Browsing by Author "Aly, Wael I. A"

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Numerical study on turbulent heat transfer and pressure drop of nanofluid in coiled tube-in-tube heat exchangers
(PERGAMON-ELSEVIER SCIENCE LTD., 2014) Aly, Wael I. A
A computational fluid dynamics (CFD) study has been carried out to study the heat transfer and pressure drop characteristics of water-based Al2O3 nanofluid flowing inside coiled tube-in-tube heat exchangers. The 3D realizable k-epsilon turbulent model with enhanced wall treatment was used. Temperature dependent thermophysical properties of nanofluid and water were used and heat exchangers were analyzed considering conjugate heat transfer from hot fluid in the inner-coiled tube to cold fluid in the annulus region. The overall performance of the tested heat exchangers was assessed based on the thermo-hydrodynamic performance index. Design parameters were in the range of; nanoparticles volume concentrations 0.5%, 1.0% and 2.0%, coil diameters 0.18, 0.24 and 0.30 m, inner tube and annulus sides flow rates from 2 to 5 LPM and 10 to 25 LPM, respectively. Nanofluid flows inside inner tube side or annular side. The results obtained showed a different behavior depending on the parameter selected for the comparison with the base fluid. Moreover, when compared at the same Re or Dn, the heat transfer coefficient increases by increasing the coil diameter and nanoparticles volume concentration. Also, the friction factor increases with the increase in curvature ratio and pressure drop penalty is negligible with increasing the nanoparticles volume concentration. Conventional correlations for predicting average heat transfer and friction factor in turbulent flow regime such as Gnielinski correlation and Mishra and Gupta correlation, respectively, for helical tubes are also valid for the tested nanofluids which suggests that nanofluids behave like a homogeneous fluid. (C) 2013 Elsevier Ltd. All rights reserved.
Thermal and Hydrodynamic Performance of Aqueous CuO and Al2O3 Nanofluids in an Annular Coiled Tube Under Constant Wall Temperature and Laminar Flow Conditions
(ASME, 2016-10) Aly, Wael I. A
Laminar flow and heat transfer behaviors of two different metal oxide, Al2O3 (36 nm) and CuO (29 nm), nanofluids flowing through an annular coiled tube heat exchanger (ACTHE) with constant wall temperature boundary condition have been numerically studied to evaluate their superiority over the base fluid (water). Simulations covered a range of nanoparticles volume concentrations of 1.0-6.0% and mass flow rates from 0.025 to 0.125 kg/s. Numerical results indicated that a considerable heat transfer enhancement is achieved by both nanofluids. Results at the same Reynolds number for the pressure drop and heat transfer coefficient show an increase with increasing particle volumetric concentration. The maximum enhancements in heat transfer coefficient were 44.8% and 18.9% for CuO/water and Al2O3/water, respectively. On the other hand, the pressure loss was seven times in comparison to water for CuO/water and about two times for Al2O3/water nanofluid. Also, comparing to the base fluid, nanofluids at low concentrations (up to 3%) can provide the same heat transfer amount at lower pumping power. The overall performance of the enhanced heat transfer technique utilized has been evaluated using a thermohydrodynamic performance index which indicated that Al2O3/water nanofluid is a better choice than CuO/water nanofluid. Moreover, conventional correlations for helical circular tubes for predicting friction factor and average heat transfer in laminar flow regime such as the correlations of Mori and Nakayam and Manlapaz and Churcill, respectively, are also valid for water and the tested nanofluids with small nanoparticle loading in the ACTHE.