• International Journal of Air-Conditioning and Refrigeration
• /
• 제9권3호
• /
• pp.63-71
• /
• 2001

This paper presents a model-based method for detecting and diagnosing some faults in the cooling tower of healing, ventilating, and air-conditioning systems. A simple model for the cooling tower is employed. Faults in cooling tower operation are detected through the deviations in the values of system characteristic parameters such as the heat transfer coefficient-area product, the tower approach, the tower effectiveness, and fan power. Three distinct faults are considered: cooling tower inlet water temperature sensor fault, cooling tower pump fault, and cooling tower fan fault. As a result, most values of the system characteristics parameter variations due to a fault are much higher or lower than the values without faults. This allows the faults in a cooling tower to be detected easily using above methods. The diagnostic rules for the faults were also developed through investigating the changes in the different parameter due to each faults.

• 한국유체기계학회 논문집
• /
• 제18권6호
• /
• pp.76-80
• /
• 2015

The purpose of this study is to understand the cavitation phenomena in centrifugal pumps through computational fluid dynamics method. NPSH characteristic curve is measured from different flow operating conditions. Steady state, liquid-vapor homogeneous method with two equations transport turbulence model is employed to estimate the NPSH curve in centrifugal pumps. The Rayleigh-Plesset cavitation model is adapted as source term for inter-phase mass transfer in order to understand cavitation phenomena in centrifugal pumps. The cavitation incipient curve is clearly estimated at different flows operating conditions. A relationship is made between cavitation incipient and NPSH curve. Also the effects on water vapor volume fraction and pressure load distributions on the impeller blade are also described.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2010년도 추계학술대회 초록집
• /
• pp.88.1-88.1
• /
• 2010

In recent days, the study for the renewable energy is required to supplement traditional energy source. One of the renewable energy of Fuel Cell is classified according to the electrolytes. It is the MCFC (Molten Carbonate Fuel Cell) for this study. One of the equipments of the heat exchangers is important component for efficiency and cost. In MCFC system, several heat exchangers are used according to the application. It is named for the humidifier because it is to preheat the fuel and water so that a reactor will convert some of the incoming fuel to hydrogen. Then, hot side fluid service is used the exhausted gas from the fuel cell and cold side fluid service is the fuel and water. The operation temperature range is about 25~500 Celsius Degree. This heat exchanger has the problems of heat transfer considering to multiphase fluid and phase changing. So it is necessary to analyze the heat transfer characteristics and to propose the reasonable design methodology for the humidifier. In this study, the thermal characteristic for the humidifier is estimated by using commercial tool of heat exchanger design and rating. And this study provides the testing methodology and presents the results for test facility of fabrication and for testing.

• 태양에너지
• /
• 제18권3호
• /
• pp.63-69
• /
• 1998

일반적으로 건물 단열재는 건조된 것이 사용되며 이 상태에서 열전도율을 측정하여 열 손실을 산정할 때 기초자료로 이용될 수 있다. 그러나 이러한 단열재가 흡습성 재료인 경우에는 습도평형 혹은 다른 작용에 의해 습도가 높아지기에 이에 따라 열전도율도 상승하게된다. 이처럼 재료 열전도율의 상승효과는 건축물에 흡습성 재료가 사용될 경우 그 사이에 비흡습성 단열재료가 시공됐을 때도 양쪽재료의 흡습성으로 인하여 단열재의 열전도율이 상승하게 되며 이에 따른 열손실 또한 높아진다. 본 논문에서는 이러한 열전도율의 상승을 간단하게 계획단계에서 적용할 수 있도록 실측에 의해 검증된 약산식을 통해 산출될 수 있도록 하였다.

• 한국세라믹학회지
• /
• 제51권2호
• /
• pp.57-63
• /
• 2014

Bottom ash can be used as pelletizing seeds in unsintered artificial lightweight aggregates, so it can be called as 'cold-bonded aggregates'. In the present study, the mechanical and chemical characteristics of bottom ash aggregates cold-bonded with fly ash were investigated. The crushing strength and the water transfer characteristic of the aggregates, which may affect the strength gain of the concrete, were evaluated. Moreover, the degree of hydration and the hydration products of the aggregates were analyzed to verify the chemical stability of the aggregates. Compared to commercialized artificial lightweight aggregates manufactured by sintering process, cold-bonded fly/bottom ash aggregates had similar levels of water transfer characteristics, while having lower strengths. The calcium hydroxide in the aggregates was almost completely consumed after 28 days moist curing.

• Environmental Engineering Research
• /
• 제24권3호
• /
• pp.382-388
• /
• 2019

Although nanobubbles attract significant attention, their characteristics and applications have not been thoroughly defined. There are diverse opinions about the definition of nanobubbles and controversy regarding methods that verify their characteristics. This study defines nanobubbles as having a size less than $1{\mu}m$. The generation of these sub-micron (nano) bubbles may be verified by induced coalescence or light scattering. The size of a sub-micron (nano) bubbles may be measured by optical, and confocal laser scanning microscopy. Also, the size may be estimated by the relationship of bubble size with the dissolved oxygen concentration. However, further research is required to accurately define the average bubble size. The zeta potential of sub-micron (nano) bubbles decreases as pH increases, and this trend is consistent for micron bubbles. When the bubble size is reduced to about 700-900 nm, they become stationary in water and lose buoyancy. This characteristic means that measuring the concentration of sub-micron (nano) bubbles by volume may be possible by irradiating them with ultrasonic waves, causing them to merge into micron bubbles. As mass transfer is a function of surface area and rising velocity, this strongly indicates that the application of sub-micron (nano) bubbles may significantly increase mass transfer rates in advanced oxidation and aeration processes.

