Collaborations with OIT Researchers

200 Frame MPEG movie (778kbytes)

(Note: The following description is a lightly edited snippet from one of Tom's emails).

[...] The data was gathered [...]using a Capacitance Imaging Device developed at FETC. The device consists of 4 rings (hence the 4x) surrounding the fluidized bed column, surrounding the volume to be imaged. Each ring consists of many (N ... I forget) electrodes. These electrodes are rapidly activated in pairs (N things, taken two at a time) and the capacitance of the bed between all the pairs is measured, instantaneously. This requires very rapid electronics. This capacitance data, between all possible pairs of electrodes at an instant in time, is the raw data used to generate each time frame. Information from calibration experiments (know voidages placed at know locations) where used to post-process this raw data. It is deconvoluted into a voidage value at 193 pixels per ring (hence the 193x), at each instance in time. This is the (processed) experimental information that is being visualized. It shows a voidage region in the bed (know and loved as a "bubble", although it is really a shock front in the granular phase --- there is no surface tension), moving up through the bed of granular material. This void doesn't trap gas and carry it though the bed, like a bubble would. Rather, it provides a by-pass for the fluidizing gas, since the gas can avoid the resistance of the bed by flowing through the bubble; the velocity of the gas is higher through the "bubble" than it is through the surrounding gas(* see below). This by-passing of the bed is not good from a chemical-contacting perspective, since the gas can't react with the particles unless it passes through the bed. However, the passage of the "bubbles" creates lots of mixing of the particles, which enhances reactions and heat transfer, so this is a positive feature ... life is a compromise!