Influence of Double-sided Delta-wing Tape Insert with Alternate-axes on Flow and Heat Transfer Characteristics in a Heat Exchanger Tube

The convective heat transfer and friction behaviors of turbulent tube flow through a straight tape with double-sided delta wings（T-W）have been studied experimentally.In the current work,the T-W formed on the tape was used as vortex generators for enhancing the heat transfer coefficient by breakdown of thermal boundary layer and by mixing of fluid flow in tubes.The T-W characteristics are（1）T-W with forward/backward-wing arrangement,（2）T-W with alternate axis（T-WA）,（3）three wing-width ratios and（4）wing-pitch ratios.The experimental result reveals that for using the T-W,the increases in the mean Nusselt number（Nu）and friction factor are,respectively,up to 165%and 14.8 times of the plain tube and the maximum thermal performance factor is 1.19.It is also obvious that the T-W with forward-wing gives higher heat transfer rate than one with backward-wing around 7%. The present investigation also shows that the heat transfer rate and friction factor obtained from the T-WA is higher than that from the T-W.In addition,the flow pattern and temperature fields in the T-W tube with both backward and forward wings were also examined numerically.