## 1 Introduction  
Nanofluids are composed of base fluid such as water, ethylene glycol or mineral oil and added solid nano-sized particles. They have been extensively used in different thermal engineering applications [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14]. The nano-sized particle could be metallic or non-metallic such as Cu, Ag, CuO, Al\({}_{2}\)O\({}_{3}\), TiO\({}_{2}\), SiO\({}_{2}\) with average particle size less than 100 nm. Higher thermal conductivity of the nanoparticles increase the thermal conductivity of the heat transfer fluid and enhances the thermal performance. Size, shape and type of the particles are effective for the thermal conductivity enhancement of nanofluids. Thermophysical properties are derived from theoretical or experimental studies for nanofluids containing various particle types, shapes and sizes for different temperatures. Generally, a small amount of particle addition of the base fluid results in higher heat transfer enhancements. Application of the nanofluids for the thermal engineering systems are diverse such as in refrigeration, microelectromechanical systems (MEMs), cooling of nuclear reactors, thermal management of fuel cells, cooling of hydrogen storage, heat exchangers and many others. In the refrigeration application, nano additives are added to compressor oil to increase the coefficient of performance. In some applications, solid nano particles are added to the refrigerants. In heat exchanger design, more compact and lightweight structures can be designed when heat transfer fluid has a higher thermal conductivity with the addition of nanoparticles. Application of nanotechnology in the field of renewable energy is growing. There are many studies related to the nanofluids application in solar power. A review for the application of the nanofluid in solar energy was presented in the study by [PERSON] et al. [15]. Using nanofluids in solar collectors and solar water heaters and their impacts on the efficiency and environmental effects were also discussed. [PERSON] et al. [16] performed analytical study for the performance of a solar collector with various types of nanofluids such as Cu/water, Al\({}_{2}\)O\({}_{3}\)/water, TiO\({}_{2}\)/water, and SiO\({}_{2}\)/water nanofluids with particle size of 25 nm. System with Cu/water nanofluid has lowest entropy generation rate whereas Al\({}_{2}\)O\({}_{3}\)/water nanofluid has the highest heat transfer coefficient as compared to other nanofluids. In the study by [PERSON] et al. [17], an experimental investigation was performed for a flat plate solar collector with SiO\({}_{2}\)/ethylene glycol (EG-water nanofluid. Various mass flow rates and particle volume fraction up to 1% were tested. It was observed that, despite the low conductivity of SiO\({}_{2}\) nanoparticles, solar collector efficiency was found to be enhanced with nanofluid. [PERSON] et al. [18] studied the effects of inclusion of Au nanoparticles for the photo-thermal conversion performance numerically and experimentally for various solar intensities and particle volume fractions. The absorption efficiency was found to increase with higher nanoparticle volume fractions. Effects of SiO\({}_{2}\) nanoparticles in solar collector tubes were numerically and experimentally studied by [PERSON] et al. [19]. Heat transfer rate was found to be higher for nanofluid and, due to nanofluid agglomeration, the heat transfer rate deteriorates for longer operation times. In the Photovoltaic/Thermal modules (PV/T), heat and electricity are produced by using photovoltaic and heat extraction units. A review study for the application of nanofluids in PV/T systems and discussions about effective parameters and effectiveness of nanofluids were presented in [20]. [PERSON] et al. [21] performed an experimental study for the determination of effective thermophycsci properties of water containing SiC nanoparticles that was used as a cooler for PV/T system.