Abstract: An apparatus and method designed to introduce jets of air or other fluids at some velocity into a chamber designed to dry, combust, heat or cool solid materials and gases, such as solid fuels, biosolids, biofuels or other solid materials and their off-gases. The apparatus may be designed to introduce these jets in a particularly beneficial arrangement with some velocity and often with a vertical component (usually downward) to produce large and small scale recirculation regions combined with impingement of the jet stream onto the lower surface of a chamber, thereby greatly increasing the rates of heat and mass transfer between the fluid and the solids near the bottom (as well as other parts) of the chamber, and mixing of the gases and fluids in the chamber.