• 설비공학논문집
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• 제19권9호
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• pp.630-639
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• 2007

A $CO_2$ cycle shows large throttling loss during the expansion process. The application of an expander into the $CO_2$ cycle can reduce the throttling loss and then improve system performance. In this study, the performance of a transcritical $CO_2$ cycle with an expander was analytically investigated in order to improve the cooling performance of the system. The expander was applied to the single-stage and two-stage compression cycles. The performance was analyzed with the variations of compressor frequency, outdoor temperature, and expander efficiency. The single-stage and two-stage compression cycles with the expander showed COP improvement of 25% and 32%, respectively, over the single-stage cycle with an EEV.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1678-1683
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• 2003

DBD(Dielectric Barrier Discharge) plasma in air is well established for the production of large quantities of ozone and is more recently being applied to aftertreatment processes for HAPs(Hazardous Air Pollutants). Although DBD high electron density and energy, its potential use as nano and sub-micron sized particle charging are not well known. Aim of this work is to determine design and operating parameters of a two-stage ESP with DBD. DBD and ESP are used as particle charger and precipitator, respectively. We measured particle precipitation efficiency of two-stage ESP and estimated ozone decomposition of both pelletized $MnO_2$ catalyst and pelletized activated carbon. To examine the particle precipitation efficiency, nano and sub-micron sized particles were generated by a tube furnace and an atomizer. AC voltage of $7{\sim}10$ kV(rms) and 60 Hz is used as DBD plasma source. DC -8 kV is applied to the ESP for particle precipitation. The overall particle collection efficiency for the two-stage ESP with DBD is over 85 % under 0.64 m/s face velocity. Ozone decomposition efficiency with pelletized $MnO_2$ catalyst or pelletized activated carbon packed bed is over 90 % when the face velocity is under 0.4 m/s in dry air.

• 한국입자에어로졸학회지
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• 제16권4호
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• pp.119-130
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• 2020

In this study, we developed a separated two-stage electrostatic precipitator applicable in a subway air conditioning system. We studied the characteristics of collection efficiency of 0.3 ㎛ particle and ozone generation at different charger sizes and gaps of collector plates. Also, we compared the performance of the two-stage ESP to the MERV 10 filter with the removal efficiency of 10% used in actual subway air conditioning system. The maximum collection efficiency of 0.3 ㎛ particle was 93% at A charger (600 mm×250 mm×600 mm) and 84% at B charger (330 mm×280 mm×330 mm). Especially, with voltages applied to chargers with collection efficiency of about 80% or more, the ozone concentration of two different chargers was 5 ppb to 35 ppb. Finally, the filter quality of the collector developed in this study was 400 times higher than that of the MERV 10 filter. Therefore, it was concluded that the two-stage ESP could be a promising PM removal device suitable for subway air conditioning system.

• 한국작물학회지
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• 제43권1호
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• pp.49-53
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• 1998

Direct-seeding has major advantages such as labor and cost saving by eliminating preparation of seed bed and transplanting. But, it required increased input of fertilizers and pesticides because of the extended paddy period. Direct seeding in wet paddy (DSWP) gives faster growth and more uniform seedling emergence than direct-seeding in dry paddy. This research had an objective to develop an efficient N management practices for DSWP with split application of N fertilizer. A paddy field experiment was conducted to evaluate effects of starter N and N-topdressing which was delayed N application until 5-leaf stage, with comparison to transplanting (TP). Total amount of N application were two levels; 110kg and 77kg/ha. The N applications were split four times during rice growth stages; starter, topdressing at 5-leaf stage, top dressing at tillering stage, and topdressing at panicle initiation stage. DSWP had more tillers/$m^2$ than TP, but with the delayed heading. The DSWP plots which received N-topdressing at 5-leaf stage without starter N had higher leaf area index (LAI) and leaf greenness than the TP plot. Also, these DSWP plots had high leaf-N concentration at the heading stage, as calculated from leaf chlorophyll meter readings. Rice yield in DSWP with N-topdressing at 5-leaf stage was significantly higher than that in TP and in DSWP with starter N. Energy and N use efficiency were improved in DSWP with N-topdressing at 5-leaf stage. But, there were no significant differences in grain yield between the two levels of total amounts of N applications, 77kg and 110kg/ha. We concluded that starter N could not be used effectively by rice seedlings, but topdressing N at 5-leaf stage was an efficient N management for rice growth and yield in DSWP system.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2001년도 유체기계 연구개발 발표회 논문집
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• pp.309-314
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• 2001

