Ali,
The problem with just changing the fluid specific heat is that
the model still won't take into account the impact of the latent
heat of vaporization that occurs in air as it passes through the
collector. If you're going to approximate an air-based collector
using Type50 you at least need to put a psychrometrics component
(Type33) after the collector and pass it the collector outlet
temperature and the collector's inlet humidity ratio
since the absolute humidity won't change across the collector as
the working fluid heats up. The Type33 will correct the exiting
air state when the collector is heating the working fluid.
Correcting the air after calculating the collector performance
isn't ideal. You also have to be concerned about flow through the
collector when there isn't enough solar energy to heat up the
working fluid. If the fluid is cooling down instead of heating up
(and it certainly can unless your controls specifically prevent
it) and it cools down enough that it drops below the dewpoint
temperature then water is going to condense out of the air as it
passes through. Again the Type33 will correct the outlet air state
and account for the condensation energy but again, it will only
correct it after the fact and the correction won't impact the
collector's performance.
A preferable solution would be that if you have access to it there are a number of air-based PV/T models available in the TESS Electrical library
kind regards,
David