• 설비공학논문집
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• 제18권5호
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• pp.443-450
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• 2006

The present study has been conducted to investigate the effects of rotation on heat/mass transfer and pressure drop characteristics in a two-pass square duct with and without discrete ribs. For stationary cases, the heat/mass transfer on the surfaces with and without discrete ribs is almost the same or reduced. For rotating cases, the gap flow affects differently the heat/mass transfer on leading and trailing surfaces with discrete ribs. On the leading surface of the first pass, the heat/mass transfer is slightly enhanced due to generating strong gap flow. On the trailing surface of the first pass, however, the heat/mass transfer is much decreased because the gap flow disturbs impingement of main flow. The phenomenon, that is, the heat/mass transfer discrepancy between the leading and trailing surfaces is distinctly presented with the increment of rotation number. The friction losses on each surface with discrete ribs are reduced because the blockage ratio decreases for both non-rotating and rotating cases. Therefore, high thermal performance appears in a duct with discrete ribs.

• Journal of Biosystems Engineering
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• 제10권1호
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• pp.76-82
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• 1985

To investigate the influence of annealing heat treatment on the mechanical properties at the various weld zone, an experimental study was performed for the structural alloy steel. The results obtained from the experimental works are as follows: 1. Hardness and tensile strength showed the highest value at the heat affected zone, which was 5mm apart from bond zone. With increasing of annealing temperature, hardness and tensile strength were decreased at every weld zone, and bound in heat affected zone was increased. 2. Impact strength was the highest at the filler metal, and increased with increment of annealing temperature at filler metal and base metal. However, both at bond and heat affected zones, impact strength was increased from $700^{\circ}C$ of annealing temperature, and was decreased again over $900^{\circ}C$. 3. Mutual relationship between the mechanical properties at filler and base metals showed a similar linearty to that the common structural steel did. However, it varied unsteadly both at bond and heat affected zones. 4. It may be concluded that proper annealing temperature is $700^{\circ}C$ from the viewpoint of hardness, tensile and impact strength.

• 신재생에너지
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• 제7권4호
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• pp.30-36
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• 2011

The objective of this study is to investigate the effects of the refrigerant charge amount on the performance of a water-to-water ground source heat pump with a variation of compressor speed and the secondary fluid flow rate. The water-to-water ground source heat pump was tested by varying refrigerant charge amount from -40% to 20% of full charge. Compressor speed was changed from 30 Hz to 75 Hz and the secondary fluid flow rate was adjusted from 6 LPM to 14 LPM. For all test conditions, EWTs of an indoor heat exchanger and an outdoor heat exchanger were maintained at standard conditions of ISO 13256-2. The slope of the COP with the variation of charge amount is much steeper at undercharged conditions than that at overcharged conditions. For all compressor speed, the variation of the system performance according to charge amounts showed the similar trends. However, the optimum charge amount of the system increased a little with an increment of compressor speed. When the secondary fluid flow rate decreased, the system was optimized at higher refrigerant charge amount conditions.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.143.1-143.1
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• 2011

The objective of this study is to investigate the effects of the refrigerant charge amount on the performance of a water-to-water ground source heat pump with a variation of compressor speed and the secondary fluid flow rate. The water-to-water ground source heat pump was tested by varying refrigerant charge amount from -40% to 20% of full charge. Compressor speed was changed from 30 Hz to 75 Hz, and the secondary fluid flow rate was adjusted from 6 LPM to 14 LPM. For all test conditions, EWT of an indoor heat exchanger and an outdoor heat exchanger were maintained at standard conditions of ISO 13256-2. The slope of the COP with the variation of charge amount is much steeper at undercharged conditions than that at overcharged conditions. For all compressor speed, the variation of the system performance according to charge amounts showed the similar trends. However, the optimum charge amount of the system increased a little with an increment of compressor speed. When the secondary fluid flow rate decreased, the system optimized at higher refrigerant charge amount conditions.

