• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.3
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• pp.448-457
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• 2002

Heat treatment such as quenching of a high-temperature cylinder is being used on steel to produce high strength levels. Especially, the mist cooling with the high and uniform surface heat flux rate s expected to contribute for better products. The experimental mist cooling curve is produced for better understanding, and two distinct heat transfer regions are recognized from the cooling curve produced. It is shown that the liquid film evaporation dominated region follows the film boiling-dominated region as decreasing the temperature of test cylinder by mist flow. Based on the intuitive view from some previous investigations, a simplified model with some assumptions is introduced to explain the mist cooling curve, and it is shown that the estimation agrees well with our experimental data. In the meanwhile, it is known that the wetting temperature, at which surface heat flux rate is a maximum, increases with mass flow rate ratio of water to air ($\varkappa$ < 10). However, based on our experimental data, it is explained that there exists a critical mass flow rate ratio, at which the wetting temperature is maximum, in the range of 3 < $\varkappa$ < 130. Also, it is described that despite of the same value of $\varkappa$, the wetting temperature may increase with mist velocity.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.8
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• pp.82-88
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• 2008

This paper describes the influence of the bridge formed between electrodes by electrolyte for tracking process. Electrolytes is made by IEC(International Electrotechnical Commission) 60589, NaCl added to deionized water as each 1, 3, 5[wt%]. The used test equipment is made according to KS(Korean Industrial Standard) C IEC 00112. It is investigated voltage, current, value of resistance and thermal image when bridge formed between electrodes on tracking process. As a result, as conductivity of electrolyte gets bigger as Joule's heat on bridge also gets bigger. But It is not over electrolyte's boiling point due to evaporation heat of electrolyte. However as conductivity of electrolyte gets bigger as the necessary time of dry band gets shorter. So dry band is existed more long time between ahead of droplet to next droplet and discharge chance at dry band gets much. Therefore tracking process gets faster.

• Journal of the Korean Geotechnical Society
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• v.37 no.12
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• pp.25-31
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• 2021

Boundary conditions for thermal-hydraulic problems of soils play an essential role in the numerical accuracy. This study presents a boundary condition considering the thermo-hydraulic interaction between the ground and the atmosphere. Ground surface energy balance consists of solar radiation, ground radiation, wind convection, latent heat from water evaporation, and heat conduction to the ground. Equations for each heat flux are presented, and numerical analyses are performed in conjunction with the FEM program for the thermal-hydraulic phenomenon of unsaturated soils. Numerical results using the weather data at the Ulsan Meteorological Observatory are similar to the measured surface temperature. Latent heat caused by water evaporation during the daytime lowers the surface temperature of the bare soil, and a thermal equilibrium is reached at nighttime when the effect of the ground condition is significantly reduced. The temperature change of the surface ground is diminished at the deeper ground due to its thermal diffusion. Numerical analysis where the surface ground temperature is the primary concern requires considering the thermo-hydraulic interaction between the ground and the atmosphere.

• Korean Chemical Engineering Research
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• v.60 no.2
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• pp.255-259
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• 2022

Solar membrane steam generation is a very promising technology that can harvest purified water from seawater or wastewater during the current danger of running out of pure water. However, solar Membrane steam generation had direct contact with water, making it difficult to increase the efficient amount of evaporation. Here, we propose solar membrane steam generator composed of polydimethylsiloxane (PDMS) and graphene oxide (GO) and improved evaporation through wettability control in part throughout the water-absorbing membrane. Wettability control has shown significant improvements in thermal localization and temperature rise in the area of heat exchange with sunlight. The evaporator has an evaporation rate of 1.54 kg m^-2 h^-1 under 1 sun irradiation. The results showed that Solar membrane steam evaporation can effectively harvest pure water through an increase in evaporation.

• Journal of the Korean Society of Industry Convergence
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• v.6 no.1
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• pp.65-71
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• 2003

Infrared heating has been traditionally used in industrial applications for processes such as dehydration of food industrial. This heating method involves the application of radiation in the wavelength range of 5~50 micrometers. In this work, simultaneous heat balance equations were developed to simulate the infrared radiation heating of red peppers. The equations assume that moisture diffuses to the outer boundaries of the material in liquid form and evaporation occurs at the surface of the red peppers. Energy for moisture evaporation is supplied by the infrared radiant energy. The equations were validated with experimental data on surface temperature and average moisture content of red peppers. Average deviations of predicted surface red peppers temperature and average red peppers moisture from experimental data were 323~353K and 50~80%, respectively. The spectral extinction coefficients in the wavelength range $1.5<{\lambda}<27$ micrometer at 293K for Red Peppers were determined from results of reflection measurements and the four flux radiative heat transfer calculation. The radiation extinction coefficients were obtained from effective drying factor the temperature 373K.

