Document Type: Original Research Paper

**Authors**

Mechanical engineering Department, university of Kashan, Kashan, I.R. Iran

**Abstract**

Natural convection heat transfer has many applications in different fields of industry; such as cooling industries, electronic transformer devices and ventilation equipment; due to simple process, economic advantage, low noise and renewed retrieval. Recently, heat transfer of nanofluids have been considered because of higher thermal conductivity coefficient compared with those of ordinary fluids. In this study; natural convection and entropy generation in a triangular enclosure filled by Al_{2}O_{3 }–water nanofluid affected by magnetic field considering Brownian motion is investigated numerically. Two inclined walls are maintained at constant cold temperature (T_{c}) while the bottom wall is kept at constant high temperature (T_{h}) with (T_{h}>T_{c}). In order to investigate natural convection, a computer program (FORTRAN language) based on finite volume method and SIMPLER algorithm has been used. Analyses is performed for volume fraction of nanoparticles 0, 0.02, 0.04, Hartmann number 0, 50,100, Rayleigh numbers 10^{3},10^{4},10^{5} and angle of inclined walls 45^{0}. In investigated angles and Rayleigh numbers; average Nusselt number is increased by enhancement of volume fraction of nanoparticles in a fixed Hartmann number. It is also observed that total entropy generation variations by increasing volume fraction of nanoparticles is similar to that of Nusselt number. By the results; effect of friction is always insignificant on generated entropy. It is observed that natural convection of nanofluid is decreased by enhancement of Hartmann number and its behavior is close to thermal conduction. It is also concluded that average Nusselt number and total generated entropy are decreased.

**Keywords**

[1] B. Ghasemi, S.M. Aminossadati, Mixed convection in a lid-driven triangular enclosure filled with nanofluids, Int. Commun. in Heat Mass Transfer 37 (2010) 1142–1148.

[2] CJ. Ho, MW. Chen, ZW. Li, Numerical simulation of natural convection of nanofluid in a square enclosure: effects due to uncertainties of viscosity and thermal conductivity, Int. J. Heat Mass Transfer 51 (2008) 4506–4516.

[3] H. Oztop, E. Abu-Nada, Numerical study of natural convection in partially heated rectangular enclosures filled with nanofluids, Int. J. Heat Fluid Flow, 29, (2008),1326–1336.

[4] M. Mahmoodi, S.S. Hashemi, Numerical study of natural convection of a nanofluid in C-shaped enclosures, Int. J. Thermal Sciences 55 (2012) 76-89.

[5] A. Bejan, Second law analysis in heat transfer, Energy 5 (1980) 721-732.

[6] O. Mahian, S. Mahmud, I. Pop, Analysis of first and second laws of thermodynamics between two isothermal cylinders with relative rotation in the presence of MHD flow, Int. J. Heat Mass Transfer 55 (2012) 4808-4816.

[7] E. Dagtekin, H.F. Oztop, A. Bahloul, Entropy generation for natural convection in Γ-shaped enclosures, Int. Commun. Heat Mass Transfer 34 (2007) 502–510.

[8] G.G. Ilis, M. Mobedi, B. Sunden, Effect of aspect ratio on entropy generation in a rectangular cavity with differentially heated vertical walls, Int. Commun. Heat Mass Transfer 35(2008) 696–703.

[9] Y. Varol, H.F. Oztop, A. Koca, Entropy generation due to conjugate natural convection in enclosures bounded by vertical solid walls with different thicknesses, Int. Commun. Heat Mass Transfer 35 (2008) 648–656.

[10] A. A. Abbasian Arani, J. Amani, Experimental study on the effect of TiO2–water nanofluid on heat transfer and pressure drop, Experiment. Thermal Fluid Science 42 (2012) 107-115.

[11] A. A. Abbasian Arani, J. Amani, Experimental investigation of diameter effect on heat transfer performance and pressure drop of TiO2–water nanofluid, Experiment. Thermal Fluid Science 44 (2013) 520-533.

[12] E. Abu-Nada, Z. Masoud, A. Hijazi, Natural convection heat transfer enhancement in horizontal concentric annuli using nanofluids, Int. Commun. Heat Mass Transfer 35(2008) 657–665.

[13] A. Bejan, Entropy Generation Minimization, CRC Press New York (1995).

[14] H.C. Brinkman, The viscosity of concentrated suspensions and solution”, J. Chemical Physics 20 (1952) 571–581.

[15] J.C. Maxwell-Garnett, Colours in metal glasses and in metallic films, Philos, Trans. Roy. Soc. A 203 (1904) 385-420.

[16] J. Koo, C. Kleinstreuer, a new thermal conductivity model for nanofluids”, J.Nanoparticle Research 6 (2004) 577–588.

[17] J. Li, C. Kleinstreuer, Thermal performance of nanoﬂuid ﬂow in microchannels, Int. J. Heat Fluid Flow 29 (2008) 1221–1232

Volume 3, Issue 1

Winter and Spring 2015

Pages 37-45