Improvement of heat transfer in heat exchangers with spiral springs with the square cross-section area

Abstract

The purpose of this study is to investigate the effect of spiral springs with the square cross-section area on heat transfer and pressure drop in heat exchangers. The springs were fitted inside a circular cross-section copper tube. The diameter and length of the copper tube were 25.4 mm and 1820 mm, respectively. The experiments were performed with 9 spiral springs of 12 and 15 mm diameter in four pitches of 2, 5,10,20 mm and 21 mm diameter in three pitches 10, 20 and 30. The fluid used in all experiments was water and the Reynolds number for the hot water flow into the copper tube was in the range of 22,462 to 36,456. Cold water was used to cool around the copper tube and rate of cold water flow was also 0.1547 kg / s. The heat transfer coefficient increased by 45% after the springs were placed inside the copper tube in comparison to the no-spring condition. However, the pressure drop in the worst case increased by 77%. It can also be seen that the heat transfer coefficient increased to 20% by increasing the diameter of the springs by 75%. Meanwhile, the springs with a diameter of 21 mm and 12 mm has the most and the least effect on increasing the heat transfer coefficient, respectively.