• 기술사
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• 제34권2호
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• pp.23-27
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• 2001

Until 1996, CFC refrigerants haven't been used because it destroyed ozone that affecting In ecosystem. And HCFC will prohibit until 2020. In Europe, they attempt to move up its fulfillment. Until now the change have completed CFC into HFC134a and is considerated HCFC into HFC410A and HFC407C. But HFC41 OA has high condenser temperature and HFC407C is non-azeotropic refrigerant mixture and gliding temperature phenomenon. New refrigerant ell POE, PVE, PAG was also developed.

• 설비공학논문집
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• 제17권11호
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• pp.981-989
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• 2005

In this study, external condensation heat transfer coefficients (HTCs) are measured on a low fin tube and Turbo-C tubes 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 subcooled at $3{\~}8^{\circ}C$. The HTCs of all refrigerants decreased as increasing the saturation temperature from $30^{\circ}C$ to $50^{\circ}C$. This trend is due to better thermodynamic properties of the liquid phase at low temperature Beatty and Katz's prediction yielded a $20.0\%$ deviation for the low fin tube data. The heat transfer enhancement factors for the 26 fpi low fin tube and Turbo-C tubes are 4.0${\~}$5.5 and 3.0${\~}$8.1 respectively for the refrigerants tested. Finally the performance of Turbo-C tube is better than that of the low fin tube.

• 설비공학논문집
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• 제13권8호
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• pp.710-719
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• 2001

Pool boiling heat transfer coefficients (HTCs) of HCFC123, HFC134a, HCFC22, HFC407C, HFC410A and HFC32 wre measured on a horizontal smooth tube, 26 fpi low fin tube, Turbo-B and Thermoexcel-E enhanced tubes. AN experimental apparatus was designed such that all tubes heated by cartridge heaters could be installed at the same time to save the refrigerant. Data were taken in the pool of $7^{\circ}C$ with the heat flux decreasing from 80 kW/$m^2\;to\;5kW/m^2$. Test results showed that HTCs of pure refrigerants and those of a azeotrope were greatly influenced by reduced pressure. HTCs of HFC407C were 21~25% lower than those of HCFC22 due to mass transfer resistance. For all refrigerants, enhanced tubes with sub-surface and sub-tunnels showed the largest heat transfer enhancement. Especially the largest heat enhancement was obtained for HCFC123 whose reduced pressure is the lowest among al the refrigerants tested. This indicates that either Turbo-B or Thermoexcel-E enhanced tube would be the best choice when used with a low vapor pressure refrigerant.

• 설비공학논문집
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• 제7권3호
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• pp.435-449
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• 1995

In this paper, pressure drop through a capillary tube is modeled to determine the length of a capillary tube for a given set of conditions. HCFC-22 and its alternatives, HFC-134a, R407B, and R410A are used as working fluids. The conditions on which the model is tested are as follows : condensing temperature; 40.0, 45.0, 50.0, $55.0^{\circ}C$, degree of subcooling;0.0, 2.5, $5.0^{\circ}C$, capillary tube exit condition;choked flow, capillary tube diameter;1.2~2.4mm, mass flow rate;5.0~50.0g/sec. The results justify the use of Stoecker's model which yields the results very close to the values in ASHRAE handbook. While McAdams' method yields much better results than Duckler's in calculating the viscosity of the fluid in 2-phase, the friction factor suggested by Stoecker seems to be the best for capillary tubes of large diameter used in residential air conditioners. For each refrigerant, 372 data with various variables are calculated by the model. The results show that capillary tube length varies very uniformly with changes in condensing temperature and degree of subcooling. Based on this fact, regression analysis is performed to determine the dependence of mass flow rate on the length and diameter of a capillary tube, condensing temperature, and degree of subcooling. Thus determined correlation yields a mean deviation of 2.36% for 1,488 data, showing an excellent agreement.

• 설비공학논문집
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• 제16권5호
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• pp.444-451
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• 2004

Flow condensation heat transfer coefficients (HTCs) of R22, R134a, R407C, and R410A were measured on horizontal plain and microfin tubes. The experimental apparatus was composed of three main parts; a refrigerant loop, a water loop and a water/glycol loop. The test section in the refrigerant loop was made of both a plain and a microfin copper tube of 6.0∼6.16 mm inside diameter and 1.0 m length. Refrigerants were cooled by passing cold water through an annulus surrounding the test section. Tests were performed at a fixed refrigerant saturation temperature of 4$0^{\circ}C$ with mass fluxes of 100, 200, and 300 kg/m2s. Test results showed that at similar mass flux the flow condensation HTCs of R134a were similar to those of R22 for both plain and microfin tubes. On the other hand, HTCs of R407C were lower than those of R22 by 4∼16% and 16∼42% for plain and microfin tubes respectively. And HTCs of R410A were similar to those of R22 for a plain tube but lower than those of R22 by 3∼9% for a microfin tube. Heat transfer enhancement factors of a microfin tube were 1.3∼1.9.

