Validation of Natural Convection heat transfer problem
 

I am working on the project in which my initial results have to be validated with experimental or other theoritical methods.
The problem is fairly simple, in the cuboidal reservoir, a cyllendrical tube having constant temperature.
I am using Boussinesq hypothesis and gravity. Please can any one suggest me how to validate this fluent results. I am using the co-rellation by churchill but the error is too large.