• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.10a
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• pp.145-151
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• 1997

PAG(Polyalkylene Glycol) and esters are tested with HFC-134a as a refrigeration oil. This investigation enhances the testing method by taking the compressor's environment into account. A testing environment charged with refrigerant gas more closely simulates the conditions of a compressor. The friction coetTicient of the PAG/HFC-134a system is similar to that of the mineral oil/CFC-12 system at operating conditions. Ester oils are preferable at the start & stop condition in the lubricity aspect. PAG shows good lubricity in conditions of extreme contact pressure. Consequently, this test provides reliable results on compressor lubricity of refrigeration oils with HFC-134a. It suggests a methodological way for the proper selection of refrigeration oils that may improve the durability and performance of a compressor.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.2
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• pp.108-113
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• 2017

The performance of refrigerant oil at the thrust bearing and at the journal bearing of a scroll compressor is a significant factor. This paper presents the friction and anti-wear characteristics of nano-fluid with a mixture of a refrigerant oil and nano powders. The particle size distribution and oxidation stability of nano powders prepared by the electrical explosion method were analyzed by TEM and BET. It was found that the nanoparticles showed a spherical morphology with sizes ranging of 40-60 nm and were covered with graphite layers of 2-4 nm. The thermal conductivity of POE oil was 0.1-0.5W/mk higher than that of POE oil. The coefficient of friction of Cu-POE was found to be 0.1 higher than that of Al2O3. The cooling capacity of the heat pump with nanofluid increased to 3.67%, and the performance was improved by 5.83%.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.7
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• pp.938-944
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• 2000

Recently, micro fin tube is widely used to heat exchanger for high performance. And, as the alternative refrigerants for R-22, hydrocarbons such as R-290, R-600 and R-600a are very promising because of their low GWP and ODP. Thus, R-290 was used as working fluid in this study. Most design of heat exchanger had been based on heat transfer characteristics of pure refrigerant although refrigerant oil exists in the refrigeration cycles. So, the influence of oil on heat transfer characteristics have to be considered for investigating exact evaporation heat transfer characteristics. But, this is an unresolved problem of refrigeration heat transfer. Therefore the influence of the refrigeration oil to the evaporation heat transfer characteristics of R-290 were conducted in a horizontal micro tin tube. The mineral oil was used as refrigeration oil. The experimental apparatus consisted of a basic refrigeration cycle and a system for oil concentration measurement. Test conditions are as the follows; evaporation temperature $5^{\circ}C$, mass velocity 100 $kg/m^2s$, heat flux 10 $kW/m^2$, oil concentration 0, 1.3, 3.3, 5.7 wt.%, and quality $0.07{\sim}1.0$. When refrigeration oil was entered, oil foaming was observed at the low quality region. And, very small bubbles were observed as quality was increased. Pressure drop and heat transfer coefficient increased as the concentration of refrigeration oil increased to 5 wt.%.. The performance index of heat exchanger was the highest near 3.3 wt.%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.3
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• pp.254-261
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• 2006

The effect of enhanced geometry (pore diameter, gap width) is investigated on the pool boiling of R-123/oil mixture for the enhanced tubes having pores with connecting gaps. Tubes with different pore diameters (and corresponding gap widths) are specially made. Significant heat transfer degradation by oil is observed for the present enhanced tubes. At 5% oil concentration, the degradation is 26 to 49% for $T_{sat}=4.4^{\circ}C$. The degradation increases 50 to 67% for $T_{sat}=26.7^{\circ}C$. The heat transfer degradation is significant even with small amount of oil (20 to 38% degradation at 1% oil concentration for $T_{sat}=4.4^{\circ}C$), probably due to the accumulation of oil in sub-tunnels. The pore size (or gap width) has a significant effect on the heat transfer degradation. The maximum degradation is observed for $d_p$ = 0.20 mm tube at $T_{sat}=4.4^{\circ}C$, and for $d_p$=0.23 mm tube at $T_{sat}=26.7^{\circ}C$. The minimum degradation is observed for $d_p$=0.27 mm tube for both saturation temperatures. It appears that the oil removal is facilitated for the larger pore diameter (along with larger gap) tube. The highest heat transfer coefficient with oil is obtained for $d_p$ =0.23 mm tube, which yielded the highest heat transfer coefficient for pure R-123. The heat transfer degradation increases as the heat flux decreases.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.1
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• pp.49-59
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• 2005

