• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.946-950
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• 2006

This paper proposed the ways for reduction of the prominent peak of the tone noise in air conditioning units. In order to find out the sources of the tone noise, the resonant frequencies and modes of the fans were investigated. Also, the effects of the ambient temperatures and material properties of the fans on the tone noise were studied. From the experiments, it was shown that the tone noise was greatly influenced by the torsional resonance of the fan and motor system and commutation frequency. In other words, the torsional resonance of the fan and motor system has not to be close to the commutation frequency (torque ripple frequency) which creates a rate of change in the angular acceleration in order to reduce the tone noise in air conditioning units.

• 설비공학논문집
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• 제12권11호
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• pp.1020-1030
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• 2000

A crossflow finned tube evaporator has been investigated using tube-by-tube method. The refrigerant flows inside tubes while the air passes outside the finned tue. R134a for a refrigerant and wet air were used in this analysis. Three refrigerant circuitries, complex or simple, were compared. The effects of refrigerant circuitry and airside condensation on thermal performance such as heat transfer rate, enthalpy of refrigerant, temperature of refrigerant and air, pressure of refrigerant and average condensate layer thickness were investigated. It was found that this method could be applied to the analysis of finned tube evaporator for dehumidification and air conditioning.

• 대한기계학회논문집A
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• 제26권10호
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• pp.2060-2066
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• 2002

The closed-loop state and input observer is a pole-placement type observer and estimates unknown state and input variables simultaneously. Pole-placement type observers may have poor transient performance with respect to ill-conditioning factors such as unknown initial estimates, round-off error, etc. For the robust transient performance, the effects of these ill-conditioning factors must be minimized in designing observers. In this paper, the transient performance of the closed-loop state and input observer is investigated quantitatively by considering the error bounds due to ill-conditioning factors. The performance indices are selected from these error bounds and are related to the observer robustness with respect to the ill -conditioning factors. The closed-loop state and input observer with small performance indices is considered as a well-conditioned observer from the transient perspective.

• 한국물환경학회지
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• 제26권2호
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• pp.349-355
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• 2010

Electroflotation (EF) was conducted for activated sludge thickening to investigate the effects of sludge SVI (sludge volume index) and chemical conditioning. Return sludge samples were used for the experiment, which were collected from municipal wastewater treatment plants. The performance of sludge thickening was significantly dependent on sludge SVI. For the sludges with SVI values in a range from 50 to about 150 mL/g, the maximum float content decreased rapidly from 8.4 to 3.5% and flotation compressibility followed the same pattern. In cases of sludges with SVI higher than 150 mL/g, those results showed low content levels without large changes. Gas/solids ratio tended to increase with an increase in SVI. When polyelectrolyte was added into sludges for the conditioning, compressibility increased up to 75% and gas/solids ratio was reduced up to about 35% under the condition of microbubble production rate of 530 mL/h, however, there was no consistent effect of chemical conditioning on the maximum float solids content; some cases were positive but the others negative. It was expected that the optimum dose of electrolyte depends on sludge SVI and an excessive chemical dose causes a performance deterioration of flotation thickening.

• Archives of Plastic Surgery
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• 제44권5호
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• pp.384-389
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• 2017

Background The aim of this study was to investigate the effects of remote ischemic conditioning on ischemia-reperfusion injury in rat muscle flaps histopathologically and biochemically. Methods Thirty albino rats were divided into 5 groups. No procedure was performed in the rats in group 1, and only blood samples were taken. A gracilis muscle flap was elevated in all the other groups. Microclamps were applied to the vascular pedicle for 4 hours in order to achieve tissue ischemia. In group 2, no additional procedure was performed. In groups 3, 4, and 5, the right hind limb was used and 3 cycles of ischemia-reperfusion for 5 minutes each (total, 30 minutes) was applied with a latex tourniquet (remote ischemic conditioning). In group 3, this procedure was performed before flap elevation (remote ischemic preconditoning). In group 4, the procedure was performed 4 hours after flap ischemia (remote ischemic postconditioning). In group 5, the procedure was performed after the flap was elevated, during the muscle flap ischemia episode (remote ischemic perconditioning). Results The histopathological damage score in all remote conditioning ischemia groups was lower than in the ischemic-reperfusion group. The lowest histopathological damage score was observed in group 5 (remote ischemic perconditioning). Conclusions The nitric oxide levels were higher in the blood samples obtained from the remote ischemic perconditioning group. This study showed the effectiveness of remote ischemic conditioning procedures and compared their usefulness for preventing ischemiareperfusion injury in muscle flaps.

