• Transactions of the Korean hydrogen and new energy society
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• 제22권2호
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• pp.223-231
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• 2011

The thermal efficiency of energy-to-power conversion becomes uneconomically low when the temperature of heat source drops below $370^{\circ}C$. ORC (Organic Rankine Cycle) has attracted much attention in last few years due to its potential in reducing consumption of fossil fuels and relaxing environmental problems, and its favorable characteristics to exploit low-temperature heat sources. In this work thermodynamic performance of ORC using nine working fluids is comparatively assessed. Special attention is paid to the effect of system parameters such as turbine inlet temperature and pressure on the characteristics of the system such as volumetric flow rate and quality at turbine exit, latent heat, net work as well as thermal efficiency. Results show that in selection of working fluid it is required to consider various criteria of performance characteristics as well as the thermal efficiency. Results also show that the system efficiencies become same irrespective of kind of working fluid when the temperature of heat source decreases to low range.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• 제26권4호
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• pp.298-303
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• 2013

In this study, the W-interconnected dye-sensitized solar cell (DSSC) modules composed of a number of rectangular cells connected in series were investigated, where neighboring cells are processed in reverse. The DSSC modules, a module of dimension about 200 mm ${\times}$ 200 mm, were fabricated with different working electrode width ranging from 5 mm to 21 mm. The short-circuit current of the module increased as the working electrode width increased. Whereas, the decrease in the working electrode width resulted in the increase of the conversion energy efficiency, fill factor, and open-circuit voltage, which is explained by the fact that the possibility that electrons are recombined along their path on the transparent conductive oxide substrate decreases. The module with the conversion energy efficiency of 3.59% was obtained with the working electrode width of 5 mm.

• Journal of Biosystems Engineering
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• 제31권1호
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• pp.16-23
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• 2006

Depth and working load control is one of the most important technique in control system for tractor rotary implement automation. Keeping the depth consistent is critical to bring along crops and to improve the efficiency and quality of the following operations. Keeping the load of engine consistent is an essential factor for the efficiency of operation and engine protection of tractor. In this study we investigated the possibility of application of depth and working load control system for tractor using a proportional valve through field tests. Depth control was implemented by the ascent and descent of 3 point linkage for the change of setting depth. There were 4 mm and 5.2 mm control deviations for setting depths of 50mm and 100mm, respectively. Load control was operated appropriately by the ascent and of descent of 3 point link for the change of setting working load. The standard deviations between setting load and engine load were 171 rpm at 1.3 km/h and 164 rpm at 2.3 km/h tractor travel velocity. The results of experiment showed that the characteristics of response was sufficient to be used as the implement depth and working load control system for tractor using proportional valve.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.347-354
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• 2009

Plate Heat Exchnager(PHE) has recently become widely adopted for cogeneration systems owing to its small installation space and high thermal efficiency. The gap between plates can be changed depending on its assemble type, i.e. gasket or blazing. The gap is known to affect thermal efficiency and working pressure drop in PHE with complicated geometrical features. Numerical simulation techniques have been developed to deal with PHE with complex configuration of chevron plates. The present study is aiming at identifying the gap effect on pressure drop and thermal efficiency of the PHE. The numerical simulation results show that the gap has relatively large effects on working pressure drop than thermal efficiency in performance of PHE.

• Korean Journal of Rural Living Science
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• 제8권2호
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• pp.119-124
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• 1997

In this study we tried to give a decision on propriety of working conditions, to present ideas on reducing work loads, and to grope for efficiency of agricultural works. For this we examined the actual working conditions of cultivating welsh onion in the summer ground. And we improved harmful factors that affect farmer's health by considering results of previous study and farmer's subjective sensation. And we measured. compared, and analyzed the farmer's work loads before and after improvement. The results of this study are as follows ; 1. According to examine the actual working conditions of cultivating welsh onion in the summer ground, farmers have experienced physical and mental chronic fatigue on the basis of farmer's appel to eye - fatigue and sun - burned skin on hot working environment including excessive ultraviolet rays, the rough ground condition, inconsistent arrangement of working stand and sorter, heavy - weared habits, and unsuitable working posture. 2. When we improved harmful factors that affect farmer's health, conformed the effects on important work efficiency index such as heart rate, electromyovolume, body temperature, and microclimate inside clothing and work loads were decreased by eliminating the hillock and obstacles of ground, decreasing the clothing weight, using proper clothing appliances such as hat and sunglasses, controlling height of working stand and sorter suitably, improving the working postures and methods as using assistant appliances, alloting the working time and sequence effectively and presenting the light gymnastic exercises and rest for fatigue restoration.

