Compressor Oil Research Articles

Thermal analysis of oil sump and compression unit in a rotary compressor

Thermal analysis of the oil sump and compression unit in a hermetic rotary compressor is important for enhancing its performance and reliability. In this study, the temperature distribution, heat-transfer mechanism, and heat balance of the oil sump and compression unit in a rotary compressor were analyzed using the 3D computational fluid dynamics (CFD) fluid-solid coupled model. Considering the practical characteristics of the rotary compressor, some special treatments are proposed for the simulation model. Instead of using empirical formulations, heat-transfer coefficients in the upside of the main bearing and compressor shell were obtained using the 3D CFD simulation model; the dynamic process in the suction chamber and compression chamber was considered to be static and the oil film in the inner wall of the cylinder, rib effect of the A-frame structure at the bottom of the compressor shell, and friction loss in the side of the sliding vane were considered. The simulation results showed good agreement with experimental results. We expect that these analytical results would be of great use in further understanding the temperature distribution and heat-transfer mechanism of oil sumps and compression units and also provide guidelines for improving the performance and reliability of rotary compressors.

Optimal Fluctuation Regulation Method in Low-Speed Digital Piston Pump

AbstractIn digital displacement pump (DDP), the states of valves are nonlinear correlation with the instantaneous flow rate and flow fluctuation. For low-speed working condition, the digital valve has potential to switch several times to improve flow fluctuation. So, the relationship between the valve states and the flow rate is decoded, and a novel optimal fluctuation regulation (OFR) method including OFR-strict (OFR-S) and OFR-relaxation (OFR-R) is designed in this paper. The periodicity and the symmetry of OFR methods are proved and an optimal solution in the predefined minimum characteristic interval (MCI) is realized. Compared to the traditional sequential, partial, and pulse width modulation (PWM) methods, OFR-S has the minimum flow fluctuation, while OFR-R is preferred in low-speed ratio to reduce the digital valve switching frequency. At last, the effects of valve delay and oil compressibility are analyzed. As a theoretical precise optimal solution, OFR method demonstrates its ability in handling nonlinear problems in MCI. And it definitely will be a good base for the nonlinear controller design in the future.

Effect of Graphene and MoS2 Flakes in Industrial Oils to Enhance Lubrication.

Tribological studies of the 2D nanoadditives such as MoS2 and graphene are mostly performed in base oils such as SN500, SN150, or paraffin. We have focused on their effect in lubrication properties of industrial oils (e.g., axle, transmission, and compressor oils) along with SN500 oil employing a four-ball tester. Two types of graphene powders (GpowA with fewer defects than GpowC), MoS2 powder, and their physical mixtures are chosen as nanoadditives. The tribology performance for 0.05 wt% of additives in various industrial oils is evaluated by monitoring the coefficient of friction (COF) during rubbing and wear scar diameter (WSD) of the steel balls after rubbing. Elemental analysis and electron microscopy have been performed on the wear surfaces for evidence of any tribofilm formation. GpowA favors antifriction for axle and transmission oils with 40% reduction in axle oil, whereas it improved antiwear properties in most of the oils. GpowC shows a COF decrement by 12% only for compressor oil, but contribute to wear reduction in all oils. The observed COF reduction is attributed to the compatibility of nonfunctionalized GpowA with nonpolar axle oil and functionalized GpowC with polar compressor oil. MoS2 shows a decrease in the COF and WSD in most industrial oils; the best being 60% COF and 7% WSD reduction in axle oil. For additives in oils that favor antiwear, flakes or particles are observed on the wear surface supported by the higher elemental contribution of the constituents from the wear region. The mixtures of GpowA or C with MoS2, however, does not seem to favor improvement in the COF or WSD in industrial oils. With assistance from oleylamine surfactants, the lubrication properties of most additives are improved, particularly for the mixtures with 12–15% COF reduction and 4–7% WSD reduction in compressor oil. The study indicates that a large sheet size of high-quality graphene aids antifriction and addition of surfactant molecules facilitates a co-operative effect between MoS2 and graphene for improved tribology.

