Here are 2 ways to collect cooling data in a chassis. The anemometer is the cheapest way to do this. It is usually hand-held, but is not very accurate because the instrument needs to be in the airflow to take a measurement, thereby affecting the air stream. The double chamber measurement system is the most accurate way of collecting system impedance data. However, at a cost of a few hundred thousand dollars, it is not readily affordable. If a designer does not have ownership of these measurement devices, there are usually test labs that offer services to use them.