The high efficient steam turbine stage has been analyzed with the help of the 3-dimensional analysis tool. To increase the efficiency of steam turbine stage, the nozzle has to be designed by using the 3-dimensional stacking method. And the bucket has to be designed to cope with the exit flow of nozzle. To verify the stage design, therefore, the numerical analysis of the steam turbine stage was conducted. In this design, CFX-TASCflow was employed to predict the steam flow of the steam turbine stage. The numerical analysis was performed in parallel calculation by using the HP N4000 8 CPUs machine. The result showed the numerical analysis could be used to help to design the steam turbine stage.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2001년도 유체기계 연구개발 발표회 논문집
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• pp.143-148
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• 2001

In this study, to investigate the effect of the generalized performance curve on the performance prediction and to find the optimal ones, a systematic study is performed. For this purpose, we compared the influence of the stage performance curves with experimental data in multi-stage axial compressors. As a result, it is discovered that the optimal generalized performance curves vary according to the number of the stages in compressors. And we found that for a low-stage compressors, Muir's pressure coefficient curve gives the best prediction results at design rotational frequency regardless of the efficiency curve. On the other hand, for high-stage compressors, Stone's pressure coefficient curve gives the optimistic results about the performance prediction at design rotational frequency.

• 설비공학논문집
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• 제11권3호
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• pp.422-430
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• 1999

This paper concerns the study of a two-stage absorption heat pump cycle to utilize treated sewage. This two-stage cycle consists of coupling double-effect with parallel or series flow type and single effect cycle so that the first stage absorber and condenser produces hot water to evaporate refrigerant in the evaporator of the second stage. The effects of operating variables such as absorber temperature on the coefficient of performance have been studied for two-stage absorption heat pump cycle. The working fluid is lithium bromide and water solution. The efficiency of the two-stage absorption heat pump cycle has been studied and simulation results show that higher coefficient of performance could be obtained for the first stage with parallel flow type. The optimum ratio of solution distribution can be shown by considering the COP, the crystallization of solution and the generator temperature.

• 한국토양비료학회지
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• 제32권2호
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• pp.140-146
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• 1999

본 연구(硏究)는 2년간('97~'98) 이상고온(異常高溫)해에 벼 어린모 기계이앙비재배시(機繼移秧秘栽培時) 완효성비료(緩效性肥料)(LCU)의 시용(施用)에 따른 시비질소(施肥室素)의 토양중(土壤中) $NH_4-N$ 발현량(發現量), 질소흡수량(室素吸收量) 및 이용율(利用率), 수량성(收量性) 변이(變異)를 조사하기 위하여 호남평야지(湖南平野地) 논토양의 대표토양(代表土壤)인 전북통(全北統)에서 시험한 결과로 다음과 같이 요약할 수 있다. 시비질소(施肥窒素)의 용출(溶出)은 완효성비료(緩效性肥料)의 기비전량(基肥全量) 전층시비시(全層施肥時) 이앙후(移秧後) 50일인 최고분벽기(最高分蘗期)에 거의 완료(完了)되었으며 최고발현기(最高發現期)는 무효분벽기(無效分蘗期)였다. 또 관행(慣行)의 표층시비(表層施肥)에서는 전기간 $NH_4-N$함량(含量)이 낮았다. 완효성비료(緩效性肥料) 시용구(施用區)의 출수기(出穗期) 비절현상(肥切現象)은 SPAD 31.6에서 나타났으며 경엽(莖葉)중 질소농도(窒素濃度)는 1.29%였다. 시비질소(施肥室素) 필요량(必要量)은 출수기(出穗期)~성숙기(成熟期)까지 관행(慣行)은 $2.9kg\;ha^{-1}$였으나 완효성비료(緩效性肥料)의 기비전량(基肥全量) 전층시비구(全層施肥區)에서는 $11.9kg\;ha^{-1}$로 많았다. 질소이용율(窒素利用率)은 관행(慣行)에 비하여 완효성비료(緩效性肥料) 시용구(施用區)에서 높았고 수비(穗肥)를 시용(施用)하므로서 12.7%가 더 증가(增加)되었다. 쌀수량(收量)은 완효성비료(緩效性肥料)를 기비(基肥)로만 시용(施用)한 것에 비하여 수비(穗肥)를 시용(施用)하므로서 13%의 증수(增收)를 보였다.

