Abstract—The effect of Alumina nanoparticle size on thermophysical properties, heat transfer performance and pressure loss characteristics of Aviation Turbine Fuel (ATF)-Al 2 O 3 nanofluids is studied experimentally for the proposed application of regenerative cooling of semi-cryogenic rocket engine thrust chambers. Al2O3 particles with mean diameters of 50 nm or 150 nm are dispersed in ATF. At 50 0 C and 0.3% particle volume concentration, the bigger particles show increases of 17% in thermal conductivity and 55% in viscosity, whereas the smaller particles show corresponding increases of 21% and 22% for thermal conductivity and viscosity respectively. Contrary to these results, experiments to study the heat transfer performance and pressure loss characteristics show that at the same pumping power, the maximum enhancement in heat transfer coefficient at 50 0 C and 0.3% concentration is approximately 47% using bigger particles, whereas it is only 36% using smaller particles. Keywords—Heat transfer performance, Nanofluids, Thermal conductivity, Viscosity I. INTRODUCTION ONVENTIONAL heat transfer fluids with dispersed ultra fine particles of nanometer size are called nanofluids [1]. Numerous experimental studies on water-Al 2 O 3 nanofluids have shown significant enhancement in thermal conductivity and heat transfer performance when nanofluids are used. Chandrasekar et al. [2] measured 9.7% enhancement in thermal conductivity for water- Al 2 O 3 nanofluids with a particle volume concentration of 3%. Yoo et al. [3] obtained an enhancement of 4% in the thermal conductivity of water- Al 2 O 3 nanofluids at 1% particle volume concentration. Wang et al. [4] measured an enhancement of 16% in the thermal conductivity of water-Al 2 O 3 nanofluids at 5.5% particle volume concentration. Das et al. [5] found that the thermal conductivity of nanofluids increases with increasing temperature as well as with increasing particle concentration. They obtained an enhancement of 9.4% in the thermal conductivity at 21ºC and an enhancement of 24.3% at 51ºC for water-Al 2 O 3 nanofluids at 4% volume concentration of nanoparticles. In order to use nanofluids as working fluids for practical applications in the turbulent regime, the heat transfer performance and pressure loss characteristics have also been investigated by several researchers [6]-[9]. Heat transfer and Sandipkumar Sonawane, Upendra Bhandarkar and Bhalchandra Puranik are with the Mechanical Engineering Department, Indian Institute of Technology, Bombay, Mumbai 400076 India (phone: +91-22-25764533; fax: +91-22-25726875; e-mail: sandipsonawane@iitb.ac.in). S. Sunil Kumar is with Liquid Propulsion Systems Center, Indian Space Research Organization (ISRO), Valiamala 695547 India (e-mail: sunil_plamood@yahoo.com). fluid flow characteristics of water-Al 2 O 3 and water-TiO 2 nanofluids were experimentally investigated by Pak and Cho [6]. Their experimental results showed that the Nusselt number of a nanofluid increases with an increase in the Reynolds number as well as with an increase in the particle concentration up to 3%. They proposed a heat transfer correlation for the determination of the heat transfer coefficient for the nanofluids based on their experimental results. Xuan and Li [7] experimentally studied the convective heat transfer performance and fluid flow characteristics for water-Cu nanofluids flowing in a straight tube under laminar and turbulent flow conditions. They obtained an enhancement of 39% in the heat transfer coefficients using nanofluids at 2% concentration by volume. Xuan and Li proposed a correlation for the determination of the heat transfer coefficient based on their results. Duangthongsuk and Wongwises [8] obtained 26% enhancement in the heat transfer coefficient at 1% particle volume concentration using water-TiO 2 nanofluids flowing in a horizontal double tube heat exchanger under turbulent flow conditions. Farajollahi et al. [9] investigated heat transfer characteristics of water-Al 2 O 3 and water-TiO 2 nanofluids flowing in a shell and tube heat exchanger under turbulent flow conditions. The experimental results for both nanofluids showed that the heat transfer characteristics of nanofluids significantly improve with Peclet number. The objective of the present study is to investigate the effect of particle size on heat transfer performance of ATF- Al 2 O 3 nanofluids for its potential application of regenerative cooling of the thrust chambers of semi-cryogenic rocket engines. Semi-cryogenic rocket engines use ATF as the fuel and liquid oxygen as the oxidizer. The fuel is usually used to regeneratively cool the combustion chamber wall before it is introduced inside the chamber. For better regenerative heat transfer performance of the ATF it is proposed to add Al 2 O 3 nanoparticles to it. II. NANOFLUID PREPARATION A stable ATF-Al 2 O 3 nanofluid is prepared using a two-step method [10]. Al 2 O 3 nanoparticles with average particle size 50 nm and 150 nm are obtained commercially (Nanostructured & Amorphous Materials Inc., USA). Oleic acid and ‘Tween’ 20 LR are used as surfactants to reduce the tendency of agglomeration of nanoparticles in the base fluid. Several trials are carried out to decide the appropriate concentration of surfactants to be used to obtain a stable nanofluid solution. It is found that the nanofluid with Al 2 O 3 particles of size 150 nm Effect of Particle Size in Aviation Turbine Fuel-Al 2 O 3 Nanofluids for Heat Transfer Applications Sandipkumar Sonawane, Upendra Bhandarkar, Bhalchandra Puranik, S. Sunil Kumar C World Academy of Science, Engineering and Technology 57 2011 548