• Journal of the Korean Society for Heat Treatment
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• v.19 no.3
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• pp.141-148
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• 2006

An experimental study is presented for water droplet impingement on a steel surface in the process of heat treatment. The objective of the present work is to examine characteristic of evaporation cooling due to surface roughness and droplet diameter under conductive heat input condition. The surface temperatures varied from $80{\sim}155^{\circ}C$, surface roughness was from $R_a=0.12{\mu}m$ to $R_a=1.14{\mu}m$ and droplet diameter was from 2.4 mm to 3.0 mm. The results show that the total evaporation time is shorter for the larger surface roughness and the smaller droplet size, the time average heat flux has maximum value for the larger surface roughness and the smaller droplet size. The total evaporation time has not influence on the nuclear boiling region.

• 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.

• 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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.7
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• pp.462-469
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• 2008

A regenerative evaporative cooler has been fabricated and tested for the evaluation of cooling performance. The regenerative evaporative cooler is a kind of indirect evaporative cooler comprised of multiple pairs of dry and wet channels. The air flowing through the dry channels is cooled without any change in the humidity and at the outlet of the dry channel a part of air is redirected to the wet channel where the evaporative cooling takes place. The regenerative evaporative cooler fabricated in this study consists of the multiple pairs of finned channels in counterflow arrangement. The fins and heat transfer plates were made of aluminum and brazed for good thermal connection. Thin porous layer coating was applied to the internal surface of the wet channel to improve surface wettability. The regenerative evaporative cooler was placed in a climate chamber and tested at various operation condition. The cooling performance is found greatly influenced by the evaporation water flow rate. To improve the cooling performance, the evaporation water flow rate needs to be minimized as far as the even distribution of the evaporation water is secured. At the inlet condition of $32^{\circ}C$ and 50%RH, the outlet temperature was measured at $22^{\circ}C$ which is well below the inlet wet-bulb temperature of $23.7^{\circ}C$.

• Progress in Superconductivity and Cryogenics
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• v.9 no.3
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• pp.72-82
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• 2007

This paper relates to reducing the temperature of a cryogenic liquid by contacting it with gas bubbles, which can be characterized by diffusion-driven evaporative cooling, The characteristic of diffusion-driven evaporative cooling is thoroughly examined by theoretical. analytical and experimental methods specifically for the case of helium injection into liquid oxygen. The results reveal that if the gaseous oxygen partial pressure in helium bubbles is lower than the liquid oxygen vapor pressure, cooling occurs autonomously due to diffusion mass transfer. The method of lowering the injected helium temperature turns out to be very effective for cooling purpose.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.743-748
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• 2006

Ren et al. analyzed the performance of the indirect evaporative cooler according to the direction of the flow considering evaporation water flow and wetness. However the effect of NTU of each channel on the performance of the indirect evaporative cooler according to the direction of the flow was not analyzed exactly. In this study the effect of the direction of the flow on the Indirect evaporative cooling performance changing NTU of each channel are investigated theoretically. The cooling process of the indirect evaporative cooler by flow direction 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 evaporation water. Based on the exact solution in the case of different NTU of each channel, we study the change of the distribution of the temperature according to each flow direction and at the same time analyze the effect of the flow direction on the cooling performance.

• Nuclear Engineering and Technology
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• v.28 no.6
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• pp.532-541
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• 1996

Theoretical and numerical study on heat transfer and evaporation in the vertical channel has been carried out and basic correlations have been derived for the heat transfer evaluation of PCCS. Analysis program was developed with low-Reynolds-number k-$\varepsilon$ model and surface transfer rates were calculated for the turbulent natural convection in the vertical channel. In relation to dry cooling by buoyancy-driven air, first, the system parameters which govern overall heat transfer rate are determined through the adequate nondimensionalization procedure. After comparison with existing experimental data, numerical results are used to derive heat transfer correlation by sensitivity calculations. In relation to wet cooling by falling water film, numerical analysis are carried out for evaporation process with real film surface conditions and evaporation correlation is derived through analogy concept and correction factors.

• Journal of the Korean Society of Safety
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• v.18 no.3
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• pp.29-33
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• 2003

The objective of the present work is to examine evaporation cooling of droplet due to surface roughness on a heated surface. The surface temperatures varied from 80-$160^{\circ}C$ on aluminum alloy (AL 2024) md surface roughness was 0.l8$\mu\textrm{m}$ 1.36$\mu\textrm{m}$. The results are as follows; Regardless of surface roughness, as droplet diameter is bigger, the in-depth temperature of solid decreases and evaporation time increases. In the case of same initial temperature on the heated surface, as droplet diameter is smaller and small surface roughness is bigger, evaporation time decreases and time averaged heat flux increases.

• 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.

• Fire Science and Engineering
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• v.14 no.3
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• pp.13-18
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• 2000

The objective of the present work is to examine the cooling characteristics of water droplet on the unburned surface. The hot solid surface material used brass, carbon steel and copper at temperature ranging from 70 to $116^{\circ}$. the droplet size is from 2.4 mm to 3.0 mm. The CCD camera was used to record the evaporation histories of the droplets. and the evaporation time of the droplet on the hot solid surface could be determined by using frame-by-frame analysis of the video records. It is found that during the droplet evaporation process for copper the temperature remains nearly constant, whereas for carbon steel the temperature continuously decreases about $1^{\circ}$. During the droplet evaporation process on the hot solid surface, regardless of solid materials, nondimensional droplet volume decreases nondimensional evaporation time increases.