(40f) Pressure Drop Measurements and 3D CFD Modelling in the Netmix® Reactor

The NETmix® Reactor is a new technology consisting of a network of mixing chambers interconnected by transport channels [1]. Networks are generated by the repetition of unit cells where each unit cell consists of one chamber and two inlet and two outlet channels oriented at a 45º angle from the main flow direction. Above a critical channel Reynolds number, the system evolves to a self-sustained oscillatory laminar flow regime inside the mixing chambers inducing local strong laminar mixing. This occurs due to the geometric characteristics of NETmix®. A network model was developed to describe and predict the behaviour and performance of NETmix® [2]. From the point of view of modelling, it was shown that chambers can be assumed to behave as perfectly mixing zones and the channels as plug flow perfect segregation zones. The NETmix® Reactor can therefore be understood, along the main flow direction, as a plug flow reactor with maximum mixing. The mixing degree was defined and quantified [2, 3] showing that mixing can be controlled effectively and efficiently making it particularly suited for complex and fast kinetics reactions. However, the performance of the NETmix® reactor, in terms of energy requirements, was yet to be studied.

In this work, pressure drop was measured experimentally for one NETmix® configuration with spherical chambers and two configurations with cylindrical chambers and for several channel Reynolds numbers in the laminar regime. From the experimental data, a pressure drop model was developed which takes into account the friction effects within the channels and the inertial effects due to the sudden expansions and contractions in the interconnections between chambers and channels. The model has a single adjustable parameter that is only dependent on the geometric configuration of the network. The dynamic measurement of pressure drop was also used to evaluate the mixing dynamics in the NETmix® chambers and above the critical Reynolds number, the natural oscillation frequency was quantified. The Z factor and power number were determined to compare the performance of different NETmix® configurations with other existing static mixers.   Furthermore, a three-dimensional Computational Fluid Dynamic (CFD) transport model of a representative portion of the NETmix® was also developed and validated by comparing the experimental pressure drop data with the CFD simulation results.

NETmix®’s mixing efficiency was previously estimated. However from this work, its energetic performance was quantified and shown to be competitive with the compared existing static mixers. The new 3D CFD transport model allows the computation of transport properties and overcomes the need of experiments each time a new NETmix® configuration is designed. It also allows a better understanding of the flow patterns inside the unit cells which were not possible to visualize from previous two-dimensional CFD simulations.

[1] J.C.B. Lopes, P.E. Laranjeira, M.M. Dias, A.A. Martins, Network mixer and related mixing process. PCT/IB2005/000647, February 2005. European Patent EP172643 B1, October 2008.

[2] P.E. Laranjeira, A.A. Martins, J.C.B. Lopes, M.M. Dias, NETmix®, a new type of static mixer: Modeling, simulation, macromixing, and micromixing characterization, AIChE Journal, 55 (2009) 2226-2243.

[3] P.J. Gomes, C.P. Fonte, R.J. Santos, M.M. Dias, J.C.B. Lopes, Experimental and numerical characterization and quantification of mixing in a NETmix® reactor, in:  ECCE 7 - 7th European Congress of Chemical Engineering & CHISA 2010- 19th internation Congress and Process Engineering, Process Engineerig Publisher, Prahe, Prague, Czech Republic, 2010.