Heat transfer enhancement in turbular heat exchanger fitted with twin twisted tape swirl generators

An experimental investigation was made with aim to enhance heat transfer in a double-tube heat exchanger fitted with twin twisted tapes. The effects of the twin twisted tape inserts on heat transfer rate, friction factor and thermal performance behaviors were studied in turbulent region of Reynolds number between 5000 and 15,000. The twin twisted tapes with three twist ratios (y/w = 1.5, 2.0 and 2.5) were used for generating two longitudinal swirl flows along the test section. The experimental result indicates that heat transfer rate in term of Nusselt number (Nu) and friction loss in term of friction factor (f) increase as twisted ratio (y/w) decreases. The twin twisted tapes with y/w = 1.5 yield higher Nusselt number (Nu) than the ones with y/w = 2.0 and 2.5 up to 16% and 38%, respectively which are accompanied with the higher friction factor up to 15% and 35%, respectively. Among the tested twisted tapes, the twin twisted tapes with the smallest twist ratio (y/w = 1.5) offer the maximum thermal performance factor of 1.64. In addition, the flow structure, temperature field, turbulent kinetic energy and local heat transfer coefficient in tube fitted twin twisted tapes are also presented.