I think we talked about this over e-mail, and I advised you that it was a very awkward way of trying to achieve something you could achieve with more conventional techniques (and at considerably less cost).
First, submerging a HDD would kill it pretty much instantly. Liquid entering the drive compartment would seriously alter mechanical dynamics and cause the heads to crash to the platter, like, instantly.
I would forget about fancy liquid cooling. Just get a bunch of really quiet Samsung Spinpoint drives (18dB at active read/write) and a nice passively cooled Epia mini-ITX to drive the lot. Fanless modest PSU and you're set.
If you use eight drives, the formula for calculating total noise: total dB = source dB + ( log2(no. sources) * source dB/10) reveals that you will get 23.4 dB of noise --hardly audible.
If you arrange the components right in a well-ventilated case, you can count on convection to do the rest. It may not sound as cool as submerged cooling, but an elegant and well-designed system for the job is in my opinion just as l33t.
