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Nanofluids are the most attractive mean to enhance the performance of heat transfer devices. Several types of nanoparticles were utilized as they have high thermal conductivity. Renewable energy makes use of these nanofluids special in solar collectors. Evacuated tube solar collector is one of the most utilized solar collectors in thermal applications. CeO 2 nanoparticles were used in the presented study. The mean diameter of CeO 2 was 25 nm. A stable CeO 2 /water was made. The stability was checked using Zeta potential machine. Experiments were carried out using three different volume concentration of CeO 2 nanoparticles of 0.015%, 0.025%, and 0.035%. The thermal performance of the evacuated tube solar collector was examined at different mass flux rates. Results showed that the temperature difference between inlet and outlet flow and absorbed energy increase when nanofluids are used. The volume fraction flow rate of 0.035% at the mass flux rate of 0.017 kg/s.m 2 had the maximum heat removable factor, the thermo-optical characteristic of the collector, and the thermal loss coefficient. The thermo-optical characteristic of the collector of tube solar corrector is raised up to 34%. [ABSTRACT FROM AUTHOR]

Using nanofluids in thermal energy devices, such as flat-plate solar collectors, is gradually making progress, and getting awareness in the scientific community. Experiments were performed to study the effect of using CeO 2 -water on the efficiency of flat-plate solar collector by three different volume fractions of CeO 2 nanoparticles of 0.0167%, 0.0333% and 0.0666%, while the mean particle dimension was kept constant at 25 nm. An ultrasonic process was used for maintaining the stability of the CO 2 -water nanofluid. The working fluid mass flux rates were 0.015, 0.018 and 0.019 kg/s m 2 . The experiments were carried out in Budapest, Hungary on the latitude of 47°28′N and longitude of 19°03′E. Higher collector efficiency was achieved when using CeO 2 -water nanofluid compared to results achieved with water application. Based on present data, the efficiency of the collector is directly proportional with the mass flux rate and with the volume fraction in the ranges of the present study. Experiments indicate that the highest rise in efficiency of the collector at zero value of [(T i  – T a )/G T ] is 10.74%, for volume fraction ( φ ) 0.066%, and for mass flux rate of 0.019 kg/s m 2 compared to water. [ABSTRACT FROM AUTHOR]