Investigation of instantaneous hydrodynamics and heat transfer to a horizontal tube immersed in a high-temperature gas-solid fluidized bed of large particles.

摘要

Experimental results are presented related to the hydrodynamic and heat transfer behavior between a high-temperature, bubbling, gas-solid fluidized bed of large particles and an immersed horizontal tube.; A methodology has been developed to interpret signals from optical probes inserted in a bed which was validated by comparing experimental results to video-tape of a two-dimensional bed (2D). The optical probe signals (voltages) were filtered to calculate bubble (or emulsion) frequency, bubble velocity, pierced length, characteristic bubble size, bubble (or emulsion) residence time, and bubble (or emulsion) residence time fraction.; A fast-response heat flux sensor suitable for the high-temperature, abrasive bed environment was built and mounted on the outside of a 51 mm outside diameter tube. Experiments were performed with the optical probes and instantaneous heat flux sensor in a three-dimensional (3D) bed at temperatures ranging from 600 K to 1000 K, over a range of fluidization velocities, with 2.0 mm and 2.9 mm refractory particles. Instantaneous heat transfer information was collected at circumferential intervals on the tube of 45{dollar}spcirc.{dollar} Bubble phase and emulsion phase properties and heat transfer coefficients were determined and their dependence on bed temperature, fluidization velocity and particle size were established. Existing correlations for the prediction of time- and space-averaged heat transfer coefficients were evaluated. From these, new relations are presented to correlate local emulsion and bubble phase heat transfer coefficients. These expressions are{dollar}{dollar}rm Nusb{lcub}p,e{rcub}=8.95(1-varepsilon(theta))sp{lcub}2/3{rcub}+0.16 Arsp{lcub}0.3{rcub} Resbsp{lcub}p,mf{rcub}{lcub}0.5{rcub} Prsp{lcub}1/3{rcub}{lcub}left(1-varepsilon (theta)right)sp{lcub}0.133{rcub}over varepsilon(theta)sp{lcub}0.8{rcub}{rcub}{dollar}{dollar}for the emulsion phase, and{dollar}{dollar}rm Nusb{lcub}p,b{rcub}={lcub}Resbsp{lcub}p,mf{rcub}{lcub}0.73{rcub}over Resbsp{lcub}p{rcub}{lcub}0.3{rcub}{rcub}{dollar}{dollar}for the bubble phase. These correlations each predicted heat transfer coefficients for the conditions in the present work within {dollar}pm{dollar}15%. They apply to the range of conditions investigated in the present work: {dollar}rm44,000