Experimental studies on heat transfer and friction factor characteristics of turbulent flow through a circular tube with small pipe inserts

摘要

Heat transfer performance and pressure drop tests were performed on a circular tube with small pipe inserts. These inserts with different spacer lengths (S = 100, 142.9 and 200 mm) and arc radii (R = 5, 10 and 15 mm) were tested at Reynolds numbers between 4000 and 18,000. Tap water was used as working fluid. The use of pipe inserts allowed for a high heat transfer coefficient with relatively low flow resistance. The Nusselt number and friction factor increase with the decrease in spacer length. Optimal results were obtained for S = 100 mm (R = 10 mm). Heat transfer rates and friction factors were enhanced by 2.09-2.67 and 1.59-1.85 times, respectively, to those in the plain tube. Performance evaluation criterion (PEC) values were approximately 1.79-2.17. The Nusselt number and friction factor increase with the decrease in arc radius. Small pipe inserts with R = 5 mm and S = 100 mm show maximal heat transfer rates of 2.61-3.33 and friction factors of 1.6-1.8 times those of the empty tube. The PEC values were 2.23-2.7. Compared with other inserts, pipe inserts can transfer more heat for the same pumping power for their unique structure.