• 한국토양비료학회지
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• 제35권5호
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• pp.272-279
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• 2002

환경보전형 시비기술 개발을 목적으로 화학비료의 사용을 절감하는 한편 화학비표를 유기질비료로 대체 사용하는 방법을 구명코자 호남평야지 대표 토양인 전북통에서 2년간('99~'00) 동안벼를 공시하여 어린모 기계이앙으로 재배하였고 시비방법으로 관행(표준시비), 완효성비료(LCU) 40%를 전량기비 후 수비로 출수 30일전에 채종유박시용량을 10, 30, 50%시용구와 질소무시용구 등 5처리 하여 수행한 시험결과는 다음과 같다. 공시된 채종유박의 질소 무기화율은 72.4%였으며 전질소함량은 5.3%였다. 시험후 토양의 화학성은 관행에 비하여 유박시용구에서 pH, 유기물함량 등이 증가되었으나 칼리와 고토함량은 일정한 경향이 없었다. 시비질소의 토양중 $NH_4-N$ 발현량은 이앙 후 18일까지는 LCU시용구 보다 관행구에서 높았으나 최고분얼기 이후부터 상반되었고 출수기에는 수비유박 대체량이 많을수록 높아 졌다. 수량은 관행에 비하여 완효성비료 (LCU)40% 기비 시용후 유박시용량이 증가할수록 증수하였는데 유박을 수비로 30%시용시 2%, 50%시용시 4% 증수되었으며, 증수요인은 $m^2$당 립수의 증가에 있었다. 한편 시비질소 흡수량은 관행에 비하여 수비유박의 시용량이 증가 할수록 많았으나 질소이용율은 수비로 유박을 50%시용한 처리보다 30%시용한 처리에서 높게 나타났다. 따라서 관행의 수비요소를 유박으로 30%까지 대체할 경우 비료 절감측면이나 질소 이용효율 면에서 유리할 것으로 판단되었다.

• 한국작물학회지
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• 제50권1호
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• pp.16-21
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• 2005

This study was conducted to establish the elaborate nitrogen fertilization method to enhance N use efficiency in direct-seeded rice on flooded paddy. The nitrogen uptake by rice plants was insignificant until 25 days after seeding, and increased gradually thereafter. During this early growth stage, rice plants absorbed only the $4\%$ of basal applied N, while the $45\%$ of N fertilizer remained in the paddy soil. The absorption of basal N by rice plants was almost completed at 46 days after application. Nitrogen top-dressed at 5-leaf stage was well matched to crop nutrient demand, so it could be absorbed so actively in 8days after application. As a result, we could cut down the amount of N fertilizer to $36\%$ of the basal N level without significant difference in yield. Plant recoveries of fertilizer $^{15}N$ applied with different application timings were $7.8\%$ for basal, $9.4\%$ for 5-leaf stage, $17.1\%$ for tillering stage, and $23.4\%$ for panicle initiation stage, respectively. When urea was applied with nitrogen fertilization practice based on basal incorporation (BN), plant recovery of $^{15}N$ at harvest was $31.0\%$, which was originated from $13.7\%$ for grain, and $21.3\%$ of the fertilizer $^{15}N$ remained in the soil, and the rest could be uncounted. Plant recovery of fertilizer $^{15}N$ applied with nitrogen fertilization practice based on topdressing at 5-leaf stage (TN), where N rate was reduced by $18\%$ compared with BN, was $35.1\%$ (grain $15.6\%$), and $19.9\%$ of the fertilizer $^{15}N$ remained in the soil, and the rest could be uncounted. TN showed a higher $^{15}N$ recovery than BN because it was to apply N fertilizer at a time to well meet the demand of rice plant direct-seeded on flooded paddy. We concluded that TN would be the nitrogen fertilization method to enhance N use efficiency in direct-seeded rice on flooded paddy.