• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.16 no.1
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• pp.74-80
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• 1987

Turbulent convective heat transfer phenomenon which occur around the evaporator section of heat pump were analyzed experimentally. For this purpose a special wind tunnel and a heat pump system were designed and fabricated. Evaporator section was installed perpendicular to air flow direction and part of the evaporator was made of a glass tube for visual observation. The velocity distribution, turbulent intensity and temperature distribution were measured by hot wire technique and thermocouples. An experimental correlation for the convective heat transfer coefficient was obtained and the result is somewhat higher than the value calculated from Hilpert equation. The difference in two equations is believed to be due to the boning effect inside the evaporator tube.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.2
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• pp.142-151
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• 1991

In the present investigation, it has been proposed to utilize a direct contact heat exchanger as an evaporator to solve the difficulties such as scaling, corrosion and law thermal efficiencies, associated with the conventional evaporator. Liquified nitrozen was utilized as a working fluid to investigate basic natures of bubble dynamics in the evaporator, and spray nozzles were adopted to inject liquified nitrozen into the spray column with varying flow rates of dispersed phase fluids. Experimentations were carried out in the range of $6.54{\times}10^{-4}kg/s$ - 0.030 kg/s for dispersed phase flow rates with one, three and five nozzle holes. Observing the bubble dynamics for the evaporator the feasibility of utilizing a direct contact heat exchanger as a LNG evaporator has been evaluated. The results show that no eruption phenomena was observed in the present investigation with $LN_2$ and the interface between $N_2$ bubbles and water was fully turbulent. It is believed that the high injection velocity of $LN_2$ through the spray nozzles provide good mixing effects for both heat and mass transfers between water and $N_2$ bubbles. Ice was formed on the surface of the spray nozzle for higher $LN_2$ flow rates. However, even in this case, it is observed that the ice was detached as soon as it was formed. Under the present experimental conditions, the shapes of $LN_2$ bubbles were in the spherical-cap region according to the Clift, Grace and Weber Graphs. The height of foam region caused by the breakup of larger bubbles keeps increasing with high injection velocities until it reaches it's maximum height.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.5
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• pp.513-522
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• 2013

In the present work, a numerical study of a horizontal falling film evaporator in a multi-effect distillation (MED) plant is performed. Tube bundles in the evaporator are described as porous media, and a volume-averaged method is applied. To calculate the fluid flow and phase change in the evaporator due to heat transfer in the system, FLUENT and user-defined functions (UDF) are used. To observe the performance of the evaporator under different operational conditions, tests are conducted for a steam mass flux ranging from 0.5 to 2.5 $kg/m^2s$ in the horizontal tube, for mass fraction of the noncondensable gas in the tube inlet ranging from 0% to 1%, and for film Reynolds numbers ranging from 100 to 1,000 for the falling film. The evaporation rate increases with the steam mass flux and Reynolds number. In contrast, the evaporation rate decreases by 0.87% with a 1% increase in the mass fraction of the noncondensable gas in the tube.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.9
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• pp.953-960
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• 2012

An AMTEC (alkali metal thermal electric converter) is a device that is used for the direct conversion of heat to electricity. Sodium is used as the working fluid, and its circulation is driven by a capillary wick. The wicks used for circulation include an evaporator wick, artery wick, and condenser wick, and each wick has a pressure drop because of the circulation of liquid and vapor. For the circulation of sodium, the capillary pressure of the evaporator wick must be greater than the total pressure drop in the wicks. In this study, the pressure drop in the evaporator wick, artery wick, and condenser wick and the heat loss from the evaporator to the condenser through the artery wick were analyzed for the design of a 100 W AMTEC prototype. It was found that a particle diameter of 10 ${\mu}m$ is suitable for the evaporator wick to maintain a capillary pressure greater than total pressure drop in the circulation loop.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.30.2-30.2
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• 2005

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.11a
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• pp.595-596
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• 2010

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.12
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• pp.1071-1078
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• 2010