A novel reduced order dynamic model of axial piston motors with compression flow losses and Coulomb friction losses

Purpose The purpose of this paper is to identify the energy losses factors during the hydro-mechanical conversion process at high pressure via a novel reduced order dynamic model.Design/methodology/approach A novel reduced order dynamic model of the axial piston motor was proposed, which provides an explicit insight to the compression flow losses and the Coulomb friction losses. A fully coupled dynamic model of the piston motor was obtained based on the array bond graph method. And then, a reduced order model was obtained by the composition analysis of flow and torque of the axial piston motor. After that, the energy losses estimation model was presented to predict the energy loss of the piston motor under a wide range of working conditions. The model was verified by comparing the experimental and simulation results.Findings The simulation result indicates that the flow loss caused by oil compression accounts for 59 per cent of the total flow loss, and the Coulomb friction torque accounts for 40 per cent of the total torque loss under a specific working condition. The compression flow loss and Coulomb friction torque are the major factors that lead to the aggravation of energy loss under extreme working conditions of the piston motor.Originality/value At high-pressure condition, the compression flow losses due to fluid compressibility cannot be neglected, and the hydro-mechanical losses in varies friction pairs should involve Coulomb friction losses. Flow and torque loss analytical expression in the model involve the design and control parameters of the piston equipment, which can realize the parameter optimization of the piston equipment for the purpose of energy-saving.

Experimental investigation of compressibility of waxy crude oil subjected to static cooling

Transportation of waxy crude oil confronts many difficulties due to the formation of gel in the production pipelines, which interrupts the steady production with low transportation efficiency and this later requires a higher pumping pressure to resume the flow. However, the current conventional equation is perceived to be over-predicted, mainly due to low attention given for the compressibility effects. Compressibility of the waxy crude oil has been theoretically reported to have significant influence on the restart pressure of the flow start-up or restart. Moreover, there is limited study on compressibility of waxy crude oil induced by the formation of intra-gel voids as a result of thermal shrinkage encountered during static cooling. This study is, therefore, aimed at investigating the compressibility of waxy crude oil gel experimentally. The experiment included the use of flow loop rig to produce gel at different conditions. The pressure pump rig was designed and fabricated for the compressibility tests. Experiments were conducted at different cooling rates and seabed temperatures. It was observed that higher seabed temperature and slower cooling rates contribute to higher compressibility tendencies. The specimen with faster cooling rates is proven to be less compressible.

Performance and refrigerant mass distribution of a R290 split air conditioner with different lubricating oils

The charge mass of R290 in room air conditioners (RACs) is limited by relevant standards due to its flammability. Meanwhile, the selection of the lubricating oil for R290 RACs is not yet clear. Mineral oils (MOs) are used currently, but the system performance when using MO is constrained under the existing standards because of the high R290 solubility in compressor oil sump. Some polyalkylene glycol synthetic oils (PAGs) are less soluble with R290, but the use of PAG in R290 RACs is less studied. In this paper, the effects of different lubricating oils including a PAG and a MO on a 1.5 HP R290 split RAC were experimentally investigated under cooling and heating mode. The refrigerant mass distribution was measured at steady state by “Quick Closing Valve Technique”. The system performance and R290/oil mixture viscosity in oil sump were compared. Results showed that using the PAG could reduce the R290 mass in compressor by about 10–13 g and improve heating capacity by 1.8–2.3%, but the Coefficient of Performance (COP) was lower under heating mode due to the excessive R290/oil mixture viscosity in oil sump. Results also showed that the refrigerant mass in the liquid line accounted for about 15% of the total charge mass under heating mode, and only 4–8% under cooling mode. The results can provide guidance for the system design and selection of lubricating oil for R290 RACs.

Numerical investigation of refrigerant outgassing in the screw pump of a hermetic reciprocating compressor oil supply system

This paper reports an investigation on the phenomenon of refrigerant outgassing in the screw pump of a hermetic reciprocating compressor oil supply system. The interfacial mass transfer between the...

Effect of SiO2 nanoparticles on the heat transfer characteristics of refrigerant and tribological behaviour of lubricant

