**4. Conclusion**

RWP [25, 40]. The lowest synergy angle in the case of three pairs of perforated RWP at a velocity of 0.4 m/s are 78.25°, 77.98°, and 79.33° at x/L = 0.28, 0.52, and 0.76, respectively. Meanwhile, at velocity of 2.0 m/s, they are 81.15°, 79.42°, and

71.64°, 77.52°, and 79.04° at x/L = 0.24, 0.52, and 0.76 at 0.4 m/s, respectively. Meanwhile, at velocity of 2.0 m/s, they were 72.68o, 78.81o, and 81.57o at

x/L = 0.28, 0.52, and 0.8, respectively. The hole in VG increases the synergy angle due to a decrease in the heat transfer coefficient [41]. The increase in the mean synergy angle due to the addition of holes in the RWP and CRWP three pairs is

*Synergy angle at a speed of 2.0 m/s for the case of (a) one-pair of RWP; (b) one pair of CRWPs; (c) two pairs*

*of RWP; (d) two-pairs of CRWP; (e) three pairs of RWP; (f) three-pairs of CRWP.*

In the case of CRWP with the same configuration, the largest synergy angles are

81.19° at x/L = 0.28, 0.52, and 0.76, respectively.

*Heat Transfer - Design, Experimentation and Applications*

0.25° and 0.29° at a velocity of 2.0 m/s, respectively.

**Figure 27.**

**78**

In this study, a numerical fluid flow simulation was performed to determine the effect of installing RWP and CRWP with/without holes at 45° angle of attack on heat transfer and pressure drop in the rectangular channel. The hole in VG results in a slight decrease in the convection heat transfer coefficient. The reduction of the convection heat transfer coefficient in the channel with the installation of three pairs of perforated RWP and CRWP for the highest Reynolds number was 2% and 8% of the without holes, respectively. The hole in the VG was able to reduce the pressure drop in the channel. The highest reduction in pressure drop due to holes in RWP with variations of one, two, and three pairs was 7%, 4%, and 13%, respectively. On the other hand, the decrease in pressure drop on CRWP with the highest Reynold number for the same case was 5%, 5%, and 11%, respectively. The hole in VG caused a decrease in the mean spanwise Nusselt number in all cases. The decrease in the average spanwise Nusselt number in the perforated RWP and CRWP cases at a velocity of 0.4 m/s was the greatest of 24% at x/L = 0.32 and 11% at x/L = 0.56, respectively, from those without holes. Whereas for the same case at a velocity of 2.0 m/s, the largest decrease was 2% at x/L = 0.8 and 7% at x/L = 0.32, respectively. The synergy angle increased due to the holes in the RWP and CRWP. The average synergy angle increase in the use of RWP and CRWP three pairs was 0.25 and 0.29 at a velocity of 2.0 m/s, respectively.
