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Effects of Oil Wettability on the Performance of a Cyclone-Type Oil Separator
Abstract
The effects of oil wettability on the performance of a cyclone-type oil separator was studied through in situ experimentation and in a real refrigeration system. Based on previous research, the geometry of the oil separator in the present study was designed with an oil recovery device installed at its bottom to mount it on the actual refrigerator. The performance of the oil separator without surface treatment was predicted by applying design correlations proposed in the open literature, which were then compared with the experimental data. Through surface treatment, oleophilic or oleophobic properties were given to the inner wall and helix of the oil separator, and its performance was measured in a real refrigeration system. Oil wettability had a great effect on the performance of the oil separator, and in order to obtain high separation efficiency, oleophilic properties were found to be advantageous not only in the inner wall but also in the helix.
... (5,12) 에서 윤활유에 대해 접촉각이 작은 표면이 분리효율 측면에서 유리한 것으로 나타났다. 하지만 실제 냉동 사이클에 연계한 실험에서 접촉각이 작은 표면의 경우 압력강하도 함께 증가하는 단점이 발견되었다. ...
... 하지만 실제 냉동 사이클에 연계한 실험에서 접촉각이 작은 표면의 경우 압력강하도 함께 증가하는 단점이 발견되었다. (12,13) 수치해석을 통해 입구 유동이 유분리기 내부 구조물과 충돌하면서 난류 운동 에너지가 생성되는 것을 확인하였고 (10,11) 이를 피하기 위한 설계로서 Fig. 1 (14) 이에 본 연구에서는 Fig. 1 표면 처리의 경우 선행 연구 (12) 에서 나선구조물과 몸체 모두 친유처리를 한 경우에 가장 분리효율이 높게 나타나 본 연구에서도 Fig. 3 ...
... 하지만 실제 냉동 사이클에 연계한 실험에서 접촉각이 작은 표면의 경우 압력강하도 함께 증가하는 단점이 발견되었다. (12,13) 수치해석을 통해 입구 유동이 유분리기 내부 구조물과 충돌하면서 난류 운동 에너지가 생성되는 것을 확인하였고 (10,11) 이를 피하기 위한 설계로서 Fig. 1 (14) 이에 본 연구에서는 Fig. 1 표면 처리의 경우 선행 연구 (12) 에서 나선구조물과 몸체 모두 친유처리를 한 경우에 가장 분리효율이 높게 나타나 본 연구에서도 Fig. 3 ...
... However, it is difficult to remove fine particles smaller than 5 μm with existing cyclones [7][8][9]. Moreover, centrifugal force should be enhanced by increasing the flow rate of cyclone [10,11] in order to raise particle collection efficiency, resulting in an increased pressure drop and energy loss that ultimately leads to a rise in operation cost [12]. To address these shortcomings, various studies with the aim of increasing collection efficiency or reducing pressure drop. ...
A three-layer-type multi inner stage (MIS) cyclone capable of removing fine particles generated by electronic industrial processes was successfully developed with a high processing rate, minimal maintenance and repair cost, and low energy loss. To investigate the capability of the MIS cyclone, experiments were performed using Al2O3 particles with diameters of 1, 3, 5, 10, 15 and 20 μm under particle inlet velocities of 0.85, 2.55, 4.25, 5.94 and 8.49 m/s. Lapple (1950), Barth (1956), and Iozia and Leith (1989) prepared a cyclone efficiency prediction graph using a collection efficiency prediction model under the same operating conditions as the MIS cyclone. They verified the cyclone efficiency by comparing the efficiency prediction graph and the general cyclone experimental data with the MIS cyclone experimental data. For an Al2O3 fine particle diameter smaller than 5μm, the particle removal capability of the MIS cyclone was observed to be significantly higher than that of the predicted efficiency of a general cyclone and its actual experimental efficiency. Furthermore, the variation of collection efficiency with particle size was not as significant as that of a general cyclone, which suggested the MIS cyclone possesses a more stable removal capability. Pressure drop measurement results of the MIS cyclone showed that a maximum pressure drop of 11 mmAq occurred under an inlet velocity of 8.49 m/s, which was considerably lower than that of a general cyclone pressure drop (50∼150 mmAq).
