Heat exchanger muff project

[WesRagle]

HI Guys,

That's cheating!

I would sometimes eat lunch with an avid drag racer I used to work with. From him I learned the guiding principle that all drag racers live by. I think it applies here.

"If you ain't cheat'in, you ain't try'in".

Some observations.

Assuming you don't blast the sump, and ignoring the fact that my valve covers are hanging out in the wind, with the oil cooler cabin heat solution 100% of the thermal energy being extracted from the oil passes through the cockpit. Now, just like with the heat muff solution, it's a matter of balancing air flow with air temperature. But, you really don't have a choice with air flow. Since the primary function of the cooler is to cool the oil you have to accept whatever airflow is required to do that. The only way to change the airflow/air temperature equation is the change to a more/less efficient oil cooler.

Also, unlike the heat muff solution, there is a limited amount of heat available. It just happens to work out that the heat available is just enough.

So, it's just a matter of dumb luck that the oil cooler I chose and the amount of thermal energy available in the oil worked out to a satisfactory solution.

Concerning the heat muff solution, the problem faced is how to extract the heat from a near unlimited supply. Various techniques have been tried to increase the efficiency of heat muffs. The one that makes the most sense to me is modifying the muff by using a stretched out spring coiled around the exhaust pipe. You might pick up a little heat transfer from the spring but I believe the primary benefit would come from adding turbulence to the air flow. I don't know, I've never tested it.

One thing for sure, the pipes are hot. If you could keep the air in the muff longer (while maintaining a suitable flow rate) more heat would be transferred. The only way I see to do that is increase the diameter/volume of the muff. Since the typical muff designs aren't very "fat", and since a lot of the internal volume is taken up by the pipe itself, a small increase in diameter would double the volume of the muff thus keeping the air in the muff on average twice as long.

So, that's what I would try. Add some turbulence to the airflow through a muff of increased diameter.

Wes

[mike.smith]

HI Guys,

Assuming you don't blast the sump, and ignoring the fact that my valve covers are hanging out in the wind, with the oil cooler cabin heat solution 100% of the thermal energy being extracted from the oil passes through the cockpit. Now, just like with the heat muff solution, it's a matter of balancing air flow with air temperature. But, you really don't have a choice with air flow. Since the primary function of the cooler is to cool the oil you have to accept whatever airflow is required to do that. The only way to change the airflow/air temperature equation is the change to a more/less efficient oil cooler.

Also, unlike the heat muff solution, there is a limited amount of heat available. It just happens to work out that the heat available is just enough.

So, it's just a matter of dumb luck that the oil cooler I chose and the amount of thermal energy available in the oil worked out to a satisfactory solution.

Concerning the heat muff solution, the problem faced is how to extract the heat from a near unlimited supply. Various techniques have been tried to increase the efficiency of heat muffs. The one that makes the most sense to me is modifying the muff by using a stretched out spring coiled around the exhaust pipe. You might pick up a little heat transfer from the spring but I believe the primary benefit would come from adding turbulence to the air flow. I don't know, I've never tested it.

One thing for sure, the pipes are hot. If you could keep the air in the muff longer (while maintaining a suitable flow rate) more heat would be transferred. The only way I see to do that is increase the diameter/volume of the muff. Since the typical muff designs aren't very "fat", and since a lot of the internal volume is taken up by the pipe itself, a small increase in diameter would double the volume of the muff thus keeping the air in the muff on average twice as long.

So, that's what I would try. Add some turbulence to the airflow through a muff of increased diameter.

Wes

Hi,

The valve covers aren't hanging in the wind; they are under the baffle material and have no air flow over them. So they stay pretty toasty.

I tried the springs inside and that didn't make a difference. As I noted in the video I have tried many iterations on changing the area of the inlet and the outlet, and what I have now produces the best, though not satisfying, results.

The muffs that I have are the ones custom made by a guy for AC Spruce, and they have lots of metal "spikes" inside to capture heat, rather than using springs. The muffs are about as wide as they can get without beginning to impinge on things in the engine compartment, especially the pushrod tubes. I think the "muff" solution for a VW is just never going to prove to be effective. I would love for someone to prove otherwise, so anyone who wants to experiment should use what I've learned and let us know if you get any useful improvements in the system.

[BRS]

I asked Joe at RevMaster about moving the oil cooler (so as to use it for heat) and if the air going over the oil pan fins was important. His answer was interesting and informative (ie. Didn't realize my case is magnesium). Here is what he had to say....

The linear expiation coefficient of your magnesium engine case
is a issue. Iron is 10 aluminum is 21-24 mag is 25-26.5
The hotter the case temp the larger the main bearing bores become
and the strength of the case depreciates.

The oil temp represents the temprature of the case. We try to keep the
oil temp around 180 F or lower. Hot day climb outs included. The engine
is oil cooled as well as air cooled. Over the years our competitors have
run oil temps as high as 240F resulting in many negative issues including
damaged engine cases.

[GordonTurner]

Wes.

How is the oil cooling in the summer. Is the airflow through the cooler when the firewall valve is in “bypass” approximately the same as the normal oil cooler installation would experience? I am impressed by your setup for the heating in the winter end of the operation, but have you used it during the cooling in the summer end? Very nice fabrication.

Gordon

[WesRagle]

HI Guys,

Mark: Sorry that your thread got hijacked. It wasn't my intent.

How is the oil cooling in the summer. Is the airflow through the cooler when the firewall valve is in “bypass” approximately the same as the normal oil cooler installation would experience? I am impressed by your setup for the heating in the winter end of the operation, but have you used it during the cooling in the summer end? Very nice fabrication.

Right now the summer performance is just OK. It's pretty much balanced with CHTs. As long as CHTs aren't approaching 400 Oil temp will be fine. Last summer I don't recall seeing Oil Temp above 210.

Just looking at the setup you might expect the limiting factor to be the the small outlet at the flapper valve. That's not the case. It's all about the oil cooler input. I've learned that twice now, once on #664 and again on the Onex. Here is a link to a post I made while trying to get my Oil Temps under control.

https://sonexbuilders.net/viewtopic.php?f=5&t=5226&start=150#p43598.

If the little scoop would not have worked I would've had to flip/swap things around and figured out how to go with pure ram air, maybe off the rear baffle.

The oil temp represents the temprature of the case. We try to keep the
oil temp around 180 F or lower. Hot day climb outs included. The engine
is oil cooled as well as air cooled. Over the years our competitors have
run oil temps as high as 240F resulting in many negative issues including
damaged engine cases.

That's interesting. I doubt many VW guys keep their oil that cool on climb out. I'm curious where oil temperature is measured on the RevMaster. There can be a lot of variation depending on where it's measured and the airflow around the sensor and surrounding case. Here is a link to a discussion of oil temps showing how sensor readings can be influenced by air flow around the sensor.
https://sonexbuilders.net/viewtopic.php?f=21&t=5124&hilit=thermal+sensors&start=10#p38921

Worst case, https://shop.vansaircraft.com/cgi-bin/shop.cgi?ident=1636601427-228-249&browse=engines&product=oil_shutter

Wes

[BRS]

HI Guys,... I'm curious where oil temperature is measured on the RevMaster. ...Wes

R2300 Oil Sensor is mounted on the back right side (passenger) of the oil sump. Thus the sensor is in the oil of the sump.

[Wood]

HI Guys,

Mark: Sorry that your thread got hijacked. It wasn't my intent.

Wes

Hi Wes
No apologies needed. It’s all good, we’re all here for one reason. Thank you for the info on this and if I may say. Fabulous idea. I’ll come back to this when I get my other issue figured out.

Mark.