# Air flow via thermal power?

1. Oct 20, 2015

### William89

Hello everybody,

I have a computer case project and I need to create a fanless (passive) cooling.

I feel excited of the idea to use paltier thermoelectric coolers, but their efficiency is considered very low, because the hot side is usually exhausted via passive radiators.

So I came up with an idea but I have no idea either if it is applicable or if it is even valid.

I though of using series of paltier coolers at the bottom of the case and put 2 sheets of thermal conductive material between them. The cold side (upper side) will constantly cool a water tank which will cool the computer components. The hot side will heat an air tank (actual bottom of the case). The air there will dilate and it will become lighter so it will try to go up, so by using a tube that goes to the top it will create a very very low air flow by pushing the room temprature air. So, in order to increase its effect I though to put a spiral, with diminishing inside diameter, tube to play the role of a turbine.

Since my physics knowledge is elementary, I'm sure I'm missing something important even in theory.

Could you help me out?

Thank you

2. Oct 20, 2015

### 256bits

The hotter air rises due to bouyancy. Being less dense, and in a gravitational field, it is being displaced by the denser cooler air at room temperature.

Not sure what you mean by spiraling tube acting with diameter reducing, as acting as a turbine and increasing the effect.
Some sort of way of increasing the velocity and amount of the air passing by the hot side and increasing the convective transfer of heat perhaps.

3. Oct 24, 2015

### CWatters

Your spiral tube might increase the air speed at the expense of the flow rate. You will need to decide what matters more.

4. Oct 26, 2015

### JBA

One thing that I think you are possibly overlooking is the negative effect of heating the top of the water in your water tank. By applying the heat at that location you eliminate any of the convective water circulation that assists conducting heat and forces you to depend entirely upon the stagnant downward heat flow rate of the water in the tank, i.e, you will end up with a situation where the hottest water in the tank be stagnated against the surface you are trying to cool and the coolest water stagnated against your thermoelectric units. That is why we always heat water from the bottom and ice works for cooling because it floats to the top; both of which promote water circulation to the alternate region of the container and prevent temperature stratification.

An additional consideration you need to be careful about is insuring that the ambient air temperature in the computer's environment will always remain low enough to allow the thermoelectric coolers to operate at the heat removal rate your require. What is really required is a total source input to convection cooling output thermal balance calculation for your whole concept.