Numerical investigation of the laminar mixed convection in two-dimensional
lid driven cavity filled with water-Al2O3, water-Cu or water-TiO2 nanofluids
is done in this work. In the present study, the top and bottom horizontal
walls are thermally insulated while the vertical walls are kept at constant
but different temperatures. The governing equations are given in term of the
stream function-vorticity formulation in the non-dimensionalized form and
then solved numerically by second-order central difference scheme. The
thermal conductivity and effective viscosity of nanofluid have been
calculated by Maxwell-Garnett and Brinkman models, respectively. An excellent
agreement between the current work and previously published data on the basis
of special cases are found. The governing parameters are Rayleigh number 103
? Ra ? 106 and solid concentration 0 ? ? ?0.2 at constant Reynolds and Prandtl
numbers. An increase in mean Nusselt number is found as the volume fraction
of nanoparticles increases for the whole range of Rayleigh numbers. In
addition, it is found that significant heat transfer enhancement can be
obtained by increasing thermal conductivity coefficient of additive
particles. At Ra=1.75?105, the Nusselt number increases by about 21% for
TiO2-Water, and almost 25% for Al2O3-Water, and finally around 40% for
Cu-Water nanofluid. Therefore, the highest values are obtained when using Cu
nanoparticles. The result obtained using variable thermal conductivity and
variable viscosity models are also compared to the results acquired by the
Maxwell-Garnett and the Brinkman model.
This research presents a numerical study on heat transfer and flow characteristics for two pipe fitted by two different dimpled spiral center plate by utilizing Al 2 O 3 , CuO and TiO 2 nanofluids as cooling fluids. Considering the effect of dimples arrangement, nanoparticle diameter d p , nanofluids volume fraction φ and also the heat transfer coefficient, thermal property. Average amount of entropy generation S a and maximum local temperature of wall T max were discussed. Results demonstrate that the in-line arrangement geometry behaves better in compare to the geometry with the staggered arrangement. 47.3% is the maximum enhancement of convection heat transfer for the in-line arrangement in compare with the smooth spiral central plate with base flow. Using nanofluids improved the wall temperature distribution, and using nanofluid caused great improvement in thermal conductivity with a little raise in dynamic viscosity. Using nanofluids caused a considerable decrease in S a , which also as the result of rising φ, and S a maximum reduction is about 24.7%. T max considerably declines by using nanofluids and enhanced by a rising φ. Also, CuO-water nanofluid has a better effect on heat transfer and flow characteristics than the other nanofluids.
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