• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.3
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• pp.193-205
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• 1994

A simulation program of the plate finned-tubes condenser widely used in the air conditioning system was developed. The program took into account the variations of the flow properties and fluid friction factor of refrigerant, and the heat transfer coefficients of refrigerant and air sides. The program was applied to a copper tube condenser which has outside diameter of 10.05mm, inside diameter of 9.35mm, length of 5.20m and three rows arraied staggered. Simulation results were such that refrigerant was super-heated state from the entrance to the 0.14m point, two-phase flow from the 0.14m point to the 4.10m point, sub-cooled state from the 4.10m point to the outlet. The degree of sub-cooled was $6.1^{\circ}C$. The variations of refrigerant quality, temperature, pressure, velocity, specific enthalpy, specific volume and air temperature, tube temperature were showed.

• Journal of Energy Engineering
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• v.15 no.3 s.47
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• pp.166-173
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• 2006

R134a is considered as an alternative refrigerant to R22 for air conditioners. An experimental investigation was made to study the characteristics of the heat transfer and pressure drop for R134a flowing in a fin-and-tube heat exchanger used for commercial air-conditioning units. Experiments were carried out under the conditions of inlet refrigerant temperature of $60^{\circ}C$ and refrigerant mass fluxes of $150,\;200,\;and\;250\;kg/m^{2}s$. The inlet air has dry bulb temperature or $35^{\circ}C$, relative humidity of 40% and air velocity varying from 0.68 to 1.6 m/s. Experiments show that air velocity decreased by 5.9% is needed for R134a than that of R22 while pressure drop for R134a was $18.1{\sim}20.4%$ higher than that of R22 for the degree of subcooling $5^{\circ}C$. The results are useful in designing more compact and effective condensers for various refrigeration and air conditioning systems using refrigerant R134a.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.4
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• pp.413-418
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• 2022

This paper presents two-phase condensation heat transfer and pressure drop characteristics of R32 and R454B as an alternative refrigerant to R410A in a 9.52 mm OD microfin tube. The test facility has a straight, horizontal test section with an active length of 2.0 m and is cooled by cold water circulated in a surrounding annular space. The heat transfer coefficients of the annular space were obtained using the modified Wilson plot method. Average condensation heat transfer coefficient and pressure drop data are presented at the condensation temperature of 35℃ for the range of mass flux 100-400 kg/m²s. The average condensation heat transfer coefficients of R32 refrigerant are 35-47% higher than R410A at the mass flux considered in the study, while R454B data are similar to R410A. The average pressure drop of R32 and R454B are much higher than R410A and they are 134-224% and 151-215% of R410A, respectively. R32 and R454B have relatively low GWP and high heat transfer characteristics, so they are suitable as alternatives for R410A.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.12
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• pp.1535-1548
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• 2004

Condensation heat transfer experiments were conducted with the oblong shell and plate heat exchanger without oil in a refrigerant loop using R-l34a, R-407C and R-410A. An experimental refrigerant loop has been developed to measure the condensation heat transfer coefficient h$_{r}$ and frictional pressure drop $\Delta$p$_{f}$ of the various refrigerants in a vertical oblong shell and plate heat exchanger. The effects of the refrigerant mass flux(40∼80kg/$m^2$s), average heat flux(4∼8kW/$m^2$), refrigerant saturation temperature(30∼4$0^{\circ}C$) and vapor quality of refrigerants on the measured data were explored in detail. Similar to the case of a plate heat exchanger, even at a very low Reynolds number, the flow in the oblong shell and plate heat exchanger remains turbulent. A comparison of the performance of the various refrigerants revealed that R-410A had the highest heat transfer performance followed by R-l34a, and R-407C had the lowest performance of the refrigerants tested. The pressure drops were also reported in this paper. The pressure drops for R-410A were approximately 45% lower than those of R-l34a. R-407C had 30% lower pressure drops than R-l34a. Experimental results were compared with several correlations which predicted condensation heat transfer coefficients and frictional pressure drops. Comparison with the experimental data showed that the previously proposed correlations gave unsatisfactory results. Based on the present data, empirical correlations of the condensation heat transfer coefficient and the friction factor were proposed.tor were proposed.sed.

