• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.4
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• pp.413-418
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• 2021

In this study, as a basic study to use recycled limestone powder as a secondary product mixture for concrete, it was found that the compressive and flexural strengths were equal to or slightly improved compared to Plain up to 10% and 20% of the RLP mixing ratio, but the strength was rather decreased at 30% mixing. As a result of the heat of hydration experiment, as the RLP mixing rate increased, the heat of hydration decreased, and the elapsed time of the maximum heat was also delayed. As a result of the drying shrinkage test, as the fine powder RLP filled the internal pores of the cement mortar, the drying shrinkage decreased as the mixing rate increased. The compressive strength, water absorption rate, and compressive strength after freezing and thawing of the concrete block mixed with RLP 20% all satisfied the group standard criteria of the Korea Concrete Industry Cooperative Federation, confirming the possibility of use as a mixed material.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.9
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• pp.714-721
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• 2006

In evaporative cooling applications, the evaporation water is supplied usually sufficiently larger than the amount evaporated to enlarge contact surface between the water and the air. Especially in indirect evaporative coolers, however, if the evaporation water flow rate is excessively large, the evaporative cooling effect is not used for heat absorption from the hot fluid but spent to the sensible cooling of the evaporation water itself. This would result in a decrease in the cooling performance of the indirect evaporative cooler. In this study, the effects of the evaporation water flow rate on the cooling performance are investigated theoretically. The cooling process in an indirect evaporative cooler is modeled into a set of linear differential equations and solved to obtain the exact solutions to the temperatures of the hot fluid, the moist air, and the evaporation water. Based on the exact solutions, it is analyzed how much the cooling performance is affected by the evaporation water flow rate. The results show that the decrease in the cooling effectiveness is substantial even for a small flow rate of the evaporation water and the relative decrease is more serious for a high-performance evaporative cooler.

• Journal of Welding and Joining
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• v.35 no.3
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• pp.28-34
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• 2017

The authors derived the criteria on the process parameters of laser depositions with metal powers(SUS316L & IN718) by evaluating the surface and cross-section properties of the deposition layers. The surface characteristics of the deposition layer are investigated through optical microscopy by controlling the process parameters of laser output, powder feeding rate and gas feeding rate. The cross-section characteristics were also analyzed after polishing and chemical etching process. As the gas feeding rate increased, the amount of powder loss increased and the difference in the dilution ratio and heat affected zone depending on laser outputs was observed. In addition, the powder feeding rate used in the experiment did not interfere with the energy absorption of the base material.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.5
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• pp.594-603
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• 2004

Several desiccant cooling systems have been developed in terms of cost and performance. In this study a fin-tube exchanger has been used for liquid desiccant dehumidification system. This dehumidifier has been designed to study the absorption characteristic of the aqueous triethylene glycol(TEG) solution which has the flow range from 20 to 50 LPM. The dehumidifier performance characteristics of working factor variables such as inlet solution flow rate, air flow rate, solution concentration and brine temperature have been analyzed. This dehumidifier has the ability to provide running while saving the latent heat load of total energy. The result of this experiment can provide useful data for hybrid air conditioning system.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.13 no.3
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• pp.16-22
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• 2017

It has become important for unutilized energy to be used for air conditioning of building. Economic evaluation on energy system by using treated sewage water as heat source, which is one of unutilized energy, was performed. The floor area of the subject building and the distance between heat source equipment and sewage treatment plant was assumed $30,000m^2$ and 200m. Absorption chiller-heater system was used for comparing to the energy efficient system, and payback period method was applied to carry out economic evaluation. Although the operating cost of this system is reduced compared to general heat source system, the ratio is not meaningful compared to the initial investment cost increase, and payback period was calculated to be about 36.1 years. However, when calculated based on the 2014 rate of electricity and city gas, it will be greatly reduced to 3.1 years. International commodity prices are constantly changing, and therefore national policy on the spread of unutilized energy should be maintained.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.12
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• pp.85-93
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• 2009

This research is intended to grasp the characteristics of heat flow inside auxiliary power device engine room to obtain the design basic data through numerical analysis and experiment. For experiment cost reduction, numerical analysis was done to obtain quantitative data by observing the change in temperature distribution of major parts according to changes in normal condition, incompressible condition, engine surface heat emission rate and absorption temperature with the use of commercial STAR-CD. The experiment was done by grasping the temperature distribution of major interested parts inside engine room in loaded and unloaded conditions during engine operation. The temperature distribution data here will serve as useful design data during APU engine room designing.

