• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.112.2-112.2
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• 2010

슬러리 기포탑 반응기는 열 및 물질 전달의 용이성, 낮은 운전비용 및 장치의 간단성의 장점을 가지고 있어서 Fischer-Tropsch 반응, bio-reaction 등에 많이 응용되고 있다. 그러나 기포탑 반응기 내의 물질 거동은 매우 복잡하기 때문에 많은 연구가 이루어지고 있음에도 불구하고 그 현상에 대한 명확한 이해는 어려운 상황이다. 특히 기포탑반응기내에 기체의 포집율(gas hold-up)을 증가시키는 것을 목적으로 하는 연구들이 활발히 진행되고 있다. 본 연구에서는 기체의 분사 방향에 따른 기체 포집율의 변화를 관찰하였다. 기체 분사는 0.6 mm의 pore가 66개로 구성된 perforated plate를 통해서 이루어졌고, 수직방향, 수평방향, 45도 그리고 수직/수평 조합의 네 가지 분사방향에 대해서 실험을 수행하였다. 반응기는 내경이 0.15 m이고 높이 2.0 m 아크릴 반응기를 이용하였다. 사용된 연속상은 수돗물을 사용하였고 분산상 기체로는 압축 공기를 이용하였다. 전체적인 기체 포집율은 수직방향의 분사방향에서 가장 높게 측정되었다. 그리고 수직/수평의 조합 분사방향의 경우, 기체 포집율이 가장 낮게 관찰되었다. 이것은 분사방향이 수직/수평으로 서로 엇갈릴 경우, 기포간의 충돌 가능성이 높아지고 bubble coalescence가 증가하였기 때문인 것으로 보인다. 실제로 homogeneous flow regime에서 heterogeneous flow regime으로 전환되는 기체선속도는 분사방향이 수직, 45도, 수평, 수직/수평 조합의 순서로 감소하였다. 즉 이 순서로 기체흐름의 와류가 증가하는 것을 알 수 있었다. 또한 Dynamic Gas Disengagement(DGD) 분석을 통하여 큰 기포가 발생하기 시작하는 기체 선속도의 변화를 관찰하였다. 이 경우, 예상되듯이 수직/수평 조합에서는 1.5 cm/sec 기체 선속도에서 큰 기포가 발생하기 시작한 반면 수직 방향 분사의 경우에는 2.5 cm/sec의 보다 높은 기체 선속도에서 관찰되기 시작하였다. 이러한 현상들을 종합하였을 때, 기체 분사방향을 수직으로 일정하게 했을 때, 기포간 출동을 최소화하고 와류발생을 최대한 지연시키며 전체 기체 포집율을 증가시킬 수 있음을 알 수 있다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.5
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• pp.495-501
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• 2012

Spray characteristics of liquid jets in crossflow, which can be observed in the liquid jet injection system of a gas turbine or ramjet engine, were experimentally investigated. By measuring liquid jet penetration in the case of single orifice and double orifice injectors, the experimental formula for jet penetration was modified to consider penetration distances greater than that considered in a previous study. The changes in spray characteristics resulting from changes in the liquid jet and crossflow pressure, including SMD and jet disintegration, were carefully studied. Specifically, the jet penetration was measured for different injector shapes, and in the case of a double orifice injector, the penetration of the rear orifice jet was found to be greater by approximately 20% ($L_h$ = 4 mm) compared to that in the case of a single orifice injector because of the influence of the front orifice.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.6
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• pp.61-68
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• 2002

Combustion characteristics of dual transverse injection of hydrogen in supersonic air flows were studied using computational methods. Three-dimensional Navier-Stokes with a non-equilibrium chemical reaction model and the k-$\omega$ SST turbulence model were used. A parametric study was conducted with the variation of the distance between two injectors. Combustion characteristics of dual injection are very different from those of single injection. The combustion characteristics of two injection flows are very different from each other, and the ignition and combustion characteristics of the rear injection flow are strongly influenced by those of the front injection flow. The increase of the distance between two injectors up to a specific distance results in the increase of burning rate. However, the increase of the distance over the specific distance gives no increase of burning rate but makes more losses of stagnation pressure. From the results it can be stated that there exists a distance between two injectors for optimum combustion characteristics.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2002.04a
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• pp.61-61
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• 2002

스크램 제트 엔진의 설계에서 초음속으로 유입된 공기의 짧은 잔류시간으로 인한 연료-공기의 혼합은 가장 중요하며 해결하기 힘든 문제이다. 전헝적인 비행 조건에서 흡입 공기가 극초음속 비행기 엔진 내에서 잔류하는 시간의 단위는 1 ms 정도이어서 짧은 시간 동안 연료와 공기는 효율적으로 혼합되어야 하며, 최대의 추진력을 얻기 위하여 과도한 공력저항없이 연소 가능한 연료-공기 혼합기를 생성시킬 수 있는 효율적인 연료-공기의 혼합 방법이 요구된다. 현재까지 가장 많이 연구되어 온 혼합 방법은 엔진 입구로 들어오는 공기 유동에 수직 방향으로 연료를 분사하는 것으로 이 방법은 연료 유동 방향과 공기 유동 방향이 수직이기 때문에 추력 손실이 생기는 단점을 갖고 있지만, 초음속으로 유입되는 공기에 수직으로 연료를 분사하게되면 분사 위치 앞에 궁형 충격파가 생겨서 감속되어 유동이 회전하는 재순환영역이 생기고 연료의 혼합이 잘 이루어지는 장점이 있다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.6
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• pp.53-60
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• 2002

Based on the analyses of the single transverse injection in supersonic flow fields, the mixing characteristics of dual transverse injection of hydrogen in supersonic air flow are studied with computational methods. Three-dimensional Navier -Stokes and the k-$\omega$ SST turbulence model were used. A parametric study is conducted with the variation of the distance between two injectors. The flow patterns and the mixing characteristics of two injection flows are very different from each other, and the flow patterns and the mixing characteristics of the rear injection flow are strongly influenced by those of the first injection flow. The increase of the distance between two injectors up to a specific distance results in the increase of mixing rate and penetration of fuel. However, the increase of the distance over the specific distance results in the decrease of mixing rate and penetration of fuel. From the results it can be stated that there exists a distance between two injectors for optimum mixing characteristics.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.1
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• pp.61-69
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• 2004

This paper describes numerical efforts to characterize the flame-holding and air-fuel mixing process of model SCRamjet engine combustor, where a hydrogen jet injected into a supersonic cross flow and in a cavity Combustion phenomena in a model SCRamjet engine, which has been experimentally studied at University of Queensland and Australian National University using a free-piston shock tunnel, was observed around separation region of upstream of the normal injector and inside of cavity. The results show that the separation region and cavity generates several recirculation zones, which increase the fuel-air mixing. Self ignition occurs in the separation-freestream and cavity-freestream interface.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.6
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• pp.38-47
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• 2008

The liquid column and spray trajectory have been experimentally studied in liquid jets injected into subsonic crossflow. With water as fuel injection velocity, injection angle were varied to provide of jet operation conditions. The Pulsed Shadowgraph Photography and Planar Liquid Laser Induced Fluorescence technique was used to determine the injection characteristics in a subsonic crossflow of air. And the mainly objectives of this research was to get a empirical formula of liquid column and spray region trajectory with forward and reversed injection of air stream. As the result, This research has been shown that each trajectories were spatially dependent on air-stream velocity, fuel injection velocity, various injection angle, and normalized injector exit diameter. Furthermore, the empirical formula of liquid column trajectories has been some different of drag coefficient results between forward and reversed angled injection.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.3
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• pp.53-64
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• 2018

In this study, computational simulation was performed to investigate the characteristics of air/fuel mixing according to the shape of the injector exit when the transverse jet was injected into a supersonic flow. Non-reacting flow simulation was conducted with fixed mass flow rate and the same cross-sectional area. To validate the results, free stream Mach number and jet-to-crossflow memetum ratio are set to 3.38 and 1.4, respectively, which is same as the experimental condition. Further, separation region, structure of the under-expended jet, jet penetration height, and flammable region of hydrogen for five different injectors compared.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.1
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• pp.28-39
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• 2003

Effects of the orifice internal flow such as cavitation and hydraulic flip on transverse injection into subsonic crossflows have been studied. The liquid column breakup length and the liquid column trajectory were measured by changing the orifice diameter (d), the orifice length/orifice diameter (L/d), the injection pressure and the shapes (sharp and round) of orifice entrance, and were compared with previous results. It is found that cavitation bubbles, which occur inside the sharp-edged orifice, make the liquid jet very turbulent and especially in the orifices with L/d ＝ 5 hydraulic flip appear as cavitation bubbles are emitted from the orifice. The breakup length is shorter as cavitation bubbles grows and hydraulic flip appears. However, the liquid column trajectories normalized by the effective diameter and the effective momentum ratio have a similar tendency irrespective of cavitation and hydraulic flip.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.949-952
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• 2017

Spray characteristics of the impinging injectors in subsonic crossflows were experimentally studied and compared with the plain-orifice injectors. By changing the impingement angle (60, 90, 120) which is the same orifice length to diameter ratio (L/d = 5), spray characteristics were investigated. In the view of the top view from the impinging injectors, as the impingement angle increases, the liquid column breakup length in the y-direction was decreased. On the other hand, when the impinging injector is viewed from the side view, the breakup length in the x direction is smaller than the previous plain-orifice injectors, which mean that the atomizing performance of the impingement-type injector is better than that of the single-hole orifice.