Optimum angles of non-standard diffusers and reducers for engineering application

The fittings such as diffusers and reducers are essential flow elements in a piping system, which play a role to connect the different sized pipes or to branch a part of main stream to other piping. However, their central role is to convert the dynamic energy (velocity) of a flow into the static energy (pressure), or vice versa. When designing a piping system, the pressure drop calculation is very important due to the estimation of power consumption for maintaining a required flowrate. For this reason, many coefficient values of the standard sized fitting products are usually provided by manufacturers or by engineering handbooks. In this study, some analytical calculations were performed to find the optimum angles of non-standard reducers and diffusers based on a dimensionless aspect ratio (length/diameter). The results showed that the optimum angles decreased exponentially as the aspect ratio increased and vice versa. Especially, the optimum angle of a diffuser converged to about 5° when the aspect ratio is over 10. Furthermore, these results were verified through the CFD calculations and the previous reported data.