• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.12
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• pp.1234-1268
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• 2004

A review on the papers published in the Korean Journal of Air-Conditioning and Refrigerating Engineering in 2002 and 2003 has been carried out. Focus has been put on current status of research in the aspect of heating, cooling, air-conditioning, ventilation, sanitation and building environment/design. The conclusions are as follows. (1) Most of fundamental studies on fluid flow were related with heat transportation in diverse facilities. Drop formation and rivulet flow on solid surfaces were interesting topics related with condensation augmentation. Research on micro environment considering flow, heat transfer, humidity was also interesting to promote comfortable living environment. It can be extended considering biological aspects. Development of fans and blowers of high performance and low noise were continuing research topics. Well developed CFD technologies were widely applied for analysis and design of various facilities and their systems. (2) Heat transfer characteristics of enhanced finned tube heat exchangers and heat sinks were extensively investigated. Experimental studies on the boiling heat transfer, vortex generators, fluidized bed heat exchangers, and frosting and defrosting characteristics were also conducted. In addition, the numerical simulations on various heat exchangers were performed and reported to show heat transfer characteristics and performance of the heat exchanger. (3) A review of the recent studies shows that the performance analysis of heat pump have been made by various simulations and experiments. Progresses have been made specifically on the multi-type heat pump systems and other heat pump systems in which exhaust energy is utilized. The performance characteristics of heat pipe have been studied numerically and experimentally, which proves the validity of the developed simulation programs. The effect of various factors on the heat pipe performance has also been examined. Studies of the ice storage system have been focused on the operational characteristics of the system and on the basics of thermal storage materials. Researches into the phase change have been carried out steadily. Several papers deal with the cycle analysis of a few thermodynamic systems which are very useful in the field of air-conditioning and refrigeration. (4) Recent studies on refrigeration and air-conditioning systems have focused on the system performance and efficiency enhancement when new alternative refrigerants are applied. Heat transfer characteristics during evaporation and condensation are investigated for several tube shapes and new alternative refrigerants including natural refrigerants. Efficiency of various compressors and performance of new expansion devices are also dealt with for better design of refrigeration/air conditioning system. In addition to the studies related with thermophysical properties of refrigerant mixtures, studies on new refrigerants are also carried out. It should be noted that the researches on two-phase flow are constantly carried out. (5) A review of the recent studies on absorption refrigeration system indicates that heat and mass transfer enhancement is the key factor in improving the system performance. Various experiments have been carried out and diverse simulation models have been presented. Study on the small scale absorption refrigeration system draws a new attention. Cooling tower was also the research object in the respect of enhancement its efficiency, and performance analysis and optimization was carried out. (6) Based on a review of recent studies on indoor thermal environment and building service systems, it is noticed that research issues have mainly focused on several innovative systems such as personal environmental modules, air-barrier type perimeterless system with UFAC, radiant floor cooling system, etc. New approaches are highlighted for improving indoor environmental conditions and minimizing energy consumption, various activities of building energy management and cost-benefit analysis for economic evaluation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.12
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• pp.1102-1139
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• 2002

A review on the papers published in the Korean Journal of Air-Conditioning and Refrigerating Engineering in 2000 and 2001 has been done. Focus has been put on current status of research in the aspect of heating, cooling, ventilation, sanitation and building environment. The conclusions are as follows. (1) Most of fundamental studies on fluid flow were related with heat transportation of facilities. Drop formation and rivulet flow on solid surfaces were interesting topics related with condensation augmentation. Research on micro environment considering flow, heat, humidity was also interesting for comfortable living environment. It can be extended considering biological aspects. Development of fans and blowers of high performance and low noise were continuing topics. Well developed CFD technologies were widely applied for developing facilities and their systems. (2) Most of papers related with heat transfer analysis and heat exchanger shows dealt with convection, evaporation, and channel flow for the design application of heat exchanger. The numerical heat transfer simulation studies have been peformed and reported to show heat transfer characteristics. Experimental as well as numerical studies on heat exchanger were reported, while not many papers are available for the system analysis including heat exchanger. (3) A review of the recent studies on heat pump system shows that performance analysis and control of heat pump have been peformed by various simulations and experiments. The research papers on multi-type heat pump system increased significantly. The studies on heat pipe have been examined experimently for change of working characteristics and strut lure. Research on the phase change has been carried out steadily and operation strategies of encapsulated ice storage tank are reported experimentally in several papers. (4) A review of recent studies on refrigeration/air conditioning system have focused on the system performance and efficiency for new alternative refrigerants. Evaporation and condensation heat transfer characteristics are investigated for tube shapes and new alternative refrigerants. Studies on components of refrigeration/air conditioning system are carried to examine efficiency for various compressors and performance of new expansion devices. In addition to thermophysical properties of refrigerant mixtures, studies on new refrigerants are also carried out, however research works on two-phase flow seemed to be insufficient. (5) A review of the recent studies on absorption cooling system indicates that heat and mass transfer phenomena have been investigated to improve absorber performance. Various experimental data have been presented and several simulation models have been proposed. A review of the recent studies on duct and ventilation shows that ventilation indices have been proposed to quantify the ventilation performance in buildings and tunnels. Main efforts have been focused on the applications of ventilation effectiveness in practice, either numerically using computational fluid dynamics or experimentally using tracer gas techniques. (6) Based on a review of recent studies on indoor thermal environment and building service systems, research issues have mainly focused on many innovative ideas such as underfloor air-conditioning system, personal environmental modules, radiant floor cooling and etc. Also, the new approaches for minimizing energy consumption as well as improving indoor environmental conditions through predictive control of HVAC systems, various activities of building energy management and cost-benefit analysis for economic evaluation were highlighted.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2391-2400
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• 2015