The aim of the present work was to study the passive film stability and pitting corrosion behavior of the AISI 409 stainless steel. The electrochemical tests were carried out in 0.1 M NaCl solution at room temperature. The general electrochemical behavior was assessed using electrochemical impedance spectroscopy (EIS) measurements whereas the semiconducting properties of the passive film were evaluated by the Mott-Schottky approach. Pitting corrosion was investigated using potentiodynamic and potentiostatic polarization tests. Surface morphology was examined using confocal laser scanning microscopy and scanning electron microscopy (SEM). Energy dispersive X-ray spectroscopy (EDS) analyses were carried out to identify the composition of precipitates that could act as preferential sites for the onset of pitting corrosion. The results showed that the passive film presents n-type semiconductive behavior. Grain boundaries played an important role as pitting initiation sites for the AISI 409 stainless steel.
A simple fabrication technique is described for preparing Ag-doped ZnO nanorods using a rapid hydrothermal technique to create a superamphiphilic surface on SS-400 substrates. The high roughness resulting from Ag-doped ZnO nanorod surfaces is responsible for generating the superamphiphilic property of the SS-400 substrate. The fabricated surface shows contact angles (CAs) of almost 0° for water and olive oil, resulting in complete spreading of water and oily liquids. The fabricated surface also exhibits excellent superamphiphilic properties after long-term storage, thermal, and mechanical testing. However, after modification with a lowsurface-energy material (stearic acid), the fabricated surface exhibits superhydrophobic properties with water CAs of 158° and sliding angles (SAs) of less than 5°. We also applied our fabrication method to a helical-type oil separator. The oil separator, when treated with Ag-doped ZnO nanorods with a superamphiphilic surface, improved its oil separation efficiency and pressure drop compared with those of a commercial oil separator. Thus, our surface fabrication technique can be implemented easily to large-area, three-dimensional surfaces. Due to their ease and rapidity of manufacture and long-term wetting stability, these surfaces are potentially suitable for large-scale industrial applications in a variety of fields.
We have demonstrated a facile fabrication of copper oxide hierarchical structures on copper substrates by the oxidation of copper in hot alkaline solutions. The flowerlike hierarchical structures are synthesized by simply immersing a copper substrate into ammonium hydroxide alkaline solutions and heating at a particular temperature. The wettability of the surface was changed by chemical modification with 1H,1H,2H,2H-perfluorooctyltrichloro silane. We also discuss the effect of heating time on the morphology of the as-prepared copper oxide and hydrophobicity/oleophobicity. It is a unique method to generate both superhydrophobic and superoleophobic conditions in the same copper plate. The developed fabrication procedures allow the large area, cost-effective fabrication of copper oxide films. Our method might provide a general route towards the preparation of novel hierarchical films on metal substrates for various industrial applications including fluid transfer, fluid power systems, stain resistant, and antifouling.
A very high accuracy, straight vibrating tube type of density flow meter has been used online to measure oil concentraiton of flowing R-134a/oil mixtures. The calibrations covered oil concentrations from 0-6 wt.% oil over the temperature range from -9.4 to 5.9°C. The oil concentrations were correlated statistically as a function of density, temperature and liquid compressibility to an average error of 0.09 wt.% oil with a 95% confidence limit of 0.21 wt.% oil. In addition, a simplified method not requiring calibration tests was developed for general industrial application of the density flowmeter to any refrigerant-oil mixture combination, with an average error of 0.22 wt.% oil and 95% confidence limit of 0.67 wt.% oil for the present data set.
