• 제목/요약/키워드: Convection heat transfer coefficient

검색결과 192건 처리시간 0.027초

대형 LPG 엔진 피스톤의 온도 분포 해석을 위한 열전도 역문제에 관한 연구 (Research on the Inverse Heat Conduction Problem for Thermal Analysis of a Large LPG Engine Piston)

  • 이부윤;박철우;최경호
    • 한국정밀공학회지
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    • 제19권11호
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    • pp.146-159
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    • 2002
  • An efficient method to predict the convection heat transfer coefficients on the top surface of the engine piston is proposed. The method is based on the inverse method of the thermal conduction problem and uses a numerical optimization technique. In the method, the heat transfer coefficients are numerically obtained so that the difference between analyzed temperatures from the finite element method and measured temperatures is minimized. The method can be effectively used to analyze the temperature distribution of engine pistons in case when application of prescribed-temperature boundary condition is not reasonable because of insufficient number of measured temperatures. A hollow sphere problem with an analytic solution is taken as a simple example and accuracy and efficiency is demonstrated. The method is applied to a practical large liquid petroleum gas(LPG) engine piston and the heat transfer coefficients on the top surface of the piston is successfully calculated. Resulting analyzed temperature favorably coincides with measured temperature.

소구경 원관내의 R-22 응축열전달에 대한 실험 (Experiments on R-22 condensation heat transfer in small diameter tubes)

  • 김내현;조진표;김정오;김만회;윤재호
    • 설비공학논문집
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    • 제10권3호
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    • pp.271-281
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    • 1998
  • In this study, condensation heat transfer experiments were conducted with two small diameter(ø7.5, ø4.0) tubes. Comparison with existing in-tube condensation heat transfer correlations indicated that the correlations overpredict the present data. For example, Akers correlation overpredicts the data upto 104%. The condensation heat transfer coefficient of the ø4.0 I.D. tube was smaller than that of the ø7.5 I.D tube; at the mass velocity of 300kg/$m^2$s, the difference was 12%. The pressure drop data of the small diameter tubes ware highly(two to six times) overpredicted by the Lockhart-Martinelli correlation. Subcooled forced convection heat transfer test confirmed that Gnielinski's single phase heat transfer correlation predicted the data reasonably well.

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Laminar Forced Convective Heat Transfer to Near-Critical Water in a Tube

  • Lee, Sang-Ho
    • Journal of Mechanical Science and Technology
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    • 제17권11호
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    • pp.1756-1766
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    • 2003
  • Numerical modeling is carried out to investigate forced convective heat transfer to near-critical water in developing laminar flow through a circular tube. Due to large variations of thermo-physical properties such as density, specific heat, viscosity, and thermal conductivity near thermodynamic critical point, heat transfer characteristics show quite different behavior compared with pure forced convection. With flow acceleration along the tube unusual behavior of heat transfer coefficient and friction factor occurs when the fluid enthalpy passes through pseudocritical point of pressure in the tube. There is also a transition behavior from liquid-like phase to gas-like phase in the developing region. Numerical results with constant heat flux boundary conditions are obtained for reduced pressures from 1.09 to 1.99. Graphical results for velocity, temperature, and heat transfer coefficient with Stanton number are presented and analyzed.

NATURAL CONVECTION HEAT TRANSFER CHARACTERISTICS IN A CANISTER WITH HORIZONTAL INSTALLATION OF DUAL PURPOSE CASK FOR SPENT NUCLEAR FUEL

  • Lee, Dong-Gyu;Park, Jea-Ho;Lee, Yong-Hoon;Baeg, Chang-Yeal;Kim, Hyung-Jin
    • Nuclear Engineering and Technology
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    • 제45권7호
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    • pp.969-978
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    • 2013
  • A full-sized model for the horizontally oriented metal cask containing 21 spent fuel assemblies has been considered to evaluate the internal natural convection behavior within a dry shield canister (DSC) filled with helium as a working fluid. A variety of two-dimensional CFD numerical investigations using a turbulent model have been performed to evaluate the heat transfer characteristics and the velocity distribution of natural convection inside the canister. The present numerical solutions for a range of Rayleigh number values ($3{\times}10^6{\sim}3{\times}10^7$) and a working fluid of air are further validated by comparing with the experimental data from previous work, and they agreed well with the experimental results. The predicted temperature field has indicated that the peak temperature is located in the second basket from the top along the vertical center line by effects of the natural convection. As the Rayleigh number increases, the convective heat transfer is dominant and the heat transfer due to the local circulation becomes stronger. The heat transfer characteristics show that the Nusselt numbers corresponding to $1.5{\times}10^6$ < Ra < $1.0{\times}10^7$ are proportional to 0.5 power of the Rayleigh number, while the Nusselt numbers for $1.0{\times}10^7$ < Ra < $8.0{\times}10^7$ are proportional to 0.27 power of the Rayleigh number. These results agreed well with the trends of the experimental data for Ra > $1.0{\times}10^7$.

