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

Abstract

Magnetic resonance, PEPT and X-ray radiography were used complementarily. Length of jet of gas entering bed of Group B particles via 2 mm id orifice measured. Lengths were in good agreement for orifice velocities 50-100 m/s. Technique developed to use PEPT measurements to quantify jet length. a b s t r a c tMeasurements 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 (50 mm i.d.) of poppy seeds: air at 298 K was admitted to the base of the bed through a single, central orifice, 2 mm in diameter. Poppy seeds (Geldart Group B, measured minimum fluidisation velocity with air at 298 K and 1 atm of 0.13 m/s and particle density $ 1060 kg/m 3 ) 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 50 m/s o U o o 100 m/s, where U o is the superficial velocity through the orifice. Below U o ¼50 m/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 5 mm, detectable in a 50 mm 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.

Regimes of jetting and bubbling in a fluidized bed studied using real-time magnetic resonance imaging

“…Recently, magnetic resonance imaging (MRI) has proven to be a powerful tool for non-invasively investigating the dynamics of the particle [13,23] and gas phase [24,25] in 3D fluidized beds. This has included some works on the dynamics and geometry of gas jets [26][27][28]. However, those works have been applied largely to systems with a small bed diameter [26][27][28] and have not provided any temporally resolved measurements [27][28][29].…”

X-ray imaging of horizontal jets in gas fluidised bed nozzles

“…This result has been proven by Yates [11,19] and Newton [10] to be imputable to the invasive measuring technique based on the use of 2D reactors: here the walls exert a stabilizing effect on the jet, causing an increase in the penetration. Therefore correlation developed in 2D reactors are not accurate to predict the jet penetration in 3D reactors and, generally, in industrial cases [12,32]. The data gathered have then been compared with Yates correlation for the jet penetration prediction [11].…”

“…Non-invasive experimental techniques are invaluable for providing a detailed insight into jet penetration and general hydrodynamic patterns of fluidised beds at larger scale [12]. One such technique involves the use of X-rays to observe and quantify gas and solid flow patterns.…”

Magnetic Resonance Imaging and Velocity Mapping in Chemical Engineering Applications

“…The predictions of the DEM code were compared with the MR measurements of solids distribution, solids velocity and granular temperature as a function of the drag-force correlation used, as well as studying the effects of the value of coefficient of restitution and the thickness of the bed used in the simulation. Müller et al (122) have summarised much of the work that has used MR to validate DEM simulation codes.There has also been interest in comparing the data obtained from MR, ECT, X-ray and positron emission particle tracking methods to study gas-solid fluidisation(123)(124)(125). The take home message from these comparisons is not: 'which method is best?'…”