You need to be more specific in your question.

No matter where you have studied the laws of physics remain the same.

Start here - what is the face area of your evaporator?

Let us say it is 2sq.m.

Your fan handles 50 cu.m/s.

What is the velocity of the air through the evaporator?

Now change the fan size and speed but maintain 50 cu.m/s airflow.

Once again - What is the velocity of the air through the evaporator? If you say it has changed please explain how.