The dependency of the sublimation rate of Cu(thd)2solid particles on the space height in the sample cell and under various gas velocities was investigated. Our results can be satisfactorily explained via a working model based on the combined effects of diffusion and convection. We also showed that due to the ever decreasing precursor quantity during a CVD process, its sublimation rate will decrease accordingly. Nevertheless, this decrease can be minimized and be made negligible by using a pelletized sample and placing this pellet in flush with the cell rim (i.e. zero space height).