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• pp.81-89
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• 2014

Tandem-ejector has been devised for engine-bay cooling. In this study, 1-D model has been developed to analyze Tandem-ejector. In the model, the primary, the secondary and the tertiary flow conditions have been analyzed with isentropic process. The mixing process has been analyzed with conservation laws based on the control volume analysis. The total pressure loss of the primary flow has been analyzed under the matching condition between the static pressure of Tandem-ejector discharge flow and atmospheric pressure. Consequently, 1-D model can predict Tandem-ejector performance accurately and provide the performance map.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.304-310
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• 2018

The aim of the research is to provide possibility of quality controlling by rheological properties for lightweight foamed concrete. The lightweight foamed concrete achieves its low density by containing air bubbles (foam) produced during the mixing process. Therefore, containing foamed volume during setting period is critical for the securing the performance as an insulating material. In this research, regarding foam collapse during the setting period, rheolgocial properties of fresh state lightweight foamed concrete were assessed to get its relationship with volume stability, or foam stability. For the experiment regarding foaming factors including mixing time, mix design of contents for materials, rheological properties of fresh state lightweight foamed concrete were tested with its density and settling depth. Based on the settling depth with various factors, relationship with rheological properties was analyzed, and especially, close relationship of plastic viscosity and settling depth was found. Therefore, from the results of this research, it is considered to contribute on suggesting a new approach of quality controlling for lightweight foamed concrete using rheological test method.

• Nuclear Engineering and Technology
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• v.53 no.4
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• pp.1119-1126
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• 2021

Spacer grid with mixing vane had been widely used in nuclear reactor core. One of the main feather of spacer grid with mixing vane was that strong swirl flow was formed after the spacer grid. The swirl flow not only changed the bubble generation in the near wall field, but also affected the bubble behaviors in the center region of the subchannel. The interaction between bubble and the swirl flow was one of the basic phenomena for the two phase flow modeling in fuel assembly. To obatin better understanding on the bubble behaviors in swirl flow, full three dimension numerical simulations were conducted in the present paper. The swirl flow was assumed in the cylindral calculation domain. The bubble interface was captured by Volume Of Fluid (VOF) method. The properties of saturated water and steam at different pressure were applied in the simulation. The bubble trajectory, motion, shape and force were obtained based on the bubble parameters captured by VOF. The simulation cases in the present study included single bubble with different size, at different angular velocity conditions and at different pressure conditions. The results indicated that bubble migrated to the center in swirl flow with spiral motion type. The lateral migration was mainly related to shear stress magnitude and bubble size. The bubble moved toward the center with high velocity when the swirl magnitude was high. The largest bubble had the highest lateral migration velocity in the present study range. The effect of pressure was small when bubble size was the same. The prelimenery simulation result would be beneficial for better understanding complex two phase flow phenomena in fuel assembly with spacer grid.

• Journal of the Society of Disaster Information
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• v.20 no.2
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• pp.390-397
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• 2024

Purpose: In this study, PCM was used to give thermal performance to concrete and analyze its effect on durability to prevent disasters that may occur in concrete when exposed to hot and cold environments. Method: After preparing concrete specimens containing 10, 30, and 50% of the two types of PCMs compared to the cement volume, the pore volume, freeze melting resistance, and scaling resistance were evaluated. Result: Regardless of the type, when PCM powder was mixed with concrete, the amount of pores decreased, and when 10% and 30% were mixed, the freeze-melting resistance was also improved. It was also confirmed that the higher the mixing amount, the better the scaling resistance. Conclusion: When mixing powdered PCM into concrete, it is believed that durability can be improved to a certain level by the filling effect, and additional various studies should be supported for actual field application.

• Korean Chemical Engineering Research
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• v.46 no.3
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• pp.479-485
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• 2008

Porous $TiO_2$ nanostructured particles containing both mesopores and macropores were fabricated by utilizing an aerosol templating method from two kinds of starting materials (colloidal mixture of $TiO_2$ nanoparticles and PS particles, and that of TTIP solution and PS particles). The effects of mixing ratio of PS to $TiO_2$ and reactor temperature on the particle properties were investigated. When $TiO_2$ nanoparticles were used as starting materials, the increase of macropores number was observed by SEM and the specific surface area and total pore volume were increased from $31.6m^2/g$ to $39.1m^2/g$ and $0.068cm^3/g$ to $0.089cm^3/g$, respectively, by increasing the weight mixing ratio of $PS/TiO_2$ from 0.79 to 1.31. When TTIP was used as precursor, the specific surface area and mesopore volume of particles prepared at same condition decreased by 67% and 75%, respectively.

• International Journal of Highway Engineering
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• v.15 no.2
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• pp.29-37
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• 2013

PURPOSES : This study aims to review the possibility of developing a road snow-melting system that can prevent slip accidents by maintaining a constant temperature of the winter roads and enhance performance of structures, including improvement of compressive strength by mixing carbon nanotube (hereafter referred to as CNT) with cement paste, the basic material. METHODS : To achieve the above purpose, an experiment was conducted by mixing power-type CNT and wrap-type CNT up to cement paste formulation by weight of 0.0wt%~4.1wt% in accordance with "KS L ISO 679(of cement strength test method)", and compressive strength was measured at 28 days of curing. In addition, the volume resistivity of the specimen was measured to test thermal and electrical characteristics, and the rate of temperature changes in specimen surface by power consumption was measured by passing electricity through the cross-sections of the specimen. Meanwhile, the criteria for checking the performance as a road snow-melting system was determined as volume resistivity of $100{\Omega}{\cdot}cm$ or less. RESULTS : A comparative analysis between specimen with 0wt% CNT content in plain status and specimen containing various types of CNTs was carried out. From its results, it was found that compressive strength increased approximately 19%, showing the highest rate when 0.2wt% of wrap-type CNT was contained, but volume resistivity of $100{\Omega}{\cdot}cm$ or less appeared only in specimens containing more than 0.2wt% CNT. In addition, it was observed that the surface temperature increased by $4.62^{\circ}C$ per minute on average in specimens containing 3.2wt% CNT. CONCLUSIONS : In this study, CNT was examined as an underlying material for a road snow-melting system, and the possibility of developing the road now-melting system was reviewed by conducting various experiments using CNT-Cement composites. From the experimental results, the specimens were found to have a superior performance when compared to the existing road snow-melting systems that place the heat transfer medium such as copper on the road. However, satisfactory strength performance were not obtained from the specimen containing CNT(2.0% or more) that functions as a heating element, which leads to the need for reviewing methods to increase the strength by using plasticizer or admixture.