Abstract

Natural convection heat transfer enhancement by utilizing various nanofluids (Ag, Cu and TiO2)flow in a three – dimensional horizontal and an inclined annulus with two heated fins attached on the inner cylinder have been studied numerically .The inner cylinder and two fins are maintained at constant wall temperature (CWT), while the outer cylinder is diathermal (adiabatic). The problem was solved numerically using Alternating Direction Implicit (ADI) method.The numerical results represent streamlines, isotherms, Local Nusselt number around inner cylinder and fins surfaces, axial profile of the peripheral average Nusselt number and average skin friction coefficient. The two types of nanoparticles used in this study metallic silver(Ag), copper (Cu) and nonmetallic titanium oxide (TiO2). This study indicating to the effect the Rayleigh number, volume fraction, fin length, fin inclination angles and annulus inclination angles. The numerical results show that as the solid volume fraction increases, the heat transfer is enhanced for all values of Rayleigh number. This enhancement is more significant at high Rayleigh number. The lowest heat transfer was obtained for TiO2 (50 nm) due to domination of conduction and large nanoparticles .whereas Ag (20 nm), Cu (30 nm) – distilled water nanofluids has the highest heat transfer, respectively. As well as the enhancement in heat transfer of nanofluids for annulus with fins attached to the inner cylinder at (5 %) volume concentration of (Ag , Cu and TiO2 ) nanoparticles increases (41.5 %, 35%,19 %) respectively compared with the base fluid (distilled water). The average Nusslet number increases with increasing both Rayleigh number and the volume fraction of nanoparticles. The average Nusselt number decreases by increasing fins' length. Moreover the increase of the average Nusslet number is attributed to the increase of the thermal conductivity of nanofluid with increasing the volume fraction of the nanoparticles

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The article was added to IASJ on 2015-08-04

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