• Title/Summary/Keyword: Evaporative latent heat

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Analysis of Heat and Mass Transfer in an Evaporative Cooler with Fully Wetted Channel (채널이 수막으로 완전히 덮여 있는 증발식 냉각기에서의 열 및 물질전달 해석)

  • Song, Chan-Ho;Lee, Dae-Yeong;No, Seung-Tak
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.12
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    • pp.1766-1775
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    • 2001
  • A theoretical analysis on the heat and mass transfer in an evaporative cooler is presented in this work. The evaporative cooler is modeled as a channel filled with porous media the interstitial surface of which is covered by thin water film. Assuming that the Lewis number is unity and the water vapor saturation curve is linear, exact solutions to the energy and vapor concentration equations are obtained. Based on the exact solutions, the characteristics of the heat and mass transfer in the evaporative cooler are investigated. The comparison of the cooling performance between the evaporative cooler and the usual sensible heat exchanger is also carried out. Obviously, the evaporative heat exchanger shows better cooling performance than the sensible heat exchanger. This is due to the latent heat of water vaporization, which results in apparent increases both in the interstitial heat transfer coefficient and the specific heat of the air stream in the evaporative cooler.

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.

Conceptual Development of a Subminiature Cool Pad Applying Sorption Cooling Effect (흡습 냉각 원리를 이용한 소형 냉각 패드에 관한 연구)

  • 황용신;이대영;김우승
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.16 no.2
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    • pp.121-127
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    • 2004
  • This paper describes conceptual development and idea-verification of a sub-miniature portable cooler which dose not necessitate any pre-cooling nor any external energy supply. The basic principle of the cooling mechanism is the vaporization of water and sub-sequent cooling due to the evaporative latent heat loss. In this work, the vaporization of the water is stimulated by desiccant material to improve the cooling effect. The evaporative cooling caused by the desiccant is modeled and analyzed considering the sorption characteristics of the desiccant. In addition, the portable cooler is fabricated in the shape of a thin pad, and its cooling characteristics are tested and compared with the analytic results.

Dynamic Simulation of a Hybrid Cooling System utilizing Heat Pump, Desiccant and Evaporative Cooler (열펌프, 데시칸트 및 증발식 냉각기를 조합한 하이브리드 냉방 시스템의 동특성 해석 연구)

  • Seo, Jung-Nam;Kim, Young-Il;Chung, Kwang-Seop
    • Journal of the Korean Society for Geothermal and Hydrothermal Energy
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    • v.7 no.1
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    • pp.45-50
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    • 2011
  • Hybrid desiccant cooling system(HDCS) consists of desiccant rotor, regenerative evaporative cooler, heat pump and district heating hot water coil. In this study, TRNSYS and EES, dynamic and steady simulation programs were used for studying hybrid desiccant cooling system which is applied to an apartment house from June to August. The results show that power consumption of the hybrid desiccant cooling system is 70 kWh in June, 199 kWh in July and 241 kWh in August. Sensible and latent heats removed by the hybrid desiccant cooling system are 300 kWh, 301 kWh in June, 610 kWh, 858 kWh in July and 719 kWh, 1010 kWh in August. COP of the hybrid desiccant cooling system is 8.6 in June, 7.4 in July and 7.2 in August. COP of the hybrid desiccant cooling system decreases when latent heat load increases. Operation time of the system is 70 hours in June, 190 hours in July and 229 hours in August. Since the cooling load is largest in August, the operation time of August is longest for maintaining the indoor temperature at $26^{\circ}C$. Due to the characteristics of hybrid desiccant cooling system for efficiently handling both sensible and latent loads, this system can handle sensible and latent heat loads efficiently in summer.

Theoretical Analysis on the Heat and Mass Transfer in a Sorption Cool Pad (흡습 냉각 패드에서의 열 및 물질전달에 관한 연구)

  • 황용신;이대영;박봉철
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.16 no.2
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    • pp.167-174
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    • 2004
  • A sorption cool pad brings cooling effect without any pre-cooling, nor any external energy supply. It uses evaporative cooling effect stimulated by the desiccative sorption. In this paper, heat and mass transfer in the sorption cool pad are investigated theoretically. The evaporative cooling process caused by the desiccant is modeled and analyzed considering the sorption characteristics of the desiccant. Two nondimensional parameters are found to dominate the cooling process: one is related to the psychrometric characteristics and the other is to the sorption capacity of the desiccant. The former decides the time to reach the lowest temperature and the later controls the time duration of the cooling effect being sustained.

