Hydrodynamics and Transient Heat Transfer Characteristics in Fluidized and Spouted Beds

Abstract

Hydrodynamics and heat transfer characteristics found in fluidization were studied in a small scale laboratory fluidized bed. Experiments were designed to capture field data on multiple slit jet gas distributor systems for the validation of computational models. Localized data was quantified through the use of several novel non-intrusive experimental measurement techniques. The analyses provide a unique study that connects full field-of-view multiphase flow dynamics with transient heat transfer distributions.

The gas-solid hydrodynamics were captured through three non-invasive measurement techniques, viz. Particle Image Velocimetry (PIV), Digital Image Analysis (DIA), and pressure drop spectral analysis. The effects of inlet gas flowrate, Geldart B and D classified particle types, and the number inlet gas slit jets were investigated. Frequency analysis of a differential pressure signal resulted in the classification of four difference flow regimes. The coupling of PIV with DIA captured particle velocity, solid circulation rates, average cycle times, dead zone sizes, jet merging effects, gas void fraction distributions, and maximum expanded bed heights.

The heat transfer in fluidized and spouted beds containing a heated inlet gas source was studied through transient heat transfer measurements and analyses. Innovative experimental procedures were introduced to quantify bed-to-wall and gas-to-particle heat transfer characteristics. Two techniques were developed to overcome the spatial, time varying, and instrumental intrusive limitations often found in multiphase flow heat transfer studies. Infrared thermography was utilized along with derived discrete differential equations, and an inverse heat conduction analysis to solve for transient localized heat flux profiles and heat transfer coefficient distributions. As a result new data containing increased spatial resolution is presented on gas, wall, and particle temporal maps. Computations based from the thermal gradients quantified bed-to-wall heat flux profiles, gas-to-particle heat transfer coefficients, and localized rates of energy stored.