도시가스 저압용 정압기의 발생 소음에 대한 연구

최광원 서울시립대학교 산업대학원 2009 국내석사

우리나라는 1970년대 초에 도시가스가 배관을 통하여 처음 공급되기 시작하여 값이 싸고 무공해와 안전성을 장점으로 경제의 도약적 발전 및 주거형태의 밀집과 변화를 타고 1990년대 중반 빠른 속도로 배관연장 및 공급량이 증가하였다. 그와 더불어 부작용 또한 증가하였는데 그중에서도 도시가스를 공급하기 위한 가스시설 중 하나인 정압기에서 가스유동소음이 발생한다. 이는 여름철 보다 가스 소비량이 많은 겨울철에 소음이 더 많이 발생하며 주택가가 밀집되어 있는 곳에 설치하는 경우가 많아 공급회사는 소음을 해결하고자 흡음재나 방음벽으로 1차 소음을 차단하는 실정이다. 또한 이러한 소음으로 인하여 주민들과의 법정분쟁을 하고 많은 비용을 들여 이전하는 경우도 있으며 그나마 이전할 부지가 없으면 계속 분쟁거리로 남는다. 그리하여 이러한 가스정압기의 발생 소음의 특성을 이해하고 분석하여 소음 저감 대책이 절실히 필요하다. 특히 정압기는 내부 형상이 복잡 다양하고 작동 조건에 따른 유동변화가 크다. 이에 본 연구는 AFV식 정압기에서 소음 특성에 대하여 고유주파수를 분석하여 정압기에서 소음에 영향을 주는 여러 요인의 변화를 연구 하여 소음저감을 위한 다각적인 측면에서 연구 분석해 보았다. 그 결과 정압기의 AFV에서 나는 가스유동 소음은 3kHz와 6kHz대의 주파수로 이물질의 유동 따른 다른 음도 섞여 있는 것으로 사료되고, 소음방지시설 또한 고주파수대에 맞춰 불연성 및 하절기 정압기실의 결로현상을 고려해 내습성에 강하고 곰팡이 및 균류에 대한 저항성을 고려해서 설계를 하고 흡음재료를 선택한다면 비용대비 큰 효과를 볼 수 있다. 또한 지금까지는 외부로의 소음이 나가는 것을 막는데 많은 노력을 하였으나 향후에는 저소음설계를 통한 기본적인 소음을 줄여 쾌적한 관리환경을 만들 필요가 있다. 가스 사용량이 많아질 수 록 Sleeve가 많이 벌어지고 관내를 지나는 유속은 선행적으로 빨라지며, 이로 인해 음압레벨은 사용량에 비례하여 선형적으로 이루어지고 있음을 알 수 있었다. 또한 Sleeve가 벌어질수록 고주파수의 가스소음이 형성될 것으로 보이기 때문에 적절한 제어가 필요할 것으로 여겨졌다. Korea had started to be served with the pipe to Natural Gas in the early 1970s, Gas pipe extension and supply was speedily increased in the mid-1990s because of brilliant economic development also change and close of our dwelling form and Natural Gas has merit that cheap, clean and safe. At the same time it gave rise to side effect, above all Gas Regulator is one of Gas installations for serve the Natural Gas that occurs the noise of gas flow. That happen much more winter than summer season to use a lot of gas and The Regulator is apt to be installed in dense residential areas so The Gas company blocking off the noise with sound-absorbing materials and soundproofing material walls to solve the noise problem. Also the company involved in a serious of legal battle over the noise and there is a case to move the facilities to spend a lot of money and if they don't find a place to move it, that will still remain to trouble thing. therefore we need to understand and analyze the feature of flow noise that the same as the Gas-noise and we need to make sure reduction of noise. Especially The Regulator diversity inner shape and big change of flow as the condition of working. Accordingly this study analyzed natural frequency about the flow feature of AFV(Axial Flow Valve) Regulator and analyzed various ways of the flow feature to reduce noise and study several the properties of noise to Regulator. As a result the noise of gas flow to AFV Regulator is considered 3kHz and 6kHz frequency and comes to the conclusion that mixed other noise as the flow of impurities. We will get the effect if they choose suitable the sound-absorbing materials that the facilities to protect of noise need to design to consider about mold and bacteria of resistance also it has to take high moisture-proof for condensation of AFV Regulator equipment in summer season and nonflammability as high frequency. Now we are trying to protect noise from spreading to outside but Next we need to make comfortable environment to reduce basic noise as the design of low noise. As use of Gas as more open the sleeve then the flow velocity getting accelerate and we could find that sound pressure level make up linear type in proportion as consumed. Also we should appropriate control the AFV Regulator because the more open sleeve the more make the flow noise of high frequency.