• 설비공학논문집
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• 제14권12호
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• pp.1014-1022
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• 2002

This paper analyzed the characteristics of heat transfer in quadangle duct with absorber plate by solar radiation. Effects o( Reynolds number on increasing temperature at outlet for variation of absorber plate temperature were analyzed by using numerical analysis technique. And also the effects of turbulent intensity of inlet flow on increasing temperature at outlet for various duct height and effects of inlet aspect ratio of quadrangle duct and position of heating surface on the outlet temperature were analysed. As the results, Outlet temperature was greatly influenced in low Reynolds number. And the highest outlet temperature distribution appeared on the inlet aspect ratio 2 because of the buoyancy effect.

• 설비공학논문집
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• 제10권4호
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• pp.381-388
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• 1998

Hot and humid weather in summer generally brings about discomfort. Experiments on which relative humidity makes effects on the comfort sensation were performed to the young and the aged using sensation vote. From July to October 1996, seven college students and eleven aged people were exposed for 2 hours under six different conditions in the Pukyong National University test chamber so as to determine the effects of relative humidity on thermal and comfort sensations. Subjects were wearing same clothes, and the mean clo value was 0.5. The mean radiant temperature was equal to the air temperature and air velocity in the occupied zone around 0.lm/s. In the experiments, it was found that discomfort could be largely reduced when the humidity is controlled to low values in the settled high temperature.

• 설비공학논문집
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• 제2권3호
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• pp.177-187
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• 1990

This paper presents that in the Korean Ondol Heating System using hard coal as an usual fuel, what effects an insulation of chimney with the low temperature gas flow has on the optimum chimney height which gives a maximum gas weight flow rate under the general weather data and actual design condition of chimney is compared with the bared chimney and studied. And also, the effects of chimney materials and diameter, dimensionless temperature difference, insulating materials and thickness which have on the optimum chimney height were researched and a good results increasing a maximum gas weight flowrate is obtained by insulating the chimney.

• 설비공학논문집
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• 제9권3호
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• pp.333-342
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• 1997

An experimental study has been carried out to investigate the effects of the combination of the different wire mesh number in a regenerator and the tube number in a cooler on the cooling performance of a Vuilleumier cycle heat pump. Effects of operating conditions, such as charging pressure, operating speed, and heat input, on the cooling performance are also studied. The experimental results obtained indicate that the cooling performance could be improved with the proper combination of different wire meshes in a regenerator. More tubes in a cooler are desirable for better cooling performance. It is also found that the cooling capacity is enhanced, whereas COP is reduced with an increase in the heater tube temperature and the revolution speed. Both the cooling capacity and COP are incereased with a higher charging pressure.

• International Journal of Air-Conditioning and Refrigeration
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• 제9권2호
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• pp.19-27
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• 2001

In the present study, the effects of film Reynolds number (60∼200) and volumetric content of non-absorbable gases (0∼10%) in water vapor on the absorption process of aqueous LiBr solution were investigated experimentally. The formation of solution film on the horizontal tubes of six rows was observed to be complete for Re>100. Transition film Reynolds number was found to exist above which the Nusselt number and Schmidt number diminishes with solution flow rate. As the concentration of non-absorbable gases increased, mass transfer rate decreased more seriously than heat transfer rate did. the degradation effects of non-absorbable gases seemed to be significant especially when small amount of non-absorbable gases was introduced to the pure water vapor.