04/00534 Mineral oil residues on HVAC components: measuring methods: Asikainen, V. et al. Building and Environment, 2003, 38, (8), 1057–1061.

Abstract

An inviscid model is developed to describe gross solid circulation and gas backmixing in axisymmetric fluidized beds. Two distinct cases are shown to arise: 1.interstitial gas moves upwards everywhere; and2.interstitial gas circulates giving rise to loop formation in an annular region near the wall.It is shown that gas back-mixing is a highly local phenomenon which explains the anomalously high “apparent wake fractions” estimated in the literature. The model predictions as well as analysis of published observations indicate the “onset” of gas backmixing near the wall to occur just above the minimum fluidization (or minimum bubbling) plint. An analytical expression derived to estimate the fraction of bed area available for fresh gas movement upwards indicates that the “dead volume” of the bed is usually greater than 50% and at times can approach even 90%.