The effects of eccentricity between the centers of helical screw tapes and tube on heat transfer, friction factor and performance evaluation criteria are numerically studied in this paper. A three-dimensional turbulence model is used to simulate the flow inside the tube with helical screw tape insert. All simulations are performed for four values of eccentricity (0, 0.5, 2, and 3.5) and Reynolds numbers in the range of 5000 to 12000. The obtained results indicated that the swirling effects created by helical screw tape insert are transferred from the tube core to near wall of the tube. This leads to the more mixing of fluid and centrifugal force near the wall, which has significant ability to improve the heat transfer rate at this region. There are 33%, 16.94%, 8.45%, and 7.3% increments in performance evaluation criteria for Re = 5000, 7500, 10233, and 12000 when the eccentricity value is increased from 0 to 3.5.

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