Reply To: I am trying to find heat transfer rate from radiator through fins.

[Rob]

First off you'll need many more cells across the flow nanofluid channel: you need at least 6-10 cells across a flow channel to have a hope of predicting the flow. The other problem you have is that the fins are interacting with the bounding box to give skew (distorted) cells.
Have you done any of the tutorials? If not, go and review those and the other help videos. You also need to consider how much flow channel is needed to allow the flow profile to develop.