The heat transfer coefficient between a vertical cylinder and a fluidized bed at ambient temperature is measured for corundum in the case of five average diameters : 282 µm, 450 µm, 900 µm, 1425 µm and 1800 µm and four particle size distributions (PSD) : a reference powder (narrow cut), a gaussian powder , a binary mixture and a flat (wide) powder. The heat transfer (h) variations versus gas velocity (U_f) are presented. For the reference and the gaussian powders, the effect of particle diameter is discussed with respect to literature data and a new correlation is proposed. The PSD is proved to affect significantly the h vs U_f variation for all considered diameters. For segregative mixtures (binary and flat PSD) the h versus U_f curves are analyzed varying the vertical location of the heat exchange zone. Segregation phenomena are shown to affect strongly the heat transfer coefficient in the fluidization domain between incipient and complete fluidization velocities. The comparison between hydrodynamic and thermal experimental data for segregative mixtures shows that thermal measurements are well-adapted for segregation diagnostic and transition velocities measurement.