**ABSTRACT**

The problem of free convection fluid flow and heat transfer in a square cavity with a flush mounted heat source on its bottom wall and two heat sinks on its vertical side walls has been investigated numerically. Via changing the location of the heat sinks, six different arrangements have been generated. The cavity was filled with Cu-water nanofluid. The governing equations were discretized using the finite volume method and SIMPLER algorithm. Using the developed code, a parametric study was undertaken, and effects of Rayleigh number, arrangements of the heat sinks and volume fraction of the nanoparticles on fluid flow and heat transfer inside the cavity were investigated. Also for the middle-middle heat sinks arrangement, capability of five different water based nanofluids on enhancement of the rate of heat transfer was examined and compared. From the obtained results it was found that the average Nusselt number, for all six different arrangements of the heat sinks, was an increasing function of the Rayleigh number and the volume fraction of the nanoparticles. Also it was found that at high Rayleigh numbers, maximum and minimum average Nusselt number occurred for middle-middle and top-bottom arrangement, respectively. Moreover it was found that for the middle-middle arrangement, at high Rayleigh numbers, maximum and minimum rate of heat transfer was obtained by Cu-water and TiO2-water nanofluids respectively.

**KEYWORDS**

PAPER SUBMITTED: 2011-04-06

PAPER REVISED: 2012-12-05

PAPER ACCEPTED: 2013-01-30

PUBLISHED ONLINE: 2013-04-13

**THERMAL SCIENCE** YEAR

**2014**, VOLUME

**18**, ISSUE

**Supplement 2**, PAGES [S283 - S300]

- Ostrach, S., Natural convection in enclosures, ASME J. Heat Transfer 110 (1988) 1175-1190.
- Choi, U.S., Enhancing thermal conductivity of fluids with nanoparticles, ASME FED, 231 (1995), pp. 99-105
- Kang, H.U., Kim, S.H., Oh, J.M., Estimation of thermal conductivity of nanofluid using experimental effective particle volume, Exp. Heat Transfer, 19 (2006), pp. 181-191.
- Velagapudi, V., Konijeti, R.K., Aduru, C.S.K., Empirical correlation to predict thermophysical and heat transfer characteristics of nanofluids, Thermal Science, 12 (2008), pp. 27-37.
- Turgut, A., Tavman, I., Chirtoc, M., Schuchmann, H. P., Sauter, C., Tavman, S., Thermal Conductivity and Viscosity Measurements of Water-Based TiO2 Nanofluids, Int J Thermophys, 30 (2009), pp. 1213-1226.
- Rudyak, V.Y., Belkin, A.A., Tomilina, E.A., On the Thermal Conductivity of Nanofluids, Technical Physics Letters, 36 (2010), pp. 660-662.
- Murugesan, C., Sivan, S., Limits for thermal conductivity of nanofluids, Thermal Science, 14 (2010), pp. 65-71.
- Nayak, A.K., Singh, R.K., Kulkarni, P.P., Measurement of Volumetric Thermal Expansion Coefficient of Various Nanofluids, Technical Physics Letters, 36 (2010), pp. 696-698.
- Khanafer, K., Vafai, K., Lightstone, M., Buoyancy-driven heat transfer enhancement in a two-dimensional enclosure utilizing nanofluid, Int. J. Heat Mass Tran., 46 (2003), pp. 3639-3653
- Santra, A.K., Sen, S., Chakraborty, N., Study of heat transfer augmentation in a differentially heated square cavity using copper-water nanofluid, Int. J. Thermal Sci., 47 (2008), pp. 1113-1122
- Oztop, H.F., Abu-Nada, E., Numerical study of natural convection in partially heated rectangular enclosures filled with nanofluids, Int. J. Heat Fluid Flow, 29 (2008), pp. 1326-1336