• 한국산학기술학회논문지
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• 제14권2호
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• pp.523-528
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• 2013

본 실험에서는 산업용 발전 설비에 사용되는 인버터 내부의 압입형과 압출형 두 종류 히트싱크의 방열 성능을 평가하였다. 실험에 사용된 압입형 히트싱크는 62개의 핀을 가지고 있고, 압출형은 38개의 핀을 가지고 있으며 두 히트싱크의 외형의 크기는 같다. 반면 압출형 히트싱크는 핀의 표면에 반경 1mm의 곡률을 주어 전열면적을 압입형과 같게 하였다. 결과적으로 압입형과 압출형 히트싱크는 전체 입력열량에 대해 각각 70.7%, 63.8%를 방열하였다. 입력열량 중 나머지는 자연대류 및 복사를 통해 외부로 방열되었다. 압출형 히트싱크는 단순히 핀의 개수로 보면 압입형 히트싱크보다 40% 감소했지만, 방열양은 6.9% 만 감소하였다. 이는 표면 곡률을 통한 유효 전열면적의 증가와 압출형 히트싱크의 상대적으로 우수한 전열특성의 효과로 판단하였다.

• 열처리공학회지
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• 제3권4호
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• pp.41-52
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• 1990

This research has been performed in order to investigate the effect of prior deformation on the Ms temperature and reversed As of Fe-Ni alloy. The Ms temperature rose with increment of strain to 30% but lowered over 50%. It can be analysed that martensitic transformation was promoted by partial dislocation in low strain, but suppressed by dislocation cell structures in high strain. The As temperature was substantially increased with higher deformation to 20% but slowly above 50%. It may be caused that as the transition bands formed by deformation constrained shear strain, therefore austenitic transformation was hindered.

• 비파괴검사학회지
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• 제29권1호
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• pp.43-48
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• 2009

The fatigue crack growth behavior of high strength X80 pipeline steel was investigated with compact tension specimens that crack growth directions were aligned either parallel or normal to the rolling direction of the pipeline. Also, the fatigue crack growth rates for welded joint of X80 pipeline steel were investigated with compact tension specimens that crack growth directions were aligned either parallel or normal to the welding line. The experimental results indicated the fatigue crack growth behavior was markedly different in three zones, weld metal, heat affected zone and base metal of welded joints. There was a trend toward increment in the fatigue life of weld metal and heat affected zone as compared with the X80 pipeline steel.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.609-613
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• 2008

The fire whirl occurring by the instability of atmosphere is a rare phenomenon, but highly destructive because it has high inhalation and lift force, caused by the rotating velocity. And it is difficult to extinguish the fire, because of increment of the spread rate with the flame height. In this study, for investigation of the flow characteristic of fire whirl for various heat release rate, numerical analysis is performed in same conditions with experiments, using the FDS which is developed at NIST. For validating of the numerical study, the results are compared with the experiment. The result shows that the relation between the characteristic length and the ratio of circulation versus the buoyancy force is $z_f$/D$^{\ast}$ = 0.304(${\Omega}/{\alpha}$)^2 - 1.334${\Omega}/{\alpha}$ + 5.516.

• 한국주조공학회지
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• 제13권6호
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• pp.555-562
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• 1993

A study was investgated the relationship between fracture characteristics and microstructure changes according to Cu addition and heat treatment methods on the ductile cast iron. According to increment of Cu addition pearlite volume fraction was increased due to the deffect of anti-ferritizing of Cu. At the case of austempering heat treatment, fracture toughness of Cu contained specimen was decreased. The reason for the results seems to be responsible for decrement of plastic zone size at the crack tip. It was observed that the excellent fracture toughness can be obtained at the condition of normalizing and the specimen was not contained Cu. Under the such conditions, fractographs is composed of dimple pattern and fracture toughness 71.6MPa $\sqrt{m}$, tensile strength determined as the value of 961.6MPa, respectively.

• 한국공작기계학회논문집
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• 제14권6호
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• pp.45-51
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• 2005

Braking performance of a vehicle can be significantly affected by the temperature increment in the brake system. Therefore, the important problem in brake system is to reduce the thermal effect by friction heat. Recently, many studies have been performed and good results have been reported on the prediction of the brake disk temperature. However, the study on the pad, piston and brake fluid temperature is rarely found despite of its importance. In this study, the temperature distribution of the disc brake system is studied according to the material properties of brake piston. Vehicle deceleration, weight distribution by deceleration, disc-pad heat division and the cooling of brake components are considered in the analysis of heat transfer. Unsteady state temperature distributions are analyzed by using the finite element method and the numerical results are compared with the experimental data.