• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.9
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• pp.796-803
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• 2004

The stack effect of a new type condenser installed in a high-rise apartment building was studied numerically A sirocco fan is introduced to the new type condenser instead of an axial flow In. The new type condenser intakes the cold air through the lower inlet and exhausts the hot air through the upper outlet. The effects of the building height and frontal wind on the performance of an air-conditioner were analyzed. The performance of an air-conditioner was evaluated by using COP (coefficient of performance) and CGPI (condenser group performance indicator). the hot air was exhausted by the new type condenser at an angle of 50$^{\circ}$ from the outer wall of the building. If there was no draft, the new type condenser installed in the high-rise apartment building had a good performance and its performance on each floor is not influenced by the stack effect. It is shown that the efficiency of the air-conditioner installed in several floors below the top floor decreased when the frontal wind velocity was greater than 8 m/s.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.11
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• pp.784-791
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• 2012

The casing has been used as a protective conduit during all phases of drilling operations and productions for the oil and gas industries. The casing is manufactured in various diameters, wall thicknesses, lengths, strengths, and connections. When the casing is designed, it has to be considered to withstand a variety of forces, such as collapse, burst, and tensile failure, as well as chemically aggressive brines. Once the casing is damaged, serious problems in geothermal well have been detected continuously. Therefore, this paper describes the casing design for stability of geothermal well to determine influence of casing parameters on the strength and load. In addition, the casing design program was developed. The estimated collapse, burst, tension and depth pressure can provide benefit in the casing design and completion method. This program provides a safety factor and predicts the casing stress more easily.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.9
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• pp.571-580
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• 2008

In this work, pool boiling heat transfer coefficients(HTCs) of 5 refrigerants of differing vapor pressure are measured on horizontal smooth square surface of 9.52 mm length. Tested refrigerants are R123, R152a, R134a, R22, and R32 and HTCs are taken from $10\;kW/m^2$ to critical heat flux of each refrigerant. Wall and fluid temperatures are measured directly by thermocouples located underneath the test surface and by thermocouples in the liquid pool. Test results show that pool boiling HTCs of refrigerants increase as the heat flux and vapor pressure increase. This typical trend is maintained even at high heat fluxes above $200\;kW/m^2$. Zuber's prediction equation for critical heat flux is quite accurate showing a maximum deviation of 21% for all refrigerants tested. For all refrigerant data up to the critical heat flux, Stephan and Abdelsalam's well known correlation underpredicted the data with an average deviation of 21.3% while Cooper's correlation overpredicted the data with an average deviation of 14.2%. On the other hand, Gorenflo's and lung et al.'s correlation showed only 5.8% and 6.4% deviations respectively in the entire nucleate boiling range.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.10
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• pp.481-485
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• 2014

Low solar gain glazing should be applied on windows in order to reduce the solar radiation load. In a country where a cooling and a heating load coexist throughout the year, such as in Korea, a high solar gain glazing is need to reduce the heating load, but a low solar gain glazing should be applied to reduce the cooling load. Recently, dynamic windows have been developed for which the solar shading performance switches according to the amount of solar radiation flowing into the indoor space through the glazing, and these have been used in building to solve such problems. The purpose of this research is to analyze the energy performance of the electrochromic glazing for dynamic windows that has been extensively commercialized for office buildings in Incheon and Ulsan through an energy simulation implemented in the eQUEST program.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.8
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• pp.714-721
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• 2005

The water jet impingement cooling with boiling is one of the techniques to remove heat from high heat flux equipments. The configuration of surface roughness is one obvious condition of affecting the performance on heat transfer in nucleate boiling, The present study investigates the water jet impinging single-phase convection and nucleate boiling heat transfer for the effect of surface roughness to enhance the heat transfer in free surface and submerged jet. The distributions of the averaged wall temperature as well as the boiling curves are discussed. Jet velocities are varied from 0.65 to 1.7 m/s. Surface roughness by sand blast and sand paper varies from 0.3 to 2.51 ${\mu}m$ and cavity shapes on surface are semi-circle and v-shape, respectively The results showed that higher velocity of the jet caused the boiling incipience to be delayed more. The incipient boiling and heat transfer increase with increasing surface roughness due to a large number of cavities of uniform size.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.8
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• pp.729-735
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• 2005

