International Conference on Mechanical Engineering Research (ICMER2013), 1-3 July 2013 Bukit Gambang Resort City, Kuantan, Pahang, Malaysia Organized By Faculty of Mechanical Engineering, Universiti Malaysia Pahang Paper ID: P253
NUMERICAL INVESTIGATION OF TURBULENT FORCED CONVECTION FLOW IN THE HORIZANTAL TUBES HAVING CONSTANT HEAT FLUX O. Bedir, A. Bolukbasi1* and B. Sahin1 1
Faculty of Mechanical Engineering, Ataturk University, 25240 Erzurum, Turkiye * Email:
[email protected] ABSTRACT
In this study, the turbulent forced flow of nanofluids on convective heat transfer in a circular tube has been studied numerically. Nanofluids consist of CuO (dp=33 nm) and Al2O3 (dp=47 nm) particles in water. Single phase and two-phase mixture model have been implemented. The comparison is made between calculated and experimental results. Calculated convective heat transfer coefficient for nanofluids is higher than the base liquid. Heat transfer augmentation increases with the Reynolds number and nanoparticle volume fraction. The nanofluids containing CuO has showed bigger heat transfer enhancement than Al2O3. Keywords: Nanofluids; heat transfer; convection; nanoparticles. INTRODUCTION Conventional heat transfer fluids such as water, engine oil and ethylene glycol are normally used as heat transfer fluids. Since these conventional fluids have low heat transfer performance the heat transfer enhancement is limited with these conventional fluids. The use of solid particles as an additive suspended into the base fluid is a technique for the heat transfer enhancement. Innovative heat transfer fluids with nanoparticules suspended in them are called “nanofluids”. Many researchers studied experimental and numerical investigations on convectional heat transfer of nanofluids (Behzadmehr et al., 2007; Akbarinia et al., 2007; Akbarinia, 2008; Akbarinia et al., 2009; Akbari et al., 2011; Mirmasoumi et al., 2008; Bianco et al., 2009; Lotfi et al., 2010; Ghaffari et al., 2010; Fard et al., 2010; Mokmeli et al., 2010; Allahyari et. al., 2011; Moghari et al., 2011). In this study single phase and mixture model have been applied to study heat transfer turbulent forced convection flow of nanofluids in a uniformly heated tube. Nanofluids consist of water and CuO with 33 nm and Al2O3 with 47 nm mean diameter. Two-dimensional axisymmetric steady simulation has been considered. The CFD code (Fluent 6.3) was used for simulation. The horizontal circular tube has a diameter of 0.0115 m and a length of 0.77 m. The numerical results were compared with the theoretical and experimental data. MATHEMATICAL MODEL Governing equations Figure 1 shows the figure of present simulation. The simulation is a two-dimensional (axisymmetric) steady forced turbulent convection flow of nanofluids. The nanofluid is
behaved as a normal fluid in the single phase model. Properties of the nanofluids are computed by adding nanoparticles.
Figure 1. Geometry figure used in present study, axisymmetric from x-axis. The mixture model is based on a single fluid two phase approach. Each phase has its own velocity and own volume fraction. The dimensional equations are independent from the time. The following formulation presents mixture model governing equations (Behzadmehr et al., 2007; Akbarinia et al., 2009; Akbarina et al., 2008): Continuity equation:
.( mVm ) 0
(1)
Momentum equation: n .( mVmVm ) pm .( t ) m g . k kVdr,kVdr,k k 1
(2)
Energy equation: n
. kVk ( k hk p) (keff T C p m vt)
(3)
k 1
Volume fraction: .( p pVm ) .( p pVdr, p )
(4)
Vdr,k is the drift velocity for secondary phase velocity. V pf is slip velocity(relative
velocity). V f is primary phase and V p is secondary phase velocity. Vdr,k Vk Vm ,
mVm ,
n
t k k vk vk ,
Vpf Vp V f
(5)
k 1
Vdr, p is the drift velocity related to the relative velocity( V pf ) is given by (Manninen et al.,
1996).
V pf k k V fk , k 1 m n
Vdr, p
0.687 1 0.15 Re p f drag 0.0183 Re p
pd p2 ( p m) V pf a 18 f f drag p
Re p 1000 , Re p 1000
a g (Vm .)Vm
(6)
(7)
There are also other drag correlations in the literatures (Clift and Gauvin, 1970; Ossen, 1913; Proudman and Pearson, 1957). But the drag function given by (Schiller and Naumann, 1935) is quite simple and accurate for Rep
