• 한국항공우주학회지
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• 제31권3호
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• pp.65-71
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• 2003

일반적으로 액체로켓 엔진의 추력실에서 연소중 어느 정도의 열 유속을 발생하는가를 아는 것은 추력실을 냉각하기 위한 가장 중요한 사항 중에 하나이다. 이에 본 연구에서는 Kerosen/LOx를 추진제로 사용하는 소형 액체로켓 엔진의 추력실에서 발생하는 heat flux를 측정하기 위하여 thin wall chamber를 제작하였다. wall thickness는 1mm로 하였으며 추력실 외벽에 총 9개의 열전쌍을 부착하여 연소시험을 수행함으로써 연소중 변화하는 추력실의 외벽온도를 측저하였다. System을 1차원 비정상상태로 가정하고 측정된 추력실의 외벽온도로부터 one-dimensional the transient energy equation을 이용하여 추력실에서 발생하는 열유속 및 열전달계수를 예측하였다. 혼합비 2,0의 조건에서 실험변수로서 연소압에 변화를 주었으며 실험결과 열전달계수가 연소압에 0.88승에 비례하는 관계식을 얻어낼 수 있었다.

• 한국가스학회지
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• 제11권4호
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• pp.35-40
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• 2007

본 연구는 마이크로핀관에서 이소부탄과 프로판의 증발 열전달 특성에 대해 실험적으로 조사하였다. 시험부는 외경 12.70 mm이고, 높이가 0.25 mm인 75개 핀이 원주방향으로 삽입되어 있다. 실험결과, 탄화수소계 냉매의 평균 열전달계수는 프레온계 냉매인 HCFC22보다 높을 것으로 나타났고, 높은 질랑유속에서는 이소부탄 > 프로판 순으로 나타났다. 마이크로핀관에서 증발 열전달 계수는 평활관에 비해 약 $80{\sim}100%$ 정도가 향상되었다. 이러한 본 연구 결과로부터 탄화수소계 냉매를 냉동 공조 시스템의 냉매로 사용하여 열교환장치를 설계할 경우에는 유리하리라 생각된다.

• 설비공학논문집
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• 제10권4호
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• pp.411-422
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• 1998

In this study, experiments were carried out to provide nucleate pool boiling heat transfer data for a plain tube and 4 different low fin tubes employing 2 refrigerant mixtures of R410A, R407C, and 12 pure fluids. Low fin tubes were machined on a 19.05mm nominal outside diameter copper block according to the manufacturer's low fin tube specifications. Cartridge heaters were used to generate uniform heat flux on the tubes. For all refrigerants, heat flux varied from 10㎾/$\m^2$ to 80㎾/$\m^2$. It is found that heat transfer coefficients(HTCs) of high vapor pressure refrigerants are usually higher than those of low pressure fluids. On the other hand, the fin effect was more prominent with low pressure refrigerants than with high pressure ones. Optimum fin density as well as the increase in heat transfer coefficient with the increase in fin density were found to be strongly fluid dependent. HTCs of Rl23, a low pressure alternative refrigerant, were similar to those of Rll while HTCs of R134a, an intermediate pressure alternative refrigerant, were roughly 20% higher than those of Rl2. Finally, HTCs of R32, R125, R143a, and R410A were all higher than those of R22 by 30~50%.

• 방사성폐기물학회지
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• 제8권3호
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• pp.189-199
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• 2010

고준위 방사성 폐기물 처분장의 경우 폐기물의 방사성 붕괴에 의해 열이 발생되며, 암반을 통한 열전달에 의해 처분장 주변 환경이 변화됨으로써 처분장의 안전성에 영향을 미칠 수 있다. 그러므로 지하 처분장 대기의 열전달계수를 결정하는 것은 매우 중요하다. 이에 본 연구에서는 Korea Atomic Energy Research Institute Underground Research Tunnel (KURT)에서 내부 환경 인자들의 측정을 통해 강제대류시 열전달계수를 산정하였다. 실험을 위해 KURT 내 히터구간의 막장 벽면에는 길이 2 m, 용량 5 kw의 히터를 삽입하여 암반 내부를 $90^{\circ}C$로 가열하였고, 외부와 연결된 급기용 팬에 의해 신선한 공기를 공급하였다. 연구결과, 외부공기 공급 후 히터구간 대기의 기류속도는 평균 0.81 m/s로 측정되었고 레이놀즈수는 약 310,000~340,000의 값을 나타냈다. 그리고 강제대류조건에서 히터구간 내 계절별 열전달계수는 각각 여름철 $7.68\;W/m^2{\cdot}K$와 겨울철 $7.24\;W/m^2{\cdot}K$의 수치를 나타냈다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.531-536
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• 2004

In-arm type hydropeumatic suspension unit(ISU) is an equipment of armed tracked vehicle to absorb impact load and vibration from the irregular ground. During the operation of ISU, main piston moves forward and backward and oil flowing through damper transmits the external impact load to floating piston. Heat is generated in ISU by the oil pressure drop through the damper orifice and the friction between cylinder wall and two pistons. On the other hand, internal heat dissipatis outside via heat convection. Occurrence of high temperature can deteriorate durability of major components and basic function of ISU. And, it can cause fatal problem in the ISU life time and the sealing performance of piston rings. As well, the spring constant change of nitrogen gas that is caused by the temperature rise exerts the negative effect to the vehicle stability. Therefore, in this paper, we analyze the heat transfer analysis of the entire ISU unit, by finite element method, with the outside flow velocities 8m/s and 10m/s.

