Noninvasive measurements of gas exchange in a three-dimensional   fluidized bed using hyperpolarized 129Xe NMR
  We present a novel NMR technique that provides a non-invasive, direct measurement of gas exchange in a three-dimensional gas-fluidized bed of solid particles. The NMR spectrum of hyperpolarized 129Xe gas in an Al2O3 particle bed displays three resolved peaks corresponding to xenon in bubbles, the interstitial spaces (emulsion), and adsorbed on particles. Modified NMR exchange and saturation-recovery sequences, together with data analysis based on an exchange-coupled set of Bloch equations, yield gas exchange rate constants between the emulsion and adsorbed phases, and between the bubble and emulsion phases. The results are in approximate agreement previously unverified predictions from well-known models of fluidized bed behavior. Incorporation of NMR imaging methodologies would straightforwardly allow similar measurements on a spatially-resolved basis. 
Tina Pavlin, Ruopeng Wang, Ryan McGorty, Matthew S. Rosen, David G.   Cory, Donald Candela, Ross W. Mair and Ronald L. Walsworth