As wetting behavior is a key factor affecting boiling heat transfer performance of refrigerant-oil mixture, the influence of oil concentration on wetting behavior during evaporation of refrigerant-oil mixture on copper surface was experimentally investigated. The wetting behavior was analyzed by capillary rise method, and the test conditions covered oil concentrations of 1, 3, 5 and 10 wt%, and surface roughness of 0.028, 0.079, 0.144, 0.419 and 1.166 μm. The experimental results show that protuberant liquid film occurs in front of meniscus during evaporation of refrigerant-oil mixture; and contact line velocity, contact angle, liquid film length and rising liquid height increase as oil concentration increases. It is also found that the ratio of the rising liquid height of refrigerant-oil mixture to that of pure refrigerant is larger than 1, and ranges between 1.42 and 2.18 under present test conditions, indicating that the presence of oil significantly enhances the surface wettability of refrigerant. © 2015 Elsevier Ltd and International Institute of Refrigeration.
The efficiency and pressure drop in the oil separator of a multi heat pump system were experimentally investigated. R410A and polyvinylether (PVE) oil were used as the refrigerant and lubricant of the system, respectively. The refrigerant mass flow rate and the liquid circulation ratio were varied between 30 and 150 g s⁻¹ and between 1.5% and 4.5%, respectively. Five different oil separators were considered, and the measured efficiencies and pressure drops were analyzed with respect to the height and diameter of the oil separators. The analytical results were used to develop empirical equations for predicting the efficiency and pressure drop of the oil separator. The mean absolute percentage errors between the predicted and measured efficiencies and pressure drops for the oil separators were 0.4% and 11.7%, respectively.
In order to improve a refrigeration system’s energy efficiency, the separation efficiency of its oil separator should be improved. To do so, we turned to nature for inspiration. A Namib Desert beetle collects water in fog by using its skin, which combines hydrophilic and hydrophobic surfaces. Inspired by nature’s design, we applied a surface with oleophilic and oleophobic patterns to an oil separator used in a refrigeration system. In order to make the oil separator, an appropriate design was established using computational fluid dynamics. A cyclone-type oil separator was produced with an oleophobic-treated surface on its lower cup. The efficiency of the treated surface of this oil separator was tested with an open-type experimental setup using an oil mist generator. To obtain conditions similar to those of a refrigeration system in the open-type experimental setup, the oil particle diameter and working fluid pressure were set to yield a Stokes number similar to that of oil particles in the oil separator of the refrigeration system. The oil separator with the treated oleophilic–oleophobic surface improved its oil separation efficiency by 1.67% and its pressure drop by 2.48% compared to a conventional cyclone-type oil separator. © 2015, Korean Society for Precision Engineering and Springer-Verlag Berlin Heidelberg.
A series of numerical simulation has been carried out to study performance of a cyclone type oil separator, which is designed for the compressor of a refrigeration system. Working fluid is R22, which is a typical refrigerant, and mineral oil droplet is supplied. Pitch of the helix is considered as design parameters to make a compact separator. Depending on the helix pitch, separation efficiency varies from 97.5 to 99%, while predicted pressure drop ranges from 5 to 6.5 kPa. Considering both of the pressure drop and separation efficiency, helix pitch of the separator has been designed as 50 mm.
In this work, a residential air conditioning compressor designed for vapor injection has been modified in order to inject large quantities of oil into the working chamber in order to approach an isothermal compression process. The compressor was tested with oil injection mass flow fractions of up to 45%. At an evaporating temperature of −10 °C and condensing temperature of 30 °C, the overall isentropic efficiency was up to 70% at the highest oil injection rate. Overall, over the testing envelope investigated, there are no significantly negative effects experienced for the compressor and the compressor isentropic efficiency and refrigerant mass flow rate improve monotonically as the oil injection rate is increased.
