Densely lined with wedge-shaped hollow shaft hollow blades, heat medium through the hollow axial flow through blades. Unit effective volume of a very large area of heat transfer, heat medium temperature from -40 ℃to 320℃ , can be water vapor, may also be liquid-type: such as water, oil and so on. Indirect conduction heating, the air does not carry away the heat, the heat is used to heat materials.