마이크로 가스센서 어레이를 이용한 유해 혼합가스 감지특성에 관한 연구

최우석 高麗大學校 大學院 2016 국내박사

Nowadays, many researches have focused on the detecting the substances which causes air pollutants because environmental problems related with the air pollution become more serious from the sudden increase of the demands for the automobiles, exhaust gases from the automotive, mainly nitrogen oxides (NOX) and carbon monoxide (CO), generated by automotives, and are extremely harmful to the human body and are released by combustion facilities, automobiles and many other exhaust emission systems. Metal oxide semiconductor (MOS) gas sensors with the attractive characteristics of low cost, simplicity of use, and large number of detectable gases and possible application fields, make them one of the most studied groups of gas sensors. On the other hand, MOS gas sensors suffer from serious shortcomings related mainly to their low selectivity, response drifts and wide range of environmental conditions. The commercial technology, harmful gas flow control sensor module for automobile, generates on-off signal for air switching of external incoming air using two kind of oxide semiconductor gas sensors for CO and NOX gas dectction, but it is impossible to classify of gas concentrations and malfunction when the mixed gas flows, such as bad odors. Therefore, many researches have been reported on the enhancement of cross-sensitivity through the catalytic metal additions and the supplement of gas selectivity using the gas sensor array signals. In this paper, the representative species of harmful gases, odors, and volatile organic compound selected in circumstances of low concentration range exists in the actual road conditions, and a study was conducted with the aim of type classification and concentration measurement of mixed gas, using the oxide semiconductor type gas sensors of low power consumption characteristics. Micro-electronic gas sensor devices were developed for the detection of four harmful gases, carbon monoxide (CO), nitrogen oxides (NOX), ammonia (NH3) and formaldehyde (HCHO), with the MEMS platforms and MOS nanoparticles, and their gas sensing characteristics in binary mixed-gas systems were examined. Micro-platforms were designed and fabricated with the MEMS process technology, and four sensing materials for each target gas (CO, NOX, NH3 and HCHO) were synthesized with the sol-gel based methods. The micro-heater pattern within 16 designs were optimized using thermo-electric FEM simulation and electro-thermal evaluation, and the most efficient design was selected for the sensor array fabrication. Several types of micro-heater designs were also devised to reduce the power consumption and sensing material needed. Co-planar type gas sensor platforms were designed, analyzed and fabricated using MEMS process with various heater patterns, and the chip frame and the diaphragm size of MEMS platform were 1.8 X 1.8 mm and 0.6 X 0.6 mm, respectively. A Pt thin-film layer was patterned for the sensing electrode and micro-heater. The fabricated MEMS gas sensors had low power dissipations, and the minimum power consumption of the micro platform was 41 mW at an operating temperature of 250℃ in the S-shaped micro-heater pattern design. Four sensing materials for CO, NOX, NH3 and HCHO gases were Pd-SnO2, In2O3, Ru-WO3 and SnO2-ZnO nanoparticles. Each MEMS gas sensor showed good sensing performance for their target gases, and the optimum points for micro-heater operation were examined during temperature modulation in micro-platforms. After gas sensing characterized under single gas atmospheric conditions, the gas sensing performance of the three sensors were evaluated and scrutinized in a binary mixed system. The gas sensing behaviors to the mixed gas systems suggested that specific adsorption and selective activation of adsorption sites might occur in gas mixtures and offer the priority for the adsorption of specific gas. For the sake of approaching practical application, dataset of gas sensitivity were investigated with the pattern recognition technique of principal component analysis (PCA) method. The discrimination characteristics of data patterns among six gas mixture systems were investigated. The PCA plot results showed good separation among the mixed gas systems, and it suggested that the gas mixture tests could be well classified and discriminated in the noxious gases and their mixtures. Thorough analysis of the sensing performance of the sensor arrays will make it possible to discriminate the components in gas mixtures as well as their concentrations.

