• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.9
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• pp.714-721
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• 2006

In evaporative cooling applications, the evaporation water is supplied usually sufficiently larger than the amount evaporated to enlarge contact surface between the water and the air. Especially in indirect evaporative coolers, however, if the evaporation water flow rate is excessively large, the evaporative cooling effect is not used for heat absorption from the hot fluid but spent to the sensible cooling of the evaporation water itself. This would result in a decrease in the cooling performance of the indirect evaporative cooler. In this study, the effects of the evaporation water flow rate on the cooling performance are investigated theoretically. The cooling process in an indirect evaporative cooler is modeled into a set of linear differential equations and solved to obtain the exact solutions to the temperatures of the hot fluid, the moist air, and the evaporation water. Based on the exact solutions, it is analyzed how much the cooling performance is affected by the evaporation water flow rate. The results show that the decrease in the cooling effectiveness is substantial even for a small flow rate of the evaporation water and the relative decrease is more serious for a high-performance evaporative cooler.

• Geomechanics and Engineering
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• v.21 no.3
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• pp.237-245
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• 2020

The process of evaporation from free water surface was simulated in a large scale environmental chamber under various controlled atmospheric conditions and also was modelled by a new mass transfer model. Six evaporation tests were conducted with increasing wind speed and air temperature in the environmental chamber, and hence the effect of atmosphere parameters on the evaporation process and the corresponding response of water were investigated. Furthermore, based on the experiment results, seven general types of mass transfer models were evaluated firstly, and then a new model consisted of wind speed function and air relative humidity function was proposed and validated. The results show that the free water evaporation is mainly affected by the atmospheric parameters and the evaporation rate increases with the increasing air temperature and wind speed. Both the air and soil temperatures are affected by the energy transformation during water evaporation. The new model can satisfactorily describe the evaporation process from free water surface under different atmospheric conditions.

• Korean Journal of Agricultural and Forest Meteorology
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• v.4 no.4
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• pp.197-202
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• 2002

A new method is used to estimate the amount of water evaporation from Class A Pan with higher precision and accuracy. The principle of method is to detect the weight change of a buoyant sinker resulting from a change in water level of Class A Pan. A strain-gauge load cell is used to measure the weight change. Field observation of evaporation was done at Pohang Meteorological Station from June 24 to August 4, 2002. By using this new method, it is possible to measure hourly evaporation accurately even under a strong solar radiation and wind disturbance, enabling a direct comparison of evaporation with other meteorological elements. At night, under low humidity and high wind speed conditions, more evaporation was recorded than during daytime. Maximum evaporation rates observed during this period exceed 1.0 mm/hour under the sunny and windy conditions with low humidity. To understand relationships between meteorological elements and latent heat flux at ground level, we suggest intensive held experiments using high accuracy evaporation recording instruments with hourly time interval.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.5
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• pp.393-401
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• 2006

The regenerative evaporation water cooler is devised and analysed in this study. The regenerative evaporation water cooler is composed of a sensible heat exchanger to cool the incoming air, followed by a latent heat exchanger to cool the water evaporatively with the cooled air flowing out of the sensible heat exchanger. By linearizing psychrometric characteristics, the heat and mass transfer in the regenerative evaporation water cooler is analyzed theoretically. The results show that the water can be cooled down even lower than the wet-bulb temperature of the inlet air. When the inlet air is $32^{\circ}C$ and 20% in relative humidity, and the inlet temperature of the water is $20^{\circ}C$, the regenerative evaporation water cooler provides a larger cooling capacity than the conventional evaporation water cooler if the effectiveness of the latent heat exchanger is higher than 0.6 and that of the sensible heat exchanger is higher than 0.5.

• Journal of Environmental Science International
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• v.10 no.5
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• pp.323-327
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• 2001

A new method is developed to estimate the evaporation of water from a surface with high accuracy and resolution. The principle of new method is to detect a weight change of buoyant weight according to a change in water level of Class A Pan mesured by the use of a strain-gauge load cell. Field test of evaporation recording new instrument was carried out at Suwon for 10 days July 1999. It is possible in field observation to measure hourly evaporation amount by newly developed evaporation recording instrument in Class A Pan against strong solar radiation. Present study provide a possibility of domestic high accuracy instrument development below than 0.1mm water level measurement accuracy. If there is low humidity and high wind speed conditions which is possible to evaporate from water surface during night time. And it needs continuous study to understand between meteorological elements and latent heat effect at ground level by field observation study using high accuracy evaporation recording instrument.

