• 제목/요약/키워드: water spray systems

검색결과 171건 처리시간 0.023초

Intelligent Tuning of the Two Degrees-of-Freedom Proportional-Integral-Derivative Controller On the Distributed Control System for Steam Temperature Control of Thermal Power Plant

  • Dong Hwa Kim;Won Pyo Hong;Seung Hack Lee
    • KIEE International Transaction on Systems and Control
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    • 제2D권2호
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    • pp.78-91
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    • 2002
  • In the thermal power plant, there are six manipulated variables: main steam flow, feedwater flow, fuel flow, air flow, spray flow, and gas recirculation flow. There are five controlled variables: generator output, main steam pressure, main steam temperature, exhaust gas density, and reheater steam temperature. Therefore, the thermal power plant control system is a multinput and output system. In the control system, the main steam temperature is typically regulated by the fuel flow rate and the spray flow rate, and the reheater steam temperature is regulated by the gas recirculation flow rate. However, strict control of the steam temperature must be maintained to avoid thermal stress. Maintaining the steam temperature can be difficult due to heating value variation to the fuel source, time delay changes in the main steam temperature versus changes in fuel flow rate, difficulty of control of the main steam temperature control and the reheater steam temperature control system owing to the dynamic response characteristics of changes in steam temperature and the reheater steam temperature, and the fluctuation of inner fluid water and steam flow rates during the load-following operation. Up to the present time, the Proportional-Integral-Derivative Controller has been used to operate this system. However, it is very difficult to achieve an optimal PID gain with no experience, since the gain of the PID controller has to be manually tuned by trial and error. This paper focuses on the characteristic comparison of the PID controller and the modified 2-DOF PID Controller (Two-Degrees-Freedom Proportional-Integral-Derivative) on the DCS (Distributed Control System). The method is to design an optimal controller that can be operated on the thermal generating plant in Seoul, Korea. The modified 2-DOF PID controller is designed to enable parameters to fit into the thermal plant during disturbances. To attain an optimal control method, transfer function and operating data from start-up, running, and stop procedures of the thermal plant have been acquired. Through this research, the stable range of a 2-DOF parameter for only this system could be found for the start-up procedure and this parameter could be used for the tuning problem. Also, this paper addressed whether an intelligent tuning method based on immune network algorithms can be used effectively in tuning these controllers.

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급속열분해를 통하여 생산된 바이오오일 액적의 증발 특성에 관한 수치해석적 연구 (Numerical Study on the Evaporation Characteristics of Biocrude-oil Produced by Fast Pyrolysis)

  • 최상규;최연석;김석준;한소영
    • 공업화학
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    • 제27권6호
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    • pp.646-652
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    • 2016
  • 바이오매스는 최근 화석연료의 고갈 및 지구온난화 등의 문제에 대응하기 위한 신재생에너지원으로 많은 관심을 받고 있다. 바이오오일은 폐목재, 농업 및 임업 부산물 등의 바이오매스로부터 급속열분해 과정을 통하여 생산되는 액체연료이다. 바이오오일은 일반적인 석유 계통의 연료에 비하여 점도가 매우 높고 고체상의 불순물을 포함하고 있어 버너 적용시 스프레이 분무 특성이 저하된다. 또한, 바이오오일은 셀룰로오스, 헤미셀룰로오스, 리그닌으로부터 유래되는 수백 종류의 화학종들로 이루어져 있어 일반적인 액체연료와는 액적의 증발 특성이 뚜렷하게 구분된다. 본 연구에서는, 바이오오일의 구성 성분을 아세트산, 레보글루코산, 페놀, 수분으로 단순화하여 액적의 증발 특성에 관한 수치해석적 연구를 수행하였다. 다양한 주위공기 온도, 액적의 초기 지름, 에탄올 혼합 비율에 대하여 액적의 증발 특성을 비교하였다. 주위공기 온도가 높아질수록 바이오오일 액적의 증발 시간은 짧아졌으며, 특히 낮은 온도 범위에서는 증발 시간이 공기온도에 매우 민감하였다. 또한 액적의 지름이 감소할수록, 에탄올 혼합 비율이 증가할수록 증발 시간이 단축됨을 알 수 있었다.

