Heat transfer and friction factor characteristics of turbulent flow through a circular tube fitted with vortex generator inserts

Local heat transfer coefficients and average pressure drop measurements for turbulent flow in a circular tube fitted with a nonconventional insert are presented here. The insert was fabricated with a central rod on which curved delta wing vortex generators were attached on opposite sides at specific axial locations. The influence of pitch to projected length ratio (p/pl), height to tube inner diameter ratio (e/d) and angle of attack (alpha) on the heat transfer performance are reported here. Air was used as the working fluid and local heat transfer measurements for both smooth and rough surface sides of the tube are reported for fully developed turbulent flow with Reynolds number (Re) varying between 10,000 and 45,000. The average Nusselt number ratio with and without the insert (Nu(a)/Nu(s)), at constant Reynolds number (Re) is found to be in the range of 1.3-5.0. The Nusselt number ratio (Nu(a)/Nu(c)), based on equal pumping power is found to be in the range of 1.0-1.8. Empirical correlations are developed for Nusselt Number and friction factor in terms of Reynolds number (Re), pitch to projected length ratio (p/pl), height to tube inner diameter ratio (e/d) and angle of attack (alpha). (C) 2014 Elsevier Ltd. All rights reserved.