• Title/Summary/Keyword: Latent Heat of Evaporation

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Numerical study of heat and mass transfer around an evaporative condenser tube by multi-zone method (다중 영역법을 이용한 증발식 응축관 주위의 열 및 물질전달 해석)

  • ;;Yun, In-Chul;Yoo, Je-In
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.12
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    • pp.3317-3328
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    • 1995
  • The objective of the present study is to predict the characteristics of heat and mass transfer around an evaporative condenser. Numerical calculations have been performed using multi-zone method to investigate heat transfer rate and evaporation rate with the variation of inlet condition(velocity, relative humidity and temperature) of the moist air, the flow rate of the cooling water and the shape of the condenser tube. From the results it is found that the profile of heat flux is the same as that of evaporation rate since heat transfer along the gas-liquid interface is dominated by the transport of latent heat in association with the vaporization(evaporation) of the liquid film. The evaporation rate and heat transfer rate is increased as mass flow rate increases or relative humidity and temperature decrease respectively. But the flow rate of the cooling water hardly affect the evaporation rate and heat flux along the gas-liquid interface. The elliptic tube which the ratio of semi-minor axis to semi-major axis is 0.8 is more effective than the circular tube because the pressure drop is decreased. But the evaporation rate and heat flux shown independency on the tube shape.

Investigation on the Cooling Characteristics of a Regenerative Evaporation Water Cooler (재생증발식 수냉각기의 냉각성능 해석)

  • Choi Bong-Su;Hong Hi-Ki;Lee Dae-Young
    • 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.

On Study of Summertime Ice Formation in the Ice Valley at Unchiri, Gangwon-Province (강원도 정선군 운치리 얼음골의 여름철 결빙현상에 관한 연구)

  • Jeon, Byung-Il
    • Journal of Environmental Science International
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    • v.11 no.9
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    • pp.857-863
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    • 2002
  • The meteorological elements were measured to investigate cause of summertime ice formation at Unchiri, Gangwon Province. The cause of freezing at valley was conformed as adiabatic expansion theory, latent heat of evaporation, natural convective theory, cold air remain theory, and convective freezing theory according to former study. However nither theory produced a satisfactory explanation. This studying area is not valley but ridge, and underground water surface exists at below than freezing height. wintertime temperature drop and summertime cold air spouting were explain as natural convective theory, generation of water drop on the rock was explained as cooling theory by air expansion, and ice formation on the rock was explained as adiabatic expansion theory. In conclusion, formation of ice valley at Unchiri was formed by natural convective theory, adiabatic expansion theory, and latent heat of evaporation successively.

Study on Cooling Charcteristics of Forced Evaporation by using Steam Ejector (스팀 에젝터에 의한 강제 증발 방식의 냉각 특성에 관한 연구)

  • Son, H.J.;Lee, Y.H.;Kim, Y.G.;Jeong, H.M
    • Journal of Power System Engineering
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    • v.10 no.2
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    • pp.41-46
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    • 2006
  • This study shows a water cooling system by using a steam ejector and jet condenser to drop the temperature of the water by about $5^{\circ}C\;from\;25^{\circ}C$ or higher. In this research, to replace the present water cooling system, we focused on a water cooling system by latent heat of evaporation, thus this system needs a vacuum pressure to evaporate the water in enclosed tank. The water cooling effects are depended on the vacuum pressure in the enclosed tank, and the cooling water is generated by latent head of evaporation. As the experimental results, the absolute vacuum pressure obtained was about $5{\sim}8$ mmHg using a steam driven ejector with jet condenser.

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Seasonal Variation of the Surface Heat Budget in the Gumi Reservoir of Nakdong River (낙동강 구미 보의 수면 열수지 계절 변화)

  • Kim, Hak-Yun;Seo, Kwang-Su;Cho, Chang-Bum;Kim, Hae-Dong
    • Journal of Environmental Science International
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    • v.25 no.8
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    • pp.1057-1063
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    • 2016
  • The heat budget is investigated in the Gumi Reservoir of the Nakdong river. In warm climate season, solar radiation effects play a important role in the change of water temperature. The features of the surface heat balance are almost derived by the latent heat flux and the solar radiation flux. On the other hand, in cold climate season, change of heat stored in the water is mainly dominated by latent and sensible heat transfer between water and air, since flux of solar radiation and loss of outgoing long wave radiation balance approximately. For the annual averages, net flux of radiation, evaporation(latent heat) loss are dominant in the Gumi reservoir. The evaporation losses are dominant from spring to early winter. This means that the Gumi reservoir rolls like a lake of thermal medium or deep depth.

Influences of Urban Trees on the Control of the Temperature (도시의 수목이 기온의 조절에 미치는 영향)

