• Title/Summary/Keyword: Convective Boundary Condition

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Finite Element Analysis for Circulation Phenomena in Sudden Expansion of Open Channel (유한요소법을 이용한 개수로단면급확대부의 순환현상해석)

  • 윤태훈;서승원
    • Water for future
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    • v.21 no.1
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    • pp.67-76
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    • 1988
  • Analyzed was the circulation phenomena in the open channel with sudden expansion, by applying the Galerkin's finite element method to the depth-averaged 2-dimensional continuity and momentum equations. Wave tests were done in the simplified channel in order to review the validity of this newly developed model and the computed results were within 0.5% of $L_2$-norm error, and application of this model to the simulation of simplified dam-break gave very close results compared with the analytical solution, thus, it can be concluded that this model is valid and efficient. The main flow in the expanded channel was defined as a new initial condition with given velocity and the flow in the expanded portion was at rest in simulating the circulation, and besides the Neumann's condition the slip boundary condition for lateral wall was found to be proper condition than the no-slip condition. It can be concluded, from the numerical tests in the sudden expension, that the circulating phenomena depend mainly on the convective inertia and the effect of turbulence due to bottom shear and lateral shear is insignificant.

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Experimental Study on the Secondary Flow Characteristics of a Supercritical Carbon Dioxide Flow in a Gas Cooling Process Within a Square Duct (정사각 덕트 초임계 상태 이산화탄소 가스 냉각과정 중 2차 유동 특성 측정 연구)

  • Han, Seong-Ho;Seo, Jung-Sik;Kim, Young-Chan;Kim, Min-Soo;Choi, Young-Don
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.32 no.2
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    • pp.158-165
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    • 2008
  • The carbon dioxide properties change sharply near the critical or pseudo-critical point in the heat transfer processes. The reduction in turbulent, convective heat transfer parameters observed in some supercritical data and in experiments with common gases can be due to property variation, acceleration, buoyancy or combinations of these phenomena, depending on the conditions of the applications. In this study, the measurement for the secondary flow driven by buoyancy was carried out on the supercritical carbon dioxide turbulent flows in the different boundary condition with the constant mass flow rate. The available measuring techniques were used to clarify the behaviour of any supercritical fluid. Laser Doppler Velocimeter (LDV) and a special device was used to measure the secondary velocity and turbulent characteristics of the supercritical flows.

Analysis of heat and mass transfer in a vertical tube absorber cooled by air (공랭형 수직원관 흡수기에서의 열 및 물질전달 해석)

  • Kim, Seon-Chang;O, Myeong-Do;Lee, Jae-Heon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.10
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    • pp.3293-3303
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    • 1996
  • Numerical analyses have been performed to estimate the absorption heat and mass transfer coefficients in absorption process of the LiBr aqueous solution and the total heat and mass transfer rates in a vertical tube absorber which is coolING ed by air. Axisymmetric cylindrical coordinate system was adopted to model the circular tube and the transport equations were solved by the finite volume method. Absorption behaviors of heat and mass transfer were analyzed through falling film of the LiBr aqueous solution contacted by water vapor in tube. Effects of film Reynolds number on heat and mass transfer coefficients have been also investigated. Especially, effects of tube diameter have been considered to observe the total heat and mass transfer rates through falling film along the tube. Based on the analysis it has been found that the total mass transfer rate increases rapidly in a region with low film Reynolds number(10 ~ 40) as the film Reynolds number increases, while decreases beyond that region. The total heat and mass transfer rates increase with increasing the tube diameter.

Heat Transfer Correlations for Air-Water Two-Phase Flow of Different Flow Patterns In a Horizontal Pipe

  • Kim, Dongwoo
    • Journal of Mechanical Science and Technology
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    • v.15 no.12
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    • pp.1711-1727
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    • 2001
  • Heat transfer coefficient were measured and new correlations were developed for two-phase heat transfer in a horizontal pipe for different patterns. Flow patterns were observed in a transparent circular pipe (2.54 cm I. D. and L/D=96) using an air/water mixture. Visual identification of the flow patterns was supplemented with photographic data and the results were plotted on the flow regime map proposed by Taitel and Dukler and agreed quite well with each other. A two-phase heat transfer experimental setup was built for this study and a total of 150 two-phase heat transfer data with different flow patterns were obtained under a uniform wall heat flux boundary condition. For these data, the superficial Reynolds number ranged from 640 to 35,500 for the liquid and from 540 to 21,200 for the gas. Our previously developed robust two-phase heat transfer correlation for a vertical pipe with modified constants predicted the horizontal pipe air-water heat transfer experimental data with good accuracy. Overall the proposed correlations predicted the data with a mean deviation of 1.0% and an rms deviation of 12%.

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Numerical Analysis for Thermal Response of Silica Phenolic in Solid Rocket Motor (고체 로켓 추진기관에서 실리카/페놀릭 열반응 해석 연구)

  • Seo, Sangkyu;Hahm, Heecheol;Kang, Yoongoo
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2017.05a
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    • pp.521-528
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    • 2017
  • In this paper, the numerical analysis for heat conduction of silica/phenolic composite material, which is used for solid rocket nozzle liner or insulator, was conducted. 1-D Finite Difference Method for the analysis of silica/phenolic during the firing of solid rocket motor was used to calculate the heat conduction considering the surface ablation and the thermal decomposition. The boundary condition at the nozzle wall took into account the convective heat transfer, which was obtained by integration equation. The numerical results of the surface ablation and char depth were compared with the results of test motor that is TPEM-10. It was found that the result of calculation is favorably agreed with the thermal response of test motor.