Empirical Correlations for Penetration Height of Liquid Jet in Uniform Cross Flow - A Review

  • No, Soo-Young
    • 한국분무공학회지
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    • 제16권4호
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    • pp.176-185
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    • 2011
  • The empirical correlations for the prediction of penetration height of liquid jet in crossflow are reviewed and classified in this study. Around thirty different correlations had been proposed by many investigators. It has generally known that the penetration height of a liquid jet in a cross-flow is a function of the liquid to air momentum flux ratio and the normalized downstream distance from the injector. However, several researchers incorporated the Weber number, liquid-to-water or air viscosity ratio, pressure ratio or Reynolds number, temperature ratio in the empirical correlations. The existing correlations can be grouped as correlations in a power-law, logarithmic, and exponential forms, respectively. Correlations in a power-law form can be further classified as three groups such as basic form, Weber number form and other parameters form. It should be pointed out that correlations in a logarithmic form in terms of Weber number or any other parameters could not be found. Universal correlation has still not been established due to the significant discrepancies between various correlations suggested to date. Several of the studies reported the significant discrepancies of predicted values by the existing correlations. The possible reasons for discrepancies will be summarized as measurement technique, assumptions made in defining terms in the liquid to air momentum flux ratio, difficulties in defining the boundaries of the liquid jets, and nozzle/injector geometry. Evaluation of validity for the correlations proposed recently by several investigators is essentially required. Those include eight power-law forms, two logarithmic forms, and one exponential form.

합성가스/디젤 혼소압축착화 엔진의 합성가스 혼합비와 압축비에 따른 연소 및 배출가스 특성 (Syngas/Diesel Dual Fuel Combustion in a Compression Ignition Engine with Different Composition Ratios of Syngas and Compression Ratios)

  • 이준순;정탄;이용규;김창업;오승묵
    • 한국분무공학회지
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    • 제24권1호
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    • pp.35-42
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    • 2019
  • Syngas is widely produced by incomplete combustion of coal, water vapor, and air (oxygen) in a high-temperature/high-pressure gasifier through a coal-gasification process for power generation. In this study, a simulation syngas which was mainly composed of $H_2$, CO, $CO_2$, and $N_2$ was fueled with diesel. A modified single cylinder compression ignition (CI) engine is equipped with intake port syngas supply system and mechanical diesel direct injection system for dual fuel combustion. Combustion and emission characteristics of the engine were investigated by applying various syngas composition ratios and compression ratios. Diesel fuel injection timing was optimized to increase indicated thermal efficiency (ITE) at the engine speed 1,800 rpm and part load net indicated mean effective pressure ($IMEP_{net}$) 2 to 5 bar. ITE of the engine increased with the $H_2$ concentration, compression ratio and engine load. With 45% of $H_2$ concentration, compression ratio 17.1 and $IMEP_{net}$ 5 bar, ITE of 41.5% was achieved, which is equivalent to that of only diesel fuel operation.

코로나 바이러스 대유행에 따른 치과 의료 관리 가이드라인 (Guidelines for dental clinic infection prevention during COVID-19 pandemic)

