Should air flow into the laptop or out?

Should air flow into the laptop or out?

Hello!

The answer to your question would be both. 
Air should flow in and out of the laptop so that it should not over heat.

cool air – flow in

hot air – flow out

1. If you mean by "fan"  – The built in fan of the laptop where in you might have removed it.

• solution:

you should position the fan so that it takes cool air from the outside and blows it inside into the laptop. So that this would prevent the laptop from overheating. Also,this would help the processor cool down a bit better therefore making the performance of your laptop a bit better.

2. If you mean by "fan" – another external fan or "cooling pad" 

• solution: 

then you should place this one at the bottom of the existing fan of the laptop. The one that is already built into the device which takes cool air outside. As it would help in putting in cool air into the laptop and prevent any overheating.