• Transactions of the Korean Society of Mechanical Engineers
• /
• v.1 no.3
• /
• pp.156-163
• /
• 1977

길이방향의 열전도효과가 비교적 큰유체- 고체 열교환계내에 일정한 조ㅍ은 온도를 가진 유체가 유입될 때 이에 따른 비정상 온도분포가 해석되었다. 이러한 계를 기술하는 연립편미분 방정식의 수치해가 유한차분법에 의해 구해졌으며, 열전도가 무시된 경우에 대한 해석적 해를 구하여 위의 결과를 검증하였다. 한편 이상화된 모델에 대한 실험을 행하고 이 결과를 앞서 구한 수치해와 비교 검토하였다. 여기서 구해진 온도분포를 이용하여 축열효율${\eta}_A$및 ${\eta}_B$를 ${\eta}_A$는 시간 t에서의 축열량과 정상상태에 도달했을 때의 축열량의 비로 , 그리고 ${\eta}_B$는 시간 t 동안의 축열된 양과 공급된 열량의 비고 정의하여 온도분포와 효율들에 애하여 시간변수 .tau., 위치변수 .xi.와 무차원 열확산율 .betha.가 미치는 영향을 조사하였다. 이에 따르면 온도는 .betha. 가 적어짐에 따라 점점 가파르게 분포되고 한편 ${\eta}_A$는 .tau.가 점점 커지거나, .xi.가 작아질수록 좋아지는 것을 알 수 있다. 또한 ${\eta}_B$는${\eta}_A$와는 정반대의 경향을 보여주어 축열계의 최적상태가 존재함을 알 수 있다.

• 한국신재생에너지학회:학술대회논문집
• /
• 2008.05a
• /
• pp.260-262
• /
• 2008

최근 고유가의 지속과 국제적인 환경 규제에 대응하기 위하여 환경친화적인 대체연료의 개발이 시급한 가운데 재생가능한 동식물성 유지로부터 생산되는 바이오 디젤에 대한 연구가 활발히 진행되고 있다. 특히 자원 재활용 및 에너지 생산관점에서 폐유지로부터 바이오디젤 원료로 사용하는 연구가 활발히 진행되어 왔다. 이러한 폐유지로부터 바이오디젤을 효율적으로 생산하기 위해서는 폐유지내 함유되어 있는 유리지방산을 전처리공정에서 산촉매에 의한 에스테르화 반응에 의해 전환제거하고자 한다. 본 연구에서는 폐유지내 함유된 유리지방산 전환제거에 효과적인 불균일계 이온교환수지 촉매를 이용하여 공정변수 즉 사용된 촉매의 양, 반응온도, 유리지방산 농도에 따른 유리지방산 전환제거특성을 조사해 보았다. 또한 각각의 반응조건에서 속도상수를 계산하여 이온교환수지 촉매를 사용한 유리지방산 전환 제거에 필요한 활성화 에너지 값을 구하였다.

• Korean Journal of Mineralogy and Petrology
• /
• v.36 no.1
• /
• pp.33-40
• /
• 2023

Todorokite is a manganese oxide mineral containing Mg²⁺ in a tunnel structure in which MnO₆ octahedra share corners. In order to investigate the suitability and efficiency of high temperature-treated todorokite as a material for adsorption and fixation of Cs, Cs was ion exchanged and the amount of leached Cs from todorokite was measured. The todorokite used in this study was synthesized by transforming Na-birnessite to Mg-buserite and used as a precursor. After high temperature treatment, Cs exchanged todorokite changed to birnessite and hausmannite as the temperature increased. The amount of leached Cs was investigated for Cs exchanged todorokite which was reacted with distilled water and 1 M NaCl solution at different reaction times. In general, for the samples reacted with 1 M NaCl solution, the fixation of Cs was quite effective, although the amount of leached Cs was greater due to the ion exchange reaction with Na. As the treatment temperature increased, the amount of leached Cs increased and then decreased again, which was related to the mineral phases formed at each temperature. As birnessite was formed, the amount of leached Cs increased, but as birnessite decreased, that decreased again. As the mineral phase changed to hausemanite, the amount of Cs decreased rapidly. The results of our study show that Cs exchanged todorokite can be used as a material that effectively fixes Cs and prevents its diffusion by high temperature treatment.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.12
• /
• pp.924-930
• /
• 2018

The objective of this study was to investigate heating performance characteristics of electric heat pump system in a fuel cell electric vehicle (FCEV). In order to analyze heating performance characteristics of electric heat pump system with plate-type heat exchanger using stack coolant to evaporate the refrigerant, R-134a, each component was installed and tested under various operating conditions, such as air inlet temperature of inner condenser and compressor speed. When the air inlet temperature of inner condenser was varied from $0.0^{\circ}C$ to $-20.0^{\circ}C$, heating capacity was not quite different due to similar temperature gap between inlet and outlet of inner condenser with electric-driven expansion valve (EEV). However, COP increased until certain EEV opening, especially under 45.0%, because of decreasing power consumption. According to the compressor speed variation from 2,000 to 4,000 RPM, heating capacity and COP were found to have opposite trend. In the future works, stack coolant conditions as the heat source for tested heat pump system were analyzed with respect to heating performance, such as heating capacity and COP.

• Journal of Life Science
• /
• v.7 no.2
• /
• pp.73-78
• /
• 1997

Ion exchange performence to remove nitrate in water studied using commercially available strong vase anin exchange resin of $Cl^{-}$ type in the batch reactors. Anion exchange resin was more effective than activated carbon or zeolite. With large resin amount or high temperature or low initial concentration, nitrate removal characteristics for a typical gel-type resin was increased. The curves showed the generally accepted selectivity sequence as ${SO_4}^{2-}>{No_3}^->NO_{2-}>{HCO_3}^-$.

