• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.12
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• pp.984-991
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• 2006

The applications of multi air-conditioners into multiplex and high-rise buildings have been increased by replacing central air-conditioning systems. The pipe length and altitude difference between the indoor and outdoor units can be increased based on installation conditions, which may increase the possibility of flash gas generation at the expansion device inlet. The flash gas generation causes rapid reduction of refrigerant flow rate passing through the expansion device, yielding lower system efficiency. Accumulator heat exchangers have been widely used in multi air-conditioners in order to minimize flash gas generation and obtain system reliability. However, the studies on the heat transfer characteristics and pressure drops of accumulator heat exchangers are very limited in open literature. In this study, the heat transfer rates and pressure drops of accumulator heat exchangers were measured with refrigerant flow rate and operating conditions by using R-22. The heat transfer rate increased with the increase of refrigerant flow rate, while subcooling decreased. The heat transfer rate enhanced with the reduction of inlet superheat and subcooling due to the increased temperature difference between the accumulator and inner heat exchanger.

• Corrosion Science and Technology
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• v.19 no.1
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• pp.23-30
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• 2020

Heat sinks are most widely used in thermal management systems; however, the heat dissipation efficiency is usually limited. Therefore, in order to increase heat dissipation efficiency of the heat sink, the heat-dissipating paint using 2D materials (hexagonal boron nitride (h-BN) and graphene) as thermally conductive additive was designed and evaluated in the present study. The heat dissipation performance of the paint was calculated from temperature difference between the paint-coated and -uncoated specimens mounted on the heat source. The highest heat dissipation performance was obtained when the ratio of h-BN to resin was 1/10 in the paint. In addition, further reduction in the temperature of the test specimen by 6.5 ℃ was achieved. The highest heat dissipation performance of the paint prepared using graphene was achieved at a 1/50 ratio of graphene to the resin, and a 6.5 ℃ reduction was attained. In addition, graphene exhibited enhanced corrosion resistance property of heat-dissipating paint by inhibiting the growth of the paint blisters.

• Journal of the Korean Society for Heat Treatment
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• v.30 no.6
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• pp.251-257
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• 2017

The effect of annealing temperature on the martensitic transformation behavior, tensile deformation chracteristics and shape recovery etc., has been studied in TiNi based shape memory ribbon fabricated by coldrolling of wire. TiNi based shape memory wire (${\phi}=500{\mu}m$) of which structure is intermetallic compound could be cold-rolled without process annealing up to the reduction rate in thickness of 50%, but a few cracks appear in cold-rolled ribbon in the reduction rate in thickness of 65%. The $B2{\rightarrow}R{\rightarrow}B19^{\prime}$ martensitic transformation or $B2{\rightarrow}B19^{\prime}$ martensitic transformation occurs in annealing conditions dissipating lattice defects introduced by coldrolling. However, in case of higher reduction rate or lower annealing temperature, martensitic transformation in cold-rolled and then annealed ribbons does not occur. The maximum shape recovery rate of cold-rolled ribbons with the reduction rate of 35 and 65% could be achieved at annealing temperatures of 250 and $350^{\circ}C$, respectively. The shape recovery rate seems to be related to the stress level of plateau region on stress-strain curve.

• Journal of the Korean Society of Combustion
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• v.10 no.2
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• pp.18-25
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• 2005

An experimental study has been conducted to evaluate the effects of reburning on $NO_x$ reduction and also to examine heat transfer characteristics from LPG flame. Experiments were performed in flames stabilized by a co-flow swirl burner, which was mounted at the bottom of the furnace. Tests were conducted using LPG gas as main fuel and also as reburn fuel. The effects of reburn fuel fraction and injecting location of reburn fuel are studied. The paper reports data on flue gas emissions, temperature distribution in furnace and various heat fluxes at the wall for a wide range of experimental conditions. In a steady state, the total as well as radiative heat flux from the flame to the wall of furnace has been measured using a heat flux meter. Temperature distribution and emission formation in furnace have been also measured and compared.

• Journal of Power System Engineering
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• v.4 no.1
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• pp.13-19
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• 2000

This study was conducted for the heat transfer reduction due to the clinker formed in the furnace of the thermal power plant. The thermal properties of clinker such as thermal conductivity, specific heat, density and void fraction were measured. The thermal conductivities of the clinker were ranged $0.32-0.54W/m{\cdot}K$ and the average specific heat and the void fraction were $930J/kg{\cdot}K$ and 0.36 respectively. The thermal resistance of clinker was the greatest among the thermal resistances. It was found that the clinker reduces more than 90% of the heat transfer if the clinker is thicker than 10 cm.

