A comparison of magnetic resonance, X-ray and positron emission particle tracking measurements of a single jet of gas entering a bed of particles

M Pore,G.H Ong,C.M Boyce,M Materazzi,J Gargiuli,T Leadbeater,A.J Sederman,J.S Dennis,D.J Holland,A Ingram,P Lettieri,D.J Parker

doi:10.1016/j.ces.2014.09.029

Abstract

Measurements of the lengths of a single jet of gas entering a packed bed were made using magnetic resonance imaging (MRI), positron emission particle tracking (PEPT) and X-ray radiography and the results compared. The experiments were performed using a Perspex bed (50mm i.d.) of poppy seeds: air at 298K was admitted to the base of the bed through a single, central orifice, 2mm in diameter. Poppy seeds (Geldart Group B, measured minimum fluidisation velocity with air at 298K and 1atm of 0.13m/s and particle density ~1060kg/m3) were used because of their high content of oil, which contains mobile protons and hence is suitable for MRI examination. The lengths of jet measured using the three techniques were in agreement between 50m/s<Uo<100m/s, where Uo is the superficial velocity through the orifice. Below Uo=50m/s, X-ray measurements of jet lengths were shorter than those measured using MRI. This was attributed to the minimum diameter of void, found to be 5mm, detectable in a 50mm bed using ultra-fast X-ray measurements. PEPT is most commonly used to calculate particle velocities, whilst jet lengths are usually calculated from determinations of voidage. However, the particle locations determined in this work by PEPT were used to calculate a fractional occupancy count, from which a jet length could be inferred.

Highlights

Measurements of the lengths of a single jet of gas entering a packed bed were made using magnetic resonance imaging (MRI), positron emission particle tracking (PEPT) and X-ray radiography and the results compared
X-ray radiography has been used to image beds non-invasively but early work was limited to projections through the bed which did not allow local values of properties to be calculated in 3D beds (Cleaver et al, 1995, Rowe et al, 1979)
The jet lengths measured using the three techniques were in agreement using orifice velocities in the range 50 m/s oUoo 100 m/s for the Geldart Group B particles used in the present work

Summary

Introduction

Measurements of the lengths of a single jet of gas entering a packed bed were made using magnetic resonance imaging (MRI), positron emission particle tracking (PEPT) and X-ray radiography and the results compared. To reduce discrepancies arising from the experiment itself, the techniques were compared by imaging the same, temporally-stable system: a single, axisymmetric jet in a packed bed of Geldart Group B particles. This system is reproducible and gives the same jet shape and size when set up in different laboratories. Blake et al (1990), Müller et al (2009) and Merry (1975)) are compared, those based on observations in 2D beds usually predict longer jet lengths than those from 3D beds. (1) The definition of a jet. (2) The definitions of the geometrical parameters of jets. (3) The experimental arrangement used. (4) The measurement technique and method of data analysis used

Results

Discussion

Conclusion