  • 김진
    • 대한치과의료관리학회지
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    • 제8권1호
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    • pp.1-7
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    • 2020
  • Dental settings have unique characteristics that warrant specific infection control considerations, including (1) prioritizing the most critical dental services and provide care in a way that minimizes harm to patients due to delayed care, or harm to personnel from potential exposure to persons infected with the COVID-19 disease, and (2) proactively communicate to both personnel and patients the need for them to stay at home if sick. For health care, an interim infection prevention and control recommendation (COVID-19) is recommended for patients suspected of having coronavirus or those whose status has been confirmed. SARS-CoV-2, which is the virus that causes COVID-19, is thought to be spread primarily between people who are in close contact with one another (within 6 feet) through respiratory droplets that are produced when an infected person coughs, sneezes, or talks. Airborne transmission from person-to-person over long distances is unlikely. However, COVID-19 is a new disease, and there remain uncertainties about its mode of spreads and the severity of illness it causes. The virus has been shown to persist in aerosols for several hours, and on some surfaces for days under laboratory conditions. COVID-19 may also be spread by people who are asymptomatic. The practice of dentistry involves the use of rotary dental and surgical instruments, such as handpieces or ultrasonic scalers, and air-water syringes. These instruments create a visible spray that can contain particle droplets of water, saliva, blood, microorganisms, and other debris. While KF 94 masks protect the mucous membranes of the mouth and nose from droplet spatter, they do not provide complete protection against the inhalation of airborne infectious agents. If the patient is afebrile (temperature <100.4°F)* and otherwise without symptoms consistent with COVID-19, then dental care may be provided using appropriate engineering and administrative controls, work practices, and infection control considerations. It is necessary to provide supplies for respiratory hygiene and cough etiquette, including alcohol-based hand rub (ABHR) with 60%~95% alcohol, tissues, and no-touch receptacles for disposal, at healthcare facility entrances, waiting rooms, and patient check-ins. There is also the need to install physical barriers (e.g., glass or plastic windows) in reception areas to limit close contact between triage personnel and potentially infectious patients. Ideally, dental treatment should be provided in individual rooms whenever possible, with a spacing of at least 6 feet between the patient chairs. Further, the use of easy-to-clean floor-to-ceiling barriers will enhance the effectiveness of portable HEPA air filtration systems. Before and after all patient contact, contact with potentially infectious material, and before putting on and after removing personal protective equipment, including gloves, hand hygiene after removal is particularly important to remove any pathogens that may have been transferred to the bare hands during the removal process. ABHR with 60~95% alcohol is to be used, or hands should be washed with soap and water for at least 20 s.

전기장에 의해 생성된 미세기포를 이용한 페놀의 오존산화 (Oxidation of Phenol Using Ozone-containing Microbubbles Formed by Electrostatic Spray)

  • 신원태;정유진;성낙창
    • 대한환경공학회지
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    • 제27권12호
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    • pp.1292-1297
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    • 2005
  • 상수나 하수처리장에서 쓰이는 오존처리는 물질전달에 제약을 받는 공정임은 알려져왔다. 이런 물질전달의 한계를 극복하는 방법으로 매우 효과적인 것은 오존가스를 함유한 기포의 크기를 줄임으로써 물질전달에 필요한 접촉면적을 넓히는 것이다. 오존의 전달을 크게 하기 위한 방법으로서 본 연구에서는 전기장분사(Electrostatic spraying: ES)를 사용하였다. 실험에서는 ES와 기포발생판을 비교하였는데 ES실험에서는 전압을 0 kV에서 4 kV 범위까지 높여주어 물질전달효과를 살펴보았고 기공크기가 다른 두 가지 기포발생판(미세기공: 기공크기 $10{\sim}15{\mu}m$, 중간기공: 기공크기 $40{\sim}60{\mu}m$)을 사용하여 물질전달효율을 비교 분석 하였다. 물질전달효율은 시간의 경과에 따른 용존오존농도의 측정과 페놀의 산화시간으로 간접 계산하였다. 실험 결과 ES의 경우 전압을 0 kV에서 4 kV까지 올렸을 때 기포의 크기가 작아짐으로 인해 오존전달율을 약 40% 정도 향상시킬 수 있었다. 또한 ES와 기포발생판의 물질전달 비교실험에서 미세기공 기포발생판보다 4 kV의 ES가 더 효과적임을 알 수 있었다.

