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Hi Chad,
Good suggestion. I have no idea whether Subarus may have a cavitation problem at higher rpms. I think the rotary takes over 7500 rpm to get into that problem region. I've never had that problem {:>). However, if a cavitation problem existed which reduced the flow rate of the 50/50 mixture and then they filled up with the higher viscosity NPG, then that would tend to eliminate/reduce the cavitation due to its higher viscosity as you suggested.
Then we would end up with a higher effective flow rate for the NPG and that would indeed lower the delta T required because of the large Mass flow. Certainly sounds like a plausible possibility. I still have a tiny bit of a problem because as I recall even at lower rpms/ground run-ups for example, folks have reported lower temps with NPG - seems unlikely caviation would be present then. But, cavitation reduction could certainly be part of a the answer.
Ed
----- Original Message ----- From: "Chad Robinson" <crj@lucubration.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Saturday, February 04, 2006 9:05 PM
Subject: [FlyRotary] Re: NPG Coolant Temperature vs 50/50
Ed Anderson wrote:
Delta T = Q/cM, now if the combined effects of c and m provide 13% less heat transfer capability than the 50/50 mixture that would indicated that to carry away the same Q at the same flow rate, the delta T of NPG+ would need to increase by 13%. So if I were getting 180F with the 50/50 for the same Q load (and flow rate) then with NPG+, I would expect 180 *1.13 = 203F. Yet, if I understood correct we have reports that lesser temperatures results noted by users of NPG - this leaves me a bit puzzled.
I don't have the answer, but how about a hypothesis? Suppose they have a cavitation problem. A more viscous fluid tends to reduce the onset of cavitation, no? And is there any data on what pressure their system is being run at?
Regards,
Chad
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