Scientists and researchers are enthusiastically utilizing novel technologies that can substantially reduce energy consumption in diverse thermal systems. The foremost aim of the present investigation is to exploit the potential of nanoparticles on the enhancement of heat transfer characteristics of refrigerant and tribological capabilities of lubricant. Experimental investigations on the forced convection heat transfer characteristics of R134a/SiO2 nanorefrigerant (R134a + SiO2-polyalkylene glycol nanolubricant) are carried out. The effect of particle concentration, heat flux, mass flux, and vapour quality are investigated. The friction reduction and anti-wear properties of the nanolubricant are evaluated using four-ball tribo-tester. The results reveal that the presence of nanoparticles in the refrigerant significantly enhances the heat transfer coefficient of refrigerant and the tribological behaviour of lubricant. The maximum increase in heat transfer coefficient is 163.2% corresponding to a particle concentration of 0.4%. The presence of nanoparticles in refrigerant results in a marginal increase in pressure drop. However, the penalty in pressure drop is insignificant compared to the enhancement in heat transfer. Excellent friction reduction and anti-wear performance are also manifested by the nanolubricant. The maximum reduction in the friction coefficient is 37.76% and that of wear scar diameter is 40.83%. Considering the heat transfer and tribological characteristics, the optimum value of the particle volume fraction is 0.4%. SiO2-PAG nanolubricant can be considered as a potential energy-saving alternative to refrigerant compressor oils.

Тhermodynamic properties of isobutane/mineral compressor oil and isobutane/mineral compressor oil/fullerenes C60 solutions

In present study a new experimental data for the saturated liquid density and saturated vapor pressure along the boiling line for the solutions of the ”natural” refrigerant isobutane (R600a) with mineral compressor oil and solutions of R600a/compressor oil/fullerenes C60 is presented. Moreover, a new experimental data on the specific isobaric heat capacity, enthalpy and entropy along the boiling line for the R600a/compressor oil solutions is reported. Experimental data of the two-phase isochoric heat capacity was obtained for different compressor oil fraction in the refrigerant in the temperature range from 260 to 330 K. Obtained information was used to calculate the caloric properties of the R600a/compressor oil solutions. In addition, an influence of fullerene C60 on the specific isobaric heat capacity of mineral oil was examined. The measurements of the heat capacity for the R600a/compressor oil solutions, pure compressor oil and compressor oil containing fullerenes C60 were performed using an experimental setup that implements a direct heating method in adiabatic calorimeter. In addition, the heat capacity of oil and oil containing fullerenes C60 have been measured using differential scanning calorimetry. Finally, the heat capacity increase for the compressor oil with the additives of 0.0020 kg kg−1 of fullerenes C60 was observed.

Криволинейное радиальное течение сжимаемой вязкопластичной нефти со свободной текучестью в однородном пласте

The paper presents a solution to a steady-state hydrodynamic problem dealing with one-dimensional free-surface radial flow of compressible viscoplastic oil in a horizontal homogeneous circular formation. A vertical producing oil well is located in the centre of the formation, penetrating the pay zone fully, with no well casing or perforation present. We used generalised Darcy's law and equations of state for a compressible fluid to determine mass flow rate of the compressible viscoelastic oil and derive equations for current density, oil flow rate, current pressure distribution in the drainage area, and current pressure gradient. The equations take into account oil compressibility and initial pressure gradient. We also determined the time it takes an oil particle to reach the well starting from the current radius vector and from the external boundary. This is the case when the oil deposit lies close to the earth surface. This depth range features no shale beds or interbedded formations. Since subsurface mining is possible with shallow oil deposits, both wells and tunnels may be used for production.

EcoFlex Sponge with Ultrahigh Oil Absorption Capacity.

A paraffin microsphere-templated 3D porous EcoFlex sponge was prepared to selectively absorb oil or chemicals from water. The technology for producing this EcoFlex sponge does not need complicated synthesis processes or instruments, and the materials applied in this work are ecofriendly. Therefore, this sponge can be employed in the environmental field. EcoFlex sponges showed high hydrophobicity (contact angle = 140-143°) and oleophilicity. The developed sponge exhibits a porous three-dimensional framework inside with excellent internal connectivity, which contributes both better absorption capacity and faster absorption rate. For instance, the absorption capacity for chloroform can reach3400 wt %. Theabsorption capacity of the sponge was optimized using different size of paraffin microspheres and these sponges exhibit relatively high absorption capacity in a short time (2 min). The volume of sponge expands in some oils and organic solvents: the increased volume capacity for hexane can reach 2200%. This sponge also has great recovery capability and durability; it keeps its original shape and absorption capacity after 15 cycles of oil absorption and compression.