The evaporation heat transfer experiments are conducted with the shell and plate heat exchanger (S&PHE) without oil in the refrigerant loop using R-410A. An experimental refrigerant loop has been established to measure the evaporation heat transfer coefficient h. of R-410A in a vertical S&PHE. Two vertical counter flow channels were formed in the S&PHE by three plates haying a corrugated trapezoid shape of a $45^{\circ}C$ chevron angle. UP flow of the boiling R-410A in one channel receives heat from the hot down flow of water in the other channel The effects of the refrigerant mass flux. average heat flux. refrigerant saturation temperature and vapor qualify are explored in detail. Similar to the case of a plate heat exchanger. even at a very low Reynolds number, the flow in the S&PHE remains turbulent. The Present data shows that the evaporation heat transfer coefficients of R-410A increased with the vapor qualify. The results indicate a rise in the refrigerant mass flux caused an increase in the h.. Raising the imposed wall heat flux is found to slightly improve h., while h, is found to be lower at a higher refrigerant saturation temperature. Based on the present data. empirical correlation of the evaporation heat transfer coefficient is proposed.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.216-221
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• 2005

The heat transfer coefficient and pressure drop during gas cooling process of carbon dioxide in a helically coiled tube were investigated experimentally. The experiments were conducted without oil in the refrigerant loop. The main components of the refrigerant loop are a receiver, a variable speed pump, a mass flowmeter, a pre-heater, a gas cooler(test section) and an isothermal tank. The test section is a double pipe type heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. It was made of a copper tube with the inner diameter of 4.85 [mm], the outer diameter of 6.35 [mm] and length of 10000 [mm]. The refrigerant mass fluxes were 200${\sim}$600 [kg/$m^2$s] and the average pressure varied from 7.5 [MPa] to 10.0 [MPa]. The main results were summarized as follows: The heat transfer coefficient of supercritical $CO_2$ increases, as the cooling pressure of gas cooler decreases. And the heat transfer coefficient increases with the increase of the refrigerant mass flux. The pressure drop decreases in increase of the gas cooler pressure and increases with increase the refrigerant mass flux.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.3
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• pp.166-176
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• 2003

Experiments have been conducted in order to make comparisons of a alternative refrigerant (R-410A) cycle characteristic with an existing refrigerant (R-22) cycle characteristic in terms of cooling capacity and coefficient of performance (COP). The parameters examined in the present work include air flow rate, indoor/outdoor air temperatures, and indoor relative humidity. These two refrigeration cycles share all components except compressor, accumulator, oil separator, and piping connecting them. The measurements were made using an air-enthalpy calorimeter. The experimental results show that the R-410A cycle has many advantages over indoor conditions while the R-22 cycle has better performance over outdoor conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.638-643
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• 2021

Oil is used in various industries, including the agricultural sector, food industry, and functional cosmetics. These oils are chemically unstable and prone to oxidation when exposed to oxygen, light, moisture, or high temperatures. Therefore, various attempts have been made to encapsulate them so that they are not exposed to such environments. When oil is injected into a refrigerant with greater density, the oil can be encapsulated as it rises due to buoyancy caused by the density difference. In this study, oil encapsulation was simulated to find the optimal conditions for operating equipment using computational fluid dynamics (CFD) for multiphase flows. Water or serum can be used as a refrigerant. The viscosity of water is relatively small, and if it is used as a refrigerant, oil droplets can be produced well even if oil and water are continuously injected in the equipment. However, the viscosity of serum is very high, and if it is used, the oil is stretched out and does not leave the nozzle. The results show that when using serum as a cooling medium, oil encapsulation is possible if the injection is stopped for some time after instantaneous injection at high speed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.8
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• pp.438-442
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• 2013

The alternative refrigerant R436B is applied, to assess the application feasibility for a commercial cooling water system. The characteristic stability was verified by Sealed glass tube test and Autoclave test. R436B is chemically stable with the compressor material. The Oil miscibility test shows the usual compressor oil mixed well with R436B. Through the life acceleration test, the cooling performance is maintained. Though slight changes in oil and capillary tube diameter were found, they were within the permitted range. R436B should be applied to commercial cooling water systems as a simple replacement for the usual refrigerant.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.189-193
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• 2008

Performance of refrigerant oil at the thrust-bearing and at the journal-bearing of a scroll compressor is a significant factor. This paper presents the friction and anti-wear characteristics of nano oil with a mixture of a refrigerant oil and carbon nano particles in the journal bearing of scroll compressors. The characteristics of friction and anti-wear using nano-oil is evaluated using the disk on disk tester and the journal bearing tester for measuring friction surface temperature and the coefficient of friction at the journal bearing tester. In journal bearing test, the average friction coefficient of high concentration nano-oil was decreased down to 18% compared to raw oil under 4,500 N and 3,600 rpm. It is believed that nano particles can be coated on the wear surfaces and the interaction of nano particles between surfaces can be improved the lubrication in the friction surfaces. Worn surfaces of frictional specimen were measured with straightness. carbon nano oil enhances the characteristics of the anti-wear and friction at the joural bearing of scroll compressors.