• 설비공학논문집
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• 제10권3호
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• pp.271-281
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• 1998

In this study, condensation heat transfer experiments were conducted with two small diameter(ø7.5, ø4.0) tubes. Comparison with existing in-tube condensation heat transfer correlations indicated that the correlations overpredict the present data. For example, Akers correlation overpredicts the data upto 104%. The condensation heat transfer coefficient of the ø4.0 I.D. tube was smaller than that of the ø7.5 I.D tube; at the mass velocity of 300kg/$m^2$s, the difference was 12%. The pressure drop data of the small diameter tubes ware highly(two to six times) overpredicted by the Lockhart-Martinelli correlation. Subcooled forced convection heat transfer test confirmed that Gnielinski's single phase heat transfer correlation predicted the data reasonably well.

• 대한기계학회논문집B
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• 제22권7호
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• pp.946-955
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• 1998

Local condensation heat transfer coefficients in tubes were calculated by solving momentum and energy equations for annular film with liquid entrainment. The turbulent eddy distribution across the liquid film has been proposed and the calculated heat transfer coefficients were presented. Also turbulent Prandtl number effects on condensation heat transfer were discussed from three Pr$\_$t/ models. Finally, the calculated condensation heat transfer coefficients of R22 were compared with some correlations frequency referred to in open literature. This calculation model considering liquid entrainment predicted well the in-tube condensation heat transfer coefficient of R22 than the model not considering liquid entrainment. The effect of entrainment on heat transfer was predominant for high quality and high mass flux when the liquid film was turbulent.

• 설비공학논문집
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• 제13권7호
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• pp.602-611
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• 2001

Experiments on the condensation heat transfer characteristics inside a smooth and a microfin tube with R410A/R22 are performed in this study. The test tubes 7/9.52 mm in outside diameters and 3m in length are used. Varying the mass flux of the refrigerant and the condensation temperatures, the average heat transfer coefficients and pressure drop are investigated. Most flows in this study are in the annular and/or wavy flow regime. It is shown that the heat transfer is enhanced and the pressure drops are larger in the microfin tube than the smooth tube. From the heat transfer enhancement coefficients and the pressure drops, it is found that the high heat transfer enhancement factors are obtained in the range of small mass flux while the penalty factors are almost equal. Experiments results show that average heat transfer coefficients of R410A is larger than that of R22 and pressure drop of R410A is less than R22.

• Design & Manufacturing
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• 제13권2호
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• pp.22-29
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• 2019

This study conducted a research as to condensation heat transfer by using three types of flat micro multi-channel tubes with different processing of micro-fin and number of channels inside the pipes and different sizes of appearances. In addition, identical studies were conducted by using smoothing circular tubes with 5mm external diameter to study heat transfer coefficient. The condensation heat transfer coefficient showed an increase as the vapor quality and mass flux increased. However, each tube shows little differences compared to 400kg/m2s or identical in case the mass flux are 200kg/m2s and 100kg/m2s. The major reason for these factors is increase-decrease of heat transfer area that the flux type of refrigerant is exposed to the coolant's vapor with the effect of channel aspect ratio or micro-fin. In addition, the heat transfer coefficient was unrelated to the heat flux, and shows a rise as the saturation temperature gets lower, an effect that occurs from enhanced density. The physical factor of heat transfer coefficient increased as the channel's aspect ratio decreased. Additionally, the micro pin at the multi-channel type tube is decided as a disadvantageous factor to condensation heat enhancement factor. That is, due to the effect of aspect ratio or micro-fin, the increase-decrease of heat transfer area that the flux type of a refrigerant is exposed to the vapor is an important factor.

• International Journal of Air-Conditioning and Refrigeration
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• 제7권
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• pp.45-54
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• 1999

In this study, condensation heat transfer experiments were conducted in two small diameter (ø17.5, ø4.0) tubes. Comparison with the existing in-tube condensation heat transfer correlations indicated that these correlations over predict the present data. For example, Akers correlation over predicted the data up to 104 %. The condensation heat transfer coefficient of the ø4.0 I.D. tube was smaller than that of the ø7.5 I.D tube; at the mass velocity of 300 kg/$m^2$s, the difference was 12 %. The pressure drop data of the small diameter tubes were highly (two to six times) over predicted by the Lockhart-Martinelli correlation. Sub-cooled forced convection heat transfer test confirmed that Gnielinski's single phase heat transfer correlation predicted the data reasonably well.

