Hi Rajesh:

Find attached two review papers on heat transfer enhancement using nano-fluids. You have several examples on particle types, size and concentrations that can be used with oil as base fluid and the best methods to prepare the nano-fluids.

Good Luck 

Chaouki Ghenai  

using two step method in preparing the nanofluid is the most common method, you will find a lot in the literature about this, here is one of them

http://www.nanoscalereslett.com/content/pdf/1556-276X-6-391.pdf

Regards

Saleh Etaig

Thank You Very much Saeid, if possible then please tell me for the Al2O3 Powder(50nm size) which surfactant will be better for me.

Dear Rajesh,

There are surfactants such as CTAB, gum arabic, SDS and SDBS.

So when you search a Journal, keep them as keyword and search along with the nanoparticle you wish to use.

However you must also understand that inclusion of surfactant can also increase your nanoparticle diameter.

So I recommend, lower concentration with surfactant for an optimized test run.

However, if you are going to use this for an experimental study, that too for a turbulent flow, then, try to have the test run immediately after the nanofluid is prepared, which makes sure that the fluid is in continuous run and there is no possibity of clustering immediately.

Thanks a lot