• Title/Summary/Keyword: evaporation

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Comparison of incoming solar radiation equations for evaporation estimation (증발량 산정을 위한 입사태양복사식 비교)

  • Rim, Chang-Soo
    • Korean Journal of Agricultural Science
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    • v.38 no.1
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    • pp.129-143
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    • 2011
  • In this study, to select the incoming solar radiation equation which is most suitable for the estimation of Penman evaporation, 12 incoming solar radiation equations were selected. The Penman evaporation rates were estimated using 12 selected incoming solar radiation equations, and the estimated Penman evaporation rates were compared with measured pan evaporation rates. The monthly average daily meteorological data measured from 17 meteorological stations (춘천, 강능, 서울, 인천, 수원, 서산, 청주, 대전, 추풍령, 포항, 대구, 전주, 광주, 부산, 목포, 제주, 진주) were used for this study. To evaluate the reliability of estimated evaporation rates, mean absolute bias error(MABE), root mean square error(RMSE), mean percentage error(MPE) and Nash-Sutcliffe equation were applied. The study results indicate that to estimate pan evaporation using Penman evaporation equation, incoming solar radiation equation using meteorological data such as precipitation, minimum air temperature, sunshine duration, possible duration of sunshine, and extraterrestrial radiation are most suitable for 11 study stations out of 17 study stations.

Short-term Variation in Class A Pan Evaporation (대형증발계 증발량의 일 변화)

  • 이부용
    • 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.

A Study on the Evaporation and Ignition of Single Fuel Droplet on the Hot Surface (고온벽면에서의 액적연료의 증발 및 착화에 관한 연구)

  • 송규근
    • Journal of Advanced Marine Engineering and Technology
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    • v.26 no.1
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    • pp.132-137
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    • 2002
  • Recently, impinging spray is used for atomization of diesel engine, but it bring on adhesion of fuel. Therefore, we studied about droplet behavior on high temperature plate changing the size of droplet, surface temperatures, and surface roughness of plate. In this study, We studied to confirm experimentally about mechanism of evaporation and ignition process of single fuel droplet. We observed evaporation time, evaporation appearance and ignition delay time by the photopraphs of 8mm video camera. Experimental results are summarized as follows: 1. The boiling point of fuel affect a evaporation and ignition process. 2. The surface roughness affect a evaporation time. 3. The ignition delay time relate to evaporation characteristic.

Modelling of evaporation from free water surface

  • Song, Wei-Kang;Chen, Yibo
    • 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.

Microexplosive Vaporization of Miscible Binary Fuel Droplets (미세폭발을 가진 혼화 이성분 연료 액적의 증발 현상)

  • Ghassemi, Hojat;Baek, Seung-Wook;Khan, Qasim Sarwar
    • 한국연소학회:학술대회논문집
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    • pp.120-131
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    • 2005
  • The evaporation characteristics of single and multicomponent droplets hanging at the tip of a quartz fiber are studied experimentally at the different environmental conditions under normal gravity. Heptane and Hexadecane are selected as two fuels with different evaporation rates and boiling temperatures. At the first step, the evaporation of single component droplet of both fuels has been examined separately. At the next step the evaporation of several blends of these two fuels, as a binary component droplet, has been studied. The temperature and pressure range is selected between 400 and 700 $^{\circ}C$, and 0.1 and 2.5 MPa, respectively. High temperature environment has been provided by a falling electrical furnace. The initial diameter of droplet was in range of 1.1 and 1.3 mm. The evaporation process was recorded by a high speed CCD camera. The results of binary droplet evaporation show the three staged evaporation. In the the first stage the more volatile component evaporates. The droplet temperature rises after an almost non evaporating period and in the third stage a quasi linear evaporation takes place. The evaporation of the binary droplet at low pressure is accompanied with bubble formation and droplet fragmentation and leads to incomplete microexplosion. The component concentration affects the evaporation behavior of the first two stages. The bubble formation and droplet distortion does not appear at high environment pressure. Nomenclature

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The Effect of Microdroplet Shape on the Evaporation (미세액적의 형상이 증발에 미치는 효과)

  • Song, Hyun-Soo;Lee, Yong-Ku;Jin, Song-Wan;Yoo, Jung-Yul
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.6
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    • pp.558-565
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    • 2007
  • Many studies of microdroplet evaporation from solid surfaces were made with priority given to inkjet printing and dye painting techniques. The objective of these studies is how to evaporate a droplet quickly and uniformly. Also it is necessary to prevent evaporation of a droplet to observe cells in a droplet generated through cell-patterning. In general, an identical volume of a water droplet on hydrophobic surfaces evaporates slower than that on hydrophilic surfaces. In this study, we observe the evaporation process of a droplet on various hydrophobic surfaces and calculated the evaporation rate considering the droplet geometry such as contact angle and height. This study also proposes a new model based on the fact that evaporation mode at the edge of a droplet is different from that at the outer surface of a droplet as the contact angle changes during evaporation. Finally, we reveal the cause fur the increase of evaporation flux and show that the ratio of edge evaporation to total evaporation increases with time.

