• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1980-1985
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• 2007

The purpose of this study is to investigate the performance of an autocascade refrigeration system using the refrigerant mixtures of R-134a(64${\sim}$72wt%), R-23(20${\sim}$25wt%) and R-14(8${\sim}$12wt%) as working fluids by experiment. The experimental apparatus consisted of a autocascade system with a compressor, condenser, evaporator, gas-liquid separator and cascade condenser, etc. Two main causes to this failure were considered as follows. First, the pressure ratio in the compressor was extremely increased at the beginning of the experiment. Second, the outlet temperature in compressor was higher than its limited temperature. For a stable operation of the compressor, a portion of the mixed refrigerant was by-passed at the inlet of the heat exchanger and transferred directly to the suction of the compressor in the modified system. The experimental parameters were changed weight of R-134a(1800g, 2800g), R-23(700, 800, 900g) and R-14(300, 400, 500g). The results showed that the best performance in case of R-134a of 2800g, R-23 of 900g and R-14 of 500g.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.2
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• pp.198-209
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• 1997

This paper is concerned about the performance of alternative refrigerants of R-502 which has been widely used in transport and low temperature refrigeration. A breadboard heat pump was constructed with counterflow heat exchangers and tested with R-502 and transitional alternatives of R-402A and R-402B and long-term alternatives of R-404A and R-507 to compare the performance of each refrigerant. Measurements were conducted at two different condensing temperatures of $43.3^{\circ}C$ and $52.0^{\circ}C$ and the evaporating temperature was varied over a range from $-25^{\circ}C$ to $-5^{\circ}C$. The evaporator superheat and condenser subcooling were maintained constant at about $5^{\circ}C$ for all tests. Test results showed that all alternative fluids tested in this research work can be used as 'drop-in' fluids to replace R-502 without any major problem. It is also found that in the long run HFC alternatives are to be used due to their favorable environmental characteristics and better performance.

• International Journal of Air-Conditioning and Refrigeration
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• v.9 no.1
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• pp.20-28
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• 2001

In order to predict thermodynamic performance of refrigeration system, it is required to know the oil concentration of the refrigerant/oil mixture. The current method is to extract the working mixture and then to measure the oil weight. In this study, oil concentration is measured in si.tu way without any extraction of the working fluid. Based on the measurement, a working equation is presented as follows, C=a +b x t +c x $t^2$ +(d + e x t +f x $t^2$) x SG. C is oil concentration, t is temperature($^{\circ}C). SG Is specific gravity of mixture and a~f is coefficients The oil concentration ranges over 0~l2 wt% and the temperature ranges over 20~50$^{\circ}C. The specific gravity and temperature are measured using the on-line densimeter and thermometer. This working equation enables to predict the oil concentration without any extraction of the mixture. This equation can be applied for R-12/Naphthenic oil and R-134a/P0E oil liquid mixtures.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.1
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• pp.31-37
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• 1999

In order to predict thermodynamic performance of refrigeration system, it is required to know the oil concentration of the refrigerant/oil mixture. The current method to measure the oil concentration is to extract the working mixture and then to measure the oil weight. However, it is Quite necessary to estimate oil concentration without any extraction of the working fluid. In this study a new method and working equation is presented as follows. It is based on the measurement of spedific gravity and temperature : $$C=a+b{\times}t+c{\times}t^2+(d+e{\times}t+f{\times}t^2){\times}SG$$ C is oil concentration, t is temperature($^{\circ}C$), SG is specific gravity of mixture and a~f is coefficients. The oil concentration ranges over 0~12 wt% and the temperature ranges over $20{\sim}50^{\circ}C$. The specific gravity and temperature are measured using the on-line densimeter and thermometer. This working equation enables to predict the oil concentration without any extraction of the mixture. This equation can be applied for R-12/Naphthenic oil and R-134a/POE oil oiquid mixtures.

