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Hi Ron,
I understand your succinct and clearly spelled out process, but I guess where I depart is at step 3.
My point is if you change the core, you have changed both the mass flow and deltaT. You would not put a core 1/2 the frontal area of the original thin core without changing at least the diffuser cross section area not to mention the area after the core. So even if you left the inlet the same size, I am confident there is no way you would get the same mass flow as before, perhaps more, perhaps less, but not the same because by changing the core we have changed the parameters of the system and the flow through it.
I content that by selecting the characteristics of the thick radiator you can influence both the flow and the delta T.
But, I will readily admit that being confident does not necessarily equate to being correct - just confidently wrong {:>)
Ed
----- Original Message ----- From: "Ron Springer" <ron2369@sbcglobal.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Tuesday, November 13, 2007 2:54 PM
Subject: [FlyRotary] Thick vs Thin was : Diffuser Configuration Comparison
Assume you have two radiators:
1) Radiator 1 is twice the frontal area of Radiator 2
2) Same wetted fin area and fin spacing, so Radiator 2
is twice as thick as Radiator 1.
3) Same air inlet with same mass flow rate
4) Different diffusers, but both have no flow
separation and perfectly uniform flow arrives at the
radiator face.
5) Both radiators have the same average skin friction
coefficient and average heat transfer coefficient in
the boundary layers that develop across the fins (this
is a small stretch and could be refined, but it is not
going to change the trends in this example).
Then, because heat transfer and drag scale with
velocity squared, and velocity is twice as high for
the thick radiator, and the thick radiator would have
four times the heat transfer, but also four times the
drag. There is always a tradeoff between heat transfer
and drag.
That is my take on the situation.
Ron
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