• Bulletin of the Korean Chemical Society
• /
• 제19권7호
• /
• pp.743-746
• /
• 1998

The Belousov-Zhabotinskii (BZ) reaction, which is composed of a bromate-organic acid-metal catalyst and an acidic solution is a commonly employed chemical oscillating reaction system. Cyclohexanedione (CHD) has been used as an initial organic substrate in oscillation systems. We studied each system of 1,4-CHD/BrO3-/Ce4/H+ and 1,3-CHD/BrO3-/Ce4+/H+ oscillating reactions, and studied the control of oscillating characters in a CHD/BrO3-/Ce4+/H+ batch system using a mixed substrate of 1,4-CHD and 1,3-CHD under a fixed total CHD concentration. In the mixed reactions, 1,4-CHD was used as a main substrate and small amounts of 1,3-CHD were used in order to vary the oscillatory behaviours by changing the mixing amount ratio of two substrates.

• Bulletin of the Korean Chemical Society
• /
• 제25권2호
• /
• pp.267-270
• /
• 2004

The bromate-1,4-cyclohexanedione-ferroin oscillating reactions are uncovered to support two types of wave activities, in which spontaneous formation of circular waves has been achieved after the disappearance of initial waves. The induction period of the revival wave is typically above 10 hours and its dependence on the initial concentrations of reactants is qualitatively different from that of initial waves. In addition to their differences in propagating speed and wavelength, the initial waves and the revival patterns have different colors, suggesting that different reaction mechanisms are involved in the formation of these spatiotemporal behaviors. Our experiments further show that the addition of hydroquinone to the reacting system can significantly shorten the induction time of the revival wave, which implicates that hydroquinone is not only a product in the bromate-1,4-cyclohexanedione-ferroin oscillating reaction but also plays a critical role in the following reactions.

• Bulletin of the Korean Chemical Society
• /
• 제28권9호
• /
• pp.1489-1492
• /
• 2007

Belousov-Zhabotinsky (BZ) reaction containing oxalic acid and acetone as a mixed organic substrate catalyzed by Ce(IV) in a flow system has been investigated. The reaction system is analyzed by varying flow rate, inflow concentrations, and temperature. Interchangeable oscillating patterns are observed in a certain range of concentrations, and above or below the condition a steady state is obtained. The increase in temperature increases the frequency and decreases the amplitude of oscillations. The apparent activation energy for the system is calculated by using the Arrhenius equation, which means that temperature has a greater effect on the reaction. Bifurcation phase diagrams for the system show the region of oscillations or steady states along with a small region of multistability. Further the behavioral trend observed in this system is discussed by mechanistic character of the system.

• 한국항공우주학회지
• /
• 제37권1호
• /
• pp.62-68
• /
• 2009

하이브리드 로켓 연소에서 발생하는 산화제 난류 유동과 연료의 기화로 인한 분출유동 사이의 상호 간섭은 매우 복잡하고 특별한 유동 간섭을 일으킨다. 이를 연구하기 위하여 연소반응을 제외하고, 산화제의 난류 유동과 연료 벽면에서의 분출 유동을 모사한 채널 유동에 대한 LES 해석을 수행하였다. 고체추진 로켓의 연소 과정에서 관찰되는 현상과 매우 흡사하게 벽면 근처에서 특정주파수로 진동하는 유동 현상이 존재한다는 것을 확인하였고, 산화제와 분출 유동의 간섭에 기인한 유동의 진동현상은 벽면 근처의 매우 얇은 영역에서만 존재하였다. 큰 길이 스케일의 유동현상을 보여주는 압력 섭동장으로부터 채널 내 주유동이 특정 주파수 특성을 갖고 하류로 진행해 가는데, 이는 산화제 유동이 분출유동과 상호작용을 하면서 발생된 전단유동의 특성을 나타낸 것이다. 그러나 하이브리드 로켓 연소실 유동의 진동 특성은 고체 추진 로켓에서 관찰되는 유동 특성과는 달리, 진동의 강도가 벽면에서 온도 구배를 변화시켜 열전달의 향상을 발생시키기에는 충분하지 못한 것으로 보인다. 그러나 벽면 근처에서 특정 주파수 특성을 갖는 유동현상이 존재한다는 사실은 비슷한 크기의 주파수를 갖는 음향 가진과 같은 외부교란이 작용한다면 공진으로 발전할 수 있는 가능성을 의미한다.

• Journal of electromagnetic engineering and science
• /
• 제15권2호
• /
• pp.82-88
• /
• 2015

The magnetron, a vacuum tube, is currently the usual high-power microwave power source used for microwave heating. However, the oscillating frequency and output power are unstable and noisy due to the low quality of the high-voltage power supply and low Q of the oscillation circuit. A heating system with enhanced reliability and the capability for control of chemical reactions is desired, because microwave absorption efficiency differs greatly depending on the object being heated. Recent studies on microwave high-efficiency power amplifiers have used harmonic processing techniques, such as class-F and inverse class-F. The present study describes a high-efficiency 100 W GaN-HEMT amplifier that uses a harmonic processing technique that shapes the current and voltage waveforms to improve efficiency. The fabricated GaN power amplifier obtained an output power of 50.4 dBm, a drain efficiency of 72.9%, and a power added efficiency (PAE) of 64.0% at 2.45 GHz for continuous wave operation. A prototype microwave heating system was also developed using this GaN power amplifier. Microwaves totaling 400 W are fed from patch antennas mounted on the top and bottom of the microwave chamber. Preliminary heating experiments with this system have just been initiated.