• 한국농공학회논문집
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• 제52권5호
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• pp.11-18
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• 2010

This study was conducted to provide design data for deciding covering method in double layers greenhouse. The variation of photosynthetic photon flux (PPF) and heat flow in air inflated and conventional double layers greenhouse was analyzed. The PPF of air inflated double covering greenhouse was less than that of conventional greenhouse during summer season because the more PPF comes into conventional greenhouse through roof vent which was rolled up for ventilation. The air inflated double layers covering greenhouse was superior to conventional type in the aspect of controlling inside temperature down owing to lower irradiation. The PPF of air inflated greenhouse was greater than that of conventional greenhouse during winter season because the transmittance of conventional greenhouse decreased by dust collected on inside plastic film nearly closed for insulation. Considering the PPF not sufficient for tomato growing in winter, the air inflated double covering system with the greater transmittance was better than conventional covering system. When the inside air of air inflated greenhouse was injected into space between the double layers of covering, the PPF of air inflated greenhouse was much less than the conventional greenhouse because the transmittance of air inflated double covering decreased due to condensation of highly humidified inside air. It was concluded that the more dried outside air should be used for inflating double layers covering. The heat insulation performance of air inflated double covering system was superior to conventional double covering system when comparing the overall heat transfer coefficients for each covering method. However the differences among the overall heat transfer coefficients depending on difference between inside and outside temperatures of greenhouse were great, it is necessary to conduct additional experiment for investigating the overall heat transfer coefficient to design the double layers covering.

• 플랜트 저널
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• 제15권1호
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• pp.25-30
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• 2019

본 연구에서는 배관 곡관부의 유동가속부식을 일으키는 인자 중 수력학적 인자인 유동형태 변경에 따른 영향을 분석하고 부식을 저감시키는 연구를 추진하였다. 열전달과 물질전달, 물질전달과 유동가속부식의 상사성에 대해 이론적 분석을 통해 확인하고 상용 수치해석 프로그램을 이용하여 국소대류열전달계수를 해석함으로써 곡관부의 물질전달 특성에 대해 고찰하였다. 곡관부 상류의 직관부 내표면 안쪽과 바깥쪽에 요철을 설치하였을 때 최대 국소열전달계수는 기본유동에 비하여 현저히 감소하여 요철의 위치와 형태에 따라 차이가 있으나 24.9%까지 감소함을 확인하였으며, 곡관부 상류의 직관부에 가인드 베인을 삽입하면 가이드 베인에 의한 배관 내측면적 크기에 따라 차이가 있으나 최대 국소열전달계수가 기본유동에 비해 12.5%까지 감소함을 확인하였다.

• 설비공학논문집
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• 제12권1호
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• pp.20-25
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• 2000

An experimental study on the condensation heat transfer coefficients of R-22, R-290 and R-600a inside horizontal tube was performed. Heat transfer measurements were performed for smooth tube with inside diameter of 10.07 mm and outside diameter of 12.07 mm and inner grooved tube having 75 fins whose height is 0.25 mm. This study was performed for condensation temperatures were from 308 K to 323 K, and mass velocity of $51 kg/m^2s - 250kg/m^2s$. The test results showed that the local condensation heat transfer coefficients increased as the mass flux increased, and also the effect of mass flow rate on heat transfer coefficients of R-290 was less than R-22. In addition, heat transfer coefficient of R-22 increased to a larger extent than R-290 and R-600a as the mass flow rate increased. Average condensation heat transfer coefficients of natural refrigerants were superior to that of R-22. The present results had a good agreement with Cavallini-Zecchin's correlation for smooth and inner grooved tubes.

• 설비공학논문집
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• 제29권9호
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• pp.447-454
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• 2017

In this study, local velocity distribution of cooling air in a heat exchanger used in an air compressor for a railway car was measured and heat transfer characteristics of the heat exchanger were analyzed. First, heat transfer coefficient and fin performance of the cooling air side were predicted and was checked if the fin of the heat exchanger was effectively used. Distribution of air flow rate at high temperature side was predicted through pipe network analysis and heat resistance at high temperature and low temperature side were predicted and compared. Spatial distribution of temperature in the interior and surface of the square channel constituting high-temperature side was predicted and appropriateness of the size of the heat exchanger was examined. As a result of the analysis, the present size of the heat exchanger could be reduced and it could be effective to promote heat transfer inside the heat exchanger rather than outside to improve performance of the heat exchanger.

• 동력기계공학회지
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• 제18권5호
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• pp.22-27
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• 2014

The objectives of this paper are to obtain an empirical equations regarding the correlations between heat transfer and pressure drop of oval fin-tube heat exchanger having large diameter using wilson plot method. It was difficult to find any recommendable heat transfer and friction factor correlation available for our large diameter experimental cases. Overall heat transfer coefficients are composed of the heat transfer coefficients both inside and outside tubes. The resulting empirical correlations for the Nui and f-factor are given as $Nu_i=0.0146Re^{0.809}Pr^{0.3}$ and $f=4.366Re^{-0.64}$, respectively. The empirical correlations of the Nui and f-factors were developed for the large diameter oval finned-tube heat exchanger as a function of the Reynolds number. As the EG(Ethylene glycol) and air flow rate increases, the heat transfer rate and pressure drop is increased largely.