• 제목/요약/키워드: overall heat transfer

검색결과 426건 처리시간 0.033초

Measurement of Heat Transfer Coefficient in Dimpled Channel: Effect of Dimple Arrangement and Channel Height

  • Lee, K.S.;Shin, S.M.;Park, S.D.;Kwak, J.S.;Kang, J.S.
    • 한국추진공학회:학술대회논문집
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    • 한국추진공학회 2008년 영문 학술대회
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    • pp.39-44
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    • 2008
  • In this paper, heat transfer coefficients were measured in a channel with one side dimpled surface. The sphere type dimples were fabricated and the diameter and depth of dimple was 16mm and 4mm, respectively. Two channel heights of about 0.6 and 1.2 time of the dimple diameter, two dimple configuration were tested. The Reynolds numbers based on the channel hydraulic diameter was varied from 30000 to 50000. The improved hue detection based transient liquid crystal technique was used in the heat transfer measurement. Heat transfer measurement results showed that high heat transfer was induced downstream of dimples due to flow reattachment. Due to the flow recirculation on the upstream side in the dimple, the heat transfer coefficient was very low. As the Reynolds increased, the overall heat transfer coefficients also increased. With same dimple arrangement, the heat transfer coefficients and the thermal performance factor were higher for the lower channel height. As the distance between dimples became smaller, the overall heat transfer coefficient and the thermal performance factor were increased.

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전통 농촌주택(흙집) 심벽의 단열 특성 (Characteristics of Insulation of Core Wall for Traditional Rural House (Earthen House))

  • 리신호
    • 한국농공학회지
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    • 제45권5호
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    • pp.126-132
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    • 2003
  • The insulation characteristics of earthen core wall were studied in this paper. The overall heat transfer coefficients(U) were obtained through experiment in accordance with Korea Industrial standards. The result of the experiment are compared with the Regional Overall Heat Transfer Coefficient(U) of Building. This results inform that core wall with soil can be used as building walls because the insulation characteristics agree to the rule of building standards.

밀폐형 냉각탑의 열성능 특성에 관한 실험적 연구 (Thermal Performance Characteristics of Closed-Wet Cooling Tower)

  • ;김은필;문춘근;윤정인
    • 동력기계공학회지
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    • 제9권2호
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    • pp.88-92
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    • 2005
  • The experiment of thermal performance about closed-wet cooling tower was conducted in this study. A closed cooling tower is a device similar to a general cooling tower, but with cooling tower replaced by a heat exchanger. The test section for this experiment has the process that the cooling water flows from the top of the heat exchanger to the bottom side in the inner part of the tube, and spray water flows in the gravitational direction in the outer side. Air comes in direct contact with the spray water at the outer side of the tube while passing from the lower the upper part having a counterflow to the spray water. The heat transfer pipe used in this experiment is a bare-type tube having an outer diameter of 15.88mm. The heat exchanger is consisted of seven rows and fifteen columns. In this experiment, thermal performance of the cooling tower is derived from overall heat transfer coefficients between the process fluid and sprayed water and volumetric overall mass transfer coefficient between sprayed water and air.

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이중관 내부 나노유체의 유동방향 영향에 관한 연구 (A Study on the Effect of Nanofluids Flow Direction in Double Pipe)

  • 최훈기;임윤승
    • 한국기계가공학회지
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    • 제20권6호
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    • pp.82-91
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    • 2021
  • We compared the heat transfer characteristics of the parallel and the counterflow flow in the concentric double tube of the Al2O3/water nanofluids using numerical methods. The high- and low-temperature fluids flow through the inner circular tube and the annular tube, respectively. The heat transfer characteristics according to the flow direction were compared by changing the volume flow rate and the volume concentration of the nanoparticles. The results showed that the heat transfer rate and overall heat transfer coefficient improved compared to those of basic fluid with increasing the volume and flow rate of nanoparticles. When the inflow rate was small, the heat transfer performance of the counterflow was about 22% better than the parallel flow. As the inflow rate was increased, the parallel flow and the counterflow had similar heat transfer rates. In addition, the effectiveness of the counterflow increased from 10% to 22% rather than the parallel flow. However, we verified that the increment in the friction factor of the counterflow is not large compared to the increment in the heat transfer rate.

수평 평활관내에서 비공비혼합냉매의 강제대류 증발열전달 (Forced Convective Evaporating Heat Transfer of Non-azeotropic Refrigerant Mixtures in a Horizontal Smoothed Tube)

  • 박기원;오후규
    • 설비공학논문집
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    • 제7권2호
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    • pp.225-233
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    • 1995
  • Experiments were performed to investigate the heat transfer characteristics of nonazeotropic mixture R-22+R-114 in a heat pump system. The ranges of parameter, such as heat flux, mass flow rate, and quality were $8,141{\sim}32,564W/m^2$, 24~58kg/h, and 0~1, respectively. The overall compositions of the mixtures were 50 and 100 per-cent of R-22 by weight for R-22+R-114 mixture. The results indicated that there were distinct different heat transfer phenomena between the pure substance and the mixture. In case of pure refrigerant the heat transfer rates for cooling were strongly dependent upon quality of the refrigerant. Overall evaporating heat transfer coefficients for the mixture were somewhat lower than pure R-22 values in the forced convective boiling region. For a given flow rate, the heat transfer coefficient at the circumferential tube wall(top, side, and bottom of the test tube) for R-22/R-114(50/50wt%)mixture, however, was higher than for pure R-22 at side and bottom of the tube. Furthermore, a prediction for the evaporating heat transfer coefficient of the mixtures was developed based on the method of Yoshida et.al.'s. The resulting correlation yielded a good agreement with the data for the refrigerant mixtures.

