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Date: Sun, 30 Sep 2007 13:12:08 -0500
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Another cooling question
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Bobby J. Hughes wrote:
> Snip
> That's exactly what I HAD thought, until I was told that the air could 
> pass through too fast and not pick up as much heat. 
>  
> Mark... this is what I was trying to communicate. It could be totally 
> wrong so let's get more opinions.  Ed??
>  
> *With respect to exit area size only.  *
>  
> If the volume of air through the coolant radiator was moving faster than 
> *optimum* the air delta T would be lower than it would be with slower 
> air. Slower air at a higher delta T means less air needs to exit the 
> cowl.  What is optimum? Every install is unique so it needs to be viewed 
> \ identified on each installation. Ed uses a 30% duct air speed as a 
> reference point. If I understand this correctly the diffuser play a role 
> in duct airspeed. If the air is not being diffused optimally the 
> airspeed could be much higher than 30% through the part of the core. 
> Dennis H. and I observed airspeeds through a test core at 50% + without 
> a diffuser.
>  
> Your inlets are 72sqin with 306sqin core face for water and 24.75 
> sqin with 102 sqin for oil. Both are *competing* for the same exit area. 
> *IF* this is an exit area problem only then enlarging it should improve 
> both water and oil proportionally. Water should realize 2/3 of the 
> improvement and oil 1/3.  306 sqin vs 102 sqin. Your improvements after 
> opening the exit seem to track this very close. So increasing your exit 
> area further should show more improvements in both oil and water to a 
> point. But you do not need more water cooling improvements right?
>  
> Core 306 sqin at an airspeed of 115mph.
>  
> 40% or 46 mph = 8602 cfm   8602 cfm at a 50 deg air delta T = 7741 btu's 
> \ min
> 30% or 34.5 = 6451 cfm        6451 cfm at a 80 deg air delta T = 7741 
> btu's \ min
>  
> In this example 2151 cfm less air needs to flow through the water 
> radiator to produce the same btu rejection. So what effect would 2151 
> cfm less air through the water radiator and exit area have on the oil 
> cooler's ability to flow more air? Would it improve the oil cooler air 
> flow by 1/3 or 717 cfm? Not sure.  
>  
> Can your radiator produce a 80 deg air delta T? It may only produce 60, 
> 70 or??
>  
> Am I in left field here?
Analysis only valid if cores are identical in construction (resistance 
to air flow will likely be different with the different cores).