A Study on CO Gas Sensing Properties of TiO2 Xerogel Thin Films Prepared by Solvothermal Drying

이진석 연세대학교 대학원 2012 국내석사

Gas sensors are finding increasing number of applications in home, industrial and automotive areas. Incomplete combustion in gas and coal fired electricity plants can generate harmful gases and pollution. Various nanostructured metal oxide materials such as SnO2, WO3, TiO2, In2O3, and ZnO have been reported to be good candidates for novel semiconductor thin film gas sensors. Among them, TiO2 is a well known important functional material used in a variety of applications. And important feature of TiO2-based gas sensors is that they can be operated at relatively high temperature because of the good chemical stability of their anatase structural form at elevated temperature. For gas sensor applications, TiO2 with a large surface area has demonstrated good sensing properties to CO, H2, and NOx. And compared with dense films, the porous films show enhances gas sensing with higher sensitivity and faster response time.We investigate CO gas sensing properties of nanostructured TiO2 thin film gas sensors fabricated by porous form named xerogel. The purpose of research was to develop TiO2 xerogel thin film based materials for gas sensor to detect a low concentration (50 ∼ 100 ppm) of CO gas. Futhermore, the anatase TiO2 xerogel thin films doped with MWCNTs and graphene showed to have higher sensitivity and response time than the no doping films.

가스센서 응용을 위한 나노 구조 MoS2 소재 개발

박호연 경북대학교 대학원 2022 국내석사

Industrial development has increased the concentration of toxic gases in the environment. In this regard, there is a growing need to detect NO2 gas, one of the most common air pollutants, which is hazardous for human health. According to the previous studies, nanoscroll based gas sensors showed an enhanced gas sensing performance. For the gas sensor material, molybdenum disulfide (MoS2) has attracted a lot of attention because of its high surface-to-volume ratio and outstanding electronic properties, but MoS2 scrolls based gas sensor has not been reported yet. In this work, we realized MoS2 scrolls based gas sensor tha can sensitively detect NO2 gas. To fabricate MoS2 scrolls, we used a self-scrolling method. Specifically, a 3D nanostructured MoS2 sheet, pre-synthesized by MOCVD method, is guided to roll up into MoS2 scrolls by a drop of ethanol solution. The structure of MoS2 scrolls was analyzed by SEM and Raman spectroscopy. Compared to the MoS2 sheets based gas sensor, MoS2 scroll based gas sensor showed a better gas sensing response due to their unique scrolled structures.

A Study on Dynamic Characteristics of Gas-centered Swirl Coaxial Injectors Using Structured Laser Illumination Planar Imaging Technique

