• Energy Research

Abstract This paper presents the results of experimental study of the pool boiling process for the nanofluids isopropyl alcohol (isopropanol)/Al2O3. The test experiments on pool boiling of the isopropanol (C3H8O) and refrigerant R11 (CCl3F) were conducted to verify the reliability of developed experimental setup. The experimental values of the determined heat transfer coefficients and bubble departure diameters have been compared with several models reported in the literature. An effect of Al2O3 nanoparticles on the heat transfer coefficient and bubble departure diameter during isopropanol boiling was measured and analysed. Moreover, the experiments for determination of the isopropanol contact angle on the bare surface and surface coated by nanoparticles after nanofluid boiling have been performed in order to evaluate its effect on the boiling process. Finally, obtained experimental data for the heat transfer coefficient of isopropanol, refrigerant R11 and nanofluids isopropanol/Al2O3 using RPI heat flux partitioning model have been fitted with an uncertainty less than 10%.

Abstract This paper presents a theoretical evaluation of the influence of compressor oil admixtures on the thermodynamic performance of a vapor compression system using natural refrigerant R600a. The performance determination is based on the developed pressure–enthalpy diagrams (P–h) for the refrigerant oil solution (isobutane-mineral compressor oil Azmol). A method for calculating the enthalpy of refrigerant–oil solutions has been proposed and the influence of the compressor oil admixtures to isotherms the pressure–enthalpy diagrams has been analyzed. The change of enthalpy at the different oil concentrations in the working fluid in an evaporator has been investigated. An application of the developed refrigerant–oil P–h diagrams for the theoretical evaluation of the efficiency of the vapor compression systems is also demonstrated.

Nanofluids are promising heat carriers, which contribute to the overall efficiency of energy systems. The main obstacle to the practical application of nanocoolants based on aqueous propylene glycol solutions is the lack of accurate data on their thermophysical properties. In the paper, experimental study (adiabatic calorimetry method) of the heat capacity and parameters of solid phase – liquid phase transitions of propylene glycol and coolant based on aqueous propylene glycol solution is carried out. Experimental study of the heat capacity of the liquid phase of the coolant based on an aqueous solution of propylene glycol with additives of Al 2 O 3 nanoparticles (up to 2.01 wt. %) in the temperature range of 235...338 K and propylene glycol with additives of Al 2 O 3 nanoparticles (1.03 wt. %) in the temperature range of 268…335 K is performed. The comparison of the temperature dependence of the effective heat capacity of coolants with changes in their internal structure is made. It is shown that adding water to propylene glycol increases the temperature and heat of the solid phase – liquid phase transition (the heat of the propylene glycol phase transition is 37.85 J∙g –1 , propylene glycol/water coolant (54/46 wt. %) – 77.97 J∙g –1 ). It is shown that additives of Al 2 O 3 nanoparticles both in propylene glycol and in the coolant based on an aqueous propylene glycol solution contribute to the reduction of the heat capacity of the liquid. The heat capacity decreases approximately in proportion to the increase in the concentration of nanoparticles. The effect of heat capacity reduction is greater at high temperatures (3.9 % at 265 K and 5.0 % at 325 K for the nanocoolant with an Al 2 O 3 nanoparticle concentration of 2.01 wt. %). The results obtained will improve the design quality of heat exchange equipment using nanocoolants. The results are useful for developing methods for predicting the specific heat of nanofluids

Abstract This paper presents experimental data for the viscosity of solutions of refrigerant R600a (isobutane) with mineral compressor oils Azmol, Reniso WF 15A, and R245fa (1,1,1,3,3-pentafluoropropane) with polyolester compressor oil Planetelf ACD 100 FY on the saturation line. The experimental data were obtained for solution of R600a with mineral compressor oil Azmol in the temperature range from 294.7 to 338.1 K and the concentration range 0.04399 ≤ wR ≤ 0.3651, the solution of R600a with mineral compressor oil Reniso WF 15A at the temperatures from 285.8 to 348.4 K and the concentration range 0.03364 ≤ wR ≤ 0.2911, the solution of R245fa with polyolester compressor oil Planetelf ACD 100 FY at the temperatures from 309 to 348.2 and the concentration range 0.06390 ≤ wR ≤ 0.3845. The viscosity was measured using a rolling ball method. The method for prediction of the dynamic viscosity for refrigerant/oil solutions is reported.

A new composite heat transfer fluid consisting of tetralin and fullerene has been proposed for photovoltaic thermal hybrid solar harvesting. It features a unique absorption spectrum that is capable of sharply cutting off solar energy irradiated in the range of wavelength from 300 to 650 nm, making it a perfect candidate for simultaneous harvesting of both photovoltaic and thermal components of solar energy. The proposed composite revealed outstanding stability and facile synthesize root, which are the two main obstacles for applicability of nanofluids. It was shown experimentally that the additives of fullerene to tetralin do not alter significantly it's thermophysical properties apart from viscosity that increases moderately. Besides, tetralin/fullerene solutions show similar thermohydraulics performance to that of pure tetralin in laminar flow regime or insignificantly lower in transient and turbulent flow regimes. A new figure of merit was proposed to analyze the thermohydraulics performance that consider not only exergy losses due to the kinetic energy dissipation, but also exergy losses associated with a finite temperature difference in the heat exchanger. As a result, the proposed figure of merit indicates the decrease of the heat transfer performance of tetralin/fullerene solutions that directly proportional to fullerene concentration. The performed simulation suggests that the total energy efficiency of flat-plate photovoltaic/thermal solar collector goes up to 60.4 % estimated according regulation (EU) No. 811/2013. Finally, life cycle analysis revealed further improvement root in view of environmental impact. 27 pages, 20 figures, 6 tables

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

The methodology of the eco-energy analysis of power-intensive equipment, based on the calculation of the green house gases emission during its full life cycle, is presented. According to the presented methodology, a comparative eco-energy analysis of vapor compression and ejector air conditioners operating with R245fa at different working conditions in China and Ukraine, is carried out. New eco-energy indicators, which allow the determination of the prospective of the alternative air conditioning system implementation, are offered. It is shown, that ejector air conditioners have eco-energy prospective for the implementation if they are driven by waste heat from several industries.

Abstract In present paper we investigated the influence of Al2O3 nanoparticles on the specific heat capacity of isopropyl alcohol in the temperature range 80–186 K. The measurements of the specific heat capacity were performed by an adiabatic calorimeter. It was found that below the melting temperatures the solution of isopropyl alcohol with Al2O3 nanoparticles can be in crystalline, glassy and liquid metastable states. The presence of Al2O3 nanoparticles in isopropyl alcohol leads to a decrease of the specific heat capacity and the enthalpy of phase transitions “crystalline state – liquid” and “glassy state – liquid metastable state”. It was demonstrated that not only presence of the nanoparticles but also the existence of the adsorbed interfacial phase from the molecules of the base liquid around the nanoparticles decreases the isopropyl alcohol melting heat. Based on obtained experimental data for the melting heat of the nanofluids of isopropyl alcohol/Al2O3 the mass fraction of the base fluid in the interfacial phase and the mean equivalent radius of nanoparticles with interfacial phase have been determined at the melting point.