• International Journal of Air-Conditioning and Refrigeration
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• v.8 no.2
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• pp.80-88
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• 2000

In order to predict thermodynamic performance of refrigeration system, it is required to know the oil concentration of the refrigerant/oil mixture. The current method is to extract the working mixture and then to measure the oil weight. In this study, oil concentration is measured in si.tu way without any extraction of the working fluid. Based on the measurement, a working equation is presented as follows, C=a +b x t +c x $t^2$ +(d + e x t +f x $t^2$) x SG. C is oil concentration, t is temperature($^{\circ}C). SG Is specific gravity of mixture and a~f is coefficients The oil concentration ranges over 0~l2 wt% and the temperature ranges over 20~50$^{\circ}C. The specific gravity and temperature are measured using the on-line densimeter and thermometer. This working equation enables to predict the oil concentration without any extraction of the mixture. This equation can be applied for R-12/Naphthenic oil and R-134a/P0E oil liquid mixtures.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.5
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• pp.713-723
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• 1997

Performance and heat transfer characteristics of an air conditioning system filled with hydro- carbon refrigerants are experimentally investigated. Single component hydrocarbon refrigerants (propane, isobutane, butane and propylene) and binary mixtures of propane/isobutane and propane/butane are considered as working fluids in the air conditioning system. Performances of each refrigerant are obtained at several compressor speeds and temperature levels of secondary heat transfer fluids. The cooling capacity and the coefficient of performance are obtained as test results. Heat transfer data of selected refrigerants are achieved from overall conductance measurement. Average heat transfer coefficients at different mass fluxes are shown and they are also displayed for different heat capacities of the system. Experimental results show that some hydrocarbon refrigerants have better characteristics than R22.

• International Journal of Air-Conditioning and Refrigeration
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• v.17 no.3
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• pp.81-87
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• 2009

The effect of oil on convective boiling of R-123 in an enhanced tube bundle is experimentally investigated at $26.7^{\circ}C$ saturation temperature. The enhanced tube had pores (0.23 mm diameter) and connecting gaps (0.07 mm width), which had been optimized using pure R-123. The effects of oil concentration (0 to 5%), heat flux (10 to $40\;kW/m^2$), mass velocity (8 to $26\;kg/m2^s$) and vapor quality are investigated. The oil significantly reduces the bundle boiling heat transfer coefficient. With 1% oil, the reduction is approximately 35%. Further addition of oil further reduces the heat transfer coefficient. The data are also compared with the pool boiling counterpart. The reduction in the heat transfer coefficient is smaller in a bundle (convective boiling) than in a pool (single-tube pool boiling), with larger difference at a smaller heat flux. Similar to pure R-123 case, the effects of mass velocity and vapor quality are negligible for the convective boiling of R-123/oil mixture.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.10
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• pp.718-725
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• 2007

In the general vapor-compression refrigeration system, refrigeration lubricant circulates in refrigeration system with refrigerant. Knowledge of the amount of circulating lubricant is very important to exactly calculate capacity of the refrigeration system. An experimental study was conducted to estimate the oil concentration of a flowing $CO_2/Oil$ mixtures. POE and PAG oil are considered as test lubricants in this study. Performance tests were conducted under simulated liquid conditions for $CO_2/POE$ oil mixture in oil concentration of 0 to 10 weight-percent and $CO_2/PAG$ oil mixture in oil concentration of 0 to 6 weight-percent in the temperature ranges of $-5^{\circ}C\;to\;15^{\circ}C$. The results obtained indicate specific gravity of $CO_2/Oil$ mixture is increased as oil concentration is increased and as temperature of mixture is decreased. Oil concentration correlation of $CO_2/POE$ oil mixture and $CO_2/PAG$ oil mixture is suggested, based on the measurement of specific gravity and temperature. This correlation enable to predict the oil concentration without extraction of the mixture and can be applied for $CO_2/POE$ mixtures and $CO_2/PAG$ mixtures.

• Design & Manufacturing
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• v.13 no.2
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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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.2
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• pp.144-151
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• 2003

An experimental study was carried out in a uniformly heated horizontal tube to examine heat transfer characteristics of pure refrigerants, R134a and R123, and their mixtures during flow boiling. The flow pattern was also observed through tubular sight glasses with an internal diameter of 10 mm located at the inlet and outlet of the test section. Tests were run at a pressure of 0.6 MPa and in the heat flux ranges of 5~100 kW/$m^2$, vapor Quality 0~100 percent and mass velocity of 150-600 kg/$m^2$s. The observed flow patterns were compared to the flow pattern map of Kattan et al., which predicted well the present data over the entire range of mass velocity employed in this study. Heat transfer coefficients of the mixture were less than the interpolated values between pure fluids both in the low quality region where the nucleate boiling is dominant and in the high quality region where the convective evaporation is dominant.