정기정 서울대학교 대학원 2021 국내박사

In liquid rocket engine systems such as the staged combustion cycle with high efficiency, the propellant is introduced into the combustion chamber in the form of gas-liquid. Since a nozzle for accelerating the combustion products is connected behind the cylindrical chamber in the case of a general axisymmetric combustor, the gas which is not completed the combustion reaction may be exhausted. Therefore, it is necessary to use a swirl injector that can increase the travel distance and residence time with the same axial displacement comparing to the jet injectors. In the case of a gas-centered coaxial gas-liquid swirl injector, gas and liquid could interact inside the injector, if a recessed region is applied. Also, the liquid spray characteristics influenced by the wall of the central injector. As the wall thickness of the inner injector (lip thickness) increased, liquid film region in the swirl chamber and nozzle was invaded, and consequently, the liquid spray angle decreased. Therefore, when the gas injection angle is constant, the gas and liquid flow may collide with each other outside the injector if the liquid spray angle decreased. In this study, the spray pattern and spray angle were measured by the backlight method using a stroboscope for the internal and external mixing type sprays. However, it was difficult to figure out the mechanism of liquid breakup because the liquid film decomposed into a large number of small droplets near the outlet of the injector due to the central gas vortex. Therefore, real-time instantaneous information on the distribution of liquid ligaments and droplets in the spray section was obtained by using a planar laser and a 2-phase structured laser illumination planar imaging (2p-SLIPI) technique that eliminated multiple scattering. Also, a dynamic pressure sensor was used to measure the pressure vibration of gas injection. Since the gas vortex discharged through the swirl type injector moved in the axial direction while rotating, it pushed the inner surface of the liquid film outwardly, and at the same time, it was accompanied a entrainment effect by pressure drop in interspace of liquid and gas flow. In the internal mixing spray, a fine droplet zone was created around the injector axis as the gas stream scraped the liquid film from the mixing chamber (recessed region). In the external mixing spray, the liquid film is ruptured by gas impingement on the film. Thus, the fine droplets are distributed in a hollow cone shape. The droplets in liquid spray of a single swirl injector are created by the wave – ligament model caused by the gas-liquid interaction. However, in the case of the external mixed-type binary injector, the effect of gas was more dominant to the liquid film breakup process than the inherent liquid flow characteristics. In addition, the pressure oscillation of the gas causes the liquid film to vibrate, and as a result, the liquid film is periodically disrupted generating droplets. In this process, the fracture frequency was transited from gas acoustic frequency and the liquid film wave frequency. However, there was also some spraying condition where the fracture frequency was not appeared. In general, it was found that the fracture frequency was proportional to the gas impinging velocity and the liquid velocity, and the aerodynamic resistance of the liquid film could have different effects on the frequency and amplitude. 높은 효율을 가지는 다단연소 사이클과 같은 액체로켓엔진 시스템에서는 연소실로 기체-액체의 형태로 추진제가 유입된다. 일반적인 축대칭 연소기의 경우, 원통부 뒤에 유체를 가속시키기 위한 노즐이 연결되므로 연소반응이 완료되지 않은 추진제가 배출될 수 있다. 그러므로 동일 축 방향 변위에서 이동거리 및 체류시간을 늘릴 수 있는 와류형 분사기를 사용할 필요가 있다. 기체 중심 동축 와류형 기체-액체 분사기의 경우, 혼합실(recessed region)을 적용한다면 기체와 액체는 분사기 내부에서 만나게 된다. 또한 액체의 분무특성은 중심 분사기의 벽에 의해 영향을 받는다. 액체 분사기의 경우, 벽이 분사기 내 액막을 침범하는 정도가 커짐에 따라 저항이 증가하여 분무각이 감소한다. 그러므로 기체 분사각이 일정할 시, 액체 분무각이 감소한다면 분사기 외부에서 기체와 액체유동은 서로 충돌할 수 있다. 내부 혼합식과 외부 혼합식 분무 형상은 stroboscope를 사용한 backlight 방법으로 분무 패턴과 분무각을 측정하였다. 그러나 중심 기체 와류에 의해 액막은 분사기의 출구 근처에서 다수의 작은 액적으로 분열되므로 계측이 어렵다. 그러므로 평면 레이저를 사용하며, 다중산란을 제거하는 2-phase structured laser illumination planar imaging (2p-SLIPI) 기법을 사용하여 분무 단면에서 액막과 액적의 분포에 대한 실시간 정보를 획득하였다. 또한 동압센서를 사용하여 기체 분사의 압력진동을 계측하였다. 와류형 분사기를 빠져나온 기체는 회전하면서 축 방향으로 이동하기 때문에 액막 안쪽 표면을 바깥쪽으로 밀어내는 작용을 함과 동시에 속도증가로 인한 압력감소를 동반한다. 내부 혼합식 분무에서는 혼합실 내에서부터 기체 흐름이 액막을 긁어내기 때문에 분사기 축 주위에서 미세 액적 구역이 생성된다. 외부 혼합식 분무에서는 충돌에 의해 액막을 파열시키기 때문에 미세액적은 속이 빈 원추형으로 분포하게 된다. 단일 와류형 분사기에 의한 액체 분무의 분열은 기체-액체 간 상호작용에 의한 파동으로 분열된다. 그러나 영상의 분석 결과에서 외부 혼합식 이원 분사기의 경우 액막 분열과정에 기체의 영향은 액체 흐름 자체의 특성에 비해 더욱 지배적이었다. 또한 기체의 압력진동은 액막을 진동시키며, 결과적으로 주기적으로 액막을 분열시키면서 액적을 생성하게 된다. 이러한 과정에서 분열주파수는 기체주파수의 약 1/10, 액막 파동주파수의 약 1/2 정도로 전이된 수치를 나타내었다. 그러나 분무 조건에 따라 분열주파수가 나타나지 않는 구간도 존재하였다. 대체로 분열주파수는 기체의 충돌속도와 액체의 속도에 비례하였으며, 액막의 공기역학적 저항은 유량 진동의 진동수와 진폭에 서로 다른 영향을 줄 수 있다는 것을 파악하였다.

