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Abstract
An experimental investigation is carried out to study the heat transfer and pressure drop characteristics of multiwalled carbon nanotubes (MWCNTs)/heat transfer oil nanofluid flows inside horizontal corrugated tubes under uniform wall temperature condition. To provide the applied nanafluids, MWCNTs are dispersed in heat transfer oil with mass concentrations of 0.05, 0.1, and 0.2 wt%. The Reynolds number varies between 100 and 4,000. Three tubes with hydraulic diameters of 11.9, 13.2, and 15.5 mm are applied as the test section in the experimental setup. Tubes are corrugated four times on the cross section; that is, there are four different helices around the tube. Depths of the corrugations are chosen as 0.9, 1.1, and 1.3 mm, and pitch of corrugation is 14 mm. The acquired data confirm the increase of heat transfer rate as a result of utilizing nanofluids in comparison with the base fluid flow. However, corrugating the tubes decreases the heat transfer rate at low Reynolds numbers. The highest increase in heat transfer rate is observed for the Reynolds numbers for which the smooth tube is in the transition regime and the corrugated tube reaches the turbulent flow, that is, Reynolds number in the range of 1,000 to 3,000. Rough correlations are proposed to predict the Nusselt number and friction factor.
NOMENCLATURE
| A | = | cross-sectional area (m2) |
| B | = | base fluid |
| cp | = | specific heat capacity (J/kg-K) |
| D | = | diameter (m) |
| Dhyd | = | hydraulic diameter (m) |
| e | = | depth of corrugation (m) |
| f | = | Darcy friction factor |
| Gr | = | Grashof number |
| = | mean heat transfer coefficient (W/m2-K) | |
| k | = | thermal conductivity (W/m-K) |
| L | = | length (m) |
| = | mass flow rate (kg/s) | |
| = | mean Nusselt number | |
| P | = | perimeter (m) |
| p | = | pitch of corrugation (m) |
| Pr | = | Prandtl number, |
| Re | = | Reynolds number |
| S | = | smooth tube |
| T | = | temperature (°C) |
| = | mean velocity of fluid (m/s) |
Greek Symbols
| β | = | helix angle (°) |
| μ | = | viscosity (kg/m-s) |
| v | = | kinematic viscosity (m2/s) |
| ρ | = | density (kg/m3) |
Subscripts
| in | = | inlet |
| lmtd | = | logarithm mean temperature difference |
| out | = | outlet |
| p | = | projected |
| s | = | surface |
| w | = | wall |
Additional information
Notes on contributors
Majid Karami
Majid Karami is a Ph.D. student at the University of Tehran, Tehran, Iran. In 2009, he received his B.Sc. degree in mechanical engineering from Amirkabir University of Technology (Tehran Polytechnic). He received his M.Sc. degree in mechanical engineering–energy conversion in 2011 from the University of Tehran. He is currently working on inverse heat transfer.
Mohammad A. Akhavan-Behabadi
Mohammad A. Akhavan-Behabadi is a professor and the head of the school of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran. He received his Ph.D. from the Indian Institute of Technology at Roorkee, India, in 1993. He has co-authored more than 150 journal and conference publications. His research interests include experimental two-phase and single-phase convective heat transfer. He is currently working on augmentation of heat transfer by different passive techniques in two-phase flow and on nanofluid single- and two-phase flow.
Mohammad Fakoor-Pakdaman
Mohammad Fakor Pakdaman received his B.Sc. in mechanical engineering from Amirkabir University of Technology (Tehran Polytechnic) in 2008. He completed his master's degree in mechanical engineering (energy conversion) at Tehran University in 2011. Currently, he is pursuing his education toward a Ph.D. degree in mechatronic systems engineering at Simon Fraser University. His research is focused on thermal management of power electronics.