In this study, external condensation heat transfer coefficients (HTCs) were measured on a horizontal smooth tube at the saturated vapor temperature of $30^{\circ}C,\;39{\circ}C,\;and\;50^{\circ}C$ for R22, R410A, R407C, and R134a with the wall subcooling of $3\~8^{\circ}C$. The HTCs of all refrigerants are the highest at $30^{\circ}C,\;39{\circ}C,\;and\;50^{\circ}C$ in order. This trend is due to its excellent thermodynamic properties of the liquid phase. The measured data of HTCs were compared with the calculated ones by Nusselt's equation for a smooth tube. Measured HTCs of R22, R134a, R410A are $4.2\~7.5\%$ higher than prediction respectively while those of R407C are $15.6\~28.9\%$ lower than the prediction.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.5
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• pp.569-580
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• 1998

In this study, condensation heat transfer coefficients(HTCs) of a plain tube, low fin tube, and Turbo-C enhanced tube for CFC-11, HCFC-123, CFC-12, HFC-l34a are measured and compared against each other. All data are taken at the vapor temperature of 39$^{\circ}C$ with a wall subcooling temperature 3~8$^{\circ}C$. Test results show that HTCs of a low vapor pressure refrigerant, HFC-123, for a plain, low fin, and Turbo-C tubes are 10.5~20.5%, 8.2~12.2%, 16.5~19.2% lower than those of CFC-11, respectively. On the other hand, HTCs of a medium vapor refrigerant, HFC-l34a, for a plain, low fin, and Turbo-C tubes are 20.6~31.8%, 0.0~8.0%, 13.2~20.9% higher than those of CFC-12, respectively. For all refrigerants tested, HTCs of Turbo-C tube are the highest among the three tubes showing almost 8 times increase in HTCs as compared to those of a plain tube. Nusselt's prediction equation for a plain tube yielded 12% deviation for all plain tube data while Realty and Katz's prediction equation for a low fin tube yielded 20% deviation for all low tube data.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.12
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• pp.971-976
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• 2006

The objectives of this paper are to study the characteristics of pool boiling heat transfer for enhanced tubes used in the evaporator of turbo chiller and to provide a guideline for optimum design of an evaporator using HFC134a. Three different enhanced tubes are tested at 4 different saturation temperatures. The wall super heated temperature difference ranges from $0.5^{\circ}C\;to\;3.5^{\circ}C$. The refrigerant, HFC134a evaporates on the outside of the tube while the chilled water flows inside the tube. This study provides experimental heat transfer coefficients for evaporation on the enhanced tubes. It is found that the turbo-II tube provides the highest heat transfer coefficient.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.9
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• pp.827-835
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• 2001

In this study, condensation heat transfer characteristics were conducted with special heat transfer tubes of SH-C type. Experiments were carried out the saturated vapor temperature of 334K and the wall subcooling of 1.5-4.5K. The refrigerant was R-113 and the enhanced tubes used in the present study were SH-CDR, SH-CYR and SH-CHR. The experimental results showed that the condensation heat transfer coefficients of SH-C type tubes were about 23-66% higher than those of a low integral-fin tube. It was visualized that the condensed liquid on the outer surface of SH-C type tubes flowed continuously down unlike a low integral-fin tube and a plain tube, due to a 3-D extending fin on the outer surface of SH-C type tubes. As a result, the thermal resistance of the condensed liquid decreased and the heat transfer coefficient increased. Also, the enhancement ratio of SH-CDR tube was the highest, and it was about 9-11 times as compared to that of a plain tube.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.1
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• pp.88-98
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• 1996

The present study is concerned with the flow friction and heat transfer characteristics of the combination of various regenerator materials, using the different Darcy number and porosity, which is filled uniformly and partially in a tube under oscillating flow condition. The poros medium is adopted as Brinkmann-Forschheimer extended Darcy model. Numerical results are obtained or the flow and temperature fields and described the effect of the combination of various regenerator materials and Womersley number on the pressure drop, the heat transfer and the regenerator efficiency. The results obtained indicate that not only heat transfer between the tube wall and oscillating flow but also the pressure drop at both ends of the regenerator are increased, while the regenerator efficiency is decreased in the increase of womersley number. It is also found that the friction factor is increased as Reynolds number is increased. The comparison between the combination of the various regenerator materials and the homogeneous regenerator material shows that the regenerator efficiency can be enhanced with the proper combination of various regenerator materials even though the averaged porosity of the regenerator is same.