Numerical investigation for kinetic extraction and thermal behavior analysis of energetic materials using calorimetry

학위논문(석사)--서울대학교 대학원 :공과대학 항공우주공학과,2020. 2. 여재익.본 연구에서는 시차 주사 열량 측정법 및 수치 해석을 수행하여 지연관의 노화에 따른 성능 저하 및 반응 특성의 변화를 살펴보았다. 자연 노화, 열 및 수분 가속 노화된 지연관 샘플에 대한 시차 주사 열량 측정법을 통하여 반응 속도식 및 발열량이 추출된다. 0-D 계산은 추출된 반응 속도식 및 발열량이 점화제 및 지연제의 노화에 따른 반응 특성을 적절히 반영하는지 검증하기 위하여 수행된다. 각 노화된 샘플로 이루어진 지연관에 대한 2-D 시뮬레이션을 하기 위하여, 동일한 지배방정식에 반응 속도식과 발열량을 해당 물질에 맞게 바꿔가며 계산이 진행된다. 자연 노화 될수록 성능이 점차 감소하였고, 결국 현재 계산 조건에서의 지연관 수명을 7-9 년으로 예측하였다. 노화과정에서의 과도한 열 노출은 점화제의 성능을 크게 변화시키지 않지만 지연제의 단위 시간당 열 발생량이 감소되므로 외부의 열 손실에 취약하게 만든다. 무엇보다도, 수분 가속 노화된 샘플의 경우 점화제와 지연제 모두 치명적인 성능 감소를 보여주기 때문에 성능을 최대로 유지하기 위하여 수분의 노출을 최소화 해야함을 보았다.Differential scanning calorimetry (DSC) experiments and numerical simulation were carried out to investigate the performance degradation and the change of reaction characteristics with aging of the time-delay device. The time-delay device consists of the igniter composed of Zr and Fe2O3, and the pyrotechnic delay composed of Zr/Ni alloys and BaCrO4 and KClO4. Natural aging, thermal accelerated aging, and hygrothermal accelerated aging samples are used in the DSC experiments to extract kinetic parameters and heat of reaction for each material. The 0-D calculations are conducted to see if they properly represent the reaction characteristics with aging. These kinetic parameters are applied to reaction rate expressed in the form of an Arrhenius equation maintaining the governing equations and computational domain for 2-D simulation of time-delay device composed of each aging materials. In the case of natural aging, the delay time increases due to the gradual decrease in performance, and finally it is expected to have a life threshold of 7-9 years under the specific conditions. Excessive exposure to heat does not significantly change the performance of the igniter, but the heat generated per unit time of the pyrotechnic delay decreases and becomes vulnerable to heat loss to the outside. Best of all, it is necessary to minimize the exposure of moisture in order to maximize the performance due to aging since the hygrothermal accelerated aging sample shows a fatal decrease in the performance of the igniter and the pyrotechnic delay.제 1 장 서 론 1 제 2 장 반응 속도식 및 발열량 추출 3 2.1 대상 고에너지 물질 3 2.2 DSC 실험 4 2.3 Friedman isoconversional analysis 9 2.4 반응 속도식 및 발열량 검증을 위한 0-D 계산 12 제 3 장 수치적 모델링 16 3.1 지배 방정식 16 3.2 상태 방정식 18 3.3 계산 도메인 19 3.4 경계 조건 20 제 4 장 결과 및 논의 21 4.1 자연 노화된 지연관의 2-D 시뮬레이션 21 4.2 자연 노화된 지연제의 노화에 따른 민감도 29 4.3 가속 노화된 지연관의 2-D 시뮬레이션 32 제 5 장 결론 34 참고문헌 35 Abstract 39Maste

Modification of Mo-V-Te-Nb-Ox catalyst for the partial oxidation of propane using metal promoter

학위논문 (석사)-- 서울대학교 대학원 : 화학생물공학부, 2011.8. 문상흡.Maste

A Study on Performance Enhancement of Base Station Power Amplifier

DoctorAs the wireless communication systems evolve, the systems need to transmit a large amount of data. To manage the increased data within a limited available frequency spectrum, the systems adopt spectrally efficient modulation schemes, such as wideband code division multiple access (WCDMA), long-term evolution (LTE), and mobile world interoperability for microwave access (m-WiMAX). These modulated signals have large peak-to-average power ratio (PAPR), because the envelope of these signals varies rapidly. Therefore, the power amplifiers need to be able to operate at the back-off power level with a high efficiency. Meanwhile, the transmitters should amplify these signals with high efficiency and linearity to lower the power consumption and preserve the signal quality. Also, the PAs need to be reconfigured properly for the variation of the output power, because the total data usage can vary depending on the time of a day. For this purpose, this dissertation presents various techniques to improve the efficiency, linearity, and gain characteristics of the power amplifiers. Especially, this dissertation presents the efficiency and gain improvement methods for the Doherty amplifier and the unit cell PA. Four major works toward the enhanced RF PAs are explored in this dissertation. First, for a femto-cell base station, a highly efficient symmetric Doherty PA is proposed and implemented. The Doherty PA is designed using monolithic microwave integrated circuit (MMIC) process for PA with a small size. As a highly efficient transmitter, the Doherty technique is investigated and analyzed to improve its performance. In the PA architecture, the nonlinear capacitance of the device affects the input match and the gain characteristic can be different according to the input matching condition. To enhance the gain, a new input impedance matching concept for a proper load modulation is proposed. Second, Doherty PA, which is optimized at back-off power, is introduced. To get high efficiency for amplification of modulated signals, the efficiency at a back-off power level should be high rather than at the peak power region. An optimized offset line and output matching circuit of the carrier PA are proposed not to affect the PA performance at the back-off power level. Also the efficiency is improved at back-off output power, while the peak output power is maintained. Third, bias adaptation of a Doherty PA is presented for high efficient operation. Gate bias adaptation and drain bias control are analyzed respectively. To maximize the output power and efficiency of a Doherty power amplifier, a new gate bias adaptation method of the carrier and peaking PAs with the control profiles of the bias voltages is proposed. Then, an average power tracking (APT) Doherty PA is analyzed in terms of its biasing voltage condition, efficiency, and output power. For the optimized operation of APT Doherty PA, the drain and gate bias voltages are optimized at different output power conditions. Fourth, an optimized Doherty power amplifier is designed using all topologies described so far for high efficiency at a high power. To increase the gain at the average power level, the input matching impedance is optimized at back-off power level. In conventional design, due to the phase variation of the peaking PA with power level, the conventional offset line does not produce the proper load modulation. To solve the problem, additional offset lines are adopted and the efficiency is increased at the modulation region. Fifth, an optimal design of a highly efficient power amplifier is described using independent fundamental and second harmonic impedance control technique. In fabrication of a power amplifier, a tuning method is indispensable because the simulation models of the device and capacitor have somewhat difference with the actual device. To achieve high drain efficiency, the fundamental and harmonic impedances need to be accurately optimized. The matching circuit of the PA adopts the independent harmonic control circuit using the characteristic of a quarter-wavelength microstrip line

광대역 동작을 위한 고효율 포화전력증폭기

2

High Linearity Asymmetric Doherty Power Amplifier using GaN MMIC

2