• Journal of Korean Elementary Science Education
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• v.17 no.1
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• pp.89-103
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• 1998

We study that what kind of the concepts of evaporation and condensation students of elementary school have. The results are following. (1) The students have simple concepts of evaporation on natural circumstance. However, they don't understand about various effect on evaporation. (2) They don't know where the evaporized water is comming from. (3) They have experiences on observing condensation of wale. (70%), however don't know that the water is evaporized in the air. (4) They have more understanding about evaporation, more correct concepts on condensation in circulation of water.

• Korean Journal of Agricultural and Forest Meteorology
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• v.7 no.1
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• pp.91-97
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• 2005

Class A evaporation pan has been used throughout the world to measure free water evaporation mainly by manual observation once a day. In this study, a new automatic water level measurement method is used for understanding of free water evaporation and numerical analysis. This new technique measures the weight of buoyancy bar in water, and does not need calibration because it is not affected by water density change with water temperature. Field observations of evaporation were made near Haenam Meteorological Station over paddy field located in southwestern Korea from 20 April to 30 May 2004 and the data from ten clear days (16 - 25 May) were used for this analysis. The observed total evaporation was about 50.7mm during this period whereas the estimated from an empirical equation was 50.4mm. As expected, the pan evaporation is well correlated with wind speed and the vapor pressure deficit between the water surface and the air.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.5
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• pp.525-532
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• 2000

Evaporation heat transfer characteristics have been investigated experimentally when distilled water is sprayed on the outside wall of horizontal tubes in a evaporator. This problem is of particular interest in the design of evaporator of an absorption system. Hydrophilic surface treatment was employed to increase the wettability on copper tubes. The results indicate that evaporation heat transfer with hydrophilic tubes is shown to be 25-44% higher than that with bare tubes at evaporation pressure of 31.8 Torr(evaporation temperature$ 30^{\circ}C). Evaporation heat transfer rates of hydrophilic treatment tubes are improved substantially, comparing with those of conventional copper tubes in the wide range of operating parameters, such as water inlet temperatures, water mass flow rates and evaporation pressures.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.766-770
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• 2005

Cascade-Correlation Neural Networks Model(CCNNM) is used to estimate daily evaporation using limited climatical variables such as atmospheric temperature, dewpoint temperature, relative humidity, wind speed, sunshine duration and radiation. DeBruln equation is applied to estimate daily free-surface evaporation. It is converted into pan evaporation using pan coefficient. The results of CCNNM shows better than those of Debruin equation. This research represents that the strong nonlinear relationship such as evaporation modeling can be generalized by the CCNNM ; a special type of Backpropagation algorithm Neural Networks Model.

• Journal of ILASS-Korea
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• v.26 no.2
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• pp.96-103
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• 2021

In order to improve the overall efficiency and meet the emission regulations of boiler systems, the heat exchanging methods between inlet air and exhaust gas have been used in boiler systems, named as the waste-heat-recovery condensing boiler. Recently, to further improve the overall efficiency and to reduce the NOx emission simultaneously, the concept of the water injection into the inlet air is introduced. This study suggests the models for the optimized design parameters of water injection for waste-heat-recovery condensing boilers and performs the analysis regarding the water injection amount and droplet sizes for the optimized water injection. At first, the required amount of the water injection was estimated based on the 1^st law of thermodynamics under the assumption of complete evaporation of the injected water. The result showed that the higher the inlet air and exhaust gas temperature into the heat exchanger, the larger the amount of injected water is needed. Then two droplet evaporation models were proposed to analyze the required droplet size of water injection for full evaporation of injected water: one is the evaporation model of droplet in the inlet air and the other is that on the wall of heat exchanger. Based on the results of two models, the maximum allowable droplet sizes of water injection were estimated in various boiler operating conditions with respect to the residence time of the inlet air in the heat exchanger.