- Abu-nada, E., Oztop, H., Effect of inclination angle on natural convection in enclosures filled with Cu-Water nanofluid, Int. J. Heat Fluid Flow, 30 (2009), pp. 669-678
- Aminossadati, S.M., Ghasemi, B., Natural convection cooling of a localized heat source at the bottom of a nanofluid-filled enclosure, European Journal of Mechanic B/Fluids, 28 (2009), pp. 630-640
- Ghasemi, B., Aminossadati, S.M., Periodic natural convection in a nanofluid-filled enclosure with oscillating heat flux, Int. J. Thermal Sci., 49 (2010), pp. 1-9
- H. Saleh, R. Roslan, I. Hashim, Natural convection heat transfer in a nanofluid-filled trapezoidal enclosure, Int. J. Heat Mass Transfer 54 (2011) 194-201.
- G.A. Sheikhzadeh, A. Arefmanesh, M. Mahmoodi, Numerical Study of Natural Convection in a Differentially-Heated Rectangular Cavity Filled with TiO2-Water Nanofluid, Journal of Nano Research 13 (2011) 75-80.
- H.F. Oztop, E. Abu-Nada, Y. Varol, Kh. Al-Salem, Computational analysis of non-isothermal temperature distribution on natural convection in nanofluid filled enclosures, Superlattices and Microstructures, In Press.
- Abbasian Arani, A.A., Mahmoodi, M., Amini, M., Free convection in a nanofluid filled square cavity with an horizontal heated plate, Defect Diffusion Forum, 312-315 (2011) pp. 433-438
- Mahmoodi, M., Numerical simulation of free convection of nanofluid in a square cavity with an inside heater, Int. J. Thermal Sci., 50 (2011) pp. 2161-2175
- Mahmoodi, M., Numerical simulation of free convection of a nanofluid in L-shaped cavities, Int. J. Thermal Sci., 50 (2011) pp. 1731-1740
- Sourtiji, E., Hosseinizadeh, S.F., Heat transfer augmentation of magnetohydrodynamic natural convection in L-shaped cavities utilizing nanofluids, Thermal Sci., 16 (2012) pp. 489-501
- Nithyadevi, N., Kandaswamy, P., Lee, J., Natural convection in a rectangular cavity with partially active side walls, Int. J. Heat Mass Tran., 50 (2007), pp. 4688-4697
- Deng, Q.H., Fluid flow and heat transfer characteristics of natural convection in square cavities due to discrete source-sink pairs, Int. J. Heat Mass Tran., 51 (2008), pp. 5949-5957
- Sheikhzadeh, G.A., Arefmanesh, A., Kheirkhah, M.H., Abdollahi, R., Natural convection of Cu-water nanofluid in a cavity with partially active side walls, European Journal of Mechanics B/Fluids, 30 (2011), pp. 166-176
- Bejan, A., Convection heat transfer, John Wiley & Sons, Inc., Hoboken, New Jersey, USA, 2004.
- Brinkman, H.C., The viscosity of concentrated suspensions and solutions, J. Chem. Phys., 20 (1952), pp. 571-581
- Maxwell, J., A Treatise on Electricity and Magnetism, second ed. Oxford University Press, Cambridge, UK, 1904.
- Patankar, S.V., Numerical Heat transfer and fluid flow. Hemisphere Pub. Co. Washington. DC. 1980.
- Hoffman, J.D., Numerical methods for engineers and scientists. Second edition. Markel Dekker Inc, Newyork. 2001.
- Barakos, G., Mitsoulis, E., Natural convection flow in a square cavity revisited: laminar and turbulent models with wall fraction, Int. J. Numer. Methods Fluids 18 (1994), pp. 695-719
- Davis, G.V., Natural convection of air in a square cavity, a benchmark numerical solution, Int. J. Numer. Methods fluids 3 (1983), pp. 249-264
- Fusegi, T., Hyun, J.M., Kawahara, K., Farouk, B., A Numerical study of Tree-dimensional natural convection in a differentially heated cubical enclosure, Int. J. Heat Mass Tran., 34 (1991), pp. 1543-1557