• International Journal of Air-Conditioning and Refrigeration
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• v.16 no.2
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• pp.64-69
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• 2008

Electronic and telecommunication industries are constantly striving towards miniaturization of electronic devices. Miniaturization of chips creates extra space on PCBs that can be populated with additional components, which decreases the heat transfer surface area and generates very high heat flux. Even though an air-cooling technology for telecommunication equipment has been developed in accordance with rapid growth in electrical industry, it is confronted with the limitation of cooling capacity due to the rapid increase of heat density. In this study, liquid-cooling heat exchangers were designed and tested by varying geometry and operating conditions. In addition, air-cooling heat exchangers were tested to provide performance data for the comparison with the liquid-cooling heat exchangers. The liquid-cooling heat exchangers had twelve rectangular channels with different flow paths of 1, 2, and 12. Silicon rubber heaters were used to control the heat load to the heat exchangers. Heat input ranged from 293 to 800W, and inlet temperatures of working fluid varied from 15 to $27^{\circ}C$. The heat transfer coefficients were strongly affected by flow conditions. All liquid-cooling heat exchangers showed higher cooling performance than the air-cooling heat exchanger. The heat exchanger with 2-paths could provide more controllability on the maximum temperature than the others.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.30 no.1
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• pp.24-32
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• 2018

In this paper, analytical studies were conducted to obtain optimal design factors and analysis parameters of liquid nitrogen cooling exchanger applied in cryogenic refrigerator. The target value of heat transfer rate was more than 1 kW and pressure drop was less than 40 kPa. Design factors of cryogenic heat exchanger included width of channel and configuration of paths. Analytical factors of liquid nitrogen cooling exchanger included temperatures of coolant header surface and inlet liquid nitrogen. The width and number of channels in the design parameters were 0.0050~0.0150 m and 4~8, respectively. The configuration of channel path was 4 ways. Temperatures of coolant header surface and inlet liquid nitrogen in analytical parameters were 74 to 78K and 82 to 86K, respectively. As result, the design factor and analysis parameter satisfying the target values were obtained. The biggest heat transfer rate was 1.36 kW with pressure drop of 32.26 kPa.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.645-649
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• 2009

Liquid desiccant cooling technology can supply cooling by using waste heat and solar heat which are hard to use effectively. For compact and efficient design of a dehumidifier, it is important to sustain sufficient heat and mass transfer surface area for water vapor diffusion from air to liquid desiccant on heat exchanger. In this study, the plate type heat exchanger is adopted which has extended surface, and hydrophilic coating and porous layer coating are adopted to enhance surface wettedness. PP(polypropylene) plate is coated by porous layer and PET(polyethylene terephthalate) non-woven fabric is coated by hydrophilic polymer. These coated surfaces have porous structure, so that falling liquid film spreads widely on the coated surface foaming thin liquid film by capillary force. The temperature of liquid desiccant increases during dehumidification process by latent heat absorption, which leads to loss of dehumidification capacity. Liquid desiccant is cooled by cooling water flowing in plate heat exchanger. On the plate side, the liquid desiccant can be cooled by internal cooling. However the liquid desiccant on extended surface should be moved and cooled at heat exchanger surface. Optimal mixing and distribution of liquid desiccant between extended surface and plate heat exchanger surface is essential design parameter. The experiment has been conducted to verify effective surface treatment and distribution characteristics by measuring wall side flow rate and visualization test. It is observed that hydrophilic and porous layer coating have excellent wettedness, and the distribution can be regulated by adopting holes on extended surface.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.645-650
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• 2006

The heat transfer performance and energy transport ability are relatively high due to higher specific heat. Therefore, it can be used in fields such as heating, ventilating, air-conditioning, refrigeration and heat exchangers. In this study, liquid-cooling heat exchangers were designed and tested by varying geometry and operating conditions. In addition, liquid-cooling heat exchangers were tested to provide performance data for MPCM slurry. The liquid-cooling heat exchangers had twelve rectangular channels with flow paths of 1, 2, 4 and 12. Silicon rubber heaters were used to control the heat load to the heat exchanger. Heat input ranged from 293 to 800 W, and inlet temperatures of working fluid varied from 15S to $27^{\circ}C$. The standard deviation of surface temperature was strongly affected by the coolant of MPCM Slurry, All MPCM-cooling heat exchangers showed higher cooling performance than the water-cooling heat exchanger except one path channel heat exchanger.

• Journal of the Korean Society of Visualization
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• v.21 no.3
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• pp.33-38
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• 2023

Spray cooling is a method of cooling high-temperature heating elements by spraying droplets. Recently, spray cooling has been proposed for use in next-generation nuclear reactors. When droplets are sprayed onto the outer wall of a heat exchanger tube, a film boiling occurs on the outer wall. Over time, the outer wall temperature decreases, and a liquid film forms on the outer wall, and the heat exchanger outer wall is subsequently cooled by the liquid film. In this case, the liquid film thickness has a great influence on the heat removal performance. In this study, an experimental study was conducted to measure the liquid film thickness distribution in a droplet spray environment. For this purpose, a method using the electrical conductivity of the liquid was adopted.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.1
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• pp.24-30
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• 2006

Three liquid cooling heat exchangers for cooling of telecommunication equipment were designed and their cooling performances were tested. The liquid cooling heat exchangers had twelve rectangular channels $(5\times3 mm)$ with different flow paths of 1, 4, and 12. Silicon rubber heaters were used to provide heat flux to the test section. Heat input was varied from 75 to 400 W, while flow rate and inlet temperature of working fluid were altered from 1.2 to 4.0 liter/fin and from 15 to 3$30^{\circ}C$, respectively. The 4-path heat exchanger showed lower and more uniform average inner temperatures between heaters and the surface of heat exchanger than those of the others. To obtain optimal distribution of working fluid to each channels of liquid cooling heat exchangers, 2-3-2 and 4-3 type tube distributors were designed, and their distribution performances of working fluid were numerically and experimentally investigated. The distributor of the 2-3-2 type showed superior distribution performance compared with those of the 4-3 type distributor.

• Journal of Power System Engineering
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• v.20 no.5
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• pp.78-85
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• 2016

This paper considers the influence of internal heat exchangers to the efficiency of a refrigerating system using R170. These liquid-gas heat exchangers(internal or suction-line heat exchangers) can, in some cases, yield improved system performance while in other cases they degrade system performance. A steady state mathematical model is used to analysis the performance characteristics of refrigeration system with internal heat exchanger. The influence of operating conditions, such as the mass flowrate of R170, inner diameter tube and length of internal heat exchanger, to optimal dimensions of the heat exchanger is also analyzed in the paper. The main results were summarized as follows : the mass flowrate of R170, inner diameter tube and length of internal heat exchanger, and effectiveness have an effect on the cooling capacity, compressor work and RCI(Relative Capacity Index) of this system. Exception for the effect of inner diameter, the RCI of R170 with respect to refrigerant mass flowrate, the length and effectiveness of internal heat exchanger is about 2.1~3.3% higher than that of R13 at the same experimental conditions. With a thorough grasp of these effect, it is necessary to design the R170 compression refrigeration cycle using internal heat exchanger.

• Transactions of the Korean hydrogen and new energy society
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• v.34 no.6
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• pp.741-747
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• 2023

In this study, the heat transfer characteristics were numerically analyzed to investigate the possibility of utilizing cooling water using liquid nitrogen. From the study, as the mass flow rate of the hot fluid increased, the heat transfer rate increased by 8.9-81.7%. And lowering the inlet temperature of the hot fluid resulted in increase in the heat transfer rate by 33.8-71.5%. As for the filling level of liquid nitrogen, as higher filling level led to a decrease in the outlet temperature and an increase in the overall heat transfer coefficient.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.10
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• pp.710-717
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• 2007

Electric and telecommunication industries are constantly striving towards miniaturization of electronic devices. Miniaturization of chips creates extra space on PCBs that can be populated with additional components, which decreases the heat transfer surface area and generates very high heat flux. Even though an air-cooling technology for telecommunication equipment has been developed in accordance with rapid growth in electrical industry, it is confronted with the limitation of cooling capacity due to the rapid increase of heat density. In this study, liquid-cooling heat exchangers with MPCM slurries were designed and tested by varying geometry and operating conditions. The liquid-cooling heat exchangers with 4-paths showed higher cooling performance than the others. The cooling performance of liquid cooling heat exchanger with MPCM slurries was more enhanced than that of the air cooling system. It's performance was also slightly superior to that of the water cooling system at the inlet temperature of $19^{\circ}C$.

• International Journal of Air-Conditioning and Refrigeration
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• v.6
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• pp.148-157
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• 1998

This study presents test results of a residential window air-conditioner using R22 and two potential alternative refrigerants, R407C and R410B. A series of performance tests has been carried out for the basic and liquid-suction heat exchange cycles in a psychometric calorimeter test facility. For R407C, the same rotary compressor was used as in the R22 system. However, compressor for the R410B system was modified to provide the similar cooling capacity. The evaporator circuit was changed to get a counter-cross flow heat exchanger to take advantage of zeotropic mixture's temperature glide, and liquid-suction heat exchange cycle was also considered to improve the system performance. Test results were compared with those for the basic R22 system. The modified system with a liquid-suction heat exchanger increased cooling capacity and energy efficiency by up to 5%.