Özet:

In this study, developing laminar flow and heat transfer behaviour of ethylene glycol (EG) and water mixture based SiO2 nanofluids in an annulus have been numerically investigated. A constant heat flux was applied to the inner walls of the annulus with 100 W / m2. Water 100% - EG 0%, water 50% - EG 50% and water 0% - EG 100% mixtures have been utilized as the base fluids. SiO2 nanoparticles have been used with d = 20 nm and volume fractions ϕ =0%-4%. The Reynolds number varies from 200 to 1000. The physical model of the test section mainly consists of two concentric horizontal cylinders that form an annular space ranging from two interconnected elliptical tubes with axis ratio (r1/r2=1/2) placed at the centre of a circular cylinder with major radius of 2r2 with the length of 1 m. Governing equations have been solved with Ansys Fluent programme. The velocity distribution, temperature contours, average Nusselt number and thermal-hydraulic performance have been analysed and presented. The effects of nanofluids have been examined on heat and flow fields and it has been observed that the heat transfer increases together with the nanoparticle volume concentration. When the nanofluid is used in a forced convection, the amount of heat transfer increases as the Reynolds number increases. The highest value of the average Nusselt number was obtained in the EG based nanofluid with ϕ=4% and Re=1000 as 29.14, and the lowest value was obtained in the water-based nanofluid with ϕ=4% and Re=200 as 5.61. Results show that the use of nanofluid in the annulus channel increases the thermal performance of systems.

Anahtar Kelimeler: