AM3894 heating so hot, is there any solution for cool down?

We are using AM3894 to our maintenance project for process image capturing and transfer it through GbE.
Our AM3894 board will mount in closed place for connecting with motor controlling MCU board and special sensors.
And we have something hot problem: AM3894 going to high temperature after power enabled.
Our system has closed to working without any air flowing possible for dust-free.
In normal case, for cool down CPU for using heat-sink with fan motor, but we can't use them by really special arguments. 
For cool down temperature in mechanism, we used heat-pipe on CPU to Aluminium base anodizing chassis.

So we have to using one of these items :

1. hardware sleep (CPU only, not memory) or suspending
2. WOL (Wake On LAN)
3. Partial CPU power down (useless function will be disabled)