해수담수화를 위한 가스하이드레이트-역삼투 융합공정의 에너지 소모량 및 용존 가스 제거 가능성 평가

유현욱 부경대학교 대학원 2017 국내석사

Gas hydrate (GH) based desalination process have a potential as a novel unit desalination process. GHs are nonstoichiometric crystalline inclusion compounds formed at low temperature and a high pressure condition by water and a number of guest gas molecules. After formation, pure GHs are separated from the remaining concentrated seawater and they are dissociated into guest gas and pure water in a high temperature and a low pressure condition. The condition of GH formation is different depending on the type of guest gas. This is the reason why the guest gas is a key to success of GH desalination process. But, the salt rejection of GH based desalination process appeared to be 60.5-93%, post treatment is needed to finally meet the product water quality. This study adopted reverse osmosis (RO) as a post treatment. The energy consumption of the GH system is based on unit process like hydration, dehydration, and dissociation. Also, the cooling and heating of seawater and the heat of reaction of GH formation is needed to calculate the main GH energy. The pressure and flow rate of high pressrue pump, product flow rate are required to calculate the RO energy consumption. It can be found from simulation results using commercial RO software. As a result, the energy consumption of GH-RO and conventional RO system is compared to find out the competitiveness of GH-RO hybrid system. Also, the gas rejection test by RO process were performed because the guest gas is dissolved in a GH product (i.e., RO feed).

Design of sensitive and selective gas sensors using oxide nanowire networks

Hwang, In-Sung Graduate School, Korea University 2011 국내박사

Highly sensitive and selective gas sensors were designed using oxide nanowire (NW) networks by the control of NW density, the fabrication of NW sensors on the suspended microelectrodes and heater, the load of oxide catalyst, and the coating of nano-scale oxide semiconductor shell layer. SnO2 NWs were deposited uniformly over a defined electrode area by coating with a solution containing NWs after patterning with polydimethylsiloxane (PDMS). The hydrophobic PDMS guide wall prevented the outstretching of the deposited solution and the density of NWs could be controlled by manipulating the number of droplets deposited. The high-density NW sensors enhanced the gas response (Ra/Rg for reducing gases and Rg/Ra for oxidizing gases, Ra: resistance in air, Rg: resistance in gas) toward CO, C3H8, C2H5OH, and NO2 but reduced the response/recovery speed. The enhancement of gas response by the increase of NW density was attributed to the increase in the number of NW/NW junctions with high variation of resistance upon exposure to gas. The SnO2 NW networks gas sensors were fabricated on a microelectrode and heater suspended in a cavity. The sensors showed the selective detection to C2H5OH at a heater power during sensor operation as low as 30-40 mW. The gas response and response speed of the SnO2 NW sensors to 10-100 ppm C2H5OH were 4.6-4.7-fold faster, respectively, than those of the SnO2 nanoparticle sensors with the same electrode geometry. The enhanced gas sensing characteristics of NW networks sensors were explained by the rapid and effective diffusion of analyst gases to the entire sensors surface through the less-agglomerated configuration of NW networks. The CuO-functionalized SnO2 NW sensors were fabricated by dropping Cu nitrate aqueous solution and subsequent heat treatment. The CuO coating increased the gas responses to 20 ppm H2S up to ~74-fold. The gas response of the CuO-doped SnO2 NWs to 20 ppm H2S was as high as 809 at 300ºC, while the cross-gas responses to 5 ppm NO2, 100 ppm CO, 200 ppm C2H5OH, and 100 ppm C3H8 were negligibly low (1.5-4.0). Moreover, the 90% response times to H2S were as short as 1-2 s at 300-400ºC. The selective detection of H2S and enhancement of the gas response were attributed to the uniform distribution of the sensitizer (CuO) on the surface of the less agglomerated networks of the SnO2 NWs. The ZnO-SnO2 core-shell NWs were synthesized by a continuous two-step vapor growth method at different synthesis temperatures. A crystalline 15-20 nm-thick, SnO2 shell layer was pseudo-epitaxially coated on ZnO NWs. The gas response of the ZnO-SnO2 core-shell NW sensors to 10 ppm NO2 reached ~33 times enhancement compared to that of the ZnO NWs at 200ºC. In addition, the ZnO-SnO2 core-shell NW sensors showed selective detection to NO2 at 200-300ºC and to C2H5OH at 400ºC. The electron depletion at the SnO2 shell layer and ZnO-SnO2 interface was suggested as the reason for the enhanced gas response.

