Getting colder up here in Canada and am looking to add a second heat muff without too much modification. For those who have done this I would like to know the pros and cons of muffs in series vs parallel; and of course learn from your experience.
Getting colder up here in Canada and am looking to add a second heat muff without too much