22 and has a frame 231 and several flow guiding pieces 232 one end of each flow guiding piece 232 is connected with the frame 231 moreover the flow guiding device 23 further includes a connecting part 233 the other end of the flow guiding piece 232 is connected with the connecting part 233 the flow guiding pieces 232 in this embodiment can be disposed in a symmetric or asymmetric way in this embodiment the fan 21 is the above fan and the fan 22 is the below fan the fan 21 has a fan frame 211 an impeller 212 disposed inside the fan frame 211 several blades 2121 and a hub 2122 the blades 2121 are connected to the hub 2122 besides the fan 21 further has several static blades 213 connected with the fan frame 211 the fan 22 also has a fan frame 221 an impeller 222 disposed inside the fan frame 221 several blades 2221 and a hub 2222 the blades 2221 are connected to the hub 2222 the fan 22 further has several static blades 223 connected with the fan frame 221 in this embodiment the fans 21 22 can be axial flow fans they may have same or different structures however the rotation directions have to be the same the frame 231 of the flow guiding device 23 is connected to the fan frames 211 221 of the fans 21 22 the connection method can be fastening locking embedding or gluing the fan assembly 2 connected in.