Oh Boong Kwon

Two-dimensional Numerical Simulations on the Performance of an Annular Jet Pump

Two-dimensional numerical simulations were carried out to investigate the effects of the shape of mixing chamber on the performance of annular jet pumps for several jet flow rates. We confined the computational domain to a jet, a mixing chamber, and the outlet of the pump. Several computations have been carried out to seek the effects of reducing angles on the suction performance and the efficiency of the jet pump. Some numerical results regarding suction flow rates, head ratios, the efficiencies of the pump, flow fields and pressure distributions are shown and discussed.

Study on Flame Oscillations in Laminar Lift-off Butane Flames Diluted with Nitrogen

초록: 질소로희석된부탄층류부상화염에서발생할수있는화염진동메커니즘을살펴보기위하여실험적연구를수행하였다. 화염진동은층류자유제트부상화염에서5가지영역으로구분되었다: 화염안정화영역(I), 열손실에의한진동(II), 열손실에의한진동과부력에의한진동이혼재된영역(III),열손실에의한진동과화염날림직전의진동이혼재된영역(IV), 그리고열손실에의한진동, 부력에의한진동및화염날림직전의진동이모두혼재된영역(V). 각각의화염진동의특성을규명하기위해화염의시간에따른부상높이변화에대한FFT분석을수행하였고각영역에관련된무차원변수와스트라훌수의조합으로특성화작업을수행하였다.Abstract: The characteristics of lifted butane flames diluted with nitrogen have been investigatedexperimentally in order to elucidate the mechanism of individual flame oscillation modes. Flame oscillationsin laminar free-jet lift-off flames are classified into the following five regimes: a stabilized lift-off regime (I),a heat-loss-induced oscillation (II), a buoyancy-induced oscillation along with a heat-loss-induced oscillation(III), a combined form of an oscillation prior to blow-out and a heat-loss-induced oscillation (IV), and acombination of an oscillation prior to blow-out and a buoyancy-induced oscillation along with aheat-loss-induced oscillation (V). The characterization of the individual flame oscillations modes are presentedand discussed using Strouhal numbers and their relevant parameters by the analysis of the power spectrum fortemporal variation of the lift-off height.

Effect of Outer Edge Flame on Flame Extinction in Counterflow Diffusion Flames

The present study on nitrogen-diluted non-premixed counterflow flames with finite burner diameters experimentally investigates the important role of the outer edge flame in flame extinction. Flame stability diagrams mapping the flame extinction response of nitrogen-diluted non-premixed counterflow flames to varying global strain rates in terms of the burner diameter, burner gap, and velocity ratio are explored. There exists a critical nitrogen mole fraction beyond which the flame cannot be sustained, and also the curves of the critical nitrogen mole fraction versus the global strain rate have C-shapes in terms of burner diameter, burner gap, and velocity ratio. In flames with sufficiently high strain rates, the curves of the critical nitrogen mole fractions versus global strain rate collapse into one curve, and the flames can have the 1-D flame response of typical diffusion flames. Three flame extinction modes are identified: flame extinctions through the shrinkage of the outer edge flame with and without an oscillation of the outer edge flame prior to the extinction and flame extinction through a flame hole at the flame center. The measured flame surface temperature and a numerical evaluation of the fractional contribution of each term in the energy equation show that the radial conductive heat loss at the flame edge destabilizes the outer edge flame, and the conductive and convection heat addition to the outer edge from the trailing diffusion flame stabilizes the outer edge flame. The radial conductive heat loss at the flame edge is the dominant extinction mechanism acting through the shrinkage of the outer edge flame.

Numerical Study of Distribution Characteristics of Pulverized Coal According to Operation Condition in PM Burners

Key Words: CFD(전산 유체 역학), Concentric Coal Nozzle(미분탄 과다노즐), Numerical Analysis(수치해석), PM Burner(저공해 버너), Pulverized Coal(미분탄), Weak Coal Nozzle(미분탄 부족노즐)초록: 국내에서 널리 사용되는 500 MW급 미분탄 화력발전에서 2개의 PM (pollution minimum) 버너의 최적 운전 범위를 확인하기 위하여 DPM (discrete phase model)을 활용하여 수치계산을 수행하였다. 본 연구는 저가의 아역청탄의 활용 증진을 위하여 다양한 조건에서 탄 종별로 연구를 수행하는데 그 목적이 있다. 탄 종별로 미분탄의 질량 유량, 1차 공기의 질량 유량, 그리고 미분탄의 입자 크기 분포를 달리하여 공기/석탄의 분배비의 영향을 조사하였다. 이러한 매개변수에 관하여 PM 버너에서의 공기/석탄의 분배비의 최적운전조건을 도출하고 이에 대해 논의하고자 한다.Abstract: We performed numerical simulation using a DPM (discrete phase model) to identify the optimal operation ranges in two representative PM burners widely used in domestic 500-MW pulverized coal-fired power plants. Recently there has been an increased utilization of low-cost coals such as sub-bituminous coal. We investigate the effects of coal blends on the distribution ratio of coal to air by varying the mass flow rates of pulverized coal and primary air and the particle size. We present and discuss optimal conditions for the distribution ratio of coal to air in PM burners.

Experimental Study in H2/CO/CH4-Air and H2/CO/C3H8-Air Premixed Flames. Part 1: Laminar Burning Velocities and Markstein Lengths

Flame propagation characteristics of hydrogen/carbon monoxide/methane (or propane)–air premixed mixtures were studied in a constant pressure combustion chamber with a schlieren system at room temperature and elevated pressures. Unstretched laminar burning velocities and Markstein lengths of various mixtures were obtained by analyzing high-speed schlieren images. Also, the experimentally measured unstretched laminar burning velocities were compared with numerical predictions using the PREMIX code with a H2/CO/C1–C4 mechanism, USC Mech II, developed by Wang et al. [23]. The two data from experiments and predictions show good agreement. The results indicate a significant increase in the unstretched laminar burning velocities with hydrogen enrichment and a decrease with the addition of hydrocarbons, whereas the opposite effects for the Markstein lengths were observed.

Experimental Study in H2/CO/CH4–Air and H2/CO/C3H8–Air Premixed Flames. Part 2: Cellular Instabilities

Experiments in a constant pressure combustion chamber at room temperature and elevated pressures using schlieren system were conducted to investigate the cellular instabilities in hydrogen/carbon monoxide/methane (or propane)–air premixed flames. In the present study, hydrodynamic and diffusional-thermal instabilities were evaluated to elucidate their effects to flame instabilities. Effective Lewis numbers of premixed flames with methane addition decrease for all of the cases. Meanwhile, the effective Lewis numbers with propane addition increase for lean and stoichiometric conditions, but they increase for rich and stoichiometric cases for hydrogen-enriched flames. With propane addition, the propensity for cells formation is significantly diminished whereas the cellular instabilities for hydrogen enriched flames are promoted. With methane addition, the similar behavior of cellularity is obtained, indicating that methane is not a candidate for suppressing cells formation in hydrogen/carbon monoxide/methane–air premixed flames.