Passive cooling design is an important consideration in the environments rife with floating dust, blowing sand or other airborne particles. Though fan-assisted cooling is a more cost-efficient way to dissipate heat, its greatest disadvantage is that dust accumulation will clog fans and then reduce the cooling effect when the system is placed in a tight environment mentioned above. Users have to spend time and cost for maintenance and replacement. On the contrary, fanless passive cooling combining a ventless enclosure is free of such a problem. In addition, it can benefit users more, including silent operation and no vibration. In practice, the most common type of fanless passive cooling system is a heat sink.