I suggest you reading these articles:

1-A review on natural convective heat transfer of nanofluids

http://www.sciencedirect.com/science/article/pii/S1364032112002602?np=y

2-Natural Convection of Water-Based Nanofluids in a Square Enclosure with Non-Uniform Heating of the Bottom Wall

http://www.scirp.org/journal/PaperDownload.aspx?DOI=10.4236/jmp.2013.42021

3-A study of natural convection heat transfer in a nanofluid filled enclosure with elliptic inner cylinder

http://www.emeraldinsight.com/doi/abs/10.1108/HFF-07-2013-0225

4-Natural convection heat transfer of nanofluids along a vertical plate embedded in porous medium

http://www.nanoscalereslett.com/content/8/1/64

Hello Ravi,

Nanofluids for natural convection may augment or deteriorate the heat transfer since the results published in the open literature have shown mixed results. A majority of experiments for natural convection were conducted on Al2O3-water nanofluid and the results showed that the heat transfer coefficient degrades due to the addition of nanopartices in case of natural convection.

But its too early to say that nanofluids are not suited for natural convection applications.We must perform experiments on various  nanoparticle-base fluid combinations to get a conclusive result.

Our forced-convection experiments with CNT-based nanofluids suggest that almost none of the new theories can produce reasonable results in terms of prediction of convection coefficient enhancement. Therefore, I would not rely on any of the numerical results available in published research so far. Even with experimental studies, you have to be very careful as we found some researchers have made significant errors in their measurements.

In general, and in response to your question, I would say "Yes". But it depends on your mechanism. For some instances of augmentation, you can refer to the following papers:

Arbaban M, Salimpour M R. Enhancement of laminar natural convective heat transfer in concentric annuli with radial fins using nanofluids. Heat Mass Transfer. DOI 1 0.1007/s00231-014-1380-7 (2014).

Sheikholeslami M, Rashidi M M, Al Saad D M, Firouzi F, Rokni H B, Domairry G. Steady nanofluid flow between parallel plates considering thermophoresis and Brownian effects. Journal of King Saud University – Science (2015).

Sheikhzadeh G A, Arbaban M, Mehrabian M A. Laminar natural convection of Cu-water nanofluid in concentric annuli with radial fins attached to the inner cylinder. Heat Mass Transfer. 49 (2013) 391–403.

The following book may provide the answers on this and related topics.

Aroon Shenoy, Mikhail Sheremet, Ioan Pop. Convective Flow and Heat Transfer from Wavy Surfaces: Viscous Fluids, Porous Media, and Nanofluids, CRC Press, Taylor & Francis Group, Florida (2016).