• Journal of Biosystems Engineering
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• v.24 no.6
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• pp.513-522
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• 1999

This study was performed to get the optimal operating conditions of an water-air compact heat pump system using R-134a. The experiments was done for three elvels of the air mass flow rate and the compressor driving speed during air-heating process. The temperature of the air at the condenser inlet and outlet was 17~23$^{\circ}C$, 36~44$^{\circ}C$, respectively. The average temperature of the refrigerant at the evaporator and condenser was 1$0^{\circ}C$, 6$0^{\circ}C$, respectively. The temperature of the refrigerant was not depending on the air mass flow rate and the compressor driving speed. The pressure of the refrigerant at the condenser inlet and outlet was ranged of 10~18.5kg/$\textrm{cm}^2$ and that at the evaporator was ranged of 3.1~3.3kg/$\textrm{cm}^2$. The pressure drop at the condenser and evaporator was about 1.5, 1.2 kg/$\textrm{cm}^2$, respectively. The performance of coefficient for air heating was about 3.3~4.0.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.2
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• pp.215-223
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• 1999

Evaporation heat transfer coefficient and pressure loss were measured for three different micro-fin tubes and a smooth tube. The experiments were carried out with R-22 over a wide range of vapor Quality, mass velocity and heat flux. Heat transfer coefficient of the tube with slightly modified fin shape was found to be higher than that of the commercial reference tube by 60%. The improvement of heat transfer has been achieved without noticeable increase of pressure loss. Heat transfer coefficient was increased with increasing quality, refrigerant mass flux, and heat flux. However, the effect of refrigerant mass flux and heat flux was not great. Heat transfer coefficient at bottom was lower than that at top of the tube in low quality region, which suggested the existence of stratification in the micro-fin tube. Pressure drop was linearly increased with increasing refrigerant quality and was proportional to about square of mass flux.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.11
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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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.1
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• pp.87-94
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• 2011

Characteristics of two-phase pressure drop in microchannels were investigated experimentally. The microchannels consisted of 9 parallel trapezoidal channels with each channel having $205\;{\mu}m$ of bottom width, $800\;{\mu}m$ of depth, $3.6^{\circ}$ of sidewall angle, and 7 cm of length. Pressure drops in convective boiling of Refrigerant 113 were measured in the range of inlet pressure 105~195 kPa, mass velocity $150{\sim}920\;kg/m^2s$, and heat flux $10{\sim}100\;kW/m^2$. The total pressure drop generally increased with increasing mass velocity and/or heat flux. Two-phase frictional pressure drop across the microchannels increased rapidly with exit quality and showed bigger gradient at higher mass velocity. A critical review of correlations in the literature suggested that existing correlations were not able to match the experimental results obtained for two-phase pressure drop associated with convective boiling in microchannels. A new correlation suitable for predicting two-phase friction multiplier was developed based on the separated flow model and showed good agreement with the experimental data.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.1
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• pp.58-65
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• 2011

The specific objective of this study was to develop an IRDS (integrated receiver drier subcooling) condenser model for use in a mobile air-conditioning system. A three-zone model based on the desuperheating, two-phase, and subcooling sections of a condenser could be used to estimate the performance with a good accuracy. Overall heat transfer coefficients for each of the three sections, expressed as a function of the air velocity across the condenser and refrigerant mass flow rate and the model using the elemental difference method incorporate calculations to determine the pressure drop, heat performance within the condenser and it includes physical parameters (pass, tube hole size and length) that can be varied to analyze potential design changes without exhaustive experimental efforts. it was found that an accuracy of heat performance was within 5% in case of using the various condensers, the refrigerant pressure drop was predicted within 25% and the pressure drop of air side was well matched with experiment data within 4%.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.268-273
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• 2005

Because of environmental issues caused by CFC, HCFC or HFC refrigerants, new alternative refrigerants has gained a significant attention. This paper presents experimental information on heat transfer coefficient and pressure drop behavior during evaporation process of R32/290 mixtures in a horizontal smooth tube. A smooth tube with outer diameter of 5 mm and length of 5 m was selected as a test tube. Heat transfer coefficients and pressure drop characteristics were measured for a range of mass fluxes from 497 to 994 $kg/m^2s$, heat fluxes from 12 to 20 $kW/m^2$ and for several mixture compositions(100/0, 75/25, 58.4/41.6, 2s/75, 100/0 by wt% of R32/290). The differences of measured heat transfer characteristics among various R32/290 refrigerant mixtures were analyzed for various compositions.