• Magazine of the Korean Society of Agricultural Engineers
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• v.19 no.4
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• pp.4544-4554
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• 1977

The objective of this study was to measure and compare the radiation heat load generated through a few chosen shade-materials that would protect animals from the direct solar radiation heat in summer condition. The results obtained from this study are as follows; 1. when the materials were used in original state, the most effective material for radiation heat reduction was slate, followed by aluminum and galvanized steel successively. 2. The radiation heat load under the white top and black underside aluminum was 2.5 Cal. per hour per square cm less than that under the bare aluminum of their diurnal peak. 3. When the modified galvanized steel was used, the radiation heat load was reduced as much as 2.4 cal per hour per square cm by attaching plywood under the galvanized steel, 3.9 cal per hour per square cm by attaching plywood and coating white paint on the top of the galvanized steel. The galvanized steel covered by hay material showes similar result as that of the galvanized steel lined with plywood. 4. In case of slate, the radiation heat reduction value was increased by using bare slate, white top slate and white-top-black-underside slate in the descending order. 5. The calculated value of radiosity of inside surface of aluminum was about 20 percent of the radiation heat load, the reduced value of radiosity by coating paint was considered to be indirect indication of the effect of total radiation heat load reduction of painted surface. 6. About an hour of the time lag of radiation heat load peak on sept. 10 for slate materials should be investigated more comprehensively in future.

• Journal of the Korea Institute of Building Construction
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• v.16 no.1
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• pp.1-7
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• 2016

In this research, it used cement powder and reduction slag, which generates high hydration heat in hydration reaction without heat cure below $-5^{\circ}C$ degree. Purpose of final research is preventing freezing and thawing by making the compressive strength 5MPa in 3days below zero temperature due to own heat of concrete. and it is the result of physical characteristic and thermal property evaluation of reduction slag. Because reduction slag generates high hydration heat, compressive strength development is excellent. By generating highly hydration heat by $C_{12}A_7$ and $C_3A$ in reduction slag, compressive strength is developed in low temperature. In case of displacing only reduction slag without $SO_3$, it is indicated that quick-setting occurs by shortage of $SO_3$. For preventing quick-setting, gypsum is used essentially. According to this research result, in case of using reduction slag and gypsum as a ternary system, compressive strength developed 5MPa in 3 days below zero temperature. It is identified to prevent early frost damage of concrete below zero temperature.

• Journal of the Korea Institute of Building Construction
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• v.2 no.2
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• pp.145-150
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• 2002

The hydration of cement paste occurs when the cement is miked with water. During the hydration, hydration heat causes the thermal stress depending on the site of concrete and the cement content. Especially in the high-strength concrete, we must give care to the concrete due to its large cement content. In this study conduction calorimeter and concrete insulation hydration heat meter were used to investigation the hydration heat characteristics of cement and concrete. To reduce hydration heat of high-strength concrete, several types of replacement of fly-ash and blast-furnace slag powder were used in this experiment. As a result of this study, it was found that hydration heat of high-strength concrete was reduced by replacement of fly-ash and blast-furnace slag powder. In case of high-strength concrete using blast-furnace slag powder, the max-heat arrival time was delayed but an effect of heat reduction was lower than a case of high-strength concrete using fly-ash, because it was considered that the heat-dependence property of blast-furnace slag powder was higher than that of fly-ash.

• KIEAE Journal
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• v.14 no.5
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• pp.123-130
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• 2014

In order for effective heat island reduction policies to be proposed, this research made use of the land usage and land coverage and Temperature of cities, Coordinate axis data within 500 meters of nationwide automatic weather stations (478 points) in order to analyze the correlation of summertime temperatures through multiple regression analysis. This research also developed a model and empirically analyzed the urban heat island reduction effect of factors that affect regional temperatures. Heat islands cause environment deterioration and therefore can harm citizens' health, and also affects the city's metabolism process. Thus in order to restrain regional temperature rises the conclusion was drawn that consideration to increase forest areas on part of land usage planning is needed. Appropriate policy measures to regulate traffic related factors are also needed to restrain regional temperature rises. In order for future heat island reduction this research proposes a way to set up more effective policies and urban sustainability improvement strategies, and is significant in that it makes use of detailed data such as land usage and land coverage, Temperature of cities, Coordinate axis in analyses.

• Proceeding of Spring/Autumn Annual Conference of KHA
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• 2009.11a
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• pp.100-103
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• 2009

The impermeable area on the surface of city has been increased as buildings and artificial landcover have continually been increased. Urban development has gradually decreased the green zone in downtown and alienated the city from the natural environment on outskirt area devastating the natural eco system. There arise the environmental problems peculiar to city including urban heat island phenomenon, urban flood, air pollution and urban desertification. As one of urban plans to solve such problems, green roof system is attracting attentions. The purpose of this study was to investigate the heat reduction effect according to the development of green roof system and to quantify the heat reduction effect by analyzing through simulation the heat environment before and after green roof system. For thermal environment analysis, Thermo-Render 3.0 was used that was developed by Tokyo Industrial College to simulate. The simulation showed that the heat island index before and after the development of tree-planting on rooftop changed maximum $0.86^{\circ}C$ and the surface temperature changed about $20^{\circ}C$. Only with lawn planting, heat reduction effect was great and it means that the green roof system in low-management-light-weight type is enough to see effect. The simulation identified that only lawn planting for green rooftop brought such difference and could lower the heat island index at a narrow area. It is judged that application of green roof system to wider areas might relieve urban heat island phenomenon positively.