"

no matter which leg of the coolant system you pick up the heat from the oil cooler, you raise the temp of the coolant loop by the amount of additional heat; so the rejection temp of the rad is higher either way."

Not so fast!   Here's my take on it.  

Yes,   the total heat rejection of the rad has to end up being the same.  BUT with the cold side oil cooler, to keep the engine coolant inlet temperature (and temperature of the engine block) the same requires a 33% larger rad (compared to what we needed a separate air to oil cooler).   Actually, the rad has to be even bigger than this because we have to have the rad outlet temp even lower to compensate for the rise in coolant temp due to temp rise of oil cooler.   That means the median temp of the rad is lower and therefore less efficient.

If you cool the oil on the hot side of the coolant circuit,  the inlet temp of the rad is now higher than in the cold side scheme and the required rad size and/or the airflow through the rad size increase is smaller due to the higher delta T between air and rad.  This results in less cooling drag.

That's my story & I'm stick'n to it : )

Tracy

On Sun, Dec 19, 2010 at 12:13 PM, Al Gietzen <ALVentures@cox.net> wrote:

For maximum cooling of the oil from an oil/water HX (heat exchanger) you’ll want to plumb the oil from engine out to the cooler; and plumb the cooler between the radiator and the engine return.  And I’m not quite sure about Tracy’s point because no matter which leg of the coolant system you pick up the heat from the oil cooler, you raise the temp of the coolant loop by the amount of additional heat; so the rejection temp of the rad is higher either way.  The assumption is, of course, that you have sufficient capacity to keep the coolant exiting the engine below boiling for extended high power.

 

On my Velocity 20B installation I have a primary radiator in the cowl, and a secondary in the wing root; plumbed in parallel. The wing root rad has an in-line 170F thermostat, and generally only comes on line during extended climb. No thermostat in the engine that would restrict flow and add a potential failure mode.

 

I have an oil/air cooler and an oil/coolant HX, also plumbed in parallel. The oil/coolant HX is plumbed to the exit of the primary rad.  The oil temp runs about 20F higher than the coolant (measured at oil return and coolant out). I could probably reduce that difference by restricting flow to the oil/air cooler forcing more through the oil/coolant HX; but I’m quite happy with the way things work. 

 

Over 200 hours and lovin’ my rotary more all the time.

 

Al G

 

----- Forwarded Message ----
From: "CozyGirrrl@aol.com" <CozyGirrrl@aol.com>
To: keltro@att.net
Sent: Mon, December 13, 2010 4:05:31 PM
Subject: Re: Fw: [FlyRotary] Re: Fw: Water temps

Thanks Tracy for the adjustment in my thinking. I don't want to target temps unrealistically.

Where does that leave us with our pick up and return points for the oil/water cooling system? If the oil were being cooled with water only and we wanted the best possible chance at that, wouldn't we want to feed it the cooler water from the high pressure side of the pump prior to entering the block?

 

Whatever space we would use for an oil/air cooler takes away from potential coolant radiator space. Putting the two side by side becomes less efficient spacewise for both due to losses for structure etc. If it is not possible to cool the oil adequately with water alone then we'll need to back up a little and make other layout plans. I remember Richter's Cozy III with three P-51 scoops, it got the job done but was like dragging a parachute in drag.

 

Kelly, to your comment below, while I am sure we'd have no problem putting adequate heat into the oil, I am very concerned about keeping any more than just enough out of it. Much easier going one way then the other =)

...Chrissi

 

In a message dated 12/13/2010 2:49:02 P.M. Central Standard Time, keltro@att.net writes:

Chrissi,

    My own opinion is that after warm up and in flight the oil temp leaving the engine before the

coolers (air or water  to oil) will almost always be well above 160-180 F..............If it is not this

high then the oil to water cooler will actually help warm it to a more efficient temp.........IMHO

 

   Somebody correct me if this is a fallacy !!.......................<:)

 

Kelly Troyer
"DYKE DELTA JD2" (Eventually)

"13B ROTARY"_ Engine
"RWS"_RD1C/EC2/EM2
"MISTRAL"_Backplate/Oil Manifold

"TURBONETICS"_TO4E50 Turbo

 

 

---

From: "CozyGirrrl@aol.com" <CozyGirrrl@aol.com>
To: keltro@att.net
Sent: Mon, December 13, 2010 12:52:06 PM
Subject: Re: Fw: [FlyRotary] Re: Fw: Water temps

This is where I get confused:

 

said previously,

-ideal water temp = 160*~180*F

-ideal oil temp = 160*F

 

If we are cooling oil with water that is at best hotter than the ideal temp of the oil, then are we not adding heat to it rather than removing it?

 

If we are trying to cool oil, why would we feed the highest temp water to the oil/water cooler rather than the coolest temp water by tapping into the pump housing where it enters the block?

 

Based on feedback, the water entering the block may be as low as 150*~160*F, would this be cool enough to do an adequate job of cooling the oil?

 

Also, which model of Mocal is being used?

 

...Chrissi