This study is carried out to analyze the velocity distribution for each location and the uniformity index according to straight distance on exit side by changing the design factors of branch pipe connected to 180° circular mixing-tee using RSM(Reynolds Stress Model) turbulence model. As the results of the flow characteristics according to hydraulic diameter, the velocity profiles in the 90° sectional area are generally similar. In the 180° section, the maximum velocity point shows Y/D=0.7~0.8 after rapid increase of the flow velocity. In the result according to the distance away from inlet, the maximum velocity point in the 90° sectional area is located in outer side of the curved pipe as the distance away from inlet increases. In the 180° sectional area, the maximum velocity point is showed in Y/D=0.7~0.8 after the rapid increase of the flow velocity regardless of the variation of branched distance. In case of inclined angle, the maximum velocity point in the 90° sectional area is located in outer side of the curved pipe as the inclined angle increases. In the 180° sectional area, the maximum velocity point is observed in Y/D=0.8 regardless of the inclined angle. In addition, the uniformity index of flow velocity shows that it is stabilizing after approximately L/D=40 away from the end of the curved pipe regardless of the flow factors in the branch pipe.

In this study, velocity distribution characteristics by location and uniformity according to exit straight length in a 180° mixed pipes were numerically analyzed using RSM (Reynolds Stress Model) turbulent model by changing various flow parameters such as working fluids, inlet air velocity etc. As a result of it, the working fluids characteristics was highly indicated by the viscous force difference, the maximum velocity points according to main pipe’s inlet velocity were indicated when 90° sectional location was distributed at X/D=0.5~0.6 region and 180° sectional location was distributed at Y/D=0.5 region. And the flow characteristics according to branch pipe’s inlet velocity when 90° sectional location was distributed at X/D=0.4~0.6 region and 180° sectional location was distributed at Y/D=0.5 region. Based on the results that the most stable exit straight length in flow uniformity was indicated at L/D=25~30 region, 40D is suggested as the effective measurement distance in the straight pipe downstream curved pipe of mixed pipe.

The heat transfer characteristics of forced convection according to the geometric shapes with four rectangular blocks in a horizontal PCB channel was analyzed numerically using SST (Shear Stress Transport) turbulence model. As the boundary condition for CFD (Computational Fluid Dynamics) analysis, the inlet temperature and air velocity were respectively 300 K and 3.84 m/s and the heat flux of the block surface was 358 W/㎡. The shape factors of block were width, height, spacing and channel entrance height. As the results, the heat transfer rate was decreased as the width ratio (x/h) was increased, while it was increased as the height ratio (h/x) is increased. Also as the block spacing ratio (s/x) was increased, the heat transfer effects was not significantly affected. And as the channel entrance height ratio (H/x) was increased, the heat transfer performance was decreased.