Experimental evaluation of performance intensification of double-pipe heat exchangers with rotary elliptical inserts

In this experimental work, heat transfer and thermal performance factor of double-pipe heat exchanger pipes with rotated inclined elliptical (RIE) inserts are examined. The rotation angle of the elliptical turbulators (beta), slant angle (alpha), and the perforation diameters (dp) were in the range of 0 circle < beta < 90 circle, 15 circle < alpha < 25 circle, and 0.5mm < dp < 1.5mm, respectively. The rotated inserts with perforations can substantially intensify the flow unsteadiness and disturb the thermal boundary layer to improve the thermal performance without a perceptible effect on the pressure drop. The experimental analysis showed that the heat transfer is improved up to 30.7% by utilizing RIE turbulators in comparison with the non-rotated elliptic (NRIE) turbulators. The recirculating flows across the perforations of the elliptical inserts rise the fluid mixing amongst the tube wall and the central region. The highest thermal performance factor of 2.23 is achieved for RIE turbulators with beta = 90 circle, dp/b=0.250 and alpha = 25 circle. The thermal performance factor that is obtained in this study is noticeably higher than that of the previous studies, without increasing the manufacturing costs. The heat transfer coefficient is enhanced by 59.95% by utilizing NRIE vortex generators with dp=1.5 mm in comparison with the typical non-rotated louvered strips without perforations.