Machine-learning-assisted sensor array for selective detection of individual gases and gas mixtures

김진영 인하대학교 대학원 2023 국내박사

Gas sensors are used to detect flammable, explosive and toxic gases in order to monitor environmental pollution and to ensure safe atmosphere for living beings. Gas sensors can detect various gaseous species such as volatile organic compounds, greenhouse and pollutant gases. Volatile organic compounds (VOCs) are organic chemicals with a high vapor pressure that can harm human health and endanger the environment. Other pollutant gases emitted by industries include CO, NH3, and NO2, which can also threaten safety at work environment. All of these gases are dangerous to all living things and should be detected at lower concentrations to avoid harm. Because the threat posed by various gases is dependent on their individual concentrations, it is necessary to know the type of gas and their concentrations present in the surrounding environment. Metal oxides are viable materials to construct sensors because of their high response, low response and recovery time. Metal oxides are easily adoptable for miniaturized MEMS based platforms and batch production. Biggest drawback of metal oxide is their inherent non selectivity towards a particular gas. As metal oxide detects a gas by oxidation of gaseous species and subsequent electron transfer, any gas which can undergo oxidation can be detected. However, different metal oxide behaves differently with different gaseous species because of their difference in their surface morphology, granular structures, crystal structures and different reactivity at different temperature. This property can be efficiently utilized to detect the different gases by operating multiple sensors at a time. Response of different sensors in different gas atmosphere can be compared to gain the knowledge about gases present in surrounding atmosphere. As the discriminative detection of different gases and their concentration involves multiple sensors and various gases, it is near impossible to compare the behavior of different sensors manually. With the advancement of machine learning and computer vision algorithms, it was understood that these algorithms can be applied to discriminate different gases by analyzing the data from array of differently behaving sensors. This thesis mainly focuses modification of multiple metal oxides to achieve high response towards a particular gas and characterization of those materials to understand the nature of materials. Initially, array of differently behaving materials was constructed and operated simultaneously in different gas and their mixture atmosphere. Different machine learning algorithms such as PCA, ANN, MLP, CNN and LSTMs were adopted to analyze the data from sensor array to discriminate different gases and their mixtures. Well known metal oxides such as SnO2, ZnO, In2O3, WO3 and TiO2 were used and modified using catalytic materials such as Au, Pd, Pt to enhance the response and selectivity towards particular gaseous species. By using metal oxide based composites and covering the catalyst like gold nanoparticles, the efficiency of the five sensors utilizing In2O3, SnO2, and TiO2 was increased. Three polluting gases (CO, NO2, and NH3) were detected using an array of these sensors at various concentrations. In addition, the gas sensor array was placed to detect two type of gas mixtures at various concentrations: NO2 and CO and NO2 and NH3. To determine how effectively the sensor array could distinguish between different objects, a PCA was performed. A DNN-based model was utilized to distinguish between various gases and their mixtures using the response values. A model based on a convolutional neural network was utilized for the discriminative analysis in order to do away with stages like feature extraction and response computing. The selectivity of the six SnO2 and WO3-based sensors was improved by adding catalytic gold (Au) and palladium (Pd) nanoparticles to them. Six distinct VOCs (acetone, benzene, ethanol, formaldehyde, toluene, and xylene) with varying amounts were detected using an array of all these sensors. To distinguish between the various VOCs, CNN and LSTM models based on deep neural networks were applied. In the cross-validated training and testing methods, 100% discrimination efficiency was attained. To avoid the procedures of feature extraction and response computation, a DNN-based model was provided with raw signals as input for the discriminative analysis. We gathered the impedance spectra of many sensors for various VOCs. The impedance spectra's real (Z') and imaginary (Z") parts were examined individually to determine the material characteristics of various gases at varying gas concentrations. Metal oxide's relaxation characteristic offered the benefit of adjustable response calculations matching various frequencies. To quantify the gas and validate it for different sensors and VOCs, a separate approach of comparing numerous instantaneous Z" values at various frequencies was developed. Deep neural network-based models based on CNN and LSTM were also utilized to differentiate between impedance spectra acquired for various sensors in varying VOC atmospheres.

