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Chung H.,Yonsei University | Sohn H.-S.,Yonsei University | Park J.S.,Korea National University of Transportation | Kim K.M.,Korea District Heating Corporation | Cho H.H.,Yonsei University
Energy | Year: 2017

Thermal stress is one of major causes of cracking in high-temperature components of gas turbines. This paper presents a thermo-structural analysis of cracks on the vane of a gas turbine for power generation. The vane components include three airfoils with hub and shroud sections. The airfoils have serpentine-type internal passages and film cooling holes on the pressure-side surfaces for cooling. The conjugate heat transfer problem was solved to accurately evaluate heat transfer on the vane using computational fluid dynamics software, CFX. Based on the conjugate heat transfer result, thermal expansion and thermal stress were evaluated using structural analysis software, ANSYS. The results showed that an irregular temperature distribution induced anisotropic thermal expansion in the vane segments, including the shroud and hub sections, and that the anisotropic thermal expansion caused serious stress concentrations. Among the three airfoils, the middle one was the most stressed because the thermal expansion was constrained by deformed hub and shroud sections. The predicted locations of stress concentration coincided with the locations of cracks on the actual vane after an operating period. The prediction provides general information on the initiation of cracks on a vane segment having multiple airfoils. © 2016 Elsevier Ltd

Lee K.,Korea Institute of Energy Research | Lee S.Y.,Korea Institute of Energy Research | Lee S.Y.,Chungnam National University | Na J.-G.,Korea Institute of Energy Research | And 5 more authors.
Bioresource Technology | Year: 2013

The consumption of energy and resources such as water in the cultivation and harvesting steps should be minimized to reduce the overall cost of biodiesel production from microalgae. Here we present a biocompatible and rapid magnetophoretic harvesting process of oleaginous microalgae by using chitosan-Fe3O4 nanoparticle composites. Over 99% of microalgae was harvested by using the composites and the external magnetic field without changing the pH of culture medium so that it may be reused for microalgal culture without adverse effect on the cell growth. Depending on the working volume (20-500mL) and the strength of surface magnetic-field (3400-9200G), the process of harvesting microalgae took only 2-5min. The method presented here not only utilizes permanent magnets without additional energy for fast harvesting but also recycles the medium effectively for further cultivation of microalgae, looking ahead to a large scale economic microalgae-based biorefinement. © 2013 Elsevier Ltd.

Park S.-H.,Agency for Defense Development | Han H.-S.,Korea District Heating Corporation | Lee S.,Sejong University | Lee I.,Korea University
IEEE Transactions on Wireless Communications | Year: 2011

In this letter, we propose an efficient algorithm which reduces the complexity of conventional vector perturbation schemes by searching the real and imaginary components of a perturbation vector individually. To minimize a performance loss induced from the decoupled joint search, we apply diagonal precoding at the transmitter whose parameters are iteratively optimized to maximize the chordal distance between subspaces spanned by the real and imaginary components. We also propose a simple non-iterative method with a slight performance loss which can achieve a significant complexity reduction compared to the conventional vector perturbation schemes. © 2011 IEEE.

Hong M.-E.,Sungkyunkwan University | Hwang S.K.,Mirae Fine Chemical Co. | Chang W.S.,Korea District Heating Corporation | Kim B.W.,Sungkyunkwan University | And 2 more authors.
Applied Microbiology and Biotechnology | Year: 2015

High temperatures (30–36 °C) inhibited astaxanthin accumulation in Haematococcus pluvialis under photoautotrophic conditions. The depression of carotenogenesis was primarily attributed to excess intracellular less reactive oxygen species (LROS; O2− and H2O2) levels generated under high temperature conditions. Here, we show that the heat stress-driven inefficient astaxanthin production was improved by accelerating the iron-catalyzed Haber–Weiss reaction to convert LROS into more reactive oxygen species (MROS; O2 and OH·), thereby facilitating lipid peroxidation. As a result, during 18 days of photoautotrophic induction, the astaxanthin concentration of cells cultured in high temperatures in the presence of iron (450 μM) was dramatically increased by 75 % (30 °C) and 133 % (36 °C) compared to that of cells exposed to heat stress alone. The heat stress-driven Haber–Weiss reaction will be useful for economically producing astaxanthin by reducing energy cost and enhancing photoautotrophic astaxanthin production, particularly outdoors utilizing natural solar radiation including heat and light for photo-induction of H. pluvialis. © 2015, Springer-Verlag Berlin Heidelberg.

