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International Journal of Engineering and Technology (IJET) – Volume 3 No. 2, February, 2013 Properties of Nanofluids The coil had a stretched length of 4.073m. The effects of different parameters such as Reynolds number, fluid temperature, nanofluid particle concentration on the heat transfer and pressure drop were observed. The nanofluids were dispersed uniformly by ultrasonic processor generating ultrasonic pulses of 400W at 24KHz frequency. The heat transfer enhancement of about 18.7% and 30.4% were observed with the basefluid for the case of straight tube and helical tube respectively. TEM photographs of Au, Al2O3, TiO2 and CuO particles and carbon nanofiber S. Zeinali Heris et al [10] performed experimental investigation of convective heat transfer of alumina/water nanofluid in circular tubes. The test section consists of 6 mm diameter tube of 1m length with 0.5 mm thickness. Nanofluids flows inside the tubes while saturated steam entered the annulas section in order to maintain the constant wall temperature. The Nusselt number were obtained for the different particle concentration as well as various Peclet and Reynolds number. The experimental results were compared to the theoretical values by the use of Seider-Tate equation. The increase in the heat transfer rate is due to the higher thermal conductivity of the nanoparticles. Some other factors are dispersion and chaotic movements of nanoparticles. The Brownian motion and migration of the particles plays an importangiven twist rt role in the heat transfer enhancement. S.Suresh et al. [11] compared the thermal characterstics of Al2 O3 / water and CuO/ water nanofluid in transition flow through straight tube fitted with helical screw taper inserts. The twist ratio in screw tape inserts were 1.78, 2.44, 3. Using 0.1% volume concentration for both the Particle Mean Diameter (nm) Al2O3 20 TiO2 10 Fe3O4 36 Density Thermal Sp.Heat Kg/m3 Conductivity (J/gm-K) w/m-K 3700 46 880 3840 11.7 710 5180 80.4 670 M.Saeedinia et al. [7] studied heat transfer and pressure drop of nanofluids flow in horizontal coiled wire inserted tube at constant heat flux. The nanofluid is prepared by dispersion of CuO in base oil. Particles volume fraction ranging from 0.07% to 0.3% is used. Five coiled wires having pitch of 25-35 mm and wire diameter 0.9-1.5 mm were put one by one in the test section. Effects of different parameters such as Reynolds number, wire diameter, coil pitch, particle concentration were studied. Results shows that the increase in 45% for heat transfer coefficient and penalty of 63% in the pressure drop was observed for the coiled tubes. Nanofluids have better heat transfer performance when they flow inside the tubes with wire coil inserts instead of flowing through plain tubes. For 0.3% vol. concentration for the highest wire diameter 40.2% enhancement in the heat transfer is achieved. D.Ashtiani et al. [8] investigated effect of MWCNT inside flattened tubes at uniform wall temperature condition. The test section consists of copper tube surrounded by a steam chamber to keep temperature of the wall constant. Weight fraction of 0.0%, 0.1%, 0.2%, 0.4% were selected. Copper tube of 14.5 mm ID and test section of oblong shape with inside height of 13.4mm, 11.7mm, 10.6mm, 8.6mm were used. The heat transfer without the nanofluid is carried out so as to compare it with nanofluids. The results shows that the Nusselt number rises suddenly by 132% at the Peclet number of 420000 for 0.4wt.% whereas the corresponding value for the 0.2 wt. % nanofluid is approximately 58% for the same range of Peclet number. It can be concluded that the Nusselt number and hence the heat transfer rate goes up by increasing the nanoparticle weight fraction. SEM( Scanning electron microscope) images of (a) Single wall CNT and (b) Multi-wall CNT S.M.Hashemi and M.A.Akavan-Behabadi [9] empirically studied the heat transfer and pressure drop for CuO-base oil nanofluid in horizontal helically coiled tubes for constant heat flux. The nanofluids with mass concentration of 0.5%,1% and 2% were selected. The apparatus consists of helical coils with four turns with 14.37 mm inner diameter and wall thickness of 0.75 mm. ISSN: 2049-3444 © 2013 – IJET Publications UK. All rights reserved. 139PDF Image | Nanofluid Heat Transfer
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