Finally, there has been considerable talk here, in the

past, regarding the relationship between the intake size

and the radiator area; there have been fewer about the

relationship of the outlet size.  You have heated air

exiting your heat exchangers, that means it's expanding. 

You need enough outlet area to keep from bottlenecking

the airflow _after_ the rad, or you'll lose pressure

differential right when you need it the most.  That outlet

area has to take into account ALL the sources that are

adding heat to it - engine radiation, exhaust ...

 

My tupence,

Dale R.

 

 

We have good ol’ Charles law that says the expansion is directly proportional to the absolute temperature change.  Roughly, we may have an increase in the air temp of maybe 50 – 70 degrees F.  So if it is coming in at 80F (533R), the expansion ratio is only about 1.12.

 

Typically we would like the radiator area to at least 3-4 times the inlet area to slow the air to recover pressure and reduce drop across the core.  We’d then like to accelerate the air again before it exits; at something near the free-stream velocity.  Because of other losses, like sudden expansions at rad exit, or whatever; we don’t have good enough conservation of energy to get back up to full speed, so we need exit area greater than 1.12 time the inlet.  A rough rule of thumb might be a ratio of about 1.5.  And, of course, be sure to include all the inlet and outlet areas.

 

Al