  • 김수봉;김해동
    • Journal of the Korean Institute of Landscape Architecture
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    • v.30 no.3
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    • pp.25-34
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    • 2002
  • The purpose of this paper is to discuss the function of microclimate amelioration of urban trees regarding the environmental benefits of street trees in summer, focusing on the heat pollution-urban heat island, tropical climate day's phenomenon and air pollution. We measured the diurnal variation of air/ground temperatures and humidity within the vegetation canopy with the meteorological tower observation system. Summertime air temperatures within the vegetation canopy layer were 1-2$^{\circ}C$ cooler than in places with no vegetation. Due to lack of evaporation, the ground surface temperatures of footpaths were, at a midafternoon maximum, 8$^{\circ}C$ hotter than those under trees. This means that heat flows from a place with no vegetation to a vegetation canopy layer during the daytime. The heat is consumed as a evaporation latent heat. These results suggest that the extension of vegetation canopy bring about a more pleasant urban climate. Diurnal variation of air/ground temperatures and humidity within the vegetation canopy were measured with the meteorological tower observation system. According to the findings, summertime air temperatures under a vegetation canopy layer were 1-2$^{\circ}C$ cooler than places with no vegetation. Due mainly to lack of evaporation the ground surface temperature of footpaths were up to 8$^{\circ}C$ hotter than under trees during mid-afternoon. This means that heat flows from a place where there is no vegetation to another place where there is a vegetation canopy layer during the daytime. Through the energy redistribution analysis, we ascertain that the major part of solar radiation reaching the vegetation cover is consumed as a evaporation latent heat. This result suggests that the expansion of vegetation cover creates a more pleasant urban climate through the cooling effect in summer. Vegetation plays an important role because of its special properties with energy balance. Depended on their evapotranspiration, vegetation cover and water surfaces diminish the peaks of temperature during the day. The skill to make the best use of the vegetation effect in urban areas is a very important planning device to optimize urban climate. Numerical simulation study to examine the vegetation effects on urban climate will be published in our next research paper.

A Study on the Rapid Cooling Vacuum System for the Storage and Transportation of the Cold Agriculture and Livestock Products (농축산물의 저장 및 유통을 위한 감압증발 급냉각 시스템에 관한 연구)

  • 김성규;김원녕;김경석;최순열;전현필
    • Journal of Advanced Marine Engineering and Technology
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    • v.21 no.1
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    • pp.26-36
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    • 1997
  • Recently, the new refrigerating system, using non - fluorinated hydrocarbon refrigerants has to be developed for the agricultural fields. One of that kinds of systems is the cooling system using the water vapor and vacuum, in which the water evaporate at the low temperature under vacuum and absorb the large amount of the latent heat. If vapor with large amount of latent heat is removed from the system, the system is cooled accordingly. The characteristics of cooling under the vacuum was observed and measured using experimental apparatus, which is consisted of vacuum chamber, the ejectors, the pumps and the measurement apparatus. As the results of experiments, we know that the evaporation in the vacuum occurs vigorously when the materials to be cooled has more amounts of heat before cooling, and by which effects the materials can be cooled. The cooling vacuum system is more efficient than other methods when the agricultural products is chilled or dried.

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An Experimental Study on the Water Evaporation Conditions of the Enclosed Tank (밀폐용기내의 물의 저압 증발 최적조건에 관한 실험적 연구)

  • Kim, S.H.;Shin, Y.S.;Lee, Y.W.;Chung, H.S.;Jeong, H.M.
    • Journal of Power System Engineering
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    • v.8 no.1
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    • pp.41-47
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    • 2004
  • Cooling towers are widely used not only for cooling products and equipment in manufacturing process but HVAC(Heating, Ventilation and Air Conditioning) system. As a cooling tower is the terminal apparatus which discharges heat from industrial process, the efficiency of heat exchange in the cooling tower greatly affects to the overall performance of a thermal system. In this paper, we constituted a new water cooling system by using a Latent heat of evaporation in an enclosed tank, and this system is consisted of an enclosed vacuum tank and water driven ejector system. Several experimental cases were carried out for improvement methods of high vacuum pressure and water cooling characteristics. The ejector performance was tested in case of water temperature variations that flows into the ejector. Based on the vacuum pressure by water driven ejector, the water cooling characteristics were investigated for the vaporized air condensing effects.

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Analytical Study of heat Transfer in Evaporative Cooling of a Porous Layer (다공층의 증발냉각 열전달에 관한 해석적 연구)

  • 김홍제;이진호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.1
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    • pp.104-111
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    • 1992
  • In this study, the heat transfer characteristics of the evaporative transpiration cooled system is analytically investigated considering the occurrence of the two-phase evaporation zone. Under the condition of the external heat input, analytical solutions of the three regions (i.e., vapor, liquid and two-phase evaporation zone) are respectively obtained using the matching conditions for the steady-state problem where properties are constant. As results, the length of the evaporation zone increases with increasing heat input and with decreasing mass flow rate. It also increases with increasing particle size, system porosity, thermal conductivity of material, inlet temperature and latent heat of coolant. The position of the lower interface of the evaporation zone have a lot of efforts on the evaporation zone length, the position of the upper interface penetrates deeper into the porous layer with lower thermal conductivity of porous material, higher system porosity and larger particle size.

Change of the Warm Water Temperature for the Development of Smart Healthecare Bathing System (지능형 헬스케어 욕조시스템 개발을 위한 온수 온도변화)

  • Kim, Gi-Beom
    • Korean Chemical Engineering Research
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    • v.44 no.3
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    • pp.270-276
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    • 2006
  • In this study, heat loss through free surface of water contained in bathtub due to conduction and evaporation has been analyzed. As a result of this study, a relational equation has been derived based on the basic theory of heat transfer to evaluate the performance of bath tubes. The derived equation was rational and quantitative. The major heat loss was found to be due to evaporation. Moreover, it has been found out that the speed of heat loss depends more on the humidity of the bathroom than the temperature of water contained in the bathtub. So, it is best to maintain the temperature of bathtub water to be between 41 to $45^{\circ}C$ and the humidity of bathroom to be 95%.