In developing the ITP (induction thermal plasma) source for the thermal modification of micro-particles, it is crucial to comprehensively explore the effects of plasma torch dimensions, effects of plasma discharge conditions and particle parameters. Considering the plasma-particle interactions and particle loading impacts, a interactive flow model for argon-oxygen mixed-gas plasma is developed to investigate the performances of short (ST:138 mm) and long (LT:190 mm) induction plasma torches. Solving the model numerically using control volume algorithm, we predicted the plasma isotherm, injected particle's temperature history, trajectory, velocity and diameter at any location along its flight path for both the torches. In this model, the plasma is in local thermal equilibrium (LTE) i.e the temperatures of electron and heavy particle (ion or neutral particle) are the same. From the plasma isotherms of argon-oxygen, it is observed that higher plasma temperature (around 8000K at the torch exit) is obtained in short torch, compared with that of in long torch (around 5000 K at the torch exit). It has also been noticed that more particle diameter shrinkage is occurred in short torch than that of long torch.