• 한국물환경학회지
• /
• 제27권1호
• /
• pp.44-53
• /
• 2011

Membrane bio-reactor (MBR) has several advantages over the conventional activated sludge process, including a high biomass, low sludge production, and better permeate quality. Therefore, the MBR have gained popularity for municipal and industrial wastewater treatment. However the MBR usually were used for sewage and low streng th wastewater treatment because of membrane fouling problem and limitation of oxygen transfer into biomass. In this study, the hybrid process combining MBR and pure oxygen was tested for high strength organic wastewater treatment in the COD loading range from 2 to $10kgCOD/m^3{\cdot}day$. The hybrid process, membrane coupled pure oxygen high compact reactor (MPHCR), had been operated for one year and operation parameters, the effect of COD loading, MLSS concentration and the location of membrane module were studied for membrane fouling characteristic. Also membrane resistance test and the component of foulant was analyzed to investigate what is specific foulant in the MBR.

• 생물환경조절학회지
• /
• 제7권3호
• /
• pp.237-245
• /
• 1998

극심한 고온으로 인해 정상적인 작물의 재배가 어려운 여름철의 온실 내 기온을 억제시키기 위한 방법 중 가장 효율을 인정받고 있는 증발냉각법은 실내 습도의 증가로 인해 그 사용에 제한을 받게 된다. 본 연구에서는 온실에서 증발냉각법의 냉방효율을 높이기 위한 방법으로 냉수파이프를 설치하여, 그 열적 특성을 분석하고, 제습효과를 조사하였으며, 그 결과를 요약하면 다음과 같다. 동파이프와 아연도금스틸파이프의 총열전달량을 비교한 결과, 동파이프가 다소 크게 나타났으나, 유의성이 없었으며, 두 가지 파이프 모두 이론값 보다 실측값이 더 작게 나타났다. 냉수파이프 표면에 응축되어 제거된 수증기의 양은 동파이프와 아연도금스틸파이프 사이에서 큰 차이를 보이지 않았으나, 두 가지 파이프 모두에서 제습효과는 충분히 큰 것으로 나타났다. 냉수파이프를 설치함으로써 증발냉각시스템의 냉방효율을 평균 48%만큼 높일수 있으며, 평균 1.3$^{\circ}C$만큼의 실내기온을 추가로 냉각시킬 수 있는 것으로 예측되었다. 또한, 냉수파이프를 이용해 증발냉각시스템의 가동으로 인한 실내의 과습문제를 해결하기 위해서는 파이프표면의 응축된 수분을 효과적으로 제거할 수 있는 장치나 방법에 대한 추가적인 연구가 필요할 것으로 판단된다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 추계학술대회논문집B
• /
• pp.268-273
• /
• 2001

A fundamental study on the harvest-type ice storage system applied ice making method in-water and its temperature characteristics in ice storage system was performed experimentally of the charge and discharge of cold. This paper is concerned with the development of a new method for making and separating ice and saving floated ice by installing an evaporation plate at in-water within a storage tank. In a conventional harvest-type ice storage system, a tank saves ice by separating a formed ice from an installed evaporation plate, which is located above an ice storage tank as an ice storage system. A new harvest-type method shows very good heat transfer efficiency than a convectional method. It is because the evaporation panel is directly contacted with water in a storage tank. Also, at a conventional system a circulating pump, a circulating water distributor and a piping are installed, but these components are not necessary in a new method. In this study two kinds of ice storage systems are experimentally investigated to study the thermal characteristics of ice storage tanks.

• 한국지반공학회논문집
• /
• 제19권4호
• /
• pp.55-64
• /
• 2003

흙의 건조현상은 기상조건에 지배받는 evaporativity와 지반의 물 전달 능력에 지배받는 evaporability의 영향을 받는다. 지표면증발은 점토로 매립된 지반에서 건설장비의 주행성을 확보하기 위해서는 필요불가결한 요소이다. 본 논문에서는 준설 점토 지반에서의 증발현상을 규명할 수 있는 모델을 제시하였다. 이 모델은 포화토 및 불포화토에서의 수분과 물의 이동 및 열전달에 대한 식으로 구성되어 있다. 흙수분 특성곡선을 구하기 위하여 압력판추출시험(pressure plate extractor test)과 데시케이터실험이 수행되었으며 일차원 증발현상을 규명하기 위하여 컬럼증발실험을 수행하였다. 체적이 변하는 흙에서의 물, 증기 및 열전달 비선형 미분방정식을 풀기 위하여 유한차분프로그램을 개발하였으며 실험결과와 이론해를 비교하였다.