I wish I could have chance to measure in real model, but I only have experimental datas to compare normalized Nusselt number, that is why I am still trying to figure out what is the expressions they used. There will be some errors but at least I am looking for a true expression to find Nu number. Thanks again, my results looks close to experimental results but still a bit suspicious about expressions I used.
I have those boundary conditions based on article:
Constant heat flux at the bottom wall of channel
Constant inlet temperature
defult fluid properties ( that is also looks strange, because at undergrad degree, we were taking average temp from inlet and outlet to reach desired values)

Thanks again