• 한국농공학회지
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• 제43권2호
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• pp.105-111
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• 2001

This study is performed to develop an agricultural hydraulic structure for collecting and draining pipe using polymer concrete. The water permeability of collecting and draining pipe shows an 5.917$\ell$/$\textrm{cm}^2$/h, it is more 190 times as large as in the world maximum rainfall. The external pressure on the collecting and draining pipe is in the range of 1.85~5.25tf/m under 2-edge test, 2.6~6.2tf/m under sand mat and the vertical displacement is in the range of 0.48~1.06mm, 1.01~1.89mm, respectively. Also, an increasing rate of external pressure on the developed pipe is higher than that of PVC pipe to the variation of t/D. Accordingly, the pipe developed in this study will be used widely in agricultural hydraulic structures such as collecting and draining structure.

• 한국작물학회지
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• 제44권3호
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• pp.225-229
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• 1999

Unstable seedling stand establishment of wet direct seeding culture of rice is one of the major elements preventing the extension of its culture area. In order to develop methods of seedling stand improvement in direct seeded rice on flooded surfaces, three field experiments were conducted on silty loam soil using a cultivar 'Donjinbyeo' for three years, mainly focusing on water management after seeding and seed soaking with plant growth regulators (PGRs). Under the condition of shallow flooding after seeding, seedling stand rate increased and floating seedling rate decreased in both early and normal season seeding compared to deep flooding. With earlier draining time after seeding, there was a tendency towards preferential growth of the seminal root, increase of seedling stand and decrease of the floating seedling rate. Therefore the highest seedling numbers per unit area and the lowest floating seedling numbers were found upon drainage at 1 day after seeding (DAS), while a contrary tendency was shown upon conventional drainage at 7 DAS. Seed soaking with PGRs such as Metalaxyl or mixing of Metalaxyl with gibberellic acid (GA$_3$) significantly increased the seedling stand. In addition the effects of PGR treatment on seedling stand and the early growth of plants were greater under flooded conditions than under drained conditions after seeding, although draining of water after seeding improved the seedling establishment rate more when compared with the PGR treatment. These results suggest that draining management after seeding or maintaining of shallow flooding for a week is the most effective method to improve the seedling stand rate in wet direct seeding.

• International Journal of Air-Conditioning and Refrigeration
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• 제9권1호
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• pp.29-38
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• 2001

In this paper, the defrosting characteristics of a PTC heating sheet is investigated by means of a defrosting heat source for the fin-tube heat exchanger in a refrigerator The defrosting characteristics of the PTC heating sheet are examined and compared with those of a conventional electric heater experimentally. It is found that the characteristics of the water draining rate with the defrosting time show a smoothly oscillating pattern when the PTC heating sheet Is used, and the drained water is completely melted. The defrosting efficiency of the PTC heating sheet is found to be about 75%, which is about 25% higher than that of the electric heater. Also, the reduction of the defrosting time and the increment of the defrosting efficiency may be obtained by improving the arrangement of the heating elements of the healing sheet. It is shown that the defrosting time of the PTC heating sheet increases linearly with the amount of frost, whereas the defrosting efficiency is nearly constant. When applying the PTC heating sheet to the refrigerating system, one should notice the fact that the defrosting performance of the PTC heating sheet may be degraded due to the repetitive operations.

• 설비공학논문집
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• 제11권1호
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• pp.147-155
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• 1999

In this work, the defrosting characteristics of PTC heating sheet used as a defrosting heat source of fin-tube heat exchanger in a refrigerator have been experimentally compared with those of conventional electric heater. It is found that the characteristics of water draining rate with defrosting time show smoothly oscillating pattern when PTC heating sheet is used, and the drained water is completely melted. The defrosting efficiency of the PTC heating sheet is about 75%, which represents about 25% higher than that of the electric heater. A reduction of defrosting time and an increase of defrosting efficiency may be obtained by improving the arrangement of heating elements of the heating sheet. It is shown that the defrosting time of PTC heating sheet increases linearly with the amount of frost, however the defrosting efficiency is nearly constant. In the application to the refrigerating system, one should notice the fact that the defrosting performance of PTC heating sheet may be defraded due to the repeated operations.

