• 설비공학논문집
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• 제18권12호
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• pp.971-976
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• 2006

The objectives of this paper are to study the characteristics of pool boiling heat transfer for enhanced tubes used in the evaporator of turbo chiller and to provide a guideline for optimum design of an evaporator using HFC134a. Three different enhanced tubes are tested at 4 different saturation temperatures. The wall super heated temperature difference ranges from $0.5^{\circ}C\;to\;3.5^{\circ}C$. The refrigerant, HFC134a evaporates on the outside of the tube while the chilled water flows inside the tube. This study provides experimental heat transfer coefficients for evaporation on the enhanced tubes. It is found that the turbo-II tube provides the highest heat transfer coefficient.

• 한국태양에너지학회 논문집
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• 제21권1호
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• pp.61-69
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• 2001

The heat transfer characteristics of horizontal and vertical mantle heat storage tanks are studied in order to replace the tank-coil heat exchanger for application in thermosyphon solar water heaters. In this study, 5 mantle storage tanks with different geometric shape are manufactured into stainless steel and each tank is tested. For the test, The inlet flow rate of the heat transfer fluid is maintained 1.2 lpm consistently. The heat transfer fluid temperature through the mantle is $70{\pm}1^{\circ}C$. The temperatures of 26 points included the ambient temperature are measured at every one minute. The measured data are used to calculate the overall heat transfer coefficient(UA) using the LMTD(Log Mean Temperature Difference) method and it is used on the analysis of the heat transfer characteristics to search for optimum arrangement.

• 대한기계학회논문집A
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• 제28권5호
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• pp.632-639
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• 2004

In this paper, an inverse problem of glass forming process is studied to determine a number of unknown heat transfer coefficients which are imposed as boundary conditions. An analysis program for transient heat conduction of axi-symmetric dimension is developed to simulate the forming and cooling process. The analysis is repeated until it attains periodic state, which requires at least 30 cycles of iteration. Measurements are made for the temperatures at several available time and positions of glass and moulds in operation. Heat removal by the cooling water from the plunger is also recorded. An optimization problem is formulated to determine heat transfer coefficients which minimize the difference between the measured data and analysis results. Significant time savings are achieved in finite difference based sensitivity computation during the optimization by employing distributed computing technique. The analysis results by the optimum heat transfer coefficients are found to agree well with the measured data.

• 한국표면공학회지
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• 제55권4호
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• pp.215-221
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• 2022

In the present work, copper oxide thin films were formed by heat-treatment method with different temperatures and atmosphere, e.g., at 200 ~ 400 ℃; in air and Ar atmosphere. The morphological, electrical and optical properties of the thermally fabricated Cu oxide films were analyzed by SEM, XRD, and UV-VIS spectrometer. Thereafter, photoelectrochemical properties of the thermal copper oxide films were analyzed under solar light (AM 1.5, 100 mW/cm²). Conclusively, the highest photocurrent was obtained with Cu₂O formed under the optimum annealing condition at 300 ℃ in air atmosphere. In addition, EIS results of Cu oxide formed in air atmosphere showed relatively low resistance and long electron life-time compared with Cu Oxide fabricated in Ar atmosphere at the same temperature. This is because heat-treatment in Ar atmosphere could not form Cu₂O due to lack of oxygen, and thermally formed CuO at high temperature suppressed stability and conductivity of the Cu oxide.

• Journal of Biosystems Engineering
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• 제43권1호
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• pp.21-29
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• 2018

Purpose: The objective of this study is to evaluate the performance of the conical solar concentrator (CSC) system, whose design is focused on increasing its collecting efficiency by determining the optimal conical angle through a theoretical study. Methods: The design and thermal performance analysis of a solar concentrator system based on a $45^{\circ}$ conical concentrator were conducted utilizing different mass flow rates. For an accurate comparison of these flow rates, three equivalent systems were tested under the same operating conditions, such as the incident direct solar radiation, and ambient and inlet temperatures. In order to minimize heat loss, the optimal double tube absorber length was selected by considering the law of reflection. A series of experiments utilizing water as operating fluid and two-axis solar tracking systems were performed under a clear or cloudless sky. Results: The analysis results of the CSC system according to varying mass flow rates showed that the collecting efficiency tended to increase as the flow rate increased. However, the collecting efficiency decreased as the flow rate increased beyond the optimal value. In order to optimize the collecting efficiency, the conical angle, which is a design factor of CSC, was selected to be $45^{\circ}$ because its use theoretically yielded a low heat loss. The collecting efficiency was observed to be lowest at 0.03 kg/s and highest at 0.06 kg/s. All efficiencies were reduced over time because of variations in ambient and inlet temperatures throughout the day. The maximum efficiency calculated at an optimum flow rate of 0.06 kg/s was 85%, which is higher than those of the other flow rates. Conclusions: It was reasonable to set the conical angle and mass flow rate to achieve the maximum CSC system efficiency in this study at $45^{\circ}$ and 0.06 kg/s, respectively.

