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ABSTRACT
Detailed heat transfer coefficient distributions are obtained for high aspect ratio (width/height = 12.5) duct with rib and trench enhancement features oriented normal to the coolant flow direction. A transient thermochromic liquid crystal technique has been used to experimentally measure heat transfer coefficients from which Nusselt numbers are calculated on the duct surface featuring heat transfer enhancement features. Reynolds number (calculated based on duct hydraulic diameter) ranging from 7100 to 22400 were experimentally investigated. Detailed measurements of heat transfer provided insight into the role of protruding ribs and trenches on the fluid dynamics in the duct. Experimentally obtained Nusselt numbers are normalized by Dittus-Boelter correlation for developed turbulent flow in circular duct. The triangular trenches provide heat transfer enhancement ratios up to 1.9 for low Reynolds numbers. The in-line rib configuration shows similar levels to the trench whereas staggered rib configuration provides heat transfer enhancement ratios up to 2.2 for a low Reynolds number of 7100.
Nomenclature
| AR | = | aspect ratio |
| BL | = | boundary layer |
| CFD | = | computational fluid dynamics |
| D | = | test plate thickness (cm) |
| Dh | = | hydraulic diameter (cm) |
| dT | = | trench depth (cm) |
| dR | = | rib diameter (cm) |
| e | = | rib height (cm) |
| h | = | convective heat transfer coefficient (W/m2K) |
| H | = | height (cm) |
| k | = | thermal conductivity of air (W/mK) |
| ka | = | thermal conductivity of acrylic (W/mK) |
| Li | = | inlet length (cm) |
| Nu | = | Nusselt number, |
| NuFD | = | Dittus-Boelter Nusselt number; 0.023Re0.8Pr0.3 |
| PT | = | trench pitch (cm) |
| PR | = | rib pitch (cm) |
| Pr | = | Prandtl number |
| Re | = | Reynolds number, |
| t | = | time (s) |
| T | = | temperature (K) |
| TLC | = | thermochromic liquid crystals |
| V | = | channel average flow velocity (m/s) |
| X | = | direction of the flow |
| Y | = | direction of the longer wall of the cross-section of the test section |
| W | = | width (cm) |
| Greek symbols | ||
| α | = | thermal diffusivity (m2/s) |
| ρ | = | density of air (kg/m3) |
| μ | = | dynamic viscosity (kg/m-s) |
| Subscripts | ||
| a | = | acrylic |
| D | = | duct |
| i | = | inlet |
| m | = | mainstream |
| max | = | maximum |
| P | = | plenum |
| PC | = | plenum cover |
| R | = | rib |
| T | = | trench |
| w | = | wall |
| 0 | = | Nusselt number from Dittus-Boelter correlation for developed turbulent flow in circular duct |
Additional information
Notes on contributors
Shreyas Srinivasan
Shreyas Srinivasan is a Senior Engineer at Honda R&D Americas, Inc. in the Greater Los Angeles Area. He completed his MS in July 2013 from Virginia Tech in Mechanical Engineering. He worked at Infosys Technologies in Bangalore, India after completing his BE in Mechanical Engineering from MS Ramaiah Institute of Technology, Bangalore, India in 2009. His research during his MS was in the area of heat transfer in large electric generators.
Srinath V. Ekkad
Srinath V. Ekkad is currently the Rolls-Royce Commonwealth Professor for Aerospace Propulsion Systems and the Associate Vice President for Research at Virginia Tech. He received his PhD from Texas A&M University in 1995. He is the Director of the Rolls-Royce University Technology Center for Advanced Diagnostics and the Heat, Energy, and Fluids Laboratory. His research interests include heat transfer measurement technology, application to gas turbine heat transfer and cooling technology, electronic cooling, cooling of electric generators, and thermoelectric modules. He has co-authored over 220 refereed journal and conference publications in addition to book chapters and one seminal book on gas turbine heat transfer and cooling technology. He has received the ASME Bergles/Rohsenow Young Investigator Award in Heat Transfer in 2004 and is an ASME Fellow.
Anil Tolpadi
Anil Tolpadi is currently Technical Leader for Component Cooling at General Electric Aviation. He received his PhD from University of Minnesota in 1987. In his long career with GE, he has worked on various technologies in different GE businesses and at the Global R&D center. He has published several journal and conference papers in his career on combustion and heat transfer related to gas turbine systems. He also holds several patents with GE.