• Title/Summary/Keyword: gas transfer

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Prediction of Heat Transfer Rates to Spray Water Droplets in a High Pressure Mixture Composed of Saturated Steam and Noncondensable Hydrogen Gas (고압의 포화수증기-비응축성 수소기체 혼합기 속에서 분무수적으로의 열전달을 예측)

  • Lee, S.K.;Jo, J.C.;Cho, J.H.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.3 no.5
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    • pp.337-349
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    • 1991
  • Heat and mass transfer rates to spray water droplets for spray transients in a high pressure vessel have been predicted by two different droplet models: the complete mixing model and the non-mixing model. In this process, the ambient fluid surrounding the droplets is a real-gas mixture composed of saturated steam and noncondensable hydrogen gas at high pressure. The physical properties of the mixture are estimated by applying the concept of compressibility factor and using appropriate correlations. A computer program, DROPHMT, to calculate the heat and mass transfer rates for two different droplet models has been developed. As an illustrative application of the computer program to engineering practices, heat and mass transfer rates to spray water droplets for spray transients in a Pressurized Water Reactor (PWR) pressurizer have been calculated, and the typical results have been provided.

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Gas cooling heat transfer coefficient for $CO_2$-PEC9 mixture under supercritical condition (초임계조건에서 $CO_2$-PEC9 혼합물의 물성예측을 통한 냉각 열전달특성 연구)

  • Yun, Rin
    • Proceedings of the SAREK Conference
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    • 2009.06a
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    • pp.821-826
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    • 2009
  • Due to environmental concerns $CO_2$ has been reintroduced as a potential candidate to replace HFCs in refrigeration systems. Oils are always required in a vapor-compression cycle, and thus actual working fluid in the system is $CO_2$-oil mixtures even though the oil concentrations are low at the heat exchangers and the expansion device. The cooling heat transfer coefficients for $CO_2$-oil mixtures under supercritical condition are required to designing of the gas cooler in the $CO_2$ refrigeration system properly. In the present study, the gas cooling heat transfer coefficients for $CO_2$-PEC9 was estimated by using the Gnileinski correlation, and the Kim and Ghajar model through the previous prediction models for the thermo-physical properties of $CO_2$-oil mixture. The Gnileinski correlation was used when the oil wt.% in the mixture is less than 1.0, and for the higher oil concentration the Kim and Ghajar model was applied. The estimated results agree with the experimental results conducted by the Dang et al.

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Introduction to Flame Transfer Function in Lean Premixed Gas Turbine Combustor (희박 예혼합 가스터빈 연소기에서의 화염 전달 함수 소개)

  • Kim, Dae-Sik
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.35 no.9
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    • pp.975-979
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    • 2011
  • Lean premixed gas turbine combustors were successful in meeting current NOx emission regulations. However, these combustors have been found to be susceptible to combustion instability. In this study, general mechanisms for combustion dynamics and instabilities in lean premixed gas turbine combustors are introduced. In addition, the flame transfer functions in the combustor are experimentally determined. The inputs to the flame transfer function are the imposed velocity fluctuations of the mixture. The key results of the measurements are reviewed.

Numerical study of oxygen transport characteristics in lead-bismuth eutectic for gas-phase oxygen control

  • Wang, Chenglong;Zhang, Yan;Zhang, Dalin;Lan, Zhike;Tian, Wenxi;Su, Guanghui;Qiu, Suizheng
    • Nuclear Engineering and Technology
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    • v.53 no.7
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    • pp.2221-2228
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    • 2021
  • One-dimensional oxygen transport relation is indispensable to study the oxygen distribution in the LBE-cooled system with an oxygen control device. In this paper, a numerical research is carried out to study the oxygen transport characteristics in a gas-phase oxygen control device, including the static case and dynamic case. The model of static oxygen control is based on the two-phase VOF model and the results agree well with the theoretical expectation. The model of dynamic oxygen control is simplified and the gas-liquid interface is treated as a free surface boundary with a constant oxygen concentration. The influences of the inlet and interface oxygen concentration, mass flow rate, temperature, and the inlet pipe location on the mass transfer characteristics are discussed. Based on the results, an oxygen mass transport relation considering the temperature dependence and velocity dependence separately is obtained. The relation can be used in a one-dimensional system analysis code to predict the oxygen provided by the oxygen control device, which is an important part of the integral oxygen mass transfer models.

Gas 분산 기-액 반응조에서 기포운동이 열전달에 미치는 영향

  • Son, Byeong-Jin;Lee, Hyeon
    • The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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    • v.8 no.1
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    • pp.10-13
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    • 1979
  • The study for bubbling phenomena to influence heat transfer in gas - liquid contactors. The sparged contactor is gaining importance for gas-liquid chemical reactions. In this paper, correlations between Reynolds number and heat transfer coefficient were studied and experimental expressions were also obtained over broth of areas, namely, laminar area and turbulent area respectively.

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Heat transfer and flow characteristics of a cooling thimble in a molten salt reactor residual heat removal system

  • Yang, Zonghao;Meng, Zhaoming;Yan, Changqi;Chen, Kailun
    • Nuclear Engineering and Technology
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    • v.49 no.8
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    • pp.1617-1628
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    • 2017
  • In the passive residual heat removal system of a molten salt reactor, one of the residual heat removal methods is to use the thimble-type heat transfer elements of the drain salt tank to remove the residual heat of fuel salts. An experimental loop is designed and built with a single heat transfer element to analyze the heat transfer and flow characteristics. In this research, the influence of the size of a three-layer thimble-type heat transfer element on the heat transfer rate is analyzed. Two methods are used to obtain the heat transfer rate, and a difference of results between methods is approximately 5%. The gas gap width between the thimble and the bayonet has a large effect on the heat transfer rate. As the gas gap width increases from 1.0 mm to 11.0 mm, the heat transfer rate decreases from 5.2 kW to 1.6 kW. In addition, a natural circulation startup process is described in this paper. Finally, flashing natural circulation instability has been observed in this thimble-type heat transfer element.