Jung K.,Korea District Heating Corporation | Jang T.,Chonbuk National University | Jeong H.,Seoul National University | Park S.,Seoul National University
Agricultural Water Management | Year: 2014

The objective of this study is to assess the growth and yield components of rice irrigated with reclaimed domestic wastewater. The experimental plots consisted of four blocks of each of the three irrigation water treatments: groundwater, untreated wastewater, and reclaimed wastewater. Randomized complete block design was applied to the experimental plots (5. m. ×. 5. m). Soil and water quality were monitored during a five cropping period. Crop height and tiller number data were analyzed from 2005 to 2009 according to growth stage. Analysis of variance (ANOVA) and honestly significant difference (HSD) post-hoc tests were applied to compare the rice components and yields from the treatments with the control plot. The wastewater and reclaimed wastewater irrigation plots were significantly higher than groundwater in clum length, panicle number, and rice yield. The total nutrients supplied with irrigation water were highly correlated with rice yield data, suggesting that the higher rice yield from reclaimed wastewater resulted from nutrient supply. The heavy metal contents in the milled rice that was cultivated with the reclaimed wastewater did not show significant differences from rice irrigated with groundwater. Reclaimed wastewater irrigation plots were significantly higher than groundwater irrigation plots in the contents of protein and milled head rice ratio, which had levels similar to or in the middle of conventional rice and brand rice. This study shows that reclaimed wastewater irrigation did not have adverse environmental impacts on the agricultural ecosystem, although long-term monitoring is needed to fully understand its relationships. © 2014 Elsevier B.V.

Hong C.H.,Inha University | Zhang K.,Inha University | Choi H.J.,Inha University | Yoon S.M.,Korea District Heating Corporation
Journal of Industrial and Engineering Chemistry | Year: 2010

Polysaccharide guar gum (GG), one of the most widely used biopolymers for food applications is examined as a turbulent drag reducer, of which it reduces friction drag tremendously under a turbulent flow even though only tiny amount of guar gum is dissolved in aqueous system. Mechanical degradation of the GG is specifically being investigated in this study under a turbulent flow, in which three different molecular weights of GG were prepared using ultrasonication. Drag reduction effectiveness of the GG was measured using a rotating disk apparatus as a function of time. In order to correlate time-dependent drag reduction and mechanical degradation of GG, two different degradation models of a single-relaxation process and a stretched-exponential model were examined, and the stretched-exponential model was found to fit the experimental data better. © 2010 The Korean Society of Industrial and Engineering Chemistry.

Lee J.C.,Seoul National University of Science and Technology | Kim J.H.,Seoul National University of Science and Technology | Chang W.S.,Korea District Heating Corporation | Pak D.,Seoul National University of Science and Technology
Journal of Chemical Technology and Biotechnology | Year: 2012

BACKGROUND: Biological conversion of CO 2 to useful carbonic compounds such as methane is a potentially attractive technology for reducing its concentration in the atmosphere. One of the advantages of this technology over chemical conversion is that it requires much lower energy for reduction of CO 2. In this article, biological conversion of CO 2 to CH 4 using hydrogenotrophic methanogens was examined in a fixed bed reactor inoculated with anaerobic mixed culture from the anaerobic digestor of a sewage treatment plant. RESULTS: Methane formation commenced on the first day of operation of the fixed bed reactor. CO 2 fed to the reactor was reduced with H 2 by hydrogenotrophic methanogens. The feed ratio of CO 2 to H 2 is an important factor in determining the conversion rate of CO 2. When the feed ratio is 4, methane is produced at the expected rate according to the chemical equation. The CO 2 conversion rate was 100% when the gas retention time was 3.8 h in the fixed bed reactor. CONCLUSIONS: The results show that the fixed bed reactor employing hydrogentrophic methanogens has the potential to be effective in converting CO 2 to CH 4 with a conversion rate of 100% at 3.8 h retention time. © 2012 Society of Chemical Industry.

Korea District Heating Corporation | Date: 2016-11-16

The present invention relates to an extracting device supplying fixed quantity of exhaust gas for industrial facility, and more particularly, to an extracting device supplying fixed quantity of exhaust gas for industrial facility which supplies a certain amount of exhaust gas by installing a gas supply pipe, in which two blowers are arranged in a line, at a stack and operating each blower in accordance with a predetermined input value.

Korea District Heating Corporation | Date: 2012-10-03

The present invention relates to shape tube for district heating heat pipe having shear control ring and the method thereof, comprising: an internal pipe, bent with constant curvature, connecting the district heating heat pipe and both ends and flowing medium-temperature hot water inside the internal pipe; an external pipe forming a space and inserting the internal pipe inside, having large diameter than that of the internal pipe; a heat insulator foamed in the space between the internal pipe and the external pipe; and a shear control ring combined to the curves of the internal pipe. According to the present invention as above, the present invention enables to prevent transform in heat pipes in advance by installing shear control rings in the curves of internal pipe of heat pipes bent with constant curvature and dispersing shear stress, delivered to the heat insulator.

KOREA DISTRICT HEATING Corporation | Date: 2014-07-16

The present invention relates to an extracting device supplying fixed quantity of exhaust gas for industrial facility, and more particularly, to an extracting device supplying fixed quantity of exhaust gas for industrial facility which supplies a certain amount of exhaust gas by installing a gas supply pipe, in which two blowers are arranged in a line, at a stack and operating each blower in accordance with a predetermined input value.

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