Heat transfer in turbulent flow through tube with porous twisted tape insert

Abstract

Enhancement of heat transfer in tube flow has practical applications. Inserts of various geometry in a circular tube enhance heat transfer. An experimental investigation has been carried out for turbulent flow in a circular tube with porous/perforated twisted tape insert. In this work, mild steel twisted tape inserts with holes of different diameters termed as perforated twisted tapes are used. Heat transfer and pressure drop characteristics are examined in the tubes for the turbulent flow. The flow of air through tubes is varied thereby varying the Reynolds number. Heat transfer and pressure drop data arc generated for Reynolds numbers ranging from 1.3 x 10 4 to 5.2 x IO 4. Air velocity, its temperatures, tube wall temperatures, pressure drops are measured for smooth/plain tube. The same variables are measured after inserting twisted tapes in the tube. Heat transfer coefficients, Nusselt numbers, pumping power and heat transfer effectiveness are calculated using measured variables for the smooth/plain tube, as well as for tube with the inserts. Heat transfer rate is found to. increase with corresponding increase in friction factor and pumping power for tube with the twisted tape inserts. For the same Reynolds number, the heat transfer coefficient in the tube with the twisted tape inserts is found to increase upto 5.5 times of that for the plain tube. Whereas, the pumping power in the tube with the twisted tape insert is found to increase upto, 1.8 times of that for the plain tube. It is also found that the heat transfer effectiveness in a tube with the twisted tape insert is found to increase upto 4.0 times compared to the value for the plain tube. With the experimental data, a correlation has been developed for prediction of the heat transfer rate in the turbulent flow for the tube with the porous/perforated twisted tape insert.