**ABSTRACT**

The present study aims to evaluate the mixed convection flow and heat transfer of functionalized DWCNT/Water nanofluids with variable properties in a cavity having hot baffles. The investigation is performed at different nanoparticles volume fraction including 0, 0.0002, 0.001, 0.002, and 0.004, Richardson numbers ranging from 0.01 to 100, inclination angles ranging from 0 to 60° and at constant Grashof number of 104. The results presented as streamlines and isotherms plot and Nusselt number diagrams. According to the finding with increasing nanoparticles volume fraction and distance between the left hot baffles of nanoparticles average Nusselt number enhances for all considered Richardson numbers and cavity inclination angles. Also with increasing Richardson number, the rate of changes of average Nusselt number increase with increasing distance between the left hot baffles. For example, at Richardson number of 0.01, by increasing L1 from 0.4 to 0.6, the average Nusselt number increases 7%; while for similar situation at Richardson number of 0.1, 1.0 and 10, the average Nusselt number increases respectively 17%, 24% and 26%. At all Richardson numbers, the maximum value of average Nusselt number is achieved for a minimum length of left baffles.

**KEYWORDS**

PAPER SUBMITTED: 2016-02-25

PAPER REVISED: 2016-08-09

PAPER ACCEPTED: 2016-08-17

PUBLISHED ONLINE: 2016-09-05

- Haddad, Z., Oztop, H.F., Abu-Nada, E., Mataoui, A., A review on natural convective heat transfer of nanofluids, Renewable and Sustainable Energy Reviews, 16 (2012), pp.5363-5378.
- Huminic, G., Huminic, A., Application of nanofluids in heat exchangers: A review, Renewable and Sustainable Energy Reviews, 16 (2012), pp.5625-5638.
- Mohammed, A.H., Bhaskaran, G., Shuaib, N.H., Saidur, R., Heat transfer and fluid flow characteristics in microchannels heat exchanger using nanofluids: A review, Renewable and Sustainable Energy Reviews, 15 (2011), pp.1502-1512.
- Talebi, F., Mahmoudi, A.H., Shahi, M., Numerical study of mixed convection flows in a square liddriven cavity utilizing nanofluid, International Communication in Heat and Mass Transfer, 37 (2010), pp.79-90.
- M.A. Mansour, M.A., Mohamed, R.A., Abd-Elaziz, M.M., Ahmed, S.E., Numerical simulation of mixed convection flows in a square lid-driven cavity partially heated from below using nanofluid, International Communication in Heat and Mass Transfer, 37 (2010), pp.504-1512.
- Ghasemia, B., Aminossadati, S.M., Mixed convection in a lid-driven triangular enclosure filled with nanofluids, International Communication in Heat and Mass Transfer, 37 (2010), pp.1142-1148
- Abbasian Arani, A.A., Mazrouei Sebdani, S., Mahmoodi, M., Ardeshiri, A., Aliakbaria, M., Numerical study of mixed convection flow in a lid-driven cavity with sinusoidal heating on sidewalls using nanofluid, Superlattices and Microstructures, 51(2012), pp.893-911
- Salari, M., Mohammad Tabar, M., Mohammad Tabar, A., Ahmadi Danesh, H., Mixed convection of nanofluid flows in a square lid-driven cavity heated partially from both the bottom and side walls, Numerical Heat Transfer, Part A 62 (2012), pp.158-177
- Chamkha, A.J., Abu-Nada, E., Mixed convection flow in single- and double-lid driven square cavities filled with water-Al2O3 nanofluid: Effect of viscosity models, European Journal of Mechanics B/Fluids, 36 (2012), pp.82-96.
- Sheikhzadeh, G.A., Ebrahim Qomi, M., Hajialigol, N., Fattahi, A., Numerical study of mixed convection flows in a lid-driven enclosure filled with nanofluid using variable properties, Results in Physics, 2 (2012), pp.5-13.
- Abu-Nada, E., Chamkha, A.J., Mixed convection flow of a nanofluid in a lid-driven cavity with a wavy wall, International Communications in Heat and Mass Transfer, 57 (2014), pp.36-47.