• Journal of Powder Materials
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• v.13 no.2 s.55
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• pp.102-107
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• 2006

Recycling industrial wastes such as fly ash from a coal burning heat power plant and shell from an oyster farming were investigated to prevent environment contamination as well as to enhance the value of recycling materials. In this study, the lightweight aggregates and the red bricks were fabricated from fly ashes with other inorganic materials and wastes. The starting materials of the lightweight aggregate were fly ash powder and water glass, and the compacts of these materials were heat treated at $1100^{\circ}C$. The fabricated lightweight aggregates had low bulk density, $0.9-1.2\;g/cm^3$, hence floated on the water and had the strength of 7.0-11.0 MPa and the modulus of 2900-3300 MPa which indicates it has enough strength as the aggregate. Another type of the light weight aggregate was prepared from fly ashes, shell powders and clays. The bulk density, porosity, and compressive strength of these aggregates were $1.19-1.34\;g/cm^3,\;18.3{\sim}56.1%$ and 5-12 MPa, respectively. The addition of a small amount of fly ash powder prevented hydration of the light weight aggregates. The red brick was also fabricated from the fly ash containing materials. It is suitable for the brick facing of a building as it has moderate strength and low water absorption rate.

• Journal of the Korea Institute of Building Construction
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• v.21 no.2
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• pp.97-104
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• 2021

This study aims to develop non-sintered cement that can replace the Portland cement by utilizing industrial by-products. As a suggestion, the physical properties of non-sintered cement mortar depending on the curing method were investigated with ground granulated blast furnace slag, class C fly ash, and class F fly ash. As a result of the study, it was found that the strength performance and absorption rate were improved through the heat treatment process after steam curing. It was confirmed through crystal phase analysis that the hydration was accelerated after heat treatment, and the bonding material formed a dense internal structure.

• Laser Solutions
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• v.16 no.2
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• pp.1-6
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• 2013

Picosecond lasers are a very effective tool for micromachining metals, especially when high accuracy, high surface roughness and no heat affected zone are required. However, low productivity has been a limit to broadening the spectrum of their industrial applications. Recently it was reported that in the micromachining of copper with a 1064nm picosecond laser, there exist the optimal pulse energy and repetition rate to achieve the maximum volume ablation rate. In this paper, we used a 515nm picosecond laser, which is more efficient for micromachining copper in terms of laser energy absorption, to obtain its optimal pulse energy and repetition rate. Theoretical analysis based on the experimental data on copper ablation showed that using a 515nm picosecond laser instead of a 1064nm picosecond laser is more favorable in that the calculated threshold fluence is 75% lower and optical penetration depth is 50% deeper.

• Applied Chemistry for Engineering
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• v.31 no.5
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• pp.575-580
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• 2020

In this study, we simulated an amine regeneration process with heat-stable salts removal unit. We derived the optimal operating conditions considering the flow rate of waste, the removal rate of heat-stable salts, and the loss rate of MDEA (methyl diethanolamine). In the amine regeneration process that absorbs and removes acid gas, heat-stable salt impairs the absorption efficiency of process equipment and amine solution. An ion exchange resin method is to remove heat-stable salts through neutralization by using a strong base solution such as NaOH. The acid gas removal process was established using the Radfrac model, and the equilibrium constant of the reaction was calculated using Gibbs free energy. The removed amine solution is separated and flows to the heat-stable salts remover which is modeled by using the Rstoic model with neutralization reaction. Actual operation data and simulation results were compared and verified, and also a case study was conducted by adjusting the inflow mass of removal unit followed by suggesting optimal conditions.