This article helps to find the serial number for Fan Tray in QFX5100, as this module serial number cannot be viewed through the CLI. 

Below shows the example of the CLI output of "show chassis hardware" and "show chassis hardware extensive" on QFX5100 regarding to Fan Tray.

root@switch> show chassis hardware

Hardware inventory:

Item       Version Part number Serial number   Description

...

Fan Tray 0                        QFX5100 Fan Tray 0, Front to Back Airflow - AFO

Fan Tray 1                        QFX5100 Fan Tray 1, Front to Back Airflow - AFO

Fan Tray 2                        QFX5100 Fan Tray 2, Front to Back Airflow - AFO

root@switch> show chassis hardware extensive | match fan
Fan Tray 0                                               QFX5100 Fan Tray 0, Front to Back Airflow - AFO
                                 FRU Model Number:  QFX5100-FANAFO
Fan Tray 1                                               QFX5100 Fan Tray 1, Front to Back Airflow - AFO
                                 FRU Model Number:  QFX5100-FANAFO
Fan Tray 2                                               QFX5100 Fan Tray 2, Front to Back Airflow - AFO
                                 FRU Model Number:  QFX5100-FANAFO

In order to get the serial number for the Fan Tray module, we need to physically remove the Fan Tray module from chassis, and then read the serial number from the serial number ID label.

Below picture shows the serial number ID label location of the QFX5100-96S-FANAFO module, and it's the same location for the AFI module.

QFX5100 Hardware Guide