Bill, 

Since Charlie hasn't posted any pictures or sketches of his design, I was referencing more what you'll find in auto installations than in a/c.  Still the principles are the same, namely that the coolant naturally flows to the bottom and air goes to the top.  If it gets low enough, the pump will begin sucking air and will soon loose prime.  This will happen much quicker if you're drawing off the upper tank.  Of course, if the radiator is located below the engine it will take longer for this to happen than if it is beside the engine because the air pocket will be inside the engine rather than in the radiator.  If you have a coolant leak in flight, you'll benefit from more time to get on the ground rather than less. 

I don't see where it makes any difference which tank you return the coolant to, but when supplying the pump, any air will risk loss of prime.  So, it makes sense to me to draw from the bottom and return to the top.  At least that's how I understand it.

 In the end its Charlie's decision.

Mark

On Mon, Oct 22, 2012 at 11:10 PM, Bill Schertz <wschertz@comcast.net> wrote:

I guess that I don’t understand this (Mark’s) comment. I am assuming that the radiator is lower than the water pump in any circumstance, since in general it is either below the engine, or on the side like Tracy’s. The Mazda pump is very high, and any loss of coolant will cause loss of prime if air gets in the pump, but whether the outlet of the pump goes to the bottom of the radiator, or the top, I don’t see the difference. What am I missing?

 

Bill Schertz
KIS Cruiser #4045
N343BS
Phase one testing Completed

 

From: Mark Steitle

Sent: Monday, October 22, 2012 6:25 PM

To: Rotary motors in aircraft

Subject: [FlyRotary] Re: flow path in conventional radiator

 

Charlie, 

 

So, with the bottom-up flow what what happens if you get a little low on coolant?  My guess is the pump will start pumping air along with the coolant, and eventually loose prime altogether and the remaining coolant will stop flowing, followed shortly by a catastrophic boil-over.  This may be why auto makers favor the top-down flow design.  The Mazda's water pump is already very high up on the engine.  I wouldn't want to aggravate this even more.  Also, the cross-flow design doesn't suffer this failure mode, assuming you draw from the lower hole.

 

Mark S.   

On Mon, Oct 22, 2012 at 2:05 PM, Bill Schertz <wschertz@comcast.net> wrote:

Charlie, I am using two evap cores in parallel, with system pressure limited to 10 psi on the expansion bottle. When the engine is running, the pressure measured at the inlet to the cores (exit of the pump) is a function of RPM and can rise to as much as 20 psi (10 psi over system pressure in the expansion bottle).

 

Having the flow enter the bottom of the radiator and out the top, then going to the inlet of the pump sounds like a good way to avoid problems.

 

Bill Schertz
KIS Cruiser #4045
N343BS
Phase one testing Completed

 

From: Ben Haas

Sent: Monday, October 22, 2012 1:06 PM

To: Rotary motors in aircraft

Subject: [FlyRotary] Re: flow path in conventional radiator

 

Unless there is a serious restriction through the radiator  I can't imagine there would be anything greater then 1 psi over system pressure caused by pump output.  As for the reverse flow, ie, bottom to top,,, It's called counter flow, and yes it can work. My set up has worked flawlessly for 500 hours and I use the Moroso swirl / pressure tank and a air bleed line from the output of the radiator...  About 3 minutes into this video shows my set up.....
 
http://www.youtube.com/watch?v=rCNnEgRkdXc&context=C3e091d3ADOEgsToPDskKmHo69I6bUDuoBHd5YSUfu

Ben Haas
www.haaspowerair.com

 

---

To: flyrotary@lancaironline.net
Date: Mon, 22 Oct 2012 12:40:11 -0500
From: ceengland7@gmail.com
Subject: [FlyRotary] flow path in conventional radiator

I've been doing research on radiators, & my 1st 'experiment' will be a conventionally configured radiator (downflow design) with inlet & pressure cap on top. In reading about issues with conventional radiators, a common complaint is pressure venting due to the water pump + system pressure exceeding the cap's rating. Crossflow types like the Sirocco are supposed to avoid this because the cap is at the mid-point in the flow through the rad, which drops some of the pressure seen by the cap.

Here's my question: Is there any reason a conventional rad can't be fed from the bottom, instead of the top? This would achieve similar effect as the crossflow cap location (all the way to the end of the flow path) & any air could be vented using the existing fittings. I'm also considering the removal of the spring loaded seal, & moving the pressure cap function to a separate swirl can. By doing this, the existing over-pressure port could function as the air removal port in the top tank of the radiator.


What am I missing?

Thanks,

Charlie