Dear Sir, You have to follow thes steps:

1- get results for each case by fix one parameter and changers the others.

2- Then you can calculate the Nusselt number depending on the target section.

3-Register the results of Nusselt number vs the height

4- Register the results of Nusselt number vs the fin length

5-Register the results of Nusselt number vs the collector length

6- Resist all these results and export it to Microsoft Excel

7- Draw the figures for each parameters.

Good Luchk