RSM and Crow Search Algorithm-Based Optimization of Ultrasonicated Transesterification Process Parameters on Synthesis of Polyol Ester-Based Biolubricant

This study investigated the optimization of ultrasound-aided transesterification process variables for the synthesis of polyol ester-based biolubricant. A response surface methodology based on Box–Behnken design coupled with crow search algorithm methodology was adopted to optimize the ultrasonicated transesterification process variables such as an ultrasonic pulse, amplitude, catalyst concentration, and reaction temperature in order to maximize the yield percentage of polyol ester. The formation of pentaerythritol ester was confirmed by Fourier transform infrared spectroscopy and gas chromatography. The significant properties of the new formulation were compared with synthetic grade compressor oil. Improved yield of 81.4% of pentaerythritol ester was accomplished with an ultrasonic pulse of 15 s, an ultrasonic amplitude of 60%, a catalyst concentration of 1.5 wt%, and the reaction temperature of 100 °C. This optimization study suggested that ultrasonicated successive transesterification process is an effective method in substituting conventional successive transesterification process for the synthesis of pentaerythritol ester-based biolubricant.

How does change of the bulk concentration affect the pool boiling of the refrigerant oil solutions and their mixtures with surfactant and nanoparticles?

In present study the pool boiling process for the model system of refrigerant R11(trichlorofluoromethane or CCl3F)/mineral compressor oil solution has been examined. The experiments performed at various boiling temperatures (40, 50, 60 °C) and initial mass fractions (3.485, 7.456, 14.000 mass.%) of compressor oil in the range of the heat fluxes 5–63 kW/m2. The solutions were sampled 10 mm above, 10 mm below and at the level of the heater simultaneously with measurements of the heat transfer coefficient (HTC). We found that the oil concentration does not change with the level. However, the oil concentration considerably varies with the heat flux density and was always higher than the initial concentration value. The visual observations for the pool boiling process reveal that the concentration of solution depends on superposition between convective and diffusive components of the mass transfer. The data analysis indicates to significant underestimation of the HTC caused by change in the oil concentration. Finally, an influence of oil concentration change was examined for the refrigerant/oil solutions pool boiling with oleic acid surfactant and TiO2 nanoparticles additives.

Performance investigation and exergy analysis of vapor compression refrigeration system operated using R600a refrigerant and nanoadditive compressor oil

Compression of vaporized refrigerant is the essential process of the refrigeration cycle which is performed by using a compressor. The amount of power consumed by a refrigeration system is governed by the work input given to its compressor, which also determines the COP of the system. By reducing the work input given to the compressor, the power consumption of refrigerator is reduced along with the improvement in its COP. Nowadays, nanoparticles have emerged as the new generation additives in various working fluids because of their remarkable ability to improve the heat transfer, tribological and other thermophysical properties of the base fluid. In such a vein, we propose a compressor oil based nanofluid prepared by dispersing nanoparticles into the conventional compressor oil. In the present study, four samples of nanoadditive compressor oil were prepared by dispersing the nanoparticles like Al2O3, TiO2, and ZnO into the conventional mineral oil as a lubricant. The tribological properties of this four samples were studied, out of which one sample gave a better lubrication and heat transfer properties which are considered as one of the key parameters for reducing work input to the compressor, this can result in reduced power consumption, with enhancement of COP. These results are analyzed experimentally by carrying out performance and exergy analysis in a vapor compression refrigeration system, using R600a as a refrigerant. The experimental results show that, there is an improvement of COP by 14.61% and exergy efficiency by 7.51%. Also, the efficiency defect in the major components of vapor compression refrigeration system has been reduced effectively.

Study on key performance parameters of hydro-pneumatic tensioner for top tensioned riser

In this paper an improved mathematical model of a hydro-pneumatic tensioner (HPT) system for top tensioned riser (TTR) is derived by consideration of friction, mass of piston and piston rod, tension loss in hydraulic oil piping, and compressibility of hydraulic oil. The vertical motion of the riser string is also considered. Subsequently, the proposed detailed model and the conventional simplified model are comparatively studied. Finally, the tension characteristic and performance parameters of the HPT are analyzed based on the proposed model. Results show that the conventional simplified model indeed overestimates the tension of tensioner as it neglects some performance parameters resulting in tension loss. The diameters of piston and piston rod and the initial pressure of high pressure (HP) gas have the most significant influence on the tension of the tensioner. The initial volume of HP gas and the initial pressure of low pressure (LP) gas also have some impact. The influence of the initial volume of LP gas and the inner diameter and length of the piping is relatively small. The research has some reference value for HPT and TTR design.