• International Journal of Air-Conditioning and Refrigeration
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• 제7권
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• pp.101-111
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• 1999

The effect of various conditions of frosting and defrosting on the defrosting behavior of a fin-tube heat exchanger has been examined experimentally. An electric heater is used for defrosting in a fin-tube heat exchanger. There are several local maxima in the water draining rate. The amount of residual water on the heat exchanger after completion of defrosting is kept constant due to surface tension on the heat exchanger. Without considering degradation of the thermal performance due to the frosting, the defrosting efficiency is improved with increasing amount of frost irrespective of the frosting condition. The defrosting behavior is affected by frosting density as well as frost accumulation, both of which vary with the experimental operating conditions. The heat loss to the surrounding air decreases, and melting and defrosting efficiencies show high values with decreasing heat input.

• 유기물자원화
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• 제9권1호
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• pp.79-89
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• 2001

본 연구에서는 유기성 폐기물의 분해시 발생되는 열을 재활용하고, 혐기성 소화액의 퇴비화를 위한 혐기성 소화 - 고온 호기법(Anaerobic Digestion-Thermophilic oxic process, ADTOP)을 고안하고, 유기물 분해와 수분의 증발 그리고 생성열의 적용성을 검토하였다. 유기성 폐기물인 중화요리 잔반은 TOP에 의해 완전처리가 가능하며, 최대 용적부하는 $55kg/m^3{\cdot}d$, 투입된 수분은 거의 완전히 증발되었으며 탄소수지에 의한 탄소성 유기물의 이산화탄소 전환율은 90.5%이었다. 고온 혐기성 소화를 위한 적정온도(약$55^{\circ}C$)를 유지하기 위한 최소용적부하는 $45.0kg/m^3{\cdot}d$이었다. 혐기성 소화조의 온도는 수리학적 체류시간이 짧아짐에 따라 지수적 온도강하를 나타내었으며 고온 혐기성소화를 위한 최소 HRT는 약 10일 정도로 판단된다. 따라서 고온 호기법을 이용한 유기성폐기물의 처리시 발생되는 열에너지는 혐기성 소화와 같은 체류시간이 비교적 긴 공정에서 효과적일 것으로 판단된다. 혐기조의 유기물 부하 $1.1kg-COD/m^3{\cdot}d$, 고온 호기조 유기물의 투입량 $50kg/m^3$, 공기 유입량 $250{\ell}/m^3{\cdot}min$의 조건에서 혐기성 소화효율은 90% 이상으로 나타났다.

• 한국작물학회지
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• 제44권3호
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• pp.282-287
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• 1999

The object of this study was to determine the difference of the time course changes of transpiration, diffusion resistance and photosynthetic rate of rice at several different growth stages subjected to soil moisture stress (SMS) and recovery by irrigation. A japonica rice cultivar 'Dongjinbyeo', was grown under flooded condition in a plastic container filled with silty loam soil. At 5 main growth stages, the container was treated by SMS until initial wilting point (IWP) and then reirrigated. The duration of SMS until IWP were the longest, 13 days for tillering stage, and the shortest, 7 days for panicle initiation and meiosis stage. The transpiration rate rapidly decreased during SMS and the transpiration rate at IWP of the stressed plant showed 10∼20% compared with control, and the transpiration rate of stressed plant at most growth stages also recovered rapidly after irrigation and then reached 100% of control within a week. The shoot photosynthetic rate in all growth stages rapidly decreased by SMS, and the rates at IWP of stressed plants were de-creased nearly to 0%, beside the treatment at tillering stage. The recovery degree of photosynthetic rate by irrigation ranged from 20 to 90%, showed higher at early growth stages of SMS treatment than that of later stages. At all growth stages the leaf diffusion resistance of stressed plants was over 3 times that of the control resulting from a rapid increase at 3 to 5 days after draining for SMS, and showed quick recovery by irrigation within 3 days after drainage. The above physiological parameters changed in close relation with the decrease of the soil matric potential after SMS. These results indicate that at all main growth stages of rice plants the transpiration and photosynthesis reduction by stomatal closure reponded sensitively to the first stage of SMS closely related with decrease of soil water potential, while those recovery pattern and recovered degree by irrigation are little different by growth stage of rice.