Process Optimization and Mass Transfer Enhancement for Biological Syngas Conversion Process

남철우 포항공과대학교 일반대학원 2017 국내박사

Technological solutions to reduce greenhouse gas (GHG) emissions from anthropogenic sources are required. Heavy industrial processes, such as steel making, contribute considerably to GHG emissions. Fermentation of carbon monoxide (CO)-rich off gases with wild-type acetogenic bacteria can be used to produce ethanol, acetate, and 2,3-butanediol, thereby, reducing the carbon footprint of heavy industries. Here, the processes for the production of ethanol from CO-rich off gases are discussed and a perspective on further routes towards an integrated biorefinery at a steel mill is given. Recent achievements in gas fermentation as well as integration of other biotechnology platforms to increase the product portfolio are summarized. In this study, to utilize waste CO for mixed culture gas fermentation, carbon sources (CO, CO2) and pH were optimized in the batch system to find out the center point and boundary of response surface method (RSM) for higher acetic acid production (center points: 25% CO, 40% CO2, and pH 8). The concentrations of CO and CO2, and pH had significant effects on acetate production, but the pH was the most significant on the acetic acid production. The optimum condition for acetic acid production in the gas fermentation was 20.81% CO, 41.38% CO2, 37.81% N2, and pH 7.18. The continuous gas fermentation under the optimum condition obtained 1.66 g/L of cell DW, 23.6 g/L Acetic acid, 3.11 g/L propionate, and 3.42 g/L ethanol. The CO mass transfer was important issue in gas fermentation. Because the aqueous solubility of CO and H2 are low, synthesis-gas fermentations are typically limited by the rate of gas-to-liquid mass transfer. activated carbon can be useful a gas delivery mediator in this study. To improve CO mass transfer in gas fermentation, activated carbon were added to mixed culture fermentation system and the particle size and concentration were optimized to maximize acetic acid production yields in a mixed culture. The optimized activated carbon was applied to a continuous gas fermentation system with optimized condition to construct a high-speed CO conversion system. Various type of activated carbon was added to a synthesis gas fermentation process to investigate their influence on syngas fermentation. CO was fermented using mixed culture, resulting in an enhanced acetate concentration and production rate as a result of enhanced the CO-water volumetric mass transfer by activated carbon addition. The CO water volumetric mass transfer coefficients were enhanced by activated carbon. acetate production was increased by introduction activated carbons. The highest condition for acetate production was surface area = 700 m2/L and particle size = 6 mesh, at which the acetate production was 709.2 mg/L and CO consumption rate was 1.11 mg/L/h. The continuous gas fermentation with activated carbons 23.8 g/L of acetate, 5.20 g/L of propionate, and 2.60 g/L of ethanol. This systematic approach improved productivity and can be applied to other biological production systems.

