• International Journal of Air-Conditioning and Refrigeration
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• v.9 no.3
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• pp.63-71
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• 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.

• The KSFM Journal of Fluid Machinery
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• v.18 no.6
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• pp.76-80
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• 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
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• 2010.11a
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• pp.88.1-88.1
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• 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.

• Solar Energy
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• v.18 no.3
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• pp.63-69
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• 1998

The heat conduction and the water vapour diffusion flow through heat insulators between hygroscopical moist building materials were measured by means of the plate method. It was found that the heat transport increases with a moisture motion occuring in the temperature drop. On his basis of simplified assumptions, the increase in the thermal conductivity was calculated from the rate of diffusion flow per unit area, which generally resulted in values inferior to the measured values. The Increase in the heat transport due to water vapour diffusion measured at a large-scale wall specimen was inferior to the one measured by means of the plate method by using a comparable arrangement of layers. The overall heat transfer caused by moisture motion is not a characteristic value of the material, but a property of the whole wall structure

• Journal of the Korean Ceramic Society
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• v.51 no.2
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• pp.57-63
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• 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
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• v.24 no.3
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• pp.382-388
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• 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.

• Journal of Korean Society on Water Environment
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• v.27 no.1
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• pp.44-53
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• 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.

• Journal of Bio-Environment Control
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• v.7 no.3
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• pp.237-245
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• 1998

Greenhouse crop production under critical summer climate In Korea has considerable difficulties because of high temperature and relative humidity. In this study, some water pipes were tested as a means of the dehumidification and increment of evaporative cooling efficiency. As a result of heat transfer characteristic analysis, overall heat transfer coefficient of copper pipe was larger than steel pipe, and estimated values were smaller than measured values. The condensed quantities of vapor were not significantly different between copper pipe and steel pipe, however dehumidifying effect by the water pipes was significantly large. It was estimated based on the results that the evaporative cooling system by the water pipe will be able to increase the evaporative cooling efficiency of about 48%, and decrease the temperature of about 1.3$^{\circ}C$.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.268-273
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• 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.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.55-64
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• 2003

Desiccation of a soil is basically the removal of water by evaporation, which is controlled by evaporativity and evaporability. Surface evaporation improves the trafficability which is essential for the access of construction equipment in the area reclaimed with soft clay. The existing traditional methods for evaluating evaporation can not account for the deformation of reclaimed soft soils during evaporation. Therefore, a theoretical model for predicting the rate of evaporation from the surface of a deformable material is proposed. The model is based on a system of equations for coupled heat and mass transfer in unsaturated soils. The modified pressure plate extractor test and glass desiccator test were carried out to obtain the soil-water characteristic curve for a deformable soil. The column drying test was conducted to investigate one dimensional water flow, heat flow and evaporation in the surface. A finite difference program was developed to solve the coupled nonlinear partial differential equations, which permit the study of water, vapor and heat flows in the deformable soil. Comparison between measured and simulated values shows a reasonably good matching between the two.