• 설비공학논문집
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• 제14권9호
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• pp.706-716
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• 2002

R410A and R407C are considered to be alternative refrigerants to R22 for the air-conditioners. Experimental investigation is made to study the condensation heat transfer characteristics of slit fin-tube heat exchanger using alternative refrigerants R410A and R407C. R407C, a non-azeotropic refrigerant mixture, exhibited a quite different condensation phenomenon from those of R22 and R410A and its condensation heat transfer coefficient was much lower than that of R22 and R410A. Between the R22 and R410A, the condensation heat transfer coefficient of R410A, near-azeotropic refrigerant mixture, was a little higher than that of R22. R410A also showed the lowest condensation pressure drop across the test section. For all refrigerants, the condensation heat transfer coefficient and pressure drop increase as the mass flux increases.

• Journal of Advanced Marine Engineering and Technology
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• 제27권1호
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• pp.108-116
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• 2003

In this paper, the experimental results of condensation heat transfer were reported for the plate and shell heat exchangers(P&SHE) using R-l34a. An experimental refrigerant loop has been established to measure the condensation heat transfer coefficient of R-l34a in a vertical P&SHE. Two vertical counter flow channels were formed in the P&SHE by three plates of geometry with a corrugated trapezoid shape of a chevron angle of 45$^{\circ}$. Downflow of the condensing R-l34a in one channel releases heat to the cold up flow of water in the other channel. The effect of the refrigerant mass flux, average heat flux, system pressure and vapor quality of R-l34a on the measured data were explored in detail. The results indicate that at a higher vapor quality the condensation heat transfer coefficients are significantly higher. Condensation heat transfer coefficients were increased when the refrigerant mass flux was increased. A rise in the average heat flux causes an slight increase in the hr. Finally, at a higher system pressure the hr is found to be lower. Correlation is also provided for the measured heat transfer coefficients in terms of the Nusselt number.

• 수산해양교육연구
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• 제26권4호
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• pp.894-901
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• 2014

This study concerns the performance of condensation heat transfer in two-phase loop thermosyphons. In the present work, R134a has been used as the working fluid. Liquid fill charge ratio defined by the ratio of working fluid volume to total internal volume of thermosyphon, heat flux and wind speed of condensation have been used as the experimental parameters. The results show that the filling rate of working fluid and heat flux are very important factors for the operation of two-phase loop thermosyphons. The optimum liquid fill charge ratio for the best condensation heat transfer rate was 80%.

• Journal of Advanced Marine Engineering and Technology
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• 제20권3호
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• pp.91-100
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• 1996

Experimental results for forced convection condensation of non-azeotropic refrigerant mixtures inside a horizontal smooth tube are presented. The mixtures of R-22+R-134a and pure refrigerants R-22 and R-134a are used as the test fluids and a double pipe heat exchanger of 7.5mm ID and 4800mm long inside tube is used. The range of parameters are 100-300kg/h of mass flow rate, 0-1.0 of quality, and 0, 33, 50, 67, and 100 weight percent of R-22 mass fraction in the mixtures. The heat flux, vapor pressure, vapor temperature and tube wall temperature were measured. Using the data, the local and average heat transfer coefficients for the condensation have been obtained. In the same given experimental conditions, the liquid heat transfer coefficients for NARMs were considerally lower than that of the pure refrigerant of R-22 and R-134a. Local heat transfer characteristics for NARMs were different from pure refrigerant R-22 and R-134a. In some regions, local heat transfer coefficients for NARMs were increased in the following order ; Bottom$\rightarrow$Top$\rightarrow$Side. The condensation heat transfer coefficients for NARMs increased with mass velocity, heat flux, and quality, but were considerably lower than that of pure refigerant R-22 and R-134a.

• 설비공학논문집
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• 제13권11호
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• pp.1141-1148
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• 2001

Experiments on the condensation heat transfer and pressure drop in the brazed type plate heat exchangers are performed with refrigerants R410A/R22. To investigate the geometric effect, plate heat exchangers with the same pitch and height but different $45^{\circ},\;35^{\circ}and\;20^{\circ}$ chevron angles are used. Varying the mass flux of refrigerant (13~34 kg/$m^2$), the condensing temperatures ($20^{\circ}C\;and\;30^{\circ}C$) and the vapor quality (from 0.9 to 0.15) at the same constant heat flux ($5kW/m^2$), the condensation heat transfer coefficients and pressure drops are measured. The heat transfer coefficients decrease slightly with increasing the condensing temperature at a given mass flux in all plate heat exchangers. The pressure drop increases with increasing the mass flux and the quality and decreasing the condensing temperature and the chevron angle.