This paper discusses the experimental results of oil retention amount and pressure drop in the gas line of refrigerant. R410A and polyvinylether oil were used as refrigerant and lubricant, respectively. The experiment was conducted under various pipe inner diameters of 14.1, 17.3 and 26.0 mm, and refrigerant mass flux and oil circulation ratio (OCR) were varied from 40 to 250 kgm-2s-1 and 0.5 to 4.0%, respectively. The oil retention amount tends to increase as refrigerant mass flux decreases and OCR increases. The oil retention amount in vertical pipe was higher than that in horizontal pipe. The empirical expressions for predicting the oil retention amount and pressure drop were suggested. The mean absolute percentage errors of each expression for predicting the oil retention amount in horizontal and vertical pipes were 18.1% and 14.1%, respectively, and those for predicting the pressure drop in horizontal and vertical pipes were 22.2% and 20.1%, respectively.
Vapor compression refrigeration technology has seen great improvement over the last several decades in terms of cycle efficiency through a concerted effort of manufacturers, regulators, and research engineers. As the standard vapor compression systems approach practical limits, cycle modifications should be investigated to increase system efficiency and capacity. One possible means of increasing cycle efficiency is to flood the compressor with a large quantity of oil to achieve a quasi-isothermal compression process, in addition to using a regenerator to increase refrigerant subcooling.
In theory, compressor flooding and regeneration can provide a significant increase in system efficiency over the standard vapor compression system. The effectiveness of compressor flooding and regeneration increases as the temperature lift of the system increases. Therefore, this technology is particularly well suited towards lower evaporating temperatures and high ambient temperatures as seen in supermarket refrigeration applications. While predicted increases in cycle efficiency are over 40% for supermarket refrigeration applications, this technology is still very beneficial for typical air-conditioning applications, for which improvements in cycle efficiency greater than 5% are predicted. It has to be noted though that the beneficial effects of compressor flooding can only be realized if a regenerator is used to exchange heat between the refrigerant vapor exiting the evaporator and the liquid exiting the condenser.
The concentration of oil in refrigerants (while in liquid state) can be measured with an acoustic velocity sensor. The transit time for an acoustic signal can be related to the oil concentration and temperature of the liquid mixture. The performance of the sensor is dependent on the properties of the oil and refrigerant, and their miscibility. In general, a thorough calibration becomes necessary. It is shown in this paper that for concentrations less than 10%, an approximation can be made for the estimate of concentration hence eliminating the need for an elaborate calibration procedure.
A lubrication agent is necessary in almost all the refrigeration vapour compression systems, particularly for the correct operation of the compressor. However, a certain portion of the oil always circulates with the refrigerant through the cycle. This circulation is at the origin of a deviation from the theoretical behaviour (i.e. based on pure refrigerant) of the components. This article aims at reviewing the oil-related researches in the field of refrigeration. Previous reviews in the literature focused on the thermo-hydraulic consequences of the presence of oil; we will analyse here its thermodynamical consequences. In a first part, a brief literature review will give an overview of current scientific and technological issues concerning the impact of oil on components or on whole refrigeration systems. The typical approaches and methods employed to address this problem will be described. These researches require sound tools for the evaluation of thermodynamic properties of refrigerant-oil mixtures. The second part of this article is hence a critical review of these tools, and focuses particularly on liquid-vapour equilibrium, absorption-diffusion, and mixture enthalpy calculation.
A mathematical model has been developed for calculation of cut-off size and fractional efficiencies in cyclone separators, by taking into account the effects of flow, particle and geometrical parameters, and acceleration assuming that the mixture of fluid and particles is homogenous, and acceleration diminishes depending on the friction and geometry. Collection efficiency curves and cut-off size values predicted by the proposed model showed a good agreement with experiments over a wide range of inlet velocities for different types of cyclones. Comparison of the obtained results with semi empirical models available in literature also indicated that the present model may be used successfully for determination of the performance of a tangential inlet cyclone. Analyses of the effects of various parameters reveals that, in addition to flow and geometrical parameters, surface friction, vortex length and flow regimes play an important role on cyclone performance especially in small cyclones.
Results concerning a model of vapour compression refrigeration system using R410A, a binary HFC blend, and designed to take into account the effects of the oil rejected by the compressor, are presented. These effects are negligible when the lubricant does not exceed 0.5% of the total refrigerant weight; above this value, the performances of the system decrease significantly.