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Heat Transfer Analysis for Variable Thrust Control System Using 1-Way Coupling (일방향 연계를 활용한 연속가변 추력제어 시스템의 열전달 해석)

  • Lee, JiHun;Jang, HanNa;Kim, GyuBin;Cho, JinYeon;Kawk, JaeSu;Ko, JunBok;Park, SungHan
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2017.05a
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    • pp.388-391
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    • 2017
  • In this study, heat transfer analysis of variable thrust control system have been conducted by using commercial CFD code and FEM code. We Carried out computational fluid dynamics analysis to obtain the temperature and convective heat transfer coefficient of hot gas of variable thrust control system. Data are used as boundary condition for heat transfer analysis using mapping method. Temperature of O-ring for sealing was predicted

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Analysis of forced convective laminar film boiling heat transfer on vertical surface (垂直平板에서의 强制對流 膜沸騰 流動의 熱傳達解析)

  • 이규식;최영돈
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.3
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    • pp.425-436
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    • 1987
  • Accurate predictions of heat transfer coefficient of vertical laminar film-boiling are very important in many engineering applications. There are many predictions, however they are not exact as yet, since they have used the assumption of constant thermodynamic properties in the analysis. In this paper, heat transfer of vertical film boiling was analysized by Runnge Kutta method using veriable thermodynamic properties. 1/4 interval method was exployed for the prediction of unknown wall boundary condition. Numerical computations were performed with varying the wall temperature and the free stream velocity of liquid. Results show that assumption of constant thermodynamic properties induced considerable error in predicting the heat transfer coefficient, friction factor, film thickness, and critical length for transition to turbulent flow. Comparision of the predicted heat transfer coefficient of present analysis with that from Bromley's correlation shows that the use of general latent heat in Bromely equation instead of modified latent heat is more desireable since it makes the coefficient of Bromley equation into constant.

Numerical Analysis for Thermal Response of Silica Phenolic in Solid Rocket Motor (고체 로켓 추진기관에서 실리카/페놀릭 열반응 해석 연구)

  • Seo, Sangkyu;Hahm, Heecheol;Kang, Yoongoo
    • Journal of the Korean Society of Propulsion Engineers
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    • v.22 no.4
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    • pp.76-84
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    • 2018
  • In this paper, the numerical analysis for heat conduction of silica/phenolic composite material, used for solid rocket nozzle liners or insulators, is conducted. A 1-dimensional finite difference method for the analysis of silica/phenolic during the firing of a solid rocket motor is used to calculate heat conduction, considering surface ablation and thermal decomposition. The boundary condition at the nozzle wall, considering the convective heat transfer, is obtained via integration equations. The numerical results of the surface ablation and char depth are compared with the results of a TPEM-10 test motor, finding that the result of calculation agrees with the thermal response of the test motor.

A NUMERICAL STUDY ON THE FLOW AND HEAT TRANSFER CHARACTERISTICS OF A HEAT EXCHANGER HAVING RECTANGULAR PIN-FINS SLANTED IN THE FLOW DIRECTION (유동 방향으로 기울어진 사각 핀-휜 열교환기의 유동 및 열전달 특성에 대한 수치적 연구)

  • Seo, J.H.;Kim, M.;Ha, M.Y.;Min, J.K.
    • Journal of computational fluids engineering
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    • v.21 no.3
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    • pp.98-109
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    • 2016
  • The flow and heat transfer characteristics of a heat exchanger having rectangular pin-fin in the flow direction have been investigated numerically. On the bottom plate, the convective boundary conditions for the hot side was given, and the fins were arranged in a channel-type geometric model using the periodic boundary condition in the span-wise direction. Three-dimensional numerical calculations for the flow and conjugate heat transfer problem were conducted using SIMPLE algorithm and $k-{\varepsilon}$ turbulence model. For the slanted pin-fin models, it was found that the downward cooling flow is generated due to the downward pressure gradient component, which can enhance the heat transfer performance near the bottom surface and the fin stem region. Four different inclined angles were considered in the Reynolds number range of 13,500-55,000. The aero-thermal performance of the slanted pin-fin heat exchangers, such as the volume and area goodness factors, were summarized and compared with the baseline plate-fin type heat exchanger quantitatively.

Optimization Techniques for the Inverse Analysis of Service Boundary Conditions in a Porous Catalyst Substrate with Fluid-Structure Interaction Problems (유체 구조 상호작용 문제를 가진 다공성 촉매 담체에서 실동경계조건의 역문제 해석을 위한 최적화 기법)

  • Baek, Seok-Heum;Cho, Seok-Swoo;Kim, Hyun-Su
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.10
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    • pp.1161-1170
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    • 2011
  • This paper presents a solution to the inverse problem for the service boundary conditions of thermal-flow and structure analysis in a catalyst substrate. The exhaust-gas purification efficiency of a catalyst substrate is influenced by the shape parameter, catalyst ingredients and so on and is estimated by the thermal flow uniformity. The formulations of the inverse problem of obtaining the thermal-flow parameters (inlet temperature, velocity, heat of reaction, convective heat-transfer coefficient) and the direct problem of estimating from a given outlet temperature distribution are described. An experiment was designed and the response-surface optimization technique was used to solve the proposed inverse problem. The temperature distribution of the catalyst substrate was obtained by thermal-flow analysis for the predicted thermal-flow parameters. The thermal stress and durability assessments for the catalyst substrate were performed on the basis of this temperature distribution. The efficiency and accuracy of the inverse approach have been demonstrated through the achievement of good agreement between the thermal-flow response surface model and the results of experimental vehicle tests.