• 대한기계학회논문집B
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• 제25권2호
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• pp.180-186
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• 2001

The condensation heat transfer coefficients of pure refrigerants R-22, R-134a, and a binary refrigerant mixture R-410A flowing in a small diameter tube were investigated. The experiment apparatus consists of a refrigerant loop and a water loop. The main components of the refrigerant loop consist of a variable-speed pump, a mass flowmeter, an evaporator, and a condenser(test section). The water loop consists of a variable-speed pump, an isothermal tank, and a flowmeter. The condenser is a counterflow heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. The test section consists of smooth, horizontal copper tube of 3.38mm outer diameter and 1.77mm inner diameter. The length of test section is 1220mm. The refrigerant mass fluxes varied from 450 to 1050kg/(㎡$.$s) and the average inlet and outlet qualities were 0.05 and 0.95, respectively. The main results were summarized as follows ; in the case of single-phase flow, the heat transfer coefficients increase with increasing mass flux. The heat transfer coefficient of R-410A was higher than that of R-22 and R-134a, and the heat transfer for small diameter tubes were about 20% to 27% higher than those predicted by Gnielinski. In the case of two-phase flow, the heat transfer coefficients also increase with increasing mass flux and quality. The condensation heat transfer coefficient of R-410A was slightly higher than that of R-22 and R-134a. Most of correlations proposed in the large diameter tube showed significant deviations with experimental data except for the ranges of low quality and low mass flux.

• Design & Manufacturing
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• 제13권2호
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• pp.37-43
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• 2019

This study conducted a research as to condensation heat transfer friction loss headby 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 enhancement factor and pressure drop penalty factor. 1) The friction head loss showed an increase as the vapor quality and mass flux increased. In case of saturation temperature, it shows an increase as it gets lower. These factors are the reason occurring as the lower the saturation temperature is, the higher the density of refrigerant vapor gets. The influence of heat flux is similar as the dryness is low, but as it gets higher, it lowers in heat flux, and as the high temperature of high heat flux, it is a factor that occurs as the density gets lower. 2) RMS error of the in case of friction head loss, it showed to be predicted as 0.45~0.67 by Chisholm, Friedel, Lockhart and Martinelli. 3) As forfriction head loss penalty factor, the smaller the aspect ratio is, the larger the penalty factor gets, and as for the effect of micro-fin, the penalty factor increased because it decreases to the gas fluid the way groove for the refrigerant's flow.

• 설비공학논문집
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• 제15권9호
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• pp.744-750
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• 2003

The performance of adiabatic capillary tubes are measured to provide the database for a generalized correlation. Test conditions and capillary tube geometries are selected to cover a wide range typically observed in air-conditioning and heat pump applications. Based on extensive experimental data for R22, R290, and R407C measured in this study, a generalized correlation for refrigerant flow rate in adiabatic capillary tubes is developed by implementing dimensionless parameters for tube inlet conditions, capillary tube geometry, and refrigerant properties. The correlation yields good agreement with the present data for R22, R290, and R407C with average and standard deviations of 0.9% and 5.0%, respectively. In addition, approximately 97% of the data for Rl2, R134a, R152a, R410A, and R600a obtained in the open literature are correlated within a relative deviation of $\pm$ 15%.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.347-352
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• 2000

The pressure drop characteristics of R-22 and R-410A(a mixture of 50wt% R-32 and 50wt% R-125) flowing in a small diameter tube with 1.77[mm] inner diameter and 3.14[mm] outer diameter was investigated experimentally. the mass fluxes of refrigerants are ranged from 450 to $1050[kg/(m^2{\cdot}s)]$ and the qualites are varied from 0.05 to 0.95. The main experimental results were summarized as follows; The single-phase liquid friction factors for small diameter tubes are higher than those predicted by the Blasius equation. In case of two-phase flow, the pressure gradient of the small diameter tube increases with increasing mass velocity and vapor quality. The experimental data are not well correlated by predictions which were proposed for the large diameter tube.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.83-89
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• 2000

This paper presents a pressure drop correlation for evaporation and condensation of alternative refrigerant with oil in micro-fin tubes. The correlation was developed from a data base consisting of oil-free pure and mixed refrigerants in micro-fin tube; Rl25 R134a. R32 R410a(R32/R125 50/50% mass), R22, R407c(R32/R125/R134a, 23/25/52% mass) and R32/R134a(25/75% mass). The micro-fin tube used in this paper had 60 0.2mm high fins with a 18 helix angle. The cross sectional flow area $(A_c)$ was $60.8 mm^2$ giving an equivalent smooth diameter$(D_e)$ of 8.8mm. The hydraulic diameter $(D_h)$ was estimated to the 5.45mm. The new correlation was obtained by replacing the friction factor and the tube-diameter in Bo Pierre correlation by a friction factor derived from pressure drop data for a micro-fin tube and the hydraulic diameter, respectively. This correlation was also used to predict some pressure data with a lubricant after using a mixing viscosity rule of lubricants and refrigerants. As a result, the new correlation was also well predicted to the measured data within a mean deviation of 19.0%.