• Title/Summary/Keyword: Heat Diffusion

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Measurement of Temperature in Double-concentric Diffusion Flames by Rapid Insertion Technique (급속 삽입범에 의한 동축 이중 확산화염 내부 온도 분포의 측정)

  • Chung, J.R.;Nam, P.W.;Lee, G.W.;Jurng, J.S.
    • 한국연소학회:학술대회논문집
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    • 1999.10a
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    • pp.231-240
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    • 1999
  • The temperature distribution in double-concentric diffusion flames have been investigated experimentally by rapid insertion technique. Using a fine thermocouple and rapid insertion mechanism, the temperature has been measured before soot particles attach the thermocouple junction which can affect the temperature signal by changing the radiation heat loss. For double-concentric diffusion flames, the temperature at the axis is higher than that of normal coflow diffusion flames because of the inverse diffusion flame at the center of the flame. However, it is almost same at the periphery on which the inverse flame does not have an effect.

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A Study on Dependence of Smoke Emission in Diesel Engines Upon Diffusion Combustion (디젤기관의 스모크배출의 확산연소 의존성에 관한 연구)

  • 한성빈;문성수;이성열
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.2
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    • pp.397-404
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    • 1994
  • Smoke is emitted in diesel engines because fuel injected into the high-temperatured and high-pressured combustion chamber burns with its mixture with insufficient oxygeny. In consideration of air pollution, above all, it is necessary to illuminate the cause of smoke emission in diesel engines. The smoke emission, which is characteristic of diffusion combustion in diesel engines, results from pyrolysis of fuel not mixed with air. Therefore the smoke emission is dependent on diffusion combustion quantity, which is in turn controlled by engine parameter. The study aims at making clear and interpreting the interdependence of smoke emission in diesel engines with heat released within combustion chamber, camparing diffusion combustion quantity according to each engine parameter (air fuel ratio, injection timing, and engine speed), and showing the relation between smoke emission and fraction of diffusion combustion through experiment.

Numerical Investigation of the Flamelet Structure of Buoyant Jet Diffusion Flames (부력 영향을 받는 제트 확산화염의 화염편 구조에 관한 수치계산 연구)

  • Oh, Chang-Bo;Lee, Eui-Ju
    • Journal of the Korean Society of Safety
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    • v.24 no.1
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    • pp.14-20
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    • 2009
  • Direct numerical simulations(DNS) were performed for the prediction of transient buoyant jet diffusion flames where the Froude numbers(Fr) are 5 and 160, respectively. The thermodynamic and transport properties were evaluated using CHEMKIN package to enhance the prediction performance of the DNS code. The simulated buoyant jet diffusion flame of Fr=5 and 160 showed the transient, dynamic motion well. It was identified that the buoyant jet flames were flickered periodically, and the simulated flickering frequency of the jet diffusion flame of Fr=5 was 12.5Hz, which was in good agreement with the experimental results. The flamelet structures of the buoyant jet diffusion flames could be well understood by comparing the scalar dissipation rates(SDR) and the heat release rates(HRR) of the flames. It was found that the SDR was strongly coupled with the HRR in the buoyant jet diffusion flames.

AN APPROXIMATE ANALYTICAL SOLUTION OF A NONLINEAR HYDRO-THERMO COUPLED DIFFUSION EQUATION

  • Lee, Jeong-woo;Cho, Won-cheol
    • Water Engineering Research
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    • v.2 no.3
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    • pp.187-196
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    • 2001
  • An approximate analytical solution of a nonlinear hydro-thermo coupled diffusion equation is derived using the dimensionless form of the equation and transformation method. To derive an analytical solution, it is drastically assumed that the product of first order derivatives in the non-dimensionalized governing equation has little influence on the solution of heat and moisture behavior problem. The validity of this drastic assumption is demonstrated. Some numerical simulation is performed to investigate the applicability of a derived approximate analytical solution. The results show a good agreement between analytical and numerical solutions. The proposed solution may provide a useful tool in the verification process of the numerical models. Also, the solution can be used for the analysis of one-dimensional coupled heat and moisture movements in unsaturated porous media.

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Nonlinear Behaviors of Pulsating Instabilities in Counterflow Diffusion Flames with Radiation Heat Loss (복사 열손실을 받는 대향류 확산화염의 맥동 불안정성의 비선형 거동)

  • Lee, Su Ryong;Park, Sung Cheon
    • Journal of the Korean Society of Combustion
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    • v.17 no.3
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    • pp.9-16
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    • 2012
  • Nonlinear dynamics of pulsating instability in radiating counterflow diffusion flames is numerically investigated by imposing Damk$\ddot{o}$hler number perturbation. Stable limit-cycle solutions occur in small ranges of Damk$\ddot{o}$hler numbers past bifurcation point of instability. Period doubling cascade and chaotic behaviors appear just before dynamic extinction occurs. Nonlinear dynamics is also studied when large disturbances are imposed to flames. For weak steady flames, the dynamic extinction range shrinks as the magnitudes of disturbances are increased. However, strong steady flames can overcome relatively large disturbances, thereby the dynamic extinction range extending. Stable limit-cycle behaviors reappears prior to dynamic extinction when the steady flames are strong enough.

