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Abstract
In this work, γ-Al2O3 nanoparticles with mean diameter of 10 nm are dispersed in deionized water with four nanoparticle volume concentrations of 0.25, 0.5, 0.75, and 1%. The effect of γ-Al2O3/water nanofluids on the heat transfer enhancement of heat exchangers is investigated under turbulent regime for four different volumetric flow rates of 150, 200, 250, and 300 L/h. The experimental results showed that the convective heat transfer is increased by increasing particles volume fraction as well as flow rate. The maximum enhancement obtained in Nusselt number and heat transfer coefficient was 20 and 22.8%, respectively, at Reynolds number of 6026 and particle volume fraction of 1%. The experimental Nusselt numbers of nanofluids showed good agreement with the available empirical correlation at particle volume fractions of 0.25 and 0.5%. An empirical correlation is obtained to estimate the Nusselt number of nanofluid under the conditions of this work.
NOMENCLATURE
| A | = | area of heat transfer, m2 |
| cp | = | specific heat, J/kg-°C |
| cpbf | = | specific heat of base fluid, J/kg-°C |
| cpnf | = | specific heat of nanofluid, J/kg-°C |
| cpp | = | specific heat of nanoparticles, J/kg-°C |
| D | = | inner diameter of test tube, m |
| h | = | heat transfer coefficient, W/m2-°C |
| hnf | = | heat transfer coefficient of nanofluid, W/m2-°C |
| I | = | current, A |
| k | = | thermal conductivity of cooling water, W/m-°C |
| kbf | = | thermal conductivity of base fluid, W/m-°C |
| knf | = | thermal conctivity of nanofluid, W/m-°C |
| kr | = | thermal conductivity ratio |
| L | = | tube length, m |
| = | mass flow rate, kg/s | |
| = | mass flow rate of cooling water, kg/s | |
| = | mass flow rate of hot water, kg/s | |
| = | mass flow rate of nanofluid, kg/s | |
| Nu | = | Nusselt number |
| Nunf | = | Nusselt number of nanofluid |
| Nuw | = | Nusselt numr of pure water |
| Pe | = | Peclet number |
| Pr | = | Prandtl number |
| q | = | heat flux, Wm2 |
| Q | = | average heat transfer rate, W |
| Qaven | = | average heat transfer rate in nanofluid tests, W |
| Qavew | = | average heat transfer rate in water tests, W |
| Qc | = | heat transfer rate for cooling water, W |
| Qh | = | heat transfer rate for hot water, W |
| Qnf | = | heat transfer rate for nanofluid, W |
| qaven | = | average heat flux between heating water and nanofluid, W/m2 |
| qavew | = | average heat flux between the heating and the cooling water, W/m2 |
| Re | = | Reynolds number |
| Renf | = | Reynolds number of nanofluid |
| Tb | = | bulk temperature, °C |
| Tbi | = | inlet bulk temperature, °C |
| Tbo | = | outlet bulk temperature, °C |
| Tcw | = | bulk temperature of cooling water, °C |
| Tnf | = | bulk temperature of nanofluid, °C |
| Tw | = | average wall temperature, °C |
| U | = | uncertainty |
| V | = | voltage, V |
| wbf | = | mass of base fluid, g |
| wp | = | mass of nanoparticles, g |
Greek Symbols
| ϕ | = | particle volume concentration,% |
| ρp | = | density of nanoparticles, kg/m3 |
| ρnf | = | density of nanofluid, kg/m3 |
| ρbf | = | density of base fluid (DI water), kg/m3 |
| μ | = | viscosity, kg/m-s |
| μw | = | viscosity of cooling water, kg/m-s |
| μr | = | viscosity ratio |
| μnf | = | viscosity of nanofluid, kg/m-s |
| μbf | = | viscosity of base fluid, kg/m-s |
Additional information
Notes on contributors
Abdul Jabbar N. Khalifa
Abdul Jabbar N. Khalifa obtained his Ph.D. degree in mechanical engineering from Cardiff University, Cardiff, UK, in 1989. His main research interests include heat transfer, renewable energy, desalination, and nanofluids. He has published more than 30 papers in peer-reviewed journals. He is also a reviewer for several peer-reviewed journals published by Elsevier, Taylor & Francis, and Springer. Currently, he works as an assistant professor and Head of Mechanical Engineering Department at Nahrain University, Baghdad, Iraq.
Mohammed A. Banwan
Mohammed A. Banwan obtained his M.Sc. degree in the Mechanical Engineering Department, Nahrain University, Baghdad, Iraq, in 2012. His main research interests include thermofluid sciences and nanofluids.