Hi, it may help if you describe in a bit more detail your experimental 'set up'. also Its not clear to me what you mean by maximum and minimum pressures.

How evenly distributed is the air flow across the 'bundle' of finned tubes?

If the equipment is anything like a air-cooled heat exchanger bundle which uses finned tubes, then the empirical method in the GPSA Handbook - Air-cooled exchanger section may be a good starting point. This also has a number of potentially useful references. Sorry, I don't have experience with Comsol.

Imagine a heat exchanger made of spiral finned tube shown in the file. It consists of 4 rows of tubes diverted parallel to the air flow. In the experiments I measured the pressure drop of the air passing through the closed rectangular channel. I modeled this in COMSOL. When I take the difference in the mean pressures at the inlet and outlet in the Comsol Model, it comes out much lower than the experimental results. But when I take the difference of the maximum and minimum pressures in the Comsol model, the results are very close to the experimental results. Is the second method acceptable for finding the pressure drop in numerical models? I wanted to ask this. The problem here is that I accepted the fins as thin wall, because my computer was insufficient. There is no problem in heat transfer, but it is very low in pressure calculation because of this acceptance.