• International Journal of Air-Conditioning and Refrigeration
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• 제15권3호
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• pp.108-113
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• 2007

The performance of a solar water heater incorporating evacuated tubes was evaluated using a transient simulation program, TRNSYS. Simulations were performed for $60^{\circ}C$ of hot water load temperature and for 280 liter of daily hot water volumes and three 400 liter of storage tank volumes. Three patterns of daily hot water consumption profile were used in the present study (morning, lunch and evening). The results show that the increase in solar fraction depends on the load profile, as well as the collector efficiency coefficient. Hot water draw profile has a large effect on the performance of the SDHWS, the morning load profile has the highest solar fraction. The annual solar fraction of the system, at the weather conditions of Jinju is approximately 84% at lunch load pattern, the 280 kg of load volume, 400 kg of tank volume and the $60^{\circ}C$ of load temperature.

• 설비공학논문집
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• 제14권12호
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• pp.996-1003
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• 2002

Heat transfer characteristics were investigated for the falling film flowing down the outside of an electrically heated vertical tube. Water was used for the falling film, and its Reynolds number was varied in the range of 70～500. Because water is heated and evaporated as it flows down, both sensible and latent heat transfer should be considered. The effect of the surrounding air movement was investigated by changing the direction of the air injection; without air injection, parallel-flow, and counter-flow. For all cases, sensible teat transfer rate was almost linearly increased with the increasing film flow rate. It was found that the film heat transfer coefficient was hardly influenced by the parallel air flow. However, the counter-flow of air reduced the heat transfer coefficient, which might be caused by the uneven distribution or flooding of the film. At high heat flux, a sudden change of the film heat transfer coefficient was detected as the film flow rate reached the transition value. It is supposed that this phenomenon was caused by the change in the film flow pattern.

• 설비공학논문집
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• 제18권8호
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• pp.649-655
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• 2006

The recent indoor air quality problem in a newly-built apartment house is resulted from the improvement of airtightness performance and the use of the building material contained harmful chemical substances. As a result, these cause indoor air quality gradually to become worse and the harmful effect on occupant health called Sick House Syndrome. The most effective solution to improve the indoor air quality is to encourage the use of green building material. However, if the house is built with general building material, ventilation with outdoor air is alternative to dilute the pollutant concentration. The purpose of this re-search is to find optimum ventilation time in a newly-built apartment house at which the ventilatoris installed. It is found that the HCHO and toluene concentrations are remarkably decreased with the elapse of ventilation time and the concentration reduction rate is increased with increment of air change rate after one hour after operating the ventilator.

• 설비공학논문집
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• 제12권5호
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• pp.494-501
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• 2000

Effectiveness of a 3-pass plate finned-tube heat exchanger is calculated using heat exchangelet method by changing the shape of fin and the arrangement of tubes. The alternative refrigerant R134a is taken in this study. Conduction between neighboring tubes along the fin is taken into account in addition to convection between the fin and the surrounding air. Governing equations are obtained by using energy balance in a small control volume containing a tube and fins. They are numerically solved following the tube. Effect of tube-to-tube conduction is investigated in single-phase and two-phase flows with various fin shapes and arrangements of tubes. Improvement of effectiveness by fin perforation is studied too. The results shows that perforating fins, increasing the number of tubes, and increasing the distance between neighboring tubes at the same fin area enhance the effectiveness.

• 설비공학논문집
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• 제12권5호
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• pp.431-438
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• 2000

The major irreversibilities in absorption chillers are associated with the transfer of heat into and out from the machine and irreversible process inside the machine. By modeling only external irreversibilities(endo-reversible), a model was formulated to predict the ideal performance of a single-effect absorption chiller. Its actual performance including both external and internal irreversibilities was calculated with a in-house simulation program. The optimization of heat transfer area distribution was performed for both endo-reversible cycle and actual cycle. The equation of endo-reversible modeling was found to give about 2times higher cooling capacity than the simulation program. At optimal distribution, it was found that heat transfer area of the evaporator was about 30% of total area, that of the generator was 20%, and the rest 50% was for the absorber and condenser. The system COP for endo-reversible cycle was slightly higher than that for actual cycle. In the case of LiBr-water single-effect absorption chiller, the maximum cooling capacity was obtained near the condition that LMTD is same at all heat exchangers.