열유동을 고려한 GIS 모선의 온도상승 예측 (Temperature Rise Prediction of GIS Bus Bar Considering Thermal Flow)

  • 김중경;오년호;이지연;한성진
    • 전기학회논문지
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    • 제58권4호
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    • pp.742-747
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    • 2009
  • Many works on the temperature distribution of power apparatus have usually done by coupled magneto-thermal analysis. Such a method can not consider the internal gas or oil flow in the power apparatus such as gas insulated switchgear, GIS bus bar, and power transformer. Moreover it can not show the internal temperature distribution of the power apparatus exactly. This paper proposes a coupled magneto-thermal-flow analysis considering Navier-Stokes equations. The convection heat transfer coefficient is calculated analytically by applying Nusselt number for natural convection and is applied to the boundary condition of proposed method. Temperature distribution of the GIS bus bar model considering thermal flow is obtained by the proposed method and shows good agreement with the experimental data.

Ribbed 管의 管傾斜角이 熱傳達에 미치는 影響 (The effect of inclined ribbed tubes on heat transfer and friction loss)

  • 박성찬;김종보
    • 대한기계학회논문집
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    • 제11권1호
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    • pp.105-109
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    • 1987
  • 본 연구는 열교환기의 설치 및 사용목적에 따라 전열관내유동이 경사류가 될 때 특히 자연순환(2*$10^{6}$<Gr<15*$10^{6}$)의 경우와 강제순환(3,000<Re< 40,000)의 경우에 대해서 열전달특성과 유동마찰에 의한 손질을 규명하는데 있다. 사용되는 관은 평골관과 ribbed관이며 관경사각을 수평면에 대하여 0˚,22.5˚,45˚, 90˚로 변화시켰다.

Experimental Investigation of R-22 Condensation in Tubes with Small Inner Diameter

  • Kim, Nae-Hyun;Cho, Jin-Pyo
    • International Journal of Air-Conditioning and Refrigeration
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    • 제7권
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    • pp.45-54
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    • 1999
  • In this study, condensation heat transfer experiments were conducted in two small diameter (ø17.5, ø4.0) tubes. Comparison with the existing in-tube condensation heat transfer correlations indicated that these correlations over predict the present data. For example, Akers correlation over predicted the data up to 104 %. The condensation heat transfer coefficient of the ø4.0 I.D. tube was smaller than that of the ø7.5 I.D tube; at the mass velocity of 300 kg/$m^2$s, the difference was 12 %. The pressure drop data of the small diameter tubes were highly (two to six times) over predicted by the Lockhart-Martinelli correlation. Sub-cooled forced convection heat transfer test confirmed that Gnielinski's single phase heat transfer correlation predicted the data reasonably well.

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수평관군 흡수기의 전열촉진에 관한 실험적 연구 (Experimental investigation of heat transfer enhancement in horizontal bundle tubes on absorber)

  • 문춘근;설원실;김재돌;윤정인
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2000년도 춘계학술대회논문집B
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    • pp.328-334
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    • 2000
  • This research was concerned with the enhancement of heat transfer by surfactant added to the aqueous solution of LiBr. Different horizontal tubes were tested with and without an additive of normal octyl alcohol. The test tubes were a bare tube, floral tube, hydrophilic tube. The additive concentration was about $0.05{\sim}5.5mass%$. The heat transfer coefficient was measured as a function of solution flow rate in the range of $0.01{\sim}0.034 kg/ms$. The experimental result were compared with cases without surfactant. The enhancement of heat transfer by Marangoni convection effect which was generated by addition of the surfactant is observed in each test tube.

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전자계 결합특성 및 대류 경계조건을 적용한 수치 해석적 열전달 해석 (Numerical Heat Transfer Analysis applying Coupled Electromagnetic Characteristics and Convection Boundary Condition)

  • 김창기;김상훈;정상용
    • 전기전자학회논문지
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    • 제13권3호
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    • pp.55-61
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    • 2009
  • 본 논문에서는 정열계 해석을 위해 유한요소법(F.E.M)을 이용한 열전달 해석 기법에 대하여 다루고 있다. 특히, 열전달의 주요 쟁점인 혼합 경계조건을 띄는 대류 경계조건을 자계 문제와 비교하여 갤러킨법(Galerkin Method)으로 정식화하였다. 그리고 해의 신뢰성을 확보하기 위해 자계 해석을 통해 열원이 되는 손실을 구한 후, 반복적 알고리즘을 통해 에너지 평형 방정식을 만족하는 열전달 계수를 산정하여 열전달 문제를 고려하는 자계-열계 결합 해석을 하였다. 마지막으로, 측정치와 비교하여 제안된 방법의 효용성을 증명하였다.

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Vertical arrangement of coils for efficient cargo tank heating

  • Magazinovic, Gojko
    • International Journal of Naval Architecture and Ocean Engineering
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    • 제11권2호
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    • pp.662-670
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    • 2019
  • Tanker cargo tanks are equipped with the means of raising and maintaining the cargo discharge temperature to a suitable level. In this paper, a new heating coil design is proposed and analyzed. Contrary to conventional designs, wherein the heating coils are evenly distributed over the tank bottom, the proposed design arranges the heating coils in the central part of the tank bottom, in a vertical direction. Due to the intensive cargo circulation generated, a forced convection is superimposed on a buoyancy-driven natural convection, providing a more efficient mixed convection heat transfer mechanism. Numerical simulations performed by using a finite volume method show that in the case of 7-bar steam Bunker C heavy fuel oil heating, a five-hour circulation phase average heat transfer coefficient equals 199.2 W/m2K. This result might be taken as an impetus for the more thorough experimental examination.