Theoretical Calculation of Parabolic Rate Constant for High-Temperature Oxidation of Metals (금속의 고온 산화동안 포물선 속도상수의 이론적 계산)

  • Kim, Insoo;Cho, Weol Dong
    • Journal of the Korean Society for Heat Treatment
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    • v.14 no.5
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    • pp.282-285
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    • 2001
  • Based on the mass balance of anion and cation fluxes, the parabolic rate constant ($K_p$) of oxide grown during the high-temperature oxidation of metal is theoretically calculated. It is assumed that the diffusion of oxygen anion and metal cation through oxide scale obeys the Fick's 1st law, the growth of oxide is controlled by the diffusion of ions, electrical potential gradient as driving force for diffusion of ions is ignored, and oxidation occurs within an existing oxide layer. Then, the parabolic rate constant can be expressed by $K_p=[2{\rho}_{MmOn}{M^2}_{MmOn}(mD_oC_o{^e}+nD_MC_M{^e})/nm]$.

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Study on Diffusion Bonding of Stainless Steel to Mild Steel (연강-스테인리스강의 확산접합에 관한 연구)

  • Kim, S.T.
    • Journal of the Korean Society for Heat Treatment
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    • v.11 no.1
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    • pp.17-26
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    • 1998
  • Cladding of stainless steel on mild steel was prepared by diffusion bonding process. The bond strength increased with an increase of bonding temperature and time. It was also found that the bond strength increased as the surface roughness decreased. After the diffusion bonding of stainless steel-mild steel, the mild steel part near the bonded interface showed higher strength than the base steel due to the migration of chromium and nickel from stainless steel to mild steel. Carbon migration from mild steel gave effect on the formation of chromium carbides at grain boundaries of stainless steel, the fractograpohic features of the imperfectly bonded interface showed rather coarse dimples in the mild steel part and very fine dimples in the stainless steel part.

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Linear Stability Analysis of Cellular Counterflow Diffusion Flames with Radiation Heat Loss (복사 열손실을 받는 셀모양 대향류 확산화염의 선형 안정성 해석)

  • Lee, Su Ryong
    • Journal of the Korean Society of Combustion
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    • v.18 no.2
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    • pp.42-50
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    • 2013
  • Linear stability analysis of radiating counterflow diffusion flames is numerically conducted to examine the instability characteristics of cellular patterns. Lewis number is assumed to be 0.5 to consider diffusional-thermal instability. Near kinetic limit extinction regime, growth rates of disturbances always have real eigen-values and neutral stability condition of planar disturbances perfectly falls into quasi-steady extinction. Cellular instability of disturbance with transverse direction occurs just before steady extinction. However, near radiative limit extinction regime, the eigenvalues are complex and pulsating instability of planar disturbances appears prior to steady extinction. Cellular instability occurs before the onset of planar pulsating instability, which means the extension of flammability.

Experimental Performance Study of the Bubble Pump for the Diffusion Absorption Refrigerating System (확산형 흡수식 냉동시스템의 기포펌프 성능실험)

  • 이재효;정의갑;윤재호;정의갑
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.16 no.3
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    • pp.287-292
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    • 2004
  • An experimental investigation was carried out to study the performance of a bubble pump for the diffusion absorption refrigerating system. Ammonia was used as the refrigerant and the helium was charged in order to balance the pressure between the low and high pressure side. As experimental variables, the concentration of ammonia charged into system, heat input, and the pressure of helium were selected. Experimental results show that the generation rate of ammonia vapor and the circulation rate of diluted ammonia solution were increased as the heat input increases, but the ratio of the solution to vapor flow rate was decreased. The generation rate of refrigerant vapor and the circulation rate of diluted ammonia solution increased as the system pressure decreased. Finally under the condition of 25 bars, the concentration of rich ammonia solution was not affected by the generation rate of ammonia vapor and the circulation of diluted ammonia solution.

Structural Design for Key Dimensions of Printed Circuit Heat Exchanger (인쇄기판형열교환기 핵심치수 구조설계)

  • Kim, Yong Wan;Kang, Ji Ho;Sah, In Jin;Kim, Eung Seon
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.14 no.1
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    • pp.24-31
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    • 2018
  • The mechanical design procedure is studied for the PCHE(printed circuit heat exchanger) with electrochemical etched flow channels. The effective heat transfer plates of PCHE are assembled by diffusion bonding to make a module. PCHE is widely used for industrial applications due to its compactness, cost efficiency, and serviceability at high pressure and/or temperature conditions. The limitations and technical barriers of PCHE are investigated for application to nuclear components. Rules for design and fabrication of PCHE are specified in ASME Section VIII but not in ASME Section III of nuclear components. Therefore, the calculation procedure of key dimensions of PCHE is defined based on ASME section VIII. The effective heat transfer region of PCHE is defined by several key dimensions such as the flow channel radius, edge width, wall thickness, and ridge width. The mechanical design procedure of key dimensions was incorporated into a program for easy use in the PCHE design. The effect of assumptions used in the key dimension calculation on stress values is numerically investigated. A comparative analysis is done by comparing finite element analysis results for the semi-circular flow channels with the formula based sizing calculation assuming rectangular cross sections.