Ventilation and induced draft two ways:
① blast-style: the first air flow through the fan into the tube bundle.
② wind-induced type: air flow through the first tube into the fan.

The former operating costs more economical, the turbulence generated by heat is beneficial to use more. The latter air distribution is uniform, is conducive to precise temperature control, low noise, is the development direction. The outlet temperature of the hot fluid is mainly controlled by adjusting the air volume passing through the tube bundle, that is, adjusting the blade pitch angle, the fan speed and the opening degree of the shutter. Easily condensable winter, easy to freeze the fluid, hot air circulation or steam heating can be used to adjust the fluid outlet temperature.