What is the function of the preheating pipe under the Volkswagen intake branch pipe?

Two water pipes on the throttle body are used to heat the throttle body, one is the water inlet pipe and the other is the water outlet pipe, which can lead the engine coolant to the throttle body to heat the throttle body. This is actually heating the intake air, which is to increase the intake temperature, facilitate the evaporation and materialization of gasoline, and facilitate the mixing of gasoline and air; On the other hand, when the engine works in a low temperature environment, it is easy to freeze on the throttle due to the low intake temperature. After adding the heating water pipe of the throttle body, the temperature of the throttle body can be increased and the phenomenon of icing on the throttle can be avoided.