Comparison of Soil Evaporation Using Equilibrium Evaporation, Eddy-Covariance and Surface Soil Moisture on the Forest Hillslope (산림 사면에서 토양수분 실측 자료, 평형증발 및 에디-공분산방법을 이용한 토양증발비교)

  • Gwak, Yong-Seok;Kim, Sang-Hyun;Kim, Su-Jin
    • Journal of Environmental Science International
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    • v.22 no.1
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    • pp.119-129
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    • 2013
  • We compared equilibrium evaporation($E_{equili}$) eddy-covariance($E_{eddy}$) with soil moisture data($E_{SMseries}$) which were measured with a 2 hours sampling interval at three points for a humid forest hillslope from May 5th to May 31th in 2009. Accumulations of $E_{eddy}$, $E_{equili}$ for the study period were estimated as 2.52, 3.28 mm and those of $E_{SMseries}$ were ranged from 1.91 to 2.88 mm. It suggested that the eddy-covariance method considering the spatial heterogeneity of soil evaporation is useful to evaluate the soil evaporation. Method A, B and C were proposed using mean meterological data and daily moisture variation and the computations were compared to eddy-covariance method and equilibrium evaporation. The methods using soil moisture data can describe the variations of soil evaporation from eddy-covariance through simple moving average analysis. Method B showed a good matched with eddy-covariance method. This indicated that Dry Surface Layer (DSL) at 14:00 which was used for method B is important variable for the evaluation of soil evaporation. The total equilibrium evaporation was not significantly different to those of the others. However, equilibrium evaporation showed a problem in estimating soil evaporation because the temporal tendency of $E_{equili}$ was not related with the those of the other methods. The improved understanding of the soil evaporation presented in this study will contribute to the understandings of water cycles in a forest hillslope.

Evaporation Characteristics of Materials from an Electron Beam Evaporation Source (전자빔 증발원을 이용한 물질의 증발 특성)

  • Jeong, J.I.;Yang, J.H.;Park, H.S.;Jung, J.H.;Song, M.A.
    • Journal of the Korean institute of surface engineering
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    • v.44 no.4
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    • pp.155-164
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    • 2011
  • Electron beam evaporation source is widely used to prepare thin films by physical vapor deposition because it is very effective to vaporize materials and there is virtually no limit to vaporize materials including metals and compounds such as oxide. In this study, evaporation characteristics of various metals and compounds from an electron beam evaporation source have been studied. The 180 degree deflection type electron beam evaporation source which has 6-hearth crucibles and is capable of inputting power up to 10 kW was employed for evaporation experiment. 36 materials including metals, oxides and fluorides have been tested and described in terms of optimum crucible liner, evaporation state, stability, and so on. Various crucible liners have been tried to find out the most effective way to vaporize materials. Two types of crucible liners have been employed in this experiment. One is contact type liner, and the other is non-contact type one. It has been tried to give the objective information and the most effective evaporation method on the evaporation of materials from the electron beam evaporation source. It is concluded that the electron beam evaporation source can be used to prepare good quality films by choosing the appropriate crucible liner.

Effects of Evaporation Water Flow Rate on the Performance of an Indirect Evaporative Cooler (증발수 유량이 간접 증발식 냉각기 성능에 미치는 영향)

  • Choo, Hyun-Seon;Lee, Kwan-Soo;Lee, Dea-Young
    • 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.

The effect of fuel evaporation in the intake valve back on mixture preparation (흡기밸브에서의 연료증발이 혼합기 형성에 미치는 영향)

  • 박승현;이종화;유재석;신영기;박경석
    • Transactions of the Korean Society of Automotive Engineers
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    • v.7 no.8
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    • pp.107-115
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    • 1999
  • Hydrocarbon emission from spark ignition engines deeply relates with fuel evaporation mechanism. Therefore, fuel evaporation on the back of the intake valve is very important to understand fuel evaporation mechanism during engine warm up period. Intake valve heat transfer model was build up to estimate the amount of fuel evaporation on the intake valve back . Intake valve temperature was measured intake valve temperature is increased rapidly during few seconds right after engine start up and it takes an important role on fuel evaporation. The liquid fuel evaporation rate on the intake valve back proportionally increases as valve temperature increases, however its contribution slightly decreases as intake port wall temperature increases. The fuel evaporation rate on the valve back is about 40∼60% during engine warm-up period and it becomes about 20∼30% as intake port wall temperature increases. The estimation model also makes possible model also makes possible to review the effect of valve design parameters such as the valve mass and seat area on fuel evaporation rate through intake valve heat transfer.

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