• Korean Journal of Materials Research
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• 제21권2호
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• pp.120-124
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• 2011

Silicon heterojunction solar cells have been studied by many research groups. In this work, silicon heterojunction solar cells having a simple structure of Ag/ZnO:Al/n type a-Si:H/p type c-Si/Al were fabricated. Samples were fabricated to investigate the effect of transparent conductive oxide growth conditions on the interface between ZnO:Al layer and a-Si:H layer. One sample was deposited by ZnO:Al at low working pressure. The other sample was deposited by ZnO:Al at alternating high working pressure and low working pressure. Electrical properties and chemical properties were investigated by light I-V characteristics and AES method, respectively. The light I-V characteristics showed better efficiency on sample deposited by ZnO:Al by alternating high working pressure and low working pressure. Atomic concentrations and relative oxidation states of Si, O, and Zn were analyzed by AES method. For poor efficiency samples, Si was diffused into ZnO:Al layer and O was diffused at the interface of ZnO:Al and Si. Differentiated O KLL spectra, Zn LMM spectra, and Si KLL spectra were used for interface reaction and oxidation state. According to AES spectra, sample deposited by high working pressure was effective at reducing the interface reaction and the Si diffusion. Consequently, the efficiency was improved by suppressing the SiOx formation at the interface.

• Transactions of the Korean hydrogen and new energy society
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• 제21권6호
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• pp.570-579
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• 2010

Since the temperature of waste heat source is relatively low, it is difficult to maintain high level of efficiency in power generation when the waste heat recovery is employed in the system. In an effort to improve the thermal efficiency and power output, use of ammonia-water mixture as a working fluid in the power cycle becomes a viable option. In this work, the performance of ammonia-water mixture based Rankine cycle is thoroughly investigated in order to maximize the power generation from the low temperature waste heat. In analyzing the power cycle, several key system parameters such as mass fraction of ammonia in the mixture and turbine inlet pressure are studied to examine their effects on the system performance. The results of the cycle analysis find a substantial increase both in power output and thermal efficiency if the fraction of ammonia increases in the working fluid.

• Journal of the Korean Data and Information Science Society
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• 제24권3호
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• pp.651-658
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• 2013

For the marginal model and generalized estimating equations (GEE) method there is important full covariates conditional mean (FCCM) assumption which is pointed out by Pepe and Anderson (1994). With longitudinal data with time-varying stochastic covariates, this assumption may not necessarily hold. If this assumption is violated, the biased estimates of regression coefficients may result. But if a diagonal working correlation matrix is used, irrespective of whether the assumption is violated, the resulting estimates are (nearly) unbiased (Pan et al., 2000).The quadratic inference functions (QIF) method proposed by Qu et al. (2000) is the method based on generalized method of moment (GMM) using GEE. The QIF yields a substantial improvement in efficiency for the estimator of ${\beta}$ when the working correlation is misspecified, and equal efficiency to the GEE when the working correlation is correct (Qu et al., 2000).In this paper, we interest in whether the QIF can improve the results of the GEE method in the case of FCCM is violated. We show that the QIF with exchangeable and AR(1) working correlation matrix cannot be consistent and asymptotically normal in this case. Also it may not be efficient than GEE with independence working correlation. Our simulation studies verify the result.

• Analytical Science and Technology
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• 제27권6호
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• pp.308-313
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• 2014

The effect of electrochemical characteristics of dye-sensitized solar cells (DSSC) upon employing multi-wall carbon nanotube (MWCNT) on both working electrode and counter electrode were examined with using EIS, J-V curves and UV-Vis absorption spectrometry. When 0.1 wt% of MWCNT was employed in the $TiO_2$-MWCNT composit on working electrode, the energy conversion efficiency increased about 12.5% compared to the $TiO_2$ only working electrode. The higher light conversion efficiency may attribut to the high electrical conductivity of MWCNT in $TiO_2$-MWCNT composite which improves the electron transport in the working electrode. However, higher amount of MWCNT than 0.1 wt% in the $TiO_2$-MWCNT composite decreases the light conversion efficiency, which is mainly ascribed to the decreased transmittance of light by MWCNT and to the decreased adsorption of dye onto $TiO_2$. The MWCNT employed counter electrode exhibited much lower light conversion efficiency of DSSC than the Pt-counter electrode, while the MWCNT-Pt counter electrode showed similar in light conversion efficiency to that of Pt-counter electrode.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• 제56권3호
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• pp.223-229
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• 2020

We analyzed the cutting mechanism of laver harvesting machine in the sea area near Gooam Port in Goheung, Jeollanam-do, and investigated the change and efficiency of laver collecting operation in the working ship. The laver working ship slides uniformly from the bow to the upper part of the laver collecting machine on the deck and cuts the wet laver attached to the bottom of the net at the blade of the havesting machine. The laver farming net, which was loaded with laver turrets on the deck by gravity and collected primitives, consisted of a ship structure that led to the stern side and into the sea. The working ship operation is in harvesting process while driving in a S-shape that is separated by one space to efficiently collect the laver net. During laver working ship operation, the speed was 0.51 m/s in the access stage, 0.56 m/s in the havesting stage, and 0.52 m/s in the exit stage. Considering the cutting edge life and production efficiency of the laver harvesting machine, it is appropriate to harvest 1.15 to 1.26 kg/rpm by operating at a rotational speed of about 700 to 800 rpm rather than forcibly harvesting the product at high speed. On the deck of the working ship, 959.7 kg of starboard and 1048.7 kg of center were 964.7 kg of port side. Based on the starboard, 9.3% of the central part and 0.5% of the port side appeared. The reason for this was due to the difference in harvest time according to the turning direction of the working ship.