• 설비공학논문집
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• 제19권8호
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• pp.607-614
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• 2007

This paper investigated that the functional group and chemical structure of additives affect ice adhesion in aqueous solutions cooling with stirring. In order to compare the effect on the ice adhesion in aqueous solutions, the functional group like carboxyl (-COOH), hydroxyl(-OH) or amine($-NH_{2}$) one were compared each other. Among the functional group, the strength of the hydrogen bonding force order is amine, hydroxyl and carboxyl one. It supports that ethylene diamine 7 mass% solution including amine group was effective to suppress the ice adhesion, though it is corrosive. Also, the ice adhesion were effectively resisted and formed lots of ice slurries in cooling experiment of 7 mass% solution of 1, 2-and 1, 3-propanediol which is different molecular structure but equal molecular weight each other.

• 한국수산과학회지
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• 제50권3호
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• pp.296-301
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• 2017

We conducted a study to 1) determine the indicators of gonadal maturity in male and female Korean walleye pollock Theragra chalcogramma for the purposes of artificial insemination; 2) establish the RNA/DNA ratio of mature eggs in this species; and 3) monitor the effect of refrigerated storage on egg viability and the motility of sperm collected from dead adult males. During the spawning season, the color of female gonads changed from orange to transparent, and that of male gonads changed from pale orange to milky white. The DNA content and RNA/DNA ratio of mature eggs were maintained without significant changes for approximately 6 h when eggs were preserved at $4^{\circ}C$. Sperm could be obtained from both milt and undiluted semen. Sperm obtained from milt ceased moving on the second day after isolation, while over 60% of sperm obtained from semen showed movement until the 13th day. Seven attempts were made to artificially inseminate mature eggs, of which two resulted in successful fertilization. The successful inseminations produced 94,000 and 5,000 fertilized eggs, respectively. This study shows that artificial insemination of walleye pollock is a viable strategy when natural propagation is not possible.

• 설비공학논문집
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• 제26권9호
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• pp.447-452
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• 2014

We evaluated heat transfer characteristics of microscale wrinkles using a CFD (computational fluid dynamics) analysis. In order to verify the heat transfer effect of wrinkles having various shapes, we introduce wrinkling processes to generate few different shapes of wrinkles such as macroscale ($200{\sim}400{\mu}m$ width), microscale ($10{\sim}30{\mu}m$ width), and hierarchical (microscale on macroscale wrinkle) wrinkles, using repetitive-dividing-volume (RDV) method for single-shape of wrinkles and connected method of UV-weakly polymerization with thermal curing for hierarchical structure of winkles. The analysis results of simplified CFD model showed that heat flux on heated plate was changed by the shape of wrinkles on the plate. The increase in heat flux of about 2.6 times was achieved in the case where hierarchical wrinkle structure was used.

• 설비공학논문집
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• 제28권11호
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• pp.444-449
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• 2016

The main objective of this work is to experimentally investigate the effect of angle variation and intrusion depth of channels on the distribution of two-phase flow at header-channel junctions. The dimensions of the header and the channels in cross-section were fixed at $16mm{\times}16mm$ and $12mm{\times}1.8mm$, respectively. Air and water were used as the test fluids. Two different header-channel positions were tested : a vertical header with horizontal channels (case VM-HC) and a horizontal header with horizontal channels (case HM-HC). In all cases, the intrusion depths of the channels are 0 mm, 2 mm, and 4 mm. For the case of the intrusion depth of VM-HC, the flow distribution became more uniform. However, the intrusion depth negatively affected the flow distribution for the case of HM-HC because liquid separation delay occurred.

• 설비공학논문집
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• 제28권7호
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• pp.275-282
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• 2016

MILD (Moderate and Intense Low-oxygen Dilution) combustion using oxygen as an oxidizer is considered as one of the most promising combustion technologies for high energy efficiency and for reducing nitrogen oxide and carbon dioxide emissions. In order to investigate the effects of nozzle angle and oxygen velocity conditions on the formation of oxygen-MILD combustion, numerical and experimental approaches were performed in this study. The numerical results showed that the recirculation ratio ($K_V$), which is an important parameter for performing MILD combustion, was increased in the main reaction zone when the nozzle angle was changed from 0 degrees to 15 degrees. Also, it was observed that a low and uniform temperature distribution was achieved at an oxygen velocity of 400 m/s. The perfectly invisible oxy-MILD flame was observed experimentally under the condition of a nozzle angle of $10^{\circ}$ and an oxygen velocity of 400 m/s. Moreover, the NOx emission limit was satisfied with NOx regulation of less than 80 ppm.