Experimental investigation of heat transfer and friction factor in tubes fitted with regularly spaced rotor strands

The heat transfer and friction characteristics of tubes fitted with full length and regularly spaced grooved helical lobe rotor strands,with involved space ratios of 0.0,3.0,6.0 and 10.0,have been investigated experimentally.The Nusselt numbers of tubes with full length strands increased by factors of 0.8-1.2 times the empirical correlation results for plain tubes with the same Reynolds numbers,while the friction factor also increased by about 55%.The introduction of free spacing length weakened the disturbance of fluid flow,resulting in a decrease in heat transfer characteristics and tube side pressure drop at the same time.Performance evaluation criteria(PEC) of strands with different space ratios were compared,and the results indicated that in the experimental Reynolds number range,an increase in space ratio resulted in a beneficial increase in PEC for low Reynolds number,while the PEC values of regularly spaced strands were lower than those of full length strands when the Reynolds number was relatively high.