Lubricity of selected oils in mixtures with the refrigerants R452A, R404A, and R600a

Abstract The essential problem in the operation of refrigeration compressors is the change in lubricity of oils in the mixture with a refrigerant. The validity of the issue is intensified by the tendency to replace refrigerants with more ecological ones. For the new refrigerants, one should select the right compressor oil. The paper describes a method of assessment of lubricity on the basis of the wear of the model block-on-ring tribocontact following the operation in the oil–refrigerant mixture. The method was used for a comparative assessment of various oils in the mixture with the refrigerant R404A and its successor – R452A. In addition, three mineral oils (MO) with the natural refrigerant R600a were examined. In all of the examined instances, significant differences in lubricity in the group of compared oils (replacements) were found. The obtained results confirm the suitability of the method for assessing lubricity of a wide group of substances: POE/R404A, POE/R452A, MO/R600a. One also confirmed the suitability of the method for initial selection of oil for new refrigerants. The method can be applied for different mechanisms of oil–refrigerant mixture formation: intermolecular diffusion for R600a, intermolecular diffusion and natural convection for R452A. Furthermore, the impact of lowering the temperature (pressure) on lubricity of the oil–refrigerant mixture was examined. In the analyzed case, however, the observed differences were not significant.

Influence of Lubricant Pressure Response on Subsurface Stress in Elastohydrodynamically Lubricated Finite Line Contacts

In order to adapt to increasingly stringent CO2 regulations, the automotive industry must develop and evaluate low cost, low emission solutions in the powertrain technology. This often implies increased power density and the use of low viscosity oils, leading to additional challenges related to the durability of various machine elements. Therefore, an increased understanding of lubricated contacts becomes important where oil viscosity–pressure and compressibility–pressure behavior have been shown to influence the film thickness and pressure distribution in elastohydrodynamic lubrication (EHL) contacts, further influencing the durability. In this work, a finite line EHL contact is analyzed with focus on the oil compressibility–pressure and viscosity–pressure response, comparing two oils with relatively different behavior and its influence on subsurface stress concentrations in the contacting bodies. Results indicate that increased pressure gradients and pressure spikes, and therefore increased localized stress concentrations, can be expected for stiffer, less compressible oils, which under transient loading conditions not only affect the outlet but also the edges of the roller.

Mechanics characteristics of a kind of hydra pneumatic suspension

This paper studied a kind of off-highway truck suspension with simple structure of gas and oil sealed in same chamber. The mechanics characteristics of hydra pneumatic suspension are known to be coupled with the gas state, oil flow rate through orifice and friction force model. The reported studies on hydra pneumatic suspension involve flow rate coefficients of orifice, nonlinear characteristic of shim stack or continuity condition equations without oil compressibility. While few researches cover the suspension studied in this paper, this study characterizes gas volume, gas solubility or releasing process, oil flow rate through orifice, check valve and annulus, friction force model, etc. The validity of the suspension model is demonstrated using the test data on test rig. The gas state behavior with solubility or releasing process is investigated. Oil flow rate and pressure relationship are assessed in terms of piston velocity. Friction force model based on Lugre model is analyzed and simplified. It is shown that nonlinear characteristic of mechanics characteristics of suspension can be explained based on subsystems above. Models and method used in this paper can be a reference for mechanics characteristics analysis of cylinder system containing similar parts.

EXPERIMENTAL INVESTIGATION OF NANO COMPRESSOR OIL EFFECT ON THE COOLING PERFORMANCE OF A VAPOR-COMPRESSION REFRIGERATION SYSTEM

In this study, cooling performance of a refrigeration system under the effects of nanoparticle (TiO2) addition to the compressor oil (poly alkaline glycol (PAG)) was experimentally investigated. Thermodynamics analysis of the vapor-compression refrigeration system with various nanoparticle volume fractions of TiO2 (between 0.5%, and 1%) added to the compressor oil was performed. R-134a was used as the refrigerant. Two-step method was used to prepare the nano-lubricant for different solid particle volume fractions. It was observed that COP of the refrigeration system enhances with the addition of nanoparticles and it is an increasing function of nanoparticle volume fraction.

Effect of Ozone Oxidation and Modification with a Carbon Framework on the Tribotechnical Characteristics of a Plastic Lubricant

The tribotechnical characteristics of grease oxidized with ozone and modified with a carbon framework (CF) are studied. It is shown that, starting from the temperature of 150°C and up to 600°C, the ozone oxidation of compressor oil KS-19 (grease based) and the active components of a CF used as an additive have a favorable effect on the characteristics of the adhesive interaction under friction due to the low level of plasticity of the frictional contact.