## THERMAL SCIENCE

International Scientific Journal

### NUMERICAL STUDY OF MIXED CONVECTION HEAT TRANSFER IN LID-DRIVEN CAVITY UTILIZING NANOFLUID: EFFECT OF TYPE AND MODEL OF NANOFLUID

**ABSTRACT**

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 ≤ φ ≤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.

**KEYWORDS**

PAPER SUBMITTED: 2012-07-18

PAPER REVISED: 2013-05-14

PAPER ACCEPTED: 2013-05-14

PUBLISHED ONLINE: 2013-06-01

**THERMAL SCIENCE** YEAR

**2015**, VOLUME

**19**, ISSUE

**Issue 5**, PAGES [1575 - 1590]

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