• 설비공학논문집
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• 제22권10호
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• pp.704-709
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• 2010

The effect of oil on flow boiling of R-123 in a plain tube bundles was experimentally investigated for a range of quality and heat flux. It is shown that the heat transfer coefficient decreased as the oil concentration increased. Comparison with the previous pool boiling data reveals that the reduction of heat transfer coefficient by oil is more pronounced in pool boiling, and the difference increased with the increase of oil concentration and heat flux. Within the experimental range, the variation of mass flux or quality has negligible effect on the heat transfer coefficient.

• Journal of Advanced Marine Engineering and Technology
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• 제39권6호
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• pp.604-608
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• 2015

본 연구에서는 다심관(Multi Core Tube)에 단열재로 글라스울(Glass wool)을 사용한 단열 다심관(Insulated Multi Core Tube)의 열전달 특성에 관하여 검토하였다. 제작된 단열 다심관에 대하여 외기온도, 유압 오일 공급온도, 유압 오일 공급유량에 따른 단열 다심관 내부의 유압 오일의 온도특성에 관하여 실험 및 모델링을 통하여 검토하였다. 그 결과 본 연구의 범위 내에서 최소 유압 오일 공급유량인 0.29(l/min)인 경우 실험결과와 수치해석 결과의 온도차이가 최대 약 $3^{\circ}C$정도 발생하였다. 외기온도가 일정한 경우 유압 오일 공급온도가 높을수록 유압 오일의 공급유량에 관계없이 유압 오일 출구온도가 높아지고, 유압 오일 공급유량이 1.01(l/min)이상일 경우에는 유압 오일의 온도강하에 외기온도의 영향이 적음을 알 수 있었다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1067-1072
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• 2009

In vapor compression systems which use refrigerant as a working fluid, the oil is commonly used for compressor lubrication. Since the presence of lubrication oil can change the characteristics properties of refrigerant, the oil affects the heat transfer performance of heat exchanger to a large extent. In this paper, we focus on the effect of PVE oil experimentally on heat transfer performance of the fin-tube heat exchangers which use R410A as a refrigerant. To evaluate the heat transfer performance, the refrigerant to air type test facility chamber has been used. Fin-tube heat exchanger with grooved has been tested while according to the oil mass fraction variation from nearly zero to 1.7 wt%. It was found that the low level of oil mass fraction has an obvious effect on heat transfer performance, while the high level seems no significant influence. The influence of the oil mass fraction to heat transfer performance, however, is different between evaporation and condensation.

• International Journal of Air-Conditioning and Refrigeration
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• 제17권3호
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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.

• 한국자동차공학회논문집
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• 제15권2호
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• pp.87-94
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• 2007

It has been argued that the use of plastics can cause problems during design and manufacture owing to their low strength, relatively poor thermal conductivity and large thermal expansion. However, the advantages of plastics e.g., corrosion resistance, low cost, curtailment of weight, design flexibility etc., can compensate abundantly for the disadvantages. This study analyzes and compares the heat transfer performance characteristics of automotive compact oil cooler composed of plastic tube bundle with conventional metal oil cooler on the same core area basis as diameter, tube thickness, number of tube or tube arrangement varies. The performance analyses are accomplished by use of computational fluid dynamics program Fluent 6.2, which is verified and compared with the results of performance tests. The result of analyses is coincided with that of experiments. Flow pattern at air side according to tube arrangement is dominant factor which affects heat dissipation in case of similar total heat transfer surface area.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2609-2614
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• 2007

Shell & Tube type Oil Cooler is widely used for hydraulic presses, die casting machines, generation equipments, machine tools and construction heavy machinery. Temperature of oil in the hydraulic system changes viscosity and thickness of oil film. They have a bad effect to performance and lubrication of hydraulic machinery, so it is important to know exactly the heat exchanging efficiency of oil cooler for controlling oil temperature. But most Korean manufacturers do not have test equipment for oil cooler, so they cannot carry out the efficiency test of oil cooler and it is impossible to verify its performance. This paper includes information of construction of necessary utilities for oil cooler test and design and manufacture of test equipment. One can select the optimum product by obtaining performance data through tests of various kinds of oil coolers. And also the paper developed a program which can be easily used for design of 2D and 3D drawings of oil cooler.

• 설비공학논문집
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• 제8권1호
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• pp.140-150
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• 1996

CFC-12, which has been used most widely in automobile air conditioners and household refrigerators is scheduled to be phased out soon because of its high ozone depletion potential. Now HFC-134a is suggested as an alternative refrigerant for CFC-12. In this Study, we intended to investigate how PAG oil influence evaporation heat transfer and flow pattern, using R-134a and PAG oil influences evaporation heat transfer and flow pattern, using R-134a and PAG oil in the horizontal miro-fin evaporation tube. Experiments were conducted under the flowing est conditions : mass velocity 86-250kg/$m^2$s, heat flux 5-30 ㎾/$m^2$, oil concentration 0-21 wt.% and saturation temperature 5$^{\circ}C$. Local evaporation heat transfer coefficients were found to be higher at the top, side and bottom of the tube in this order. Average heat transfer coefficients turned out to increase with oil concentration increment up to 3 wt.% oil concentration, whereas heat transfer coefficients gradually decreased over 3 wt.% oil concentration, because of oil-rich liquid film was formed on the heat transfer surface. Flow patterns were rapidly transitioned to annular regimes up to 3 wt.% oil concentration. In case of pure refrigerant, measured heat transfer coefficients in the experiments were similar to those of Kandlikar＇s correlation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.90-95
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• 2000

Condensation heat transfer experiments for R-22 and R-407C refrigerants mixed with mineral oil and POE oil respectively were performed in straight and U-bend sections of a microfin tube. Experimental parameters were an oil concentration from 0 to 5%, a mass flux from 100 to $400 kg/m^2s$ and an inlet quality from 0.5 to 0.9. The enhancement factors for R-22 and R-407C refrigerants at the first straight section decreased continuously as the oil concentration increased. They decreased rapidly as the mass flux decreased and inlet quality increased. The heat transfer coefficients in the U-bend were the maximum at the $90^{\circ}$ position. The heat transfer coefficients at the second straight section within the dimensionless length of 48 were larger by a maximum of 33% than the average heat transfer coefficients at the first straight section.

• 설비공학논문집
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• 제27권8호
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• pp.402-408
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• 2015

A series of numerical simulations have been carried out to study the performances of cyclone-type oil separators, which are designed for refrigeration-system compressors. The corresponding working fluid is R22, which is a typical refrigerant, whereby a mineral-oil droplet is supplied (Ed-highlight-My interpretation). The outlet-tube length in relation to the total chamber volume is considered a design parameter. Depending on the tube length, the separation efficiency varies from 98.7% to 99.3%, while the predicted pressure drop is between 5.1 kPa and 6.4 kPa. Considering both the pressure drop and separation efficiency, the length of the outlet-port tube of the separator is 152 mm.

• 대한기계학회논문집B
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• 제24권7호
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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.%.