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Öğe Thermal performance enhancement of flat-plate solar collectors by means of three different nanofluids(Elsevier, 2018-12) Budak Ziyadanoğulları, Neşe; Yıldız, Cengiz; Yücel, Halit LutfiSolar energy, which comes first among renewable energy sources, enables efficient use of energy with many applications due to its low operating cost and environmental friendliness. In this study, we experimentally investigated the effects on thermal efficiency of nanofluid and water as working fluids in flat-plate solar collector hot water solar energy systems. Nanofluids were prepared by adding Al2O3, CuO, and TiO2 nanoparticles at 0.2, 0.4, and 0.8 vol% into distilled water, and then the thermophysical properties (thermal conductivity, viscosity) of the prepared nanofluids were determined. Flow rate was adjusted to 250 l/h at given concentrations for each nanofluid in the experimental setups and data such as collector inlet and outlet temperatures, ambient and tap water temperatures; radiation, humidity, and wind speed were measured and recorded. The obtained data were used to calculate efficiencies according to ASHRAE 93-2003 standards. When compared with water, the results indicated that the use of nanofluid increased collector efficiency.Öğe Experimental investigation of thermal performance in a concentric tube heat exchanger with wavy inner pipe(SpringerLink, 2012-06) Argunhan, Zeki; Çakmak, Gülşah; Yücel, Halit Lutfi; Yıldız, CengizIn this article, the heat transfer, friction factor, and thermal performance factor characteristics of a concentric-tube heat exchanger are examined experimentally. A wavy inner pipe is mounted in the tube with the purpose of generating swirl flow that would help to increase the heat transfer rate of the tube. The examination is performed for a Reynolds number ranging from 2700 to 8800. An empirical correlation is also formulated to match with experimental data of the Nusselt number using the Wilson plot method. In addition, to obtain the real benefits in using the swirl generator at a constant pumping power, the thermal enhancement factor is also determined. Over the range considered, the increases in the Nusselt number, friction factor, and thermal performance factor are found to be, respectively, about 113 %, 81 %, and 196 % higher than those obtained from a smooth-surface inner pipe.
