Performance of agitated-vessel U tube heat exchanger using spiky twisted tapes and water based metallic nanofluids

Spiky twisted tapes. [Display omitted] •Spiky twisted tapes are tested in an agitated-vessel U tube heat exchanger.•Water based metallic nanofluids are used as working fluid.•Results show great heat transfer enhancement in the heat exchanger.•Heat transfer enhancement of Ag/water nanofluid is more intensive. An experimental study is performed to investigate hydrothermal characteristics of agitated-vessel U tube heat exchanger. In order to augment the rate of heat transfer in the tube side, two passive enhancement techniques, namely spiky twisted tapes and water based metallic nanofluids, are used. Three twist ratios (α=0.33, 0.67, and 1) with different values of width/depth for peripheral cuts (β=0.33, 0.5, 0.67, 1, 1.5, 2, and 3) and three metallic nanofluids (Cu/water, Fe/water, and Ag/water) are tested. The experiments are done in turbulent flow regime for Reynolds numbers ranging from 7000 to 18,000. The Reynolds number is determined based on hydraulic dimeter of considered geometries as well as inlet flow rate and physical properties of applied working fluid. The results show that spiky twisted tapes and metallic nanofluids both realize great heat transfer enhancement in the agitated-vessel U tube heat exchanger. Utilization of spiky twisted tapes leads to an increase in the range of 11%–67% for the heat transfer coefficient compared with the smooth case. The considered performance factor displays that the most efficient configuration is the spiky twisted tape with α=β=0.33. Also, it is found that the heat transfer enhancement of Ag/water nanofluid is more intensive than Cu/water and Fe/water nanofluids; a maximum enhancement by 18.2% is identified compared with base fluid, while the maximum rise in the pressure drop is only 8.5%.