How should my air flow directions be in my Dell E510?

In what directions should the air flow in Dell E510 be.

Here is a picture of another Dell E510 very similar to mine (my PSU fitted fine in my case   , everything else seems to be very similar, except mine does not have a rear fan as of right now).



I did some research, and supposedly the Dell E510 model CPU heat sink fans exhausted the air to the front of the case, instead of blowing air onto the the CPU, or exhausting the air out to the rear of the case.

So, I bought a few small fans online and was just wondering how should I install them. For a rear fan (as mine does not have one right now), should I have it blowing toward my heat sink (the big black plastic in the middle), or have it blowing out of my computer?. The rear fan is a 80mm fan, I bought 2 of them. So that leaves me with one more 80mm to use. I bought a HDD fan off eBay so I am trying to figure out a way to make my HDD cooler by using that fan (still on the way), as I have been having trouble keeping its temperature down (been staying around 55C now). And I bought a PCI fan, which I will probably have it blowing on my Graphics card. I am up to more/different suggestions on how I should use them if you have any.

I am just a little confused because my model does not seem to be like most desktops. I heard that the front and sides are suppose to intake, and the rear and top are suppose to exhaust. However, for my model did not come with a rear fan, and it seems as if the front is for exhausting.

When I place my hand inside the cutoff of the Dell E510 case, I feel air blowing on my hand, which tells me that the heat sink fan is blowing air out of the front (I could be wrong).

I thought it would not be a bad idea to have the rear fan blowing air toward the heat sink, so that way the heat sink will intake some cool air, and exhaust it out of the front. Does that sound good or bad?

Let me know if more information is needed, and thank you reading, look forward to some response.