Gas sensing characterization of single layer graphene prepared by ICP-CVD method

김창희 서울대학교 대학원 2012 국내석사

Recently, there has been an increased demand for low cost, highly sensitive and selective gas sensing devices. Graphene, single atomic layer of graphite, has been considered as very attractive as gas sensor device application (The graphene have higher sensitivities for NO2 and NH3.). In the past few years, there have been mechanical exfoliation method using scotch tape and many chemical approaches to synthesize large-scale graphene have been developed, including epitaxial growth on silicon carbide at high temperature (1450 oC), formation of graphene in ultra-high vacuum environment and chemical vapor deposition (CVD). Recently it becomes increasingly important to form high-quality graphene layer at lower process temperature to be applied to flexible electronics. As a good candidate, Inductively-Coupled Plasma Chemical Vapor Deposition (ICP-CVD) was used to form graphene at 650 oC. However, there have been no reports on gas sensitivity and temperature effect of graphene FET by ICP-CVD method. In this master’s thesis, we report gas sensitivity and effect of temperature (T) and relativity humidity (RH) on gas sensitivity of the bottom-gate graphene FETs with single atomic layer of channel graphene fabricated by ICP-CVD method. The graphene FETs have relatively higher sensitivities for NH3 (~20% at 50 ppm) and NO2 (~30% at 50 ppm). Other gases such as CH4, C3H8, H2S, and SO2 show a sensitivity of less than ~10% at even 104 ppm. The sensitivity of graphene exposed to nitrogen oxide (NO2) and ammonia (NH3) was increased with increasing temperature and humidity. For NO2 gas, the graphene FET shows increasing ID with increasing T and also increasing ID with increasing humidity. However, the FET shows opposite trend with the T and humidity for NH3 gas. We observed that gases produce distinguishably different effects on the low-frequency noise spectra of graphene. These characterizations could be used to design more reliable graphene gas senor 최근 높은 민감도 및 선택성을 가지고 제조 비용이 낮은 가스센서의 수요가 증가하고 있다. 이러한 특성을 가진 가스센서를 구현하기 위해 현재 그라핀(grpahene)의 가스 반응에 대한 연구를 진행 중에 있다. (그라핀은 이산화질소(NO2)와 암모니아(NH3)에 큰 민감도(Sensitivity)를 가진다.) 현재 그라핀 제작 방법으로는 스카치테이프를 이용한 exfoliation방법, 실리콘카바이드(SiC)기판을 높은 온도로 가열하여 그라핀을 제조하는 방법 및 최근 높은 진공도에서 탄화수소를 촉매 금속에 흐리는 화학적 기상 증착 방법을 이용한 방식이 개발되었다. 최근에는 낮은 온도에서 고품질의 그라핀 제조 방법으로 inductively coupled plasma chemical vapor deposition (ICP-CVD)를 이용한 연구가 진행 되고 있다. ICP-CVD방법은 약 650도에서 공정이 가능하다. 하지만 ICP-CVD 방법으로 제조된 그라핀의 가스 반응 특성 및 가스 반응시 온도 및 습도가 민감도에 미치는 영향에 대해서는 자세한 연구결과가 아직까지 보고되지 않았다. 본 논문에서는 ICP-CVD 방법으로 제조된 Bottom게이트 구조의 그라핀 FET를 이용하여 가스 반응의 민감도 및 가스 반응시 온도 및 습도의 영향에 대한 연구를 진행하였다. 실험 결과 그라핀은 암모니아(농도가 50ppm 일때 대략 20 %정도) 및 이산화질소(농도가 50ppm 일때 대략 30 %정도)에서 상대 적으로 높은 가스 민감도가 나타났다. 황화수소(H2S), 이산화황(SO2), 메탄(CH4) 프로판(C3H8)에서는 반응이 크게 나타나지 않았다. 심지어 메탄 및 프로판은 각각의 가스 농도가 10000ppm 에서도 민감도가 10 %가 미만으로 나타났다. 그라핀이 일정 이산화질소 및 암모니아 농도에서 각각의 가스와 반응할 때 온도 및 수분이 증가하면 민감도가 증가하는 결과를 나타내었다. 이산화 질소에서는 온도 및 수분이 증가하면 그라핀의 드레인 전류를 증가 시켰다. 하지만 암모니아에서는 반응 온도 및 수분이 증가하면 이산화 질소와는 반대 경향이 나타났다. 이런 가스반응 특성들은 신뢰성 있는 그라핀 가스 센서 설계에 사용될 수 있을 것으로 예상된다.