• 한국패류학회지
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• 제19권1호
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• pp.1-8
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• 2003

본 연구는 바지락의 기초 생물, 생태학적 정보의 하나로써, 수온 및 염분의 변화가 바지락의 여과율에 미치는 영향을 파악하기 위하여 수행되었다. 실험에 사용된 바지락은 전남 여수시 화양면에 위치한 갯벌에서 채집하여 사용하였고, 먹이생물은 규조류, Phaeodactylum tricornutum을 실내에서 단일종 배양하여 사용하였다. 여과율측정은 간접측정법을 사용하였고 먹이생물의 농도는 광학현미경하에서 혈구계산판을 이용하여 직 접 계수하였다. 1, 2, 3년생 바지락 모두 수온이 증가할수록 여과율도 증가하였고 20-25$^{\circ}C$에서 최대여과율을 보였으며 25$^{\circ}C$이상에서 대체로 감소하는 경향이었다. 염분 변화에 대해서는 대체로 25-35 psu에서 최대여과율을 보였고 염분이 감소할수록 여과율도 감소하였다. 연령별 바지락의 여과율은 수온,염분 변화에 관계없이 1년생 바지락이 2, 3년생 바지락에 비해 뚜렷하게 높은 여과율을 나타내었다. 온도계수 Q$_{10}$값은 대체적으로 저온(5-15$^{\circ}C$) 에서 높게 나타났고 회귀분석의 결과, 수온변화에 대한 바지락의 여과율 곡선은 대체적으로 오른쪽으로 치우친 경향이었다. 이러한 결과로 바지락의 여과율은 저온의 수온범위에서 더욱 민감하게 영향을 받는 것으로 생각된다.

• Journal of Preventive Medicine and Public Health
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• 제7권1호
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• pp.107-113
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• 1974

위생공학에서 하수나 공장폐수를 처리할 때 이용하는 생물학적 처리과정은 미생물에서 생성되는 효소에 의하여 이루어 진다. 본 연구에서는 diastase의 활성에 대하여 수소이온 농도, 온도, 기질 농도 및 방해물질 등 여러가지 요인이 미치는 영향을 실험적으로 관찰하여 다음과 같은 결론을 얻었다. (1) diastase의 활성도는 pH $4.0{\sim}7.0$의 범위가 적당하였고 최적치는 pH 5.0이었다. (2) diastase의 활성도는 $30^{\circ}C{\sim}50^{\circ}C$ 높았으며 최적온도는 $40^{\circ}C$였다. (3) 기질농도의 영향을 보면 녹말농도 $750{\mu}g/ml$까지는 diastase의 활성도가 급격히 증가하였고, 그 이후에는 한정속도를 나타냈다. Michaelis 방정식을 적용시켜 보면 한정속도는 $415{\mu}g/ml$ starch removed/ml of reaction mixture/min였고 Michaelis 상수는 $340{\mu}g/ml$였다. (4) 방해물질의 영향을 보면 NaCl 농도 1.0%, $HgCl_2$ 농도 0.001%에서 diastase의 활성은 완전히 억제되었다.

• Fisheries and Aquatic Sciences
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• 제23권1호
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• pp.1.1-1.14
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• 2020

Background: Dietary protein requirements are dependent on a variety of factors and water temperature is one of the most important abiotic factors affecting protein requirement of fish. This study was, therefore, conducted to investigate effects of water temperature on dietary protein requirement of fry Heteropneustes fossilis which has high demand in most of the Asian markets. Methods: Quadruplicate groups of 30 fish per treatment (2.97 ± 0.65 cm; 5.11 ± 0.34 g) were fed seven isoenergetic diets (17.9 kJ g^-1 gross energy; 14.99 kJ g^-1 digestible energy) containing dietary protein levels ranging from 28 to 52% at two water temperatures (18 and 26 ℃). Experimental diets were fed to apparent satiation as semi-moist cakes thrice daily at 17:00, 12:00, and 17:30 h for 12 weeks. For precise information, various growth parameters, protein deposition, hematological parameters, metabolic enzymes, and stress response were analyzed, and effects of water temperature on dietary protein requirement was recommended on the basis of response from above parameters. Results: Groups held at 26 ℃ attained best growth, feed conversion, and protein deposition at 44% dietary protein indicating that temperature affected dietary protein requirement for optimum growth of H. fossilis fry and protein requirement seems to be satisfied with 44% dietary protein. Interestingly, interactive effects of both dietary protein levels and temperature were not found (P > 0.05). Fish reared at 18 ℃ had comparatively higher values for aspartate and alanine transferases than those reared at 26 ℃ water temperature which exhibited normal physiological value for these enzymes indicating that body metabolism was normal at this temperature. Hematological parameters also followed same pattern. Furthermore, fish reared at 26 ℃ water temperature exhibited more resistant to thermal stress (P < 0.05). The 95% maximum plateau of protein deposition data using second-degree polynomial regression analyses exhibited dietary protein requirement of fry H. fossilis between 40.8 and 41.8% of diet at 26 ℃ water temperature. The recommended range of dietary protein level and protein/digestible energy ratio for fry H. fossilis is 40.8-41.8% and 27.21-27.88 mg protein kJ^-1 digestible energy, respectively. Conclusions: Information developed is of high significance for optimizing growth potential by making better utilization of nutrient at 26 ℃ and, to develop effective management strategies for mass culture of this highly preferred fish species.

