Numerical analysis on enhanced performance of new coaxial cross twisted tapes for laminar convective heat transfer

Owing to the high viscosity of lubricating oil, oil coolers meet the disadvantages of low heat transfer coefficients and thus large volumes. In order to enhance the heat transfer performance, a new type of twisted tape, called coaxial cross twisted tape, is proposed based on the field synergy theory and traditional twisted tapes. The numerical analysis of the heat transfer performance is presented in the article using CFD software STAR-CCM+. The local flow characteristics, and local and average convective heat transfer coefficients are analyzed, when the Reynolds number ranges from 40 to 1050. The effects of the four different twist ratios of 2.0, 3.0, 4.0 and ∞ on the heat transfer performance are also investigated. To evaluate the effect of heat transfer enhancement under given pumping power, the performance evaluation criterion (PEC) is discussed. The results indicate that the local convective heat transfer coefficient increases markedly with the insertion of the new twisted tapes because of the increase of the velocity near wall and thickness reduction of thermal boundary layer. The more flow zones are separated by the coaxial cross twisted tapes, the larger is the temperature gradient near wall and the higher is convective heat transfer coefficient. The Nusselt number and PEC of the heat transfer tube fitted with the new coaxial cross twisted tapes have increased by 151-195% and 90-123% of the traditional twisted tape, respectively.