• Journal of the Korean Ceramic Society
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• v.38 no.4
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• pp.307-307
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• 2001

Combustion process with citrate was used to produce the LiMn$_2$O$_4$powder. Precursors are pre-ignited in open air followed by post-heating in the range from $600^{\circ}C$ to 80$0^{\circ}C$ for 4h. With varying the molar ratio (R) of ethylene glycol (EG) to citric acid (CA) from 0 to 4, the effect of EG content on powder characteristics is evaluated. Vacuum drying promote the auto-ignition at room temperature. With small addition of EG metal ion was selectively segregated with organic substances and undesired lithium evaporation occurred during post-heating. LiMn$_2$O$_4$phase which is produced by combustion reaction was decomposed back to Mn$_3$O$_4$because the reaction temperature was higher than 95$0^{\circ}C$. With increasing EG content, the homogeneity of LiMn$_2$O$_4$powder increased and specific surface area increased. And lithium evaporation during vacuum drying and/or ignition also increased.

• Transactions of the Korean hydrogen and new energy society
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• v.18 no.3
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• pp.275-283
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• 2007

본 논문은 세관(ID<7 mm) 내 R-22와 R-134a의 증발 열전달과 유동양식에 대한 실험적 연구이다. R-22와 R-134a의 유동양식을 관찰하기 위해 내경 2와 8 mm의 파이렉스 튜브를 사용하였고, 열전달 계수는 내경 1.77, 3.35, 5.35 mm의 수평 평활동관에 대해서 측정하였다. 증발 유동양식에서 내경 2 mm의 환상류 영역이 내경 8 mm에 비해 저건도 영역에서 발생하는 것을 확인할 수 있었고, 내경 2 mm의 유동양식은 Mandhane의 선도와 많은 오차를 보였다. 세관(ID<7 mm) 내 증발 열전달 계수는 종래의 대구경관(ID>7 mm)에 비해 관직경에 대한 영향이 많이 나타나는 것을 알 수 있었다. 내경 1.77 mm의 열전달 계수는 내경 3.36 mm와 5.35 mm에 비해서 20내지 30% 정도 높은 것을 나타났다. 또한 종래의 열전달 상관식(Shah's, Jung's, Kandlikar's and Oh-Katsuda's correlation)과 비교한 결과, 실험 데이터는 상관식과 많은 이탈 정도를 보였다. 따라서 실험데이타를 기초로 세관내 R-22와 R-134a에 적용할 수 있는 증발 열전달 상관식을 새로이 제안하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.5
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• pp.653-659
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• 2001

This paper is concerned with the development of a new method for making and separating ice in-water and saving floated ice by installing an evaporation panel in an ice storage tank. The new method shows very good heat transfer efficiency than that of the convectional method. It is because the evaporation panel is directly contacted with water in the storage tank. The experiments were performed by varying inlet and outlet refrigerant temperatures of its evaporator. From the experimental results, the operating characteristics of in-water harvest-type ice storage system were investigated by measuring temperature and pressure at each point of the ice storage system and power required to operating compressor respect to the changes of the inlet and outlet refrigerant temperature of evaporator. It can be think that defrost frequency decreased and heavy ice created as the refrigerant temperature of evaporator outlet and defrost setting temperature is low so gotten result can effect to release efficiency. Also, consumption power, condensing heat quantity, refrigerating capacity and performance efficiency decreased as time goes by. Therefore, these results provide the basic data for system optimization, performance improvement and the possibility of application to other fields.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.10
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• pp.862-871
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• 2012

The numerical simulations on 500-N class rocket engine using 96% hydrogen peroxide and kerosene have been conducted, considering atomization, evaporation, mixing and combustion of its propellants. The grid containing 1/6 part of combustion chamber has been generated and it is assumed that 3 kinds of liquid-phase propellants (kerosene, hydrogen peroxide and water) were injected as hollow cone spray pattern, using Rosin-Rammler function for distribution of droplet diameter. For the calculation of combustion the eddy-dissipation model was applied. Owing to small size of combustion chamber and large specific heat / latent heat of hydrogen peroxide and water the propulsion characteristics were highly influenced by the size of droplet particles, and in this analysis the engine with droplet particles of 30 micron in average has shown the best propulsion performance.

• Water for future
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• v.5 no.2
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• pp.6-16
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• 1972

It has been well studied and known that the yields from the rice fields irrigated by the cold water such as the water directly flowing in from mountain valleies, underground water and subground water are largely influenced by the water temperature. However, the best method of raising water temperature has not yet been established. This is because there are some essentially difficult problems associated. When we examine the effects of $1^{\circ}C$ rise in the water temperature under natural condition on rice growing, the necessity of this line of study is verified. The results of Mihara's study show that rice bears its fruits at the water temperature above $19^{\circ}C$ and the difference of $1^{\circ}C$ in the range of $19^{\circ}C$ to $22^{\circ}C$ can produce the 20% of difference in yields. Because of these facts, most farmers have made use of water temperature raising ponds, zigzag waterways and shelter belts. But the most important factor in raising water temperature has been found to be the heat loss due to evaporation. Recently, a good deal of experiment on raising water temperature and soil temperature by reducing the evaporation are being carried out all over the world. The reduction of evaporation does not only reduce heat loss, from the surface but also reduce the loss of water. Present study is aimed to determine the efficiency of different chemicals by which monomolecular films are formed over different surfaces such as water surface, soil surface and the surface of plant leaves with a purpose of preventing the transpiration, and aimed to observe the effects of the temperature rise and its influence on growing state as well as the durability of the plants under drought condition.