• 설비공학논문집
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• 제11권6호
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• pp.921-927
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• 1999

In this study, the defrosting behaviors according to the surface characteristics in the fin-tube heat exchanger is experimentally examined. It is found that the draining rate of the hydrophilic and hydrophobic heat exchangers are evenly dispersed during defrosting, compared with that of the bare one. It is caused by the high density frost for the hydrophilic heat exchanger, and surface characteristic for the hydrophobic heat exchanger, respectively. The rest period of the hydrophilic and hydrophobic heat exchangers are shorter and their weight of residual water are smaller than those of the bare heat exchanger The hydrophilic and hydrophobic heat exchangers are more effective than the bare one in terms of defrosting efficiency, and the hydrophobic heat exchanger is better than the hydrophilic one.

• 한국수산과학회지
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• 제10권4호
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• pp.267-273
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• 1977

1977년 4월 25일부터 1977년 11월 10일까지 199일 간실내에서 소형의 순환여과사육장치와 소량의 지하수를 이용하여 하계기온이 높은 부산지방에서 무지개송어의 사육실험을 한 바, 다음과 같이 희망적인 결과를 얻었다. 1. 실험수조 2 (Fig.2)의 크기는 가로, 세로 각각 1m, 높이 67cm의 Stainless 수조로 가운데 직경 20cm, 깊이 20cm 역 원추형의 침전부가 있고 고 끝은 직경 4cm의 파이프에 연결되어 주수되는 물이 수조밖의 Stand pipe를 통하여 밖으로 넘쳐서 배출된다. 수심은 40 cm 정도로 유지되었으며 여과조는 가로 세로 각각 23cm, 깊이 40cm의 플라스틱 통에 깊이 30cm로 직경 약 $3\~5mm$는 zeolite석을 넣어 사용하였고 순환 펌프는 1시간에 약 1030 l 용량으로 순환율은 시간당 약 2.6회였다. 2. 수조에 주수되는 소량의 물이 밖으로 나가면서 찌꺼기를 밖으로 내보내게 되는 장치는 사육수의 수질유지에 크게 도움이 되었다. 3. $17^{\circ}C$ 전후의 지하수를 약 400 l의 사육수에 1분간 0.59 l의 비율로 1일 평균 16시간 주수하였더니 7월하순 평균기온이 $27.36^{\circ}C$ 일 때 사육수의 평균 수온이 $20^{\circ}C\~22^{\circ}C$ 전후로 유지되었으나 무지개송어는 정상적인 성장을 하였다. 4. 간단한 여과장치를 하고 1분간 1 l의 물이 주수된다고 할 때 생산량은 30kg 의 계산이 나온다. 5. 남부지방에서 하계수온 $17^{\circ}C$ 전후의 적당한 지하수와 소형의 여과장치 그리고 개량된 사육수조를 이용하여 무지재송어의 양식이 가능하며 경제적으로도 충분히 성립되고 사료와 여과장치를 개선하면 생산단가는 크게 낮출 수 있고 생각된다.

• 설비공학논문집
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• 제10권6호
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• pp.649-657
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• 1998

In this study, the effects of the various conditions of frosting and defrosting on the behavior of defrosting in a fin-tube heat exchanger have been examined experimentally. The electric heater is used for defrosting in a fin-tube heat exchanger It is shown that there are several local maxima in the water draining rate. The amount of residual water on the heat exchanger after the completion of defrosting is kept constant due to surface tension on the heat exchanger. Without considering the degradation of the thermal performance due to the frosting, the defrosting efficiency is improved with increasing amount of the frost irrespective of the frosting condition. The defrosting behavior is affected by the frosting density as well as the frost accumulation, which vary with the experimental operating conditions during the frosting period. The heat loss to the surrounding air decreases, and the melting and defrosting efficiencies show high values with decreasing heat input.