- Sun, C., Yu, B., Oztop, H.F., Wang, Y., Wei, J., Control of mixed convection in lid-driven enclosures using conductive triangular fins, International Journal of Heat and Mass Transfer, 54 (2011), pp.894-909.
- Hemmat Esfe, M., Abbasian Arani, A.A., Karimipour, A., Mirtalebi Esforjani, S.S., Numerical simulation of natural convection around an obstacle placed in an enclosure filled with different types of nanofluids, Heat Transfer Res, 45 (2014), pp.279-292.
- Ray, S., Chatterjee, D., MHD mixed convection in a lid-driven cavity including heat conducting circular solid object and corner heaters with Joule heating, International Communications in Heat and Mass Transfer, 57 (2014), pp.200-207.
- Kalteh, M., Javaherdeh, K., Azarbarzin, T., Numerical solution of nanofluid mixed convection heat transfer in a lid-driven square cavity with a triangular heat source, Powder Technology, 253 (2014), pp.780-788.
- Hemmat Esfe, M., Akbari, M., Karimipour, A., Afrand, M., Mahian, O., Wongwises, S., Mixed-convection flow and heat transfer in an inclined cavity equipped to a hot obstacle using nanofluids considering temperature-dependent properties, International Journal of Heat and Mass Transfer, 85 (2015), pp.656-666.
- Aghaei, A., Khorasanizadeh, H., Sheikhzadeh, Gh. A., Abbaszadeh, M., Numerical study of magnetic field on mixed convection and entropy generation of nanofluid in a trapezoidal enclosure, Journal of Magnetism and Magnetic Materials, 403, (2016), pp. 133-145.
- Arefmanesh, A., Aghaei, A.,Ehteram, H., Mixed convection heat transfer in a CuO-water filled trapezoidal enclosure, effects of various constant and variable properties of the nanofluid, Applied Mathematical Modelling, 40, (2016), pp. 815-831.
- Hussein, A., Ahmed, S., Mohammed, H., Khan,W., Mixed convection of water-based nanofluids in a rectangular inclined lid-driven cavity partially heated from its left side wall , Journal of Computational and Theoretical Nanoscience, 10, (2013), pp. 2222-2233.
- Ahmed, S., Mansour, M., Hussein, A., Sivasankaran, S., Mixed convection from a discrete heat source in enclosures with two adjacent moving walls and filled with micropolar nanofluids , Engineering Science and Technology - an International Journal, 19, (2016), pp. 364-376.
- Hemmat Esfe, M., Saedodin, S., Mahian, O., Wongwises, S., Heat transfer characteristics and pressure drop of of COOH-funct onal zed DWC Ts/water nanoflu d n turbulent flow at low concentrations, International Journal of Heat and Mass Transfer, 73, (2014), pp.186-194.
- Abdul Hakeem, A.K., Saravanan, S., Kandaswamy, P., Buoyancy convection in a square cavity with mutually orthogonal heat generating baffles, International Journal of Heat and Fluid Flow 29 (2008) 1164-1173.
- Kandaswamy, P., Lee J., Abdul Hakeem, A.K., Saravanan, S., Effect of baffle-cavity ratios on buoyancy convection in a cavity with mutually orthogonal heated baffles, International Journal of Heat and Mass Transfer 51 (2008) 1830-1837.
- Famouri, M., Hooman, K., Entropy generation for natural convection by heated partitions in a cavity, International Communications in Heat and Mass Transfer 35 (2008) 492-502.
- Mansour, M.A., Mohamed, R.A., Abd-Elaziz, M.M., Ahmed, S.E, Numerical simulation of mixed convection flows in a square lid-driven cavity partially heated from below using nanofluid, International Communications in Heat and Mass Transfer 37 (2010) 1504-1512.
- Tiwari, R.K., Das, M.K., Heat transfer augmentation in a two-sided lid-driven differentially heated square cavity utilizing nanofluids, International Journal of Heat and Mass Transfer 50 (2007) 2002-2018.
- Abu-Nada, E., Chamkha, A.J., Mixed convection flow in a lid-driven inclined square enclosure filled with a nanofluid, European Journal of Mechanics B/Fluids 29 (2010) 472_482.