Improving the efficiency of ‘Clean-In-Place’ procedures using a four-lobed swirl pipe: A numerical investigation

• The study demonstrates that swirl pipe has the potential to enhance CIP efficiency in closed processing system.
• The swirl pipe raises wall shear stress downstream of it without increasing the velocities of cleaning fluid.
• The increase in mean wall shear stress value can be up to 23% downstream of the swirl pipe.
• The application of swirl pipe may serve as an alternative to reduce the time and cost for CIP process.

This paper presents a computational fluid dynamics model of the swirl flow that is induced in a fluid flow passing through a horizontally mounted optimized four-lobed swirl pipe. Tangential velocity, swirl type, swirl intensity and its decay rate of the swirl flow are investigated in flows with various inlet velocities. Special attention is paid to the potential of the swirl flow on improving ‘Clean-In-Place’ efficiency by increasing wall shear stress downstream of the swirl pipe. It was found that the swirl pipe induces a tangential wall shear stress on the pipe downstream and its value and variation are dependent on swirl intensity. A swirl pipe also slightly increases axial wall shear stress; however axial wall shear stress is mainly proportional to the fluid Reynolds number. Wall shear stress along the pipe circumference forms a wave-like distribution, which is attributed to the four-lobed cross-section of the swirl pipe, with the gap between peak and valley being more obvious at circumferences close to the swirl pipe exit. The mean shear stress exerted on the pipe wall downstream of the swirl pipe increases due to the presence of swirl, with the increase in value and distance more obvious in flows with a larger Reynolds number. The numerical results indicate that the swirl pipe may locally improve efficiency of ‘Clean-In-Place’ procedures without increasing inlet velocity, thus reducing downtime and costs for cleaning.