• 환경생물
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• 제36권2호
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• pp.131-139
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• 2018

기후 변화로 인한 수온의 상승은 어류 서식지에 영향을 미친다. 수온의 변화는 어류 생리 거의 모든 부분에 영향을 미치는 것으로 알려져 있다. 기후 변화에 따른 수온의 상승은 산소 용해도의 감소 및 산소 운반 헤모글로빈의 결합 능력의 감소로 인해 저산소증을 초래할 수 있다. 본 연구는 대서양 연어(Salmo salar) 치어 성장의 최적수온($15^{\circ}C$)보다 고수온($20^{\circ}C$)에 사육 시, 대서양 연어 치어의 건강상태를 평가하기 위해 수행되었다. 평가 방법은 NGS RNAseq 분석방법을 이용하여 생체지표유전자를 개발하고, RT-qPCR 분석을 이용하여 생체지표유전자의 발현양상을 조사하는 것이다. 개발한 생체지표유전자로는 interferon alpha-inducible protein 27-like protein 2A transcript variant X3, protein L-Myc-1b-like, placenta growth factor-like transcript variant X1, fibroblast growth factor receptor-like 1 transcript variant X1, transferrin, intelectin, thioredoxin-like, c-type lectin lectoxin-Thr1-like, ladderlectin-like 및 calponin-1 등이다. 선택된 생체지표 유전자는 NGS RNAseq 분석을 통해 수온변화에 민감하게 발현한 유전자들이며, RT-qPCR 분석을 통한 이들 유전자의 발현 양상은 NGS RNAseq 분석을 통한 발현 양상과 매우 유사하게 나타났다.

• 한국농공학회지
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• 제19권1호
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• pp.4312-4322
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• 1977

In order to investigate the effect of the water content and the accelerated curing on the strength of the soil-cement mixtures, laboratory test of soil cement mixtures was performed at five levels of water content, four levels of accelerated curing temperatures, three levels of normal curing periods, and six levels of accelerated curing time. Also this study was carried out to investigate the effect of grain size distribution of 21 types of soils on the strength of soil-cement mixtures at four levels of cement content and three levels of curing time. The results are summarized as follows: 1. Optimum moisture content increased with increase of the cement content, but maximum dry density was changed ununiformly with cement content. Water content corresponding to the maximum strength was a little higher than the optimum moisture content along the increase of cement content. 2. In molding the specimens with the optimum moisture content, the maximum strength appeared at the wet side of the optimum moisture content. 3. According to increase of curing temperature as 30, 40, 50, and 60$^{\circ}C$, unconiiend compressive strength of soil-cement mixtures increased, the rate of increase at the early curing period was large, and approximately 120 hours was suifficient to harden soil-cement mixtures completely. 4. The strength of soil-cement mixtures at the curing temperature of 10$^{\circ}C$ decreased at the rate of 30 to 50 percent than at the curing temperature of 20$^{\circ}C$, and the strength of soil-cement mixtures at the curing temperature of 0$^{\circ}C$ increased a little with increase of curing time. 5. Although the strength of soil-cement mixtures seemed to be a little affected by the temperature difference between day time and night, it was recommended that reasonable working period was the duration from July to August of which average maximum temperature of Korea was approximately 30$^{\circ}C$. 6. Accelerated curing time corresponding to the normal curing time of 28-day was shorten with increase of curing temperature, also it was a little affected by the cement. Accelerated curing time that the strength of soil-cement mixtures for the cement of 9 percent and the curing temperature of 60was shorten with increase of curing temperature, also it was a little affected by the cement. Accelerated curing time that the strength of soil-cement mix- tures for the cement of 9 percent and the curing temperature of 60$^{\circ}C$ was 45 hours at the KY sample, 50 hours at the MH, 40 hours at the SS, and 34 hours at the JJ respectively. 7. Accelerated curing time was depended upon the grain size distribution of soil, it decreased with increase the percent passing of No. 200 sieve. 8. Relationship between the normal curing times and the accelerated curing times showed that there was a linear relationship between them, its slope decreased with increase of curing temperature. 9. The most reasonable soil of the soil-cement mixtures was the sandy loam which was a well graded soil. Assuming the base of road requiring 7-day strength of 21 kg/$\textrm{cm}^2$ being used, the soil-cement mixtures could be obtained with adding 6 percent of cement in such a sails S-7, S-8, S-9, S-10, S-11, S-12, S-13. 10. The regression equation between the 28-day and the 7-day strength was obtained as follow; q28=1.12q7,+6.5(r=0.96).