Chapter 2 - Hydrodynamics and Flow Regimes

Abstract

This chapter presents and reviews available knowledge on hydrodynamics, flow regimes, and transport parameters in the trickle bed. Accurate estimation of hydrodynamic parameters is an indispensable step for the reactor design, performance evaluation, and scale-up studies. Hydrodynamics of trickle bed reactors is controlled by complex internal bed structure and associated interactions with the gas and liquid flows. The first step in estimating the hydrodynamic parameters is estimation of prevailing flow regimes under operating conditions. The correlations and discussion presented in flow regimes are useful for selection of criteria to evaluate the flow regime and its transition so that all further calculations will be based on the characteristics of that flow regime. Trickle bed reactors are often operated near the boundary of trickle and pulse flow regimes in practice. It is therefore important to be able to estimate the transition boundary between trickle and pulse regimes accurately. The methods and models presented in flow regime transition can be used to determine the transition boundary. Methods and correlations for estimating other key hydrodynamic parameters such as pressure drop, liquid holdup, mass and heat transfer coefficients, and axial dispersions are discussed in the estimation of key hydrodynamic parameters. It is important to note that the hydrodynamics of trickle beds is a complex function of interactions of particle properties, packing characteristics of the bed, properties of gas and liquid, and operating conditions. Therefore, literature data when correlated for particular parameters give considerably different values for the same operating parameters.