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소형박용 디젤엔진의 전열특성 (Characteristics of Heat Transfer for Small-size Marine Diesel Engine)

  • 최준섭
    • Journal of Advanced Marine Engineering and Technology
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    • 제20권4호
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    • pp.36-42
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    • 1996
  • Analysis of heat transfer on small-size Diesel engine is required for the development of high performance and efficiency engine. This basic study aims to establish heat transfer technique for marine Diesel engine. The main results from this study are as follows : 1) Overall engine heat transfer correlation of Re-Nu. 2) Radiant heat flux as fraction of total heat flux over the load range of several different Diesel engine. 3) Characteristics of heating curves on piston, cylinder liner and head. 4) Surface heat flux versus injection timing.

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친수 표면처리 종류에 따른 공기 예열 열교환기의 응축 열전달 실험적 연구 (Experimental Study of Condensation Heat Transfer in Pre-heating Exchanger to the Type of Hydrophilic Surface Treatment)

  • 석성철;정태용;신동훈;황승식;최규홍;박재원
    • 한국연소학회:학술대회논문집
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    • 한국연소학회 2012년도 제45회 KOSCO SYMPOSIUM 초록집
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    • pp.237-238
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    • 2012
  • Recently, an energy-saving due to the energy utilisation efficiency enhancement is important. In order to improve the heat efficiency of the general residential boiler, We performed an experiment of condensation heat transfer to air pre-heat exchanger adhered to the condensing boiler. In this research, We analyze the heat transfer performance through the hydrophilic surface treatment(plasma, etching). The results of the research, On plasma and etching treated surface, Overall heat transfer coefficient is displayed the tendency to increase.

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Concentric Double Pipe 열교환기에서 냉각수 급랭 현상의 모사에 대한 연구 (Study on Simulation of Cooling Water through Concentric Double Pipe Heat Exchanger )

  • 최안철;이성우;신익호;최성웅
    • 한국수소및신에너지학회논문집
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    • 제34권6호
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    • pp.741-747
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    • 2023
  • In this study, the heat transfer characteristics were numerically analyzed to investigate the possibility of utilizing cooling water using liquid nitrogen. From the study, as the mass flow rate of the hot fluid increased, the heat transfer rate increased by 8.9-81.7%. And lowering the inlet temperature of the hot fluid resulted in increase in the heat transfer rate by 33.8-71.5%. As for the filling level of liquid nitrogen, as higher filling level led to a decrease in the outlet temperature and an increase in the overall heat transfer coefficient.

전열온수식 LPG 기화기의 열전달 해석 (Heat Transfer Analysis of a Coil-Typed LPG Vaporizer with an Electrically Heating Water Bath)

  • 최성준;권정락;김광석;김효
    • 한국가스학회지
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    • 제11권3호
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    • pp.19-25
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    • 2007
  • 본 연구는 전열온수식 LPG 기화기에서의 열전달 현상을 실험적인 방법에 근거하여 분석하였다. 전기가 열식 온수 수조로부터 공급되는 열량은 처음에 액화석유가스(LPG)의 온도를 높이는 현열에 사용되고, 이후 기체가스(PG) 상태로 만들기 위한 잠열공급 및 기화된 가스의 온도 상승에 사용된다. 코일내부에서 기-액이 공존하는 two-phase flow가 형성되는 영역은 그 지역에서의 온도의 주기적인 파동현상을 통하여 확인될 수 있었으며, 이 영역 이후부터는 기상상태로 현열 효과만이 존재함을 알 수 있었다. 기화기의 열전달 능력은 총괄열용량으로 정의하였으며, 총괄열용량과 온수의 온도 및 가스유량에 따른 상관관계를 구하였다. 본 연구의 실험적 결과를 이용하면 전열온수식 LPG기화기의 열전달 특성 해석을 용이하게 수행할 수 있기 때문에, 향후 기화기 설계에 유용하게 적용할 수 있을 것이다.

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비공비혼합냉매를 사용하는 열펌프의 응축열전달 특성 (Condensing Heat Transfer Characteristics on a Heat Pump System Using Non-Azeotropic Refrigerant Mixtures)

  • 박기원;오후규;김욱중
    • 대한기계학회논문집
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    • 제19권4호
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    • pp.1125-1133
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    • 1995
  • Experiments were performed to investigate the condensing heat transfer characteristics of non-azeotropic mixtures of R-22 and R-114 in a heat pump system with a horizontal smooth tube as a condenser. The ranges of parameters, such as heating capacity, mass flow rate of refrigerant and quality were 780-3,480W, 24-71kg/h, and 0-1, respectively. The overall compositions of R-22 in a R-22/114 mixture were 25, 50, 75 and 100 per cent by wight. The results show that the overall condensing heat transfer coefficients for the mixtures were lower than the pure R-22 values. Local heat transfer coefficient of the pure R-22 was hghest at the top of the test tube. The local heat transfer coefficient of R-22/114 (50/50 wt%) at side and bottom of the test tube was higher than that at the top. From the obtained data, a prediction for the condensing heat transfer coefficients of the mixture was done based on the method of Fujii.