USB fan works with the General fan is the same, different places is that the connection between the power in different ways.
Fan's main components are: AC motors. Its working principle is: the coil in the magnetic field force and rotation. Electrical energy into mechanical energy, and due to the resistance of the coil, so inevitably some of the electrical energy into heat energy. In addition, DC motors, brushless DC motor power motor in a small electric fan is used more and more widely.
Fans working (assuming the room with no external heat transfer) indoor temperature did not reduce, but will increase. To analyze the cause of temperature rise: electric fan work, due to the electric current through the fan coil, the resistance wire is so outside inevitably generates heat to heat, the temperature will increase. But why would people feel cool? because the human body has a lot of sweat, when after the fan works, indoor air can flow up, so they can promote the rapid evaporation of sweat, combining "evaporation need to absorb a lot of heat", so people will feel cool.