Weather proof steels are used for steel bridges due to its high corrosion resistance under atmospheric conditions. However, instead of forming stabilized rust layers, general rust occurs on weather proof steels under high humidity condition close to seawater or shady places. In Japan, therefore, they perform rust stabilization treatment instead of unpainted treatment due to severe atmospheric conditions. However, most of domestic weather proof steels were constructed unpainted in the form of closed box-girder, which makes the periodical repetition of dry and wet hard to occur. For the steel bridges constructed on the Han river, the evaporation of water, dew condensation due to temperature change, and stagnant water due to rain affect harmfully on the formation of passive film on weather proof steels. Thus, in this research, in order to analyze corrosion properties inside the closed box-girder for the unpainted weather proof steel bridge in the waterworks safety zone, multiple ways of analysis such as observation with eyes, cellophane-tape test, steel thickness measurement, surface corrosion potential measurement, electron microscope analysis, and X-ray diffraction analysis of the rust were performed. As a result, unstable rust layer was observed inside the closed box-girder, and severe corrosion was observed on the top and bottom of the flanges due to the effects of stagnant water caused by rain, dew condensation, and de-icing materials.

• Journal of the Korean Institute of Gas
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• v.2 no.3
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• pp.37-48
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• 1998

A cryogenic liquid stored in the closed cryogenic tank has been studied at various liquid levels. The change of pressure, temperature, and liquid-vapor ratio in the tank depended on the liquid levels. The various phenomena were shown at different liquid levels as follows: (1) liquid level was increased with condensation of vapor: (2) liquid was vaporized in spite of liquid level going up for a certain initial period and then condensation of vapor occurred at higher pressure; (3) liquid was vaporized without liquid level change; (4) liquid was vaporized with liquid level decreasing. If the tank is full with cryogenic liquid, it is extremely dangerous because of soaring the pressure. Therefore the tank must be filled with $90\%$ liquid according to the safety rules. If the tank was filled with $0\%$ ullage, the pressure increment as high as 80bar during first 5 days. With $90\%$ liquid level, however, the pressure was increased as low as 1.5bar in the same period. No matter what the liquid level is, it is very dangerous if the tank is locked-up with filled cryogenic liquid for a long time.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.1
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• pp.61-67
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• 2015

The cooling of hot exhaust gas is an important issue for the construction of combustor test facility. Water spray is an effective method for exhaust gas cooling due to its large latent heat in process of evaporation. In this study, 1-D analysis has been performed based on continuity, energy conservation, and saturated vapor property to understand water spray cooling of combustion gas. In the exhaust duct of combustor test facility, the injected water decreases combustion gas temperature, and evaporates in the combustion gas. However, some of the injected water is collected in the sump due to condensation. The evaporation of water helps combustion gas cooling, but causes pressure increase inside the exhaust duct due to increase of vapor pressure. These phenomena has been analyzed by 1-D modeling in this study. From 1-D analysis, the adequate mass flow rate of water spray to cool combustion gas and to avoid excessive pressure rise inside the exhaust duct has been decided.

• Tunnel and Underground Space
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• v.6 no.4
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• pp.335-341
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• 1996

This fundamental study analyzes the relationship between rock thermal properties and psychrometric properties in underground space and has a ultimate goal to develope technologies for predicting major environmental variables. The study is divided into 2 subjects (1) developement of a basic model for predicting temperature and humidity, (2) analysis of the validity of the model through application to a local underground storage space for military supplies. The basic model is built for the network of tunnel-shaped underground spaces. The model takes into account rock thermal properties and changes in moisture content in the air due to condensation/evaporation on the rock surface. Using lumped-parameter analytical method, heat flux from or to the surrounding rock is calculated and then the psychrometric properties(air quantity, pressure, temperature, humidity) are estimated through network simulation. The model can be utilized regardless of the tunnel type. The study site is a local storage space built in rock, mainly granite gneiss and quartz-porphyry. It is a U-shaped tunnel, 593.5m long and 6x6.5m wide. Relative humidity inside has to be strictly controlled under 55% to avoid erosion of a certain types of supplies stored in 6 chambers with the capacity of 300~1.000 ton. The thermal conductivity varies between 2.734 and 2.779W/m$^{\circ}C$ and the thermal diffusivity is in the range of 1.119 and $1.152{\times}10^{-6}\;m^2/s$ the specific heat between 910 and $920\;J/kg^{\circ}C$. Relative errors of the predicted values of dry/wet temperature and relative humidity are 0.8~3.0%, 0~7.5% and 0~7.0%, respectively. Apparent errors associated with the rock surface temperature seems to be partly due to the intrinsic limitations in the infrared thermometer used in this study.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.4
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• pp.312-319
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• 2006

