Comparison of the heat transfer performance and friction characteristics between fixed and rotating turbine-type swirl generators fitted in a small circular tube

Abstract This paper is a continuation of the authors’ previous work [W. Duangthongsuk, S. Wongwises, An experimental investigation of the heat transfer and pressure drop characteristics of a circular tube fitted with rotating turbine-type swirl generators, Exp. Therm. Fluid Sci. 45, (2013), 8–15.]. Swirl generators inserted into a conventional smooth tube is an innovative way to increase the thermal performance of the heat exchangers. The effect of the free rotation of a swirl device on the thermal performances and friction behaviors are investigated experimentally. Five turbine-type swirl generators with and without free rotation are inserted and installed equally distant along the test section. In the present study, DI water is used as a testing fluid and flows under a turbulent flow regime. A common stainless steel tube with an OD of 10 mm, ID of 9.2 mm, and length of 2.3 m is used as the test tube. A DC power supply is used to supply the heat load to the test section in order to meet the constant heat flux boundary condition. The data for a common smooth tube are compared with the data for fixed (FTSG) and freely rotating turbine type swirl generator (RTSG). The measured data illustrate that the heat transfer performance of the tube with RTSG inserts is 6.3% and 56% higher than that of the FTSG insert and the conventional smooth tube, respectively. Moreover, the heat transfer coefficient significantly increases when the fluid flows pass the RTSG and FTSG inserts. However, inserting the RTSG and FTSG into the common smooth tube results in an increase of the pressure drop. The tube with RTSG inserts gives the lowest pressure drop.