Abstract
The optimal choice of compressor oil and the use of nanoparticles as additives are a promising way to improve the efficiency of vapor compression refrigeration systems. The main barrier for the practical implementation of this approach in the industry is the impossibility of the theoretical prediction of the expected effects on the performance parameters of the refrigeration system. Experimental data for the cooling capacity, compressor power consumption and coefficient of performance (COP) during operation of the experimental setup (refrigeration system with Embraco Aspera EMT6152U compressor) have been obtained. R290 refrigerant and four different compressor oils (RENISO SP46 alkylbenzene oil with the viscosity of 46 mm 2 ·s -1 at 40 °С, and the same oil containing 0.223·10 -4 kg·kg -1 of fullerene C 60 , ProEco® RF22S polyester oil with the viscosity of 22.26 mm 2 ·s -1 at 40 °С and the same oil containing 6.837·10 -4 kg·kg -1 of fullerene C 60 ) have been used. The experiment was performed at the refrigerant condensing temperature of 318.5±1.0 K and in the evaporating temperature range of 252…271 K. When using the two pure oils, the compressor power varied by 2...3 %. The effect of the presence of fullerene C 60 on the compressor power was different for different oils. The use of a more viscous oil, as well as the presence of fullerene C 60 in the oil, leads to an increase in cooling capacity. The application of the less viscous oil ProEco® RF22S contributes to an increase in COP (up to 20 %) at the evaporating temperatures near 270 K and has no effect on the COP at low temperatures in comparison with RENISO SP46 oil. The presence of fullerene C 60 in both oils contributes to an increase in COP up to 15...20 % in the whole range of the studied evaporating temperatures. Therefore, the expediency of adding the fullerene C 60 into compressor oils in order to increase the energy efficiency of the vapor compression refrigeration system without its modernization has been confirmed
Highlights
The choice of the fullerene C60 as an additive to the compressor oil was based on the following reasons: i) the oil-fullerene C60 solution forms systems that are stable to clusterization and precipitation without using surfactants [14, 15]; ii) using the compressor oil with fullerene C60 leads to decrease of the friction losses in the compressor [14, 16,17,18]; iii) additives of the fullerene C60 insignificantly change the base oil viscosity [15] in contrast to additives of the metal oxide nanoparticles, the presence of which leads to a significant increase of the base fluid viscosity [19]
The study [14] demonstrated that the presence of 0.0020 kg·kg-1 of fullerene C60 in the solution of the mineral compressor oil in R600a refrigerant contributes to insignificant variation in thermophysical properties in comparison with additives of metal oxide nanoparticles [19]
The results showed that using the polyalkylene glycol oil may improve the heating capacity by 1.8...2.3 %, but the coefficient of performance (COP) was lower under the heating mode due to excessive R290/oil mixture viscosity in the oil crankcase
Summary
The implementation of the working fluids that contain nanoparticles to increase the efficiency of the vapor compression refrigeration systems (VCRS) without retrofit is one of the promising directions [1,2,3,4,5,6,7,8,9,10]. In the majority of reported experimental studies devoted to an evaluation of the performance parameters for the VCRS, the working fluids that contain metal oxide nanoparticles as the additives have been used [1,2,3,4,5,6]. 5/8 ( 107 ) 2020 ondly, the fullerene C60 in liquid can be regarded both as a large molecule and small nanoparticle [11] Both facts will contribute to the high stability to clusterization and precipitation of the working fluid that contains fullerene C60. The experimental study of efficiency parameters of the VCRS operated with promising R290 refrigerant and various compressor oils is important. The study will demonstrate the influence of the viscosity of compressor oils (compatible with R290 refrigerant) on the efficiency parameters of the VCRS. All results obtained will contribute to enhancing the energy efficiency of the VCRS without retrofit due to the optimal choice of the compressor oil
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