태양열 이용 축열식 직접접촉 열교환기의 열전달에 관한 연구 (A Study on Heat Transfer of n Storage Type Direct Contact Heat Exchanger for Solar Energy Utilization)

  • 강용혁;전명석;윤환기;천원기
    • 태양에너지
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    • 제15권3호
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    • pp.3-14
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    • 1995
  • 태양열 이용 축열식 직접접촉 열교환기의 실제 적용을 위한 작동조건도출 및 열교환기내 열전달 특성 규명을 위하여 작동유체를 물보다 가벼운 경우(Texaterm)와 무거운 경우 두가지를 실제 태양열 집열회로상에서 실험하였다. 작동유체가 물보다 가벼운 경우와 무거운 경우에 대해 실제 태양열 집열회로상에서 작동하여 최적 열전달을 위한 작동유체드럽형성과 유동을 도출하였고, 작동유체가 무거운 경우가 가벼운 경우보다 열손실계수가 높음을 알 수 있었다. 작동유체가 축열유체보다 가벼운 경우와 무거운 경우에 대해 실제 태양열 직열회로에서 실험한 결과, 작동유체가 가벼운 경우 체적 열전달계수는 $1.848{\times}10^{-3}w/cm^3^{\circ}C$, 효율은 73%이고 무거운 경우는 $0.128{\times}10^{-2}w/cm^3^{\circ}C$, 효율은 82%로 작동유체가 무거운 경우가 보다 좋은 것으로 나타났다.

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Review of Production, Husbandry and Sustainability of Free-range Pig Production Systems

  • Miao, Z.H.;Glatz, P.C.;Ru, Y.J.
    • Asian-Australasian Journal of Animal Sciences
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    • 제17권11호
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    • pp.1615-1634
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    • 2004
  • A review was undertaken to obtain information on the sustainability of pig free-range production systems including the management, performance and health of pigs in the system. Modern outdoor rearing systems requires simple portable and flexible housing with low cost fencing. Local pig breeds and outdoor-adapted breeds for certain environment are generally more suitable for free-range systems. Free-range farms should be located in a low rainfall area and paddocks should be relatively flat, with light topsoil overlying free-draining subsoil with the absence of sharp stones that can cause foot damage. Huts or shelters are crucial for protecting pigs from direct sun burn and heat stress, especially when shade from trees and other facilities is not available. Pigs commonly graze on strip pastures and are rotated between paddocks. The zones of thermal comfort for the sow and piglet differ markedly; between 12-22$^{\circ}C$ for the sow and 30-37$^{\circ}C$ for piglets. Offering wallows for free-range pigs meets their behavioural requirements, and also overcomes the effects of high ambient temperatures on feed intake. Pigs can increase their evaporative heat loss via an increase in the proportion of wet skin by using a wallow, or through water drips and spray. Mud from wallows can also coat the skin of pigs, preventing sunburn. Under grazing conditions, it is difficult to control the fibre intake of pigs although a high energy, low fibre diet can be used. In some countries outdoor sows are fitted with nose rings to prevent them from uprooting the grass. This reduces nutrient leaching of the land due to less rooting. In general, free-range pigs have a higher mortality compared to intensively housed pigs. Many factors can contribute to the death of the piglet including crushing, disease, heat stress and poor nutrition. With successful management, free-range pigs can have similar production to door pigs, although the growth rate of the litters is affected by season. Piglets grow quicker indoors during the cold season compared to outdoor systems. Pigs reared outdoors show calmer behaviour. Aggressive interactions during feeding are lower compared to indoor pigs while outdoor sows are more active than indoor sows. Outdoor pigs have a higher parasite burden, which increases the nutrient requirement for maintenance and reduces their feed utilization efficiency. Parasite infections in free-range pigs also risks the image of free-range pork as a clean and safe product. Diseases can be controlled to a certain degree by grazing management. Frequent rotation is required although most farmers are keeping their pigs for a longer period before rotating. The concept of using pasture species to minimise nematode infections in grazing pigs looks promising. Plants that can be grown locally and used as part of the normal feeding regime are most likely to be acceptable to farmers, particularly organic farmers. However, one of the key concerns from the public for free-range pig production system is the impact on the environment. In the past, the pigs were held in the same paddock at a high stocking rate, which resulted in damage to the vegetation, nutrient loading in the soil, nitrate leaching and gas emission. To avoid this, outdoor pigs should be integrated in the cropping pasture system, the stock should be mobile and stocking rate related to the amount of feed given to the animals.

