• International Journal of Air-Conditioning and Refrigeration
• /
• 제16권2호
• /
• pp.44-50
• /
• 2008

This study presents test results of a mobile air-conditioning system using a potential alternative refrigerant, R152a. A series of performance tests have been carried out and cycle characteristics such as cooling capacity, energy efficiency ratio, suction and discharge pressures, and temperatures are presented, compared to those for the baseline R134a system. Tests were conducted with evaporation temperature of $5^{\circ}C$, condensation temperature of $45^{\circ}C$, subcooling temperature of $5^{\circ}C$, superheating temperature of $5^{\circ}C$, and compressor speed of 500-1500 rpm. The performance of R152a system with readjustment of an expansion valve showed better than those of R134a. The effect of oil on the pressure drop in the evaporator was also addressed.

• 대한기계학회논문집B
• /
• 제20권2호
• /
• pp.730-740
• /
• 1996

Boiling heat transfer coefficients of pure refrigerants (R22, R32, R134a, R125, R290, and R600a) and refrigerant mixtures (R32/Rl34a, R290/ R600a, and R32/R125) are measured experimentally and compared with Chen's correlation. The test section is a seamless stainless steel tube with inner diameter of 7.7mm and uniformly heated by applying electric current directly to the tube. Heat fluxes range from 10 to 30kW$^2$. Mass fluxes are set to 424 ~ 742kg/m$^{2}$s for R22, R32, R134a, R32/R134a, and R32/Rl25 ; 265 ~ 583kg/m$^{2}$s for R290, R600a, and R290/R600a. Heat transfer coefficients depend strongly on heat flux at a low quality region and become independent as quality increases. Convective boiling term in the Chen's correlation predicts experimental data of the pure refrigerants fairly well (relative error of 12.1% for the data of quality over 0.2). The correlation for pure substances overpredicts the heat transfer coefficients for nonazeotropic refrigerant mixtures.

• 대한기계학회논문집B
• /
• 제25권1호
• /
• pp.54-61
• /
• 2001

Condensing heat transfer coefficients of R-22 and R-134a were measured in smooth, horizontal copper tubes with inner diameters of 1.77mm, 3.36mm, and 5.35mm, respectively. The experiments were conducted in the closed loop, which was driven by a magnetic gear pump. Data are presented for the following range of variables : mass velocity from 200 to 500kg/$m^2$.s and quality from 0 to 1.0. The heat transfer coefficients in the small diameter tubes (ID < 7mm) were observed to be strongly affected by various diameters and the heat transfer characteristics in the small diameter tubes differed from those in the large diameter tubes. Heat transfer coefficients in the small diameter tubes are higher than those in the large diameter tubes at the same experimental condition. It was found that some well-known previous correlations(Shahs correlation and Cavallini-Zecchins correlation) were not suitable for small diameter tubes.

• 설비공학논문집
• /
• 제27권7호
• /
• pp.362-368
• /
• 2015

This paper presents a numerical study on the performance of a vapor compression cycle equipped with an ejector as an expansion device to improve the COP by reducing the expansion loss and compressor work. The simulation is carried out using a model based on the conservation of mass, energy and momentum in the ejector. From the results of the simulation, the vapor compression cycle equipped with an ejector showed a maximum COP improvement of 14.0% when using R134a refrigerant and 16.8% when using R1234yf. In addition, the performance of the system with an ejector represents the increased performance as the temperature difference between condensing and evaporating increased.

• 설비공학논문집
• /
• 제14권8호
• /
• pp.656-663
• /
• 2002

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 9.52 mm outside diameter and 1.0 m length. The refrigerant was cooled by passing cold water through an annulus surrounding the test section. Tests were performed at a fixed refrigerant saturation temperature of $40^{\circ}C$ with mass fluxes of 100, 200, and 300 kg/$m^2s$. 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 11~l5% and 23~53% 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 10~21% for a microfin tube. In general, HTCs of a microfin tube were 2.0~3.0 times higher than those of a plain tube.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.1945-1950
• /
• 2004

In this paper, The performance of Kim-Chi refrigerator with three evaporator and one compressor was investigated in employing 55% propane and 45% isobutane (R290/R600a) refrigerant mixture as an alternative refrigerant of R134a. The drop in test was performed by varying both refrigerant charge amount and capillary tube length in order to find both the performance and reliability of a small multi-refrigeration system. As a result, Both the power consumption and COP is increased by about 15% and 10%, respectively as compared to the baseline R134a system. In addition, the propane/isobutene refrigerant mixture system took advantage of the minimization of modification and redesigning of system components because of similar thermodynamic properties with R134a such as saturation pressure, temperature, normal boiling point(NBP) characteristics

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 추계학술대회논문집B
• /
• pp.248-253
• /
• 2001

An experiment was carried out to investigate the characteristics of the evaporation heat transfer for refrigerant R-134a flowing in a plate and shell heat exchanger. The data are useful in designing more compact and effective evaporators for various refrigeration and air conditioning systems. Two vertical counterflow channels were formed in the exchanger. The R-134a flows up in one channel exchanging heat with the hot water flowing down in the other channel. The effects of the average heat flux, mass flux, saturation temperature and vapor quality were examined in detail. The present data show that the evaporation heat transfer coefficient increases with the vapor quality. A rise in the refrigerant mass flux causes an increase in the $h_r$ value. A rise in the average imposed heat flux causes an increase in the $h_r$, value at the low quality. Finally, at a higer refrigerant saturation temperature the $h_r$, value is found to be lower.

• 설비공학논문집
• /
• 제12권4호
• /
• pp.363-370
• /
• 2000

Experiments have been peformed, using pure refrigerant R134a and a zeotropic refrigerant mixture R290/R600a(60%/40%) and their performances have been analyzed by the first and second laws(exergy method) of thermodynamics. From the experimental results, variations of compressor speed and air temperature have a great effect on the performance of the system. The sum of exergy losses in compressor and evaporator is about 60% of total exergy loss, using refrigerant R134a, so it is necessary to improve the performance of compressor and evaporator. According to the experimental results using refrigerant mixture of R290/R600a(60%/40%), the exergy losses in heat exchange processes are decreased but the exergy loss in throttling process is increased. The performance of the system has been improved by 20∼30% compared with that of R134a and exergy losses have been also reduced.

• 설비공학논문집
• /
• 제16권6호
• /
• pp.589-598
• /
• 2004

Flow condensation heat transfer coefficients (HTCs) of R22 and R134a were measured on a horizontal 9 hole aluminum multi-channel tube. The main test section in the refrigerant loop was made of a flat multi-channel aluminum tube of 1.4 mm hydraulic diameter and 0.53 m length. Refrigerant was cooled by passing cold water through an annulus surrounding the test section. Data were obtained in the vapor qualities of 0.1∼0.9 at mass flux of 200∼400 kg/$m^2$s and heat flux of 7.3∼7.7 ㎾/$m^2$ at the saturation temperature of 4$0^{\circ}C$. All popular correlations in single-phase subcooled liquid and flow condensation originally developed for large single tubes predicted the present data of the flat tube within 20% deviation when effective heat transfer area is used in determining experimental data. This suggests that there is little change in flow characteristics and patterns when the tube diameter is reduced down to 1.4 mm diameter range. Thermal insulation for the outer tube section surrounding the test tube for the transport of heat transfer fluid is very important in fluid heat-ing or cooling type heat transfer experimental apparatus.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 1998년도 추계학술발표회요약집
• /
• pp.128-128
• /
• 1998