DİK KONSANTRİK SİLİNDİRLER ARASINDAKİ AL2O3-ETİLEN GLİKOL VE SU KARIŞIM BAZLI NANOAKIŞKANLARIN DOĞAL KONVEKSİYONU

Abstract

Natural convection of ethylene glycol (EG) and water mixture based Al2O3 nanofluids between vertical concentric circular cylinders heated from the inner wall and cooled from the outer wall was investigated numerically in this study. The computations were carried for the Rayleigh numbers of 104, 105, 106, and 107, nanoparticle volume fractions of 0%, 4% and 8%, ethylene glycol (EG) to water volume ratios of 0:100 %, 50:50%, and 100:0%, the radius ratios of 2, 3 and 4, and aspect ratios of 0.5, 1, and 2. The Brinkman model was used to predict the viscosity and the Yu and Choi model for the thermal conductivity of nanofluid. The results show that the average Nusselt number shows a considerable increase with an increase in the Rayleigh number and radius ratio. The results also show that the average Nusselt number shows a medium increase with increasing nanoparticle volume fraction and a slight increase with increasing volume ratios of EG to water. Furthermore, the results show that the average Nusselt number experiences first an increase then a decrease with an increase in the aspect ratio except for the low Ra numbers. Finally, the average Nusselt number experiences a slight increase with the aspect ratio for the low Rayleigh numbers.