Digital X-ray Radiography (DXR), a non-destructive technique (NDT) is used to visualize and characterize the dynamics of the thermo-physical behaviour of wood during devolatilization in a hot Bubbling Fluidized Bed (BFB). X-ray radiographs of cube shaped Casuarina Equisetifolia wood of size ranging from 10 to 25 mm is used to visualize, interpret and quantify the thermal behaviour in terms of location and propagation of char front, intra-particle conversion, "true'' char formation time (CFT), and physical behaviour in terms of temporal and terminal shrinkage (transverse, longitudinal and volumetric). Also, initiation and orientation of sub-surface fissure in a devolatilizing particle, leading to fragmentation is identified and qualitatively discussed. A three dimensional (3-D) mathematical model has been used to predict the progress of intra-particle conversion and the predictions are compared with the experimental data obtained from DXR. It is found that the "true'' CFT inferred from DXR technique is 12% and 26% lower than that obtained by the Flame Extinction Time (FET) technique for a 10 and 15 mm particle, respectively. The terminal mean longitudinal, transverse and volumetric shrinkage are found to be in the range of 12-17%, 22-23% and 44-47%, respectively for all the particle sizes studied. The terminal volumetric shrinkage falls well within the range of 40-65% reported in the published literature. In contrast to the popular assumption in the devolatilization models, the variation of shrinkage with conversion is found to be non-linear in along-the-grain direction. From the present study it is verified/established experimentally (visually) for the first time the difference in rate of propagation of char front across and along the grain direction of the wood particle. The predictions of the 3-D model on progress of conversion compare well with the experimental findings of DXR technique. This technique can also be applied to other solid fuels. (C) 2013 Elsevier Ltd. All rights reserved.