HEAT TRANSFER CHARACTERISTICS IN A FAST PYROLYSIS REACTOR FOR BIOMASS (바이오매스 급속열분해 반응기내 열전달 특성)

  • Choi, Hang-Seok
    • Journal of computational fluids engineering
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    • v.15 no.1
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    • pp.9-16
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    • 2010
  • The characteristics of flow and heat transfer in a bubbling fluidized bed are investigated by means of computational fluid dynamics (CFD). To simulate two-phase flow for the gas and solid flows, Eulerian-Eulerian approach is applied. Attention is paid for a heat transfer from the wall to fluidized bed by bubbling motion of the flow. From the result, it is confirmed that heat transfer is promoted by chaotic bubbling motion of the flow by enhancement of mixing among solid particles. In particular, the vortical flow motion around gas bubble plays an important role for the mixing and consequent heat transfer. Discussion is made for the time and space averaged Nusselt number which shows peculiar characteristics corresponding to different flow regimes.

Effect of Shielding Gases on the Weldability of High Efficient GMAW Process (고능률 GMAW의 용접성에 미치는 보호가스의 영향)

  • 한기형;한종만;이민우;이은배;한용섭
    • Journal of Welding and Joining
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    • v.13 no.1
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    • pp.127-137
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    • 1995
  • The possibility of new GMAW process using economic shielding gases including CO$_{2}$ gas was investigated on the effect of shielding gas on weldabilty. In the optimum welding condition using 600A power source, FCAW process showed low depositions rate, 114 g/min at 300A, but new GMAW using other mixed shielding gases exhibited high deposition rate, 208-224 g/min at 450A. TIME gas, Ar+CO$_{2}$ gas and Ar+CO$_{2}$+O$_{2}$ gas as a shielding gas were able to be used to the very high welding current(450A), moreover TIME gas and Ar+CO$_{2}$ gas showed the highest arc stability among shielding gases studied in this experiments. The weld penetration was performed by axial spray transfer mode of weld droplet. On the basis of workability, weldability and economic point of view, Ar mixture (80%Ar+20%CO$_{2}$) gas was recommended as a shielding gas for the development and application of new GMAW process. This shielding gas showed the low spatter, good weld quality, stable arc and low cost at the region of high welding current.

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Cooling Heat Transfer Characteristics of CO2 in Helical Coil Type Gas Coolers (헬리컬 코일형 가스냉각기 내 CO2의 냉각 열전달 특성)

  • Son, Chang-Hyo;Jeon, Min-Ju;Oh, Hoo-Kyu
    • Journal of Advanced Marine Engineering and Technology
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    • v.31 no.6
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    • pp.699-706
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    • 2007
  • The cooling heat transfer coefficient and pressure drop of $CO_2$(R-744) in helical coil copper tubes were investigated experimentally The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter. a pre-heater and a inclined helical coil type gas cooler (test section). The test section consists of a smooth copper tube of 2.45 and 4.55mm inner diameter The refrigerant mass fluxes were varied from 200 to $600 [kg/m^2s]$ and the inlet pressures of 9as cooler were 7.5 to 10.0 [MPa]. The heat transfer coefficients of $CO_2$ in helical coil tubes increase with the increase of mass flux and gas cooling pressure of $CO_2$. The pressure drop of $CO_2$ in the gas cooler shows a relatively food agreement with those Predicted by Ito's correlation developed for single-phase in helical coil tubes. Though a few correlation available with the data. the local heat transfer coefficient of $CO_2$ agrees well with those presented by Pitla et al. among the predictions. However at the region near pseudo-critical temperature. the experiment data indicate higher values than the Pitla et al. correlation.

Heat Transfer and Pressure Drop Characteristics of Supercritical $CO_2$ in a Helically Coiled Tube (초임계 $CO_2$의 헬리컬 코일관 내 열선단과 압력강하 특성)

  • Yu, Tae-Guen;Kim, Dae-Hui;Son, Chang-Hyo;Oh, Hoo-Kyu
    • Proceedings of the SAREK Conference
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    • 2005.11a
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    • pp.353-358
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    • 2005
  • The heat transfer and pressure drop of supercritical $CO_2$ cooled in a helically coiled tube was investigated experimentally. The experiments were conducted without oil in the refrigerant loop. The experimental apparatus of the refrigerant loop consist of receiver, a variable speed pump, a mass flowmeter, a pre-heater, a gas cooler(test section) and an isothermal tank. The test section is a helically coiled tube in tube counter flow heat exchanger with $CO_2$ flowed inside the inner tube and coolant( water) flowed along the outside annular passage, It was made of it copper tube with the inner diameter of 4.55[mm]. the outer diameter of 6.35 [mm] and length of 10000 [mm]. The refrigerant mass fluxes were $200^{\sim}600$ [kg/m2s] and the inlet pressure of gas cooler varied from 7.5 [MPa] to 10.0 [MPa]. The main results are summarized as follows : The heat transfer coefficient of supercritical $CO_2$ increases, as the cooling pressure of gas cooler decreases. And the heat transfer coefficient increases with the increase of the refrigerant mass flux. The pressure drop decreases in increase of the gas cooler pressure and increases with increase the refrigerant mass flux.

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