계층분석법을 통한 지하차도 재해 예방 및 제어 시스템 개선 연구 (A Study on the Improvement of the Disaster Prevention and Control System for Underpasses by Analytic Hierarchy Process)

  • 김필도;김경수;문유미
    • 한국재난정보학회 논문집
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    • 제16권4호
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    • pp.734-746
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    • 2020
  • 연구목적: 지하차도의 설치 규모, 개수의 증가로 지하차도 내 화재, 침수 등의 재해가 증가하는 추세이다. 지하차도는 지하에 건설되어 재해 발생 시 일반도로 대비 피해가 크고 공용 중 재해 노출 가능성이 크다. 따라서 지하차도 내 재해를 예방·제어하기 위한 시스템 개선사항을 도출하는 데 목적이 있다. 연구방법:본 연구에서는 지하차도 내 재해 분석 및 영향요소에 관한 선행연구와 전문가 자문을 토대로 재해 영향요소 및 대안을 계층 구조화한 모형을 개발하였다. 개발된 모형은 전문가를 상대로 쌍대비교 형태의 설문에 활용하고, 개선순위 결정 등을 위해 AHP분석 기법을 사용 하였다. 연구결과: 설문조사는 일관성을 확보하였고, 재해(교통사고, 화재, 침수)와 대안(법, 제도/계획, 설계, 유지관리/인적/환경)을 상대로 가중치 등을 분석한 결과, 지하차도 재해 예방·제어를 위해 화재에 관한 법, 제도 분야 시스템개선이 최우선으로 필요한 것으로 확인되었다. 결론: 전문가 견지에서 볼 때 지하차도 내 화재 관련하여 물분무시설, 외부(지상)대피통로와 같은 방재시설과 관계된 법, 제도를 강화하는 것이 지하차도 재해예방 및 피해 최소화의 대안임을 보여 주었다.

다공성의 캐리어를 이용한 티카그렐러 함유 고형의 자가 나노유화 약물전달시스템 개발 (Development of Solid Self-nanoemulsifying Drug Delivery Systems of Ticagrelor Using Porous Carriers)

  • 최형주;김경수
    • 생명과학회지
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    • 제31권5호
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    • pp.502-510
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    • 2021
  • 자가 나노유화 약물전달시스템(SNEDDS)은 오일, 계면활성제, 공계면활성제의 균질한 혼합물로서 가벼운 교반에 의해도 에멀전 형성이 가능하고 분산 시 200 nm 이하 범위의 입자 크기를 갖는 나노 에멀전을 형성하는 약물 수송체를 말한다. SNEDDS는 난용성이며 생체이용률이 낮은 소수성약물의 흡수율을 높일 수 있는 뛰어난 가용화 방법으로 알려져 있다. 본 연구에서는 난용성인 티카그렐러에 대한 용해도가 높은 유상으로 MCT oil과, 계면활성제로 Tween 80, 공계면활성제로 Labrafil M1944CS를 사용하여 SNEDDS를 개발하고, 분무건조기술을 이용하여 다양한 다공성의 캐리어에 흡착시켜 고형의 SNEDDS를 제조하였다. 제조된 고형의 SNEDDS에 대하여 물리화학적 특성 및 분말특성을 평가한 후 용출시험을 진행하였다. 본 연구를 통해 얻어진 다공성의 캐리어에 흡착시켜 만들어진 다양한 고형 SNEDDS에서 티카그렐러의 결정형은 무정형으로 변환된 것을 확인할 수 있었다. 또한 제조된 고형의 SNEDDS 조성물들은 모두 원료에 비하여 우수한 용출양상을 나타내는 것을 확인할 수 있었다. 특히 이산화규소를 통해 얻어진 고형의 SNEDDS 조성물의 입자크기와 다분산지수가 제일 작았으며 흐름성과 압축성도 제일 우수하였다. 따라서 이산화규소를 통해 얻어진 고형의 SNEDDS 조성물은 난용성인 티카그렐러의 경구 고형제제화 연구에 적합한 약물 전달 시스템인 것을 확인할 수 있었다.