Heat transfer enhancement in double-pipe heat exchanger by means of rotor-assembled strands

Thermo-hydraulic characteristics of turbulent flow in plain tube equipped with rotor-assembled strands of different geometries and leads were reported, ahead of which an experiment considering a smooth tube had been conducted to calibrate the experimental system and data reduction method. The effects of rotor lead on heat transfer and friction characteristics were emphasized consequently. Experimental results revealed that rotor-assembled strands of different geometries employed improved heat transfer significantly with Nusselt number increased by 71.5-123.1% and friction factor increased by 37.4-74.8% compared with plain tube. There into, the helical blade rotor brought the most augmentation of heat transfer, while the blade-discreted rotor caused the largest friction loss. Generally considering, helical blade rotor with ladders offered first-class performance sequentially followed by helical blade rotor and blade-discreted rotor. For helical blade rotor with ladders, Nusselt number and friction factor both increased with the decrease of rotor lead. The best thermal performance factor was achieved when helical blade rotor with ladders was manufactured with certain parameters (rotor diameter is 22 mm, rotor lead is 150 mm). At last, the correlations of experimental results were presented based on thorough multivariate linear normal regression method. (C) 2012 Elsevier B.V. All rights reserved.