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.

Performance of Heat Recovery System using Evaporative Cooling (증발냉각을 이용한 배기열 회수장치의 성능에 관한 연구)

  • Yoo, Seong Yeon;Kim, Tae Ho;Kim, Myung Ho
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.39 no.1
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    • pp.37-43
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    • 2015
  • Evaporative cooling is a very effective way for exhaust heat recovery that uses both latent heat and sensible heat. This study investigated the performance of a heat recovery system using evaporative cooling. The experimental apparatus comprised a plastic heat exchanger, a water spray nozzle, an air blowing fan, a water circulation pump, and measuring sensors for the temperature, humidity, and flow rate. The effectiveness of the sensible heat recovery without evaporation was measured and compared with that of the total heat recovery with evaporation. The effectiveness of the sensible and total heat recoveries decreased as the air flow rate increased, and a much higher effectiveness was obtained with the counterflow arrangement in both cases. For total heat recovery, the effectiveness increased with the water flow rate, and the parallel flow arrangement was found to be more sensitive to the water flow rate than the counterflow arrangement.

Cooling Enhancement Potential of an Air-Cooled Condenser by Evaporative Cooling (증발냉각에 의한 공랭 응축기의 성능향상 가능성에 관한 연구)

  • 이대영;백영진;김영일
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.16 no.3
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    • pp.203-210
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    • 2004
  • This paper describes the potential advantages in applying evaporative cooling to air-cooled condensers. The cooling characteristics of an air-cooled condenser with its surface fully covered with thin water film are investigated and compared with that of an air-cooled condenser with usual dry surface. By applying the evaporative cooling, the cooling performance of the condenser is shown to improve enormously. When the outdoor air is 35$^{\circ}C$ and 40% in relative humidity, the condensing temperature of the refrigerant is decreased by 2$0^{\circ}C$. Even when the incoming air is fully saturated with water vapor, the evaporation from the wet surface occurs to cause a decrease in the condensing temperature by 1$0^{\circ}C$. The main reason for this improvement is assessed as the addition of an efficient cooling mechanism which is the water evaporation resulting in latent heat absorption.

A Study on Performance Characteristics of an Evaporative Heat Exchanger with Mini-channels (환경조절장치용 미세유로형 증발열교환기의 성능특성 연구)

  • Lee, Hyung-Ju;Yoo, Young-June;Min, Seong-Ki;Hwang, Ki-Young
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2011.11a
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    • pp.247-253
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    • 2011
  • An experimental study on performance characteristics of an evaporative heat exchanger based on tests for various operating conditions was presented. The heat exchanger maximizes the heat transfer rate per unit volume by applying mini-channels for both the air and coolant flow paths, and minimizes the amount of the coolant by using its latent heat of evaporation. The heat exchanger was manufactured by etching the flow paths, brazing the heat exchange plates, and welding the in/out ports of the media. The basic performance test has confirmed that the heat exchanger met its design requirements, and the results of the map test were analyzed to produce the performance characteristics quantitatively depending on the air inlet temperature, the air flow rate, and the coolant flow rate.

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Airborne Remote Sensing of Evapotranspiration over Rice Paddy

  • Chen, Y.Y.;Liou, Yuei-An
    • Proceedings of the KSRS Conference
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    • 2003.11a
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    • pp.351-353
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    • 2003
  • We present a retrieval scheme for the remote sensing of evapotranspiration (ET) over rice paddy. To perform the retrieval, high-resolution airborne imagery of multi-spectral visible and thermal infrared data, and ground-based meteorological measurements are utilized. Our ET retrieval scheme is based on the basic principal of surface energy budget, which is a result of balance in longwave and shortwave radiation, latent heat, sensible heat, and energy flux into the ground. To partition the latent and sensible heat fluxes of interest from the energy balance equation, three basic parameters are of most concern, including albedo, surface temperature, and normalized difference vegetation index (NDVI). The NDVI and albedo can be easily derived from the visible and near infrared spectral data, while the surface tem-perature can be determined through the analysis of the infrared data with the Stefan Boltzmann law. From the airborne imagery taken on 28 April 2003, we observe very good dry and wet pixels that can be easily corre-sponded to the radiation and evaporation controlled crite-ria, respectively, and, hence, for the further use in defin-ing the evaporative fraction needed to partition sensible and latent heat fluxes from the net energy flux. The de-rived ET is compared with the in situ measurements.

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