The objective of this study is to investigate the heat transfer characteristics of evaporators that have various fin configurations and are used in household refrigerators. The frosting and defrosting characteristics of a spirally coiled circular fin-tube evaporator, a discrete-plate fin-tube evaporator, and a continuous-plate fin-tube evaporator were measured and compared. Under non-frosting conditions, the heat transfer coefficient of the spirally coiled circular fin-tube evaporator was 22.3% and 40.2% higher than the coefficients of the discrete- and continuous-plate fin-tube evaporators, respectively. Under frosting conditions, the heat transfer coefficient of the spirally coiled circular fin-tube evaporator was 27.0% and 46.3% higher than the coefficients of the discrete- and continuous-plate fin-tube evaporators, respectively. In addition, the defrosting water amount of the spirally coiled circular fin-tube evaporator was 3.2% and 9.4% lower than the amounts in the case of the discrete- and continuous-plate fin-tube evaporators, respectively.

• Journal of the Korean Solar Energy Society
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• v.30 no.3
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• pp.33-38
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• 2010

The evaporative desalination system using solar thermal energy would be the efficient and attractive method to get fresh water from brine due to low carbon dioxide generation. In this research the solar desalination system as a heating source of refrigerant R123 in the evaporator was considered. The circulation of refrigerant in the evaporator can reduce the energy consumption of the system, because of using the latent heat of the refrigerant 123 instead of the sensible heat of present hot water. The system was comprised of the single-stage fresh water production unit on the capacity of 1ton/day with shell and tube type evaporator, heaters instead of solar collector to supply the proper heat to refrigerant, and refrigerant and brine circulation systems. Various operating flowrate and temperature ranges were varied in the experiments to get the optimum design data. The results showed that the optimum flow rate of brine feed rate to evaporator was 1.2Liter/min, and the yield of fresh water was increased as higher temperature of feed brine. It was confirmed that the circulation flowrate of heating source of refrigerant was decrease of one fifth of the present warm water system, and very efficient system for solar desalination.

• KSBB Journal
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• v.29 no.5
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• pp.392-398
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• 2014

It was confirmed that malodor connected with an air-conditioner in an automobile is caused by microbial volatile organic compounds (MVOCs) produced by microorganisms and through microorganisms coexisting with each other to form a biofilm on the evaporator surface. A bacterium, Methylobacterium aquaticum, can form a biofilm on the evaporator surface. The biofilm was composed of 45.79% C (Carbon), 42.36% O (Oxygen), 1.85% Na (Sodium), 5.42% Al (Aluminum), 1.39% P (Phosphorus), 0.74% Cl (Chlorine) and 2.45% K (Potassium). This result matches the composition of the biofilm formed on the surface of the used evaporator. It was determined that sulfur compounds (Hydrogen sulfide, Dimethyl sulfide) and organic acids (n-Butyric acid, n-Valeric acid, iso-Valeric acid) in the air which was blown into the automobile were generated by Methylobacterium aquaticum and Aspergillus versicolor, respectively. On the other hand, volatile organic compounds (Toluene, Xylene, 2-Ethylhexanol, 2-Phenyl- 2-propanol, Ethylbenzene) were not found. It is estimated that the reason is due to the low concentration of generated MVOCs or is caused by the change of some MVOCs depending on the nutrients (medium).

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.4
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• pp.345-353
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• 2000

In this study, the performance of five ejectors has been investigated with working fluids of water and water vapor. The diameters of nozzle and mixing tube of five ejectors were 1 and 1.5(ejector A), 1 and 2(ejector B), 1 and 2.5(ejector C), 1 and 3(ejector D), 2 and 4(ejector E) in millimeters. The length of the mixing tube was 8-10 times of its diameter. For each ejector, the ratio of mass flow rate of ejected water to that of entrained water vapor, $\mu$, was evaluated in terms of evaporator pressure, mass flow rate of ejected water, and water temperature. It was found that the performance of an ejector was not stable when the ratio of diameters was too small or too large(ejector A and D) and $\mu$ was almost the same for two ejectors with the same diameter ratio(ejector B and E). It was also found that $\mu$ increased almost linearly with an increase of evaporator pressure and the ratio $\mu$ increased as water temperature decreased. As expected, $\mu$ converged to zero as the water temperature approached the evaporator temperature. Finally, a non-dimensional correlation has been developed to predict$\mu$ terms of evaporator pressure and saturation pressure of ejected water.