Thermal characteristics and performance of Ag-water nanofluid: Application to natural circulation loops

• Published in: Energy conversion and management Vol. 135; pp. 9 - 20
• Main Authors: Koca, Halil Dogacan, Doganay, Serkan, Turgut, Alpaslan
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.03.2017; Elsevier Science Ltd
• Subjects: Ag-water nanofluid; Ambient temperature; Conductivity; Dilution; Effectiveness; Flat-plate solar collectors; Fluid dynamics; Heat transfer; Inclination angle; Nanofluids; Polyvinylpyrrolidone; PVP; Silver; Solar collectors; Studies; Temperature; Thermal conductivity; Viscosity; Water circulation; Working fluids; Viscosity; Thermal conductivity; Effectiveness; PVP; Ag-water nanofluid; Flat-plate solar collectors
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2016.12.058

•Thermal conductivity and viscosity of Ag-water nanofluid were measured.•Thermal performance of Ag-water nanofluid was compared with water.•Effectiveness enhanced up to 11% with 1wt% Ag-water nanofluid.•Effectiveness of Ag-water nanofluid samples increased with inclination angle.•Ag-water nanofluid has potential to be used in flat-plate solar collectors. The goal of this study is to investigate the thermal conductivity, viscosity and thermal performance in a single-phase natural circulation mini loop of Ag-water nanofluid which can be a potential working fluid for natural convective flat-plate solar collectors. The silver-water nanofluid with 5wt% concentration, which contains also polyvinylpyrrolidone (PVP) with 1.25wt%, was purchased. Then, the sample was diluted with de-ionized water to four different concentrations of 0.25, 0.5, 0.75 and 1wt%. Thermal conductivity and viscosity were measured by 3ω method and Brookfield rheometer, respectively. An effectiveness factor was used to define the thermal performance of Ag-water nanofluids for different inclination angles and heating powers. The results showed that nanofluid samples are thermally less conductive than the literature, at ambient temperature (23°C). The viscosity of nanofluid decreases significantly with increasing temperature and increases with increasing concentration. Our measurements appear to be more compatible with PVP solution results available in the literature. Effectiveness is enhanced up to 11% with 1wt% concentrated nanofluid compared to de-ionized water and the effectiveness of the mini loop indicates an enhancement with increase in inclination angle and particle concentration at whole applied power. According to obtained results, it is concluded that Ag-water nanofluid has a promising potential to be used in natural convective flat-plate solar collector.