International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 03 Issue: 06 | June-2016 www.irjet.net p-ISSN: 2395-0072 © 2016, IRJET | Impact Factor value: 4.45 | ISO 9001:2008 Certified Journal | Page 1709 Study of Heat Transfer Performance and Pumping Power Improvement of Nanofluid Through a Rough Circular Tube Mohammad Monjurul Ehsan 1 , Shafi Noor 2 Department of Mechanical and Chemical Engineering, Islamic University of Technology (IUT), Organisation of Islamic Cooperation, Gazipur, Bangladesh, Email- ehsan@iut-dhaka.edu, shafi@iut-dhaka.edu ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract -The higher thermal conductivity of solid nanoparticles is utilized in enhancing the overall thermal and hydrodynamic behavior of working fluid for optimum design of compact heat exchangers. The addition of nanoparticles in base fluid within a preferred volume fraction so called nanofluid provides superior thermo- physical properties compared to that of base fluid which finally assists in improving the overall heat transfer characteristics. In the present work, Al2O3-water nanofluid is employed in a rough circular tube subjected to constant heat flux to investigate the forced convection heat transfer characteristics and pumping power under turbulent flow condition. The study is performed for a wide range of Reynolds number- 10,000 to 30,000 with different volume fraction of nanoparticles (1% to 5%) and different relative roughness of pipe wall (0.001, 0.002 and 0.003). SST k-ω turbulence model for single phase analysis is adopted and finite volume method is employed for solving the transport equations (mass, momentum and energy) and turbulence quantities. The heat transfer rate is substantially enhanced by the implementation of nanofluid in rough tube compared to that of smooth tube with an increase of Reynolds number and volume fraction. Finally the optimum volume fraction of nanoparticles is determined for which nanofluid requires lower amount of pumping power compared to water. The reduction of mass flow rate for nanofluid is also calculated which results better thermal performance. Key Words:Nanofluid, heat transfer, pumping power, relative roughness, turbulent 1.INTRODUCTION This In recent years, in the field of sustainable energy, the implementation of nanofluid has been exploited tremendously in heat and mass transfer applications because of its extreme demand as an effective and suitable heat transfer fluid to reduce the size and material cost for designing compact heat exchangers. Nanofluid refers to the mechanism of stable and uniform suspension of solid metallic nanoparticles of size less than 100 nm in conventional base fluid like water, oil or ethylene glycol etc. The solid nanoparticles have higher thermal conductivity which potentially influences in enhancing the overall thermal and hydrodynamic characteristics of the working fluid [1-4]. To accomplish equivalent heat transfer rate, nanoparticles are dispersed in base fluid with low volume concentration which significantly change the thermo-physical properties of working fluid and eventually enhances the heat transfer rate [5, 6]. Numerous researches have been carried out with nanofluids employed in different geometries to enhance the heat transfer performance in many aspects of heat and mass transfer applications. Maiga et al. [7,8] investigated the forced convection heat transfer enhancement utilizing γ-Al2O3-water and γ-Al2O3- ethylene glycol nanofluids inside a uniformly heated circular tube under constant heat flux for both laminar and turbulent flow conditions. Heat transfer coefficients were augmented by the increase of Reynolds number and volume fraction. Finally a correlation was provided for mean Nusselt number in terms of Reynolds number and Prandtl number. Behzadmehr et al. [9] performed numerical investigation on turbulent heat transfer in a circular tube subjected to constant heat flux using Cu- water nanofluid with 1% volume fraction and multiphase approach was employed. Improvement of heat transfer coefficients was shown and results were compared with single phase. Zeinali et al. [10] experimented to observe the enhancement of heat transfer rate for laminar flow using Al2O3-water nanofluid through a circular pipe for a wide range of Peclet number 2,000 to 6,000 and volume fraction of 0.2% to 2.5%. Bianco et al. [11] reported improvement of Nusselt number of Al2O3 -water nanofluid in a circular tube with an increase of Reynolds number and volume fraction adopting both single and multiphase analysis. Laminar flow was considered for a range of Reynolds number 200 to 1200 and volume fraction 1% to 4%. Izadi et al. [12] studied numerically laminar forced convection in an annulus using Al2O3-water nanofluid to observe the heat transfer enhancement as well as the thermal and hydrodynamic behavior of fluid flow. Yurong et al. [13] worked on the heat transfer intensification of TiO2-water nanofluid through straight circular tube adopting both single phase and combined Euler and Lagrange method for laminar flow condition. Fotukian and Nasr [14] reported significant improvement of heat transfer and studied the pressure drop of CuO-water nanofluid through a circular tube for a range of Reynolds number of 5,000-33,000. Heat transfer coefficients were increased by 25% with a penalty of pressure drop 20%