• Korean Chemical Engineering Research
• /
• v.59 no.1
• /
• pp.60-67
• /
• 2021

This study presented techno-economic analysis of a 500 MWe oxy-coal power plant with CO2 capture. The power plant included a circulating fluidized-bed (CFB), ultra-supercritical steam turbine, flue gas conditioning (FGC), air separation unit (ASU), and CO2 processing unit (CPU). The dry flue gas recirculation (FGR) was used to control the combustion temperature of CFB. One FGR heat exchanger, one heat exchanger for N2 stream exiting ASU, and a heat recovery from CPU compressor were considered to enhance heat efficiency. The decrease in the temperature difference (ΔT) of the FGR heat exchanger that means the increase in heat recovery from flue gas enhanced the electricity and exergy efficiencies. The annual cost including the FGR heat exchanger and FGC cooling water was minimized at ΔT = 10 ℃, where the electricity efficiency, total capital cost, total production cost, and return on investment were 39%, 1371 M$, 90 M$, and 7%/y, respectively.

• Applied Chemistry for Engineering
• /
• v.32 no.2
• /
• pp.149-156
• /
• 2021

A kraft recovery boiler produces steam for power generation by the combustion of black liquor from the kraft pulping process. Since saturated steam became superheated in a superheater above the furnace, it is important to increase the heat exchange efficiency for the superheated steam production and power generation. A nose arch at the bottom of the superheater is important for blocking radiation from the furnace which causes corrosion of the superheater. But the nose arch is the main reason for creating a recirculation region and then decreasing the heat exchange efficiency by holding cold flue gas after the heat transfer to saturated steam. In this study, the size of recirculation region and the temperature of flue gas at the outlet were analyzed by the nose arch structure using computational fluid dynamics (CFD). As a result, when the nose arch angle changed from 106.5° (case 1) to 150° (case4), the recirculation region of flue gas decreased and the heat exchange efficiency between the flue gas and the steam increased by 10.3%.

• Journal of Advanced Marine Engineering and Technology
• /
• v.34 no.4
• /
• pp.470-476
• /
• 2010

The thermodynamic performance of closed ocean thermal energy conversion (OTEC) cycle with 1 MW gross power was evaluated to obtain the basic data for the optimal design of OTEC. The basic thermodynamic model for OTEC is Rankine cycle and the thermal effluent from power plant was used for the heat source of evaporator. The cycle performance such as efficiency, heat exchanger capacity, etc. was analyzed on the temperature variation of thermal effluent. The saturated pressure of evaporator increased with respect to the increase of thermal effluent temperature, so the cycle efficiency increased and necessary capacity of evaporator and condenser decreased under 1 MW gross power. As the thermal effluent temperature increases about $15^{\circ}C$, the cycle efficiency increased approximately 44%. So, it was revealed that thermal effluent from power plant is important heat source for OTEC plant. Also, if there is an available waste heat, it can be transferred heat to the working fluid form the evaporator through heat exchanger and cycle efficiency will be increased.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.14 no.4
• /
• pp.155-159
• /
• 2004

Numerical analysis which is based on finite element techniques, implicit Euler method and frontal solving algorithm was performed to study the effects of the crucible shape on the temperature of sapphire crystal and the shape of the melt/crystal interface in heat exchanger method. The computer simulation described here and effective to solving the heat transport phenomena with the transition of the interface shape from hemispherical to planar. In the work, various crucibles with differently shaped corners at their bottom are considered to improve the deflection of the melt/crystal interface. The shape of the crucible should be considered as one of the variables for the process optimization.

• Investigative Magnetic Resonance Imaging
• /
• v.5 no.1
• /
• pp.33-37
• /
• 2001

Purpose : The water exchange rate between bulk water and bound water is an important parameter in deciding the efficiency of paramagnetic contrast agents. In this study, we evaluated the water exchange rates of various Gd-chelates using oxygen-17 NMR technique. Material and Methods : The samples (Gd-DTPA, Gd-DTPA-BMA, Gd-DOTA, Gd-EOB-DTPA) were prepared by mixing 5% $^{17}O-enriched$ water (Isotech, USA). The pH of the samples was adjusted to physiological value [pH=7.0] by buffer solution. The variable temperature $^{17}O-NMR$ measurements were performed using Bruker-600 (14.1 T, 81.3 MHz) spectrometer. Bruker VT-1000 temperature control units were used to stabilize the temperature. The $^{17}O$ spin-spin relaxation times (T2) were measured using Carr-Purcell-Meiboom-Gill (CPMG)I pulse sequence with 24 echo trains. The variable temperature T2 relaxation data were then fitted into Solomon-Bloembergen equations using least square fit algorithm to estimate the water exchange times. Results : From the measured $^{17}O-NMR$ relaxation rates, the determined water exchange rates at 300K are $0.42{\;}{\mu}s$ for Gd-DTPA, $1.99{\;}{\mu}s$ for Gd-DTPA-BMA, $0.27{\;}{\mu}s$ for Gd-DOTA, and $0.11{\;}{\mu}s$ for Gd-EOB-DTPA. The Gd-DTPA-BMA showed slowest exchange whereas Gd-EOB-DTPA had fastest water exchange rate. In addition, it was found that the water exchange rates (${\tau}_m$) of all samples had exponential temperature dependence with different decay constant. Conclusion : $^{17}O-NMR$ relaxation rate measurements, when combined with variable temperature technique, provide a solid tool for studying water exchange rate, which is very important in investigating the detailed mechanism of relaxation enhancement effect of the paramagnetic contrast agents.