Experimental Investigation of Heat Transfer Enhancement in Rectangular Duct with Pentagonal Ribs

ABSTRACT

Rib turbulators are extensively used in augmentation of convective heat transfer in several applications related to heat exchange and cooling in thermal energy systems. Present experimental investigation examines the local heat transfer and friction factor characteristics of pentagonal ribs mounted on bottom heated wall of a rectangular channel. The emphasis is towards assessing and analysing the potential impact of varying chamfering angle (0 to 20°) and rib pitch to height ratio (6 to 12) on the overall heat transfer enhancement and its distribution on the surface. Experiments are performed at different Reynolds numbers ranging from 9400 to 58850. Liquid crystal thermography is applied to measure surface temperature distribution and finally to demonstrate the local heat transfer coefficient over the ribbed surface. The results depict that the local augmentation Nusselt number distribution is axisymmetric and shows 2-dimensionalty in heat transfer distribution. Pentagonal ribs show a significant improvement for the low heat transfer zones in leeward vicinity of the square rib, specially prominent at higher Reynolds number, and therefore seen as the potential benefit in terms of obviating the hotspots. It is observed that the pentagonal ribs lead to superior heat transfer enhancement in conjunction with significant reduction in pressure penalty as compared to square ribs and thus ensures an enhanced thermo-hydraulic performance.

Acknowledgements

The author acknowledges the financial support of the Ministry of Human Resource and Development (MHRD), India for initiating this research activity in Mechanical & Industrial Engineering Department at Indian Institute of Technology Roorkee, India. Further authors wish to extend sincere thanks and acknowledge the support of Department of Science and Technology (DST), India for providing the financial assistance in order to improve the laboratories at IIT Roorkee under the FIST grant.

Additional information

Notes on contributors

Naveen Sharma

Naveen Sharma is a Ph.D. student at the Solar and Aerodynamics Laboratory, Indian Institute of Technology Roorkee, India, under the supervision of Prof. Andallib Tariq and Prof. Manish Mishra. He received in 2009 a B.E. degree in Mechanical Engineering from the MDU University, India and a M. Tech. degree in computational fluid dynamics and heat transfer from the NIT Hamirpur, India. He is currently working on fluid flow and heat transfer enhancement in ribbed duct.

Andallib Tariq

Andallib Tariq has received his BE in mechanical engineering from Bangalore University and earned M.Tech. and Ph.D. from Indian Institute of Technology Kanpur, India. He has served as faculty in India and abroad, and presently working as Associate Professor in Mechanical & Industrial Engineering Department, Indian Institute of Technology Roorkee, India. He is actively involved with the use of Liquid Crystal Thermography in heat transfer research, and contributed significantly towards the progress of optical flow diagnostic tools in engineering applications. He has organized several national/international workshops related with the flow visualization and its role in thermo-fluid measurements, and published many papers in various international journals of repute. His research interest includes: experimental fluid mechanics, turbulence, optical based thermos-fluid diagnostic tools, flow visualization, heat transfer enhancement, and thermal contact conductance. He is currently associated with different government agencies as the consultant/researcher, and working on topics related with the aerodynamics, gas turbine blade cooling, interfacial heat transfer, and nuclear safety research.

Manish Mishra

Manish Mishra is an Associate Professor in the Department of Mechanical & Industrial Engineering, Indian Institute of Technology Roorkee. He did his BE in ‘Mechanical Engineering’ and ME in ‘Energy Systems and Pollution’ from GEC Raipur (now National Institute of Technology Raipur) and PhD from Indian Institute of Technology Kharagpur. He has over 22 years of experience in teaching and research. He has authored more than 70 research papers in different journals and conferences of repute. He has also contributed to number of Government and Private Organizations in terms of sponsored research and consultancy projects. His research interests are thermal and fluids engineering, heat exchanger design & dynamics, solar heating & cooling, solid desiccant cooling and the applications of soft computing tool in thermal engineering.