In this study, performance of 2 pure hydrocarbons and 7 mixtures was measured in an attempt to substitute HCFC22 used in air-conditioners and heat pumps. The mixtures were composed of R1270 (propylene), R290 (propane), HFC152a, and RE170 (Dimethyl ether, DME). The pure and mixed refrigerants tested have GWPs of $3{\sim}58$ as compared to that of $CO_2$ and the mixtures are all near-azeotropic showing the gliding temperature difference (GTD) of less than $0.6^{\circ}C$. Thermodynamic cycle analysis was carried out to determine the optimum compositions and actual tests were performed in a laboratory heat pump test bench at the evaporation and condensation temperatures of 7.5 and $45.1^{\circ}C$ respectively. Test results show that the coefficient of performance (COP) of these mixtures is up to 5.7% higher than that of HCFC22. While propane showed 11.5% reduction in capacity, most of the fluids tested had the similar capacity to that of HCFC22. Compressor discharge temperatures were reduced by $11{\sim}17^{\circ}C$ with these fluids. There was no problem with mineral oil since the mixtures were mainly composed of hydrocarbons. The amount of charge was reduced up to 55% as compared to HCFC22. Overall, these fluids provide good performance with reasonable energy savings without any environmental problem and thus can be used as long term alternatives for. residential air-conditioning and heat pumping application.

• Nuclear Engineering and Technology
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• v.56 no.6
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• pp.2029-2038
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• 2024

A deep understanding of the characteristics and mechanism of geyser boiling and capillary pumping is necessary to optimize a high-temperature sodium heat pipe. In this work, the Volume of Fluid (VOF) two-phase model and the capillary force model in the mesh wick were used to model the complex phase change and fluid flow in the heat pipe. Computational Fluid Dynamics (CFD) simulations successfully predicted the process of bubble nucleation, growth, aggregation, and detachment from the wall in the liquid pool of the evaporation section of the heat pipe in horizontal and tilted states, as well as the reflux phenomenon of capillary suction within the wick. The accuracy and stability of the capillary force model within the wick were verified. In addition, the causes of geyser boiling in heat pipes were analyzed by extracting the oscillation distribution of heat pipe wall temperature. The results show that adding the capillary force model within the wick structure can reasonably simulate the liquid backflow phenomenon at the condensation; Under the horizontal and inclined operating conditions of the heat pipe, the phenomenon of local dry-out will occur, resulting in a sharp increase in local temperature. The speed of bubble detachment and the timely reflux of liquid sodium (condensate) replenishment in the wick play a vital role in the geyser temperature oscillation of the tube wall. The numerical simulation method and the results of this study are anticipated to provide a good reference for the investigation of geyser boiling in high-temperature heat pipes.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.4
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• pp.469-474
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• 2015

In ultrasonic spray pyrolysis deposition, a precursor solution is evaporated by an ultrasonic atomizer, then gas-carried into a furnace where the solute is separated from the water vapor. After condensation, polymerization, and nucleation, the solute oxide forms a thin film. To improve the deposition efficiency, the ultrasonic atomizer was studied to optimize the evaporated gas flow. The vat cover was redesigned, using three versions with different inlet factors being tested through a computational fluid dynamic analysis as well as a water evaporation experiment. The atomization rate with a hemispherical cover with a $30^{\circ}$ inlet was found to be 2.4 times higher than that with the original. This improvement was verified with fluorine-doped tin oxide spray pyrolysis deposition. The film obtained with the modified vat cover was 2.4 times thicker than that obtained with the original vat cover.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.732-736
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• 2016

Air conditioning part designs are moving towards higher efficiency and productivity. The expansion device is one of the core parts of an air conditioning system and controls the refrigerant quantity, evaporation load, compression capacity, and condensation capacity. In this study, an electronic expansion valve for two working fluids ($CO_2$ and R134a) was developed for air conditioning systems in vehicles. The valve uses an eccentric cam driving structure instead of a lead screw to decrease manufacturing costs and increase productivity. The pressure resistance and flow rate performance was evaluated using numerical analysis. At maximum operation conditions and burst pressure conditions with $CO_2$, the maximum stresses on the valve model were about 98 MPa and 223 MPa, respectively. The maximum flow rates of $CO_2$ and R134a with different orifice openings were about 550 kg/h and 386 kg/h, respectively. The performance with R134a was verified by experiments.