Introduction to the Relation between the Residence Time Distribution and the Pipe Flow Pressure Drop

Abstract

The concept of residence time distribution (RTD) has been used in various processes to have better modeling and predictions of the process’s performance. Pipe pressure drop against flow rate can give RTD and vice versa. The RTD based on the pressure drop is independent of Reynolds number (Re) and may coincide with the usual RTD or not. A new algorithm is proposed to evaluate the shear stress (τ) versus shear rate (γ̇) using pressure drop data. It uses a more suitable definition of shear rate compared to the usual capillary viscometer relation. The experimental system gives better insight into the proposed algorithms. The newly proposed solution of the dispersion model to derive the RTD is independent of boundary conditions. For packed bed systems, the RTD based on the pressure drop tends toward the RTD of the pipe laminar flow. The prediction of the proposed RTD for the conversion of gas-phase reactants in packed bed reactors is acceptable. It accounts for the pressure drop without complicated numerical calculations.

Unified Model for Residence Time Distribution in a Recycle Reactor with Arbitrary Velocity Profiles

“…Pressure drop information is readily available and can be used as a marker for Reynolds number effects. To incorporate pressure-drop information on the residence time distribution, Emami-Meibodi 7 proposed a novel approach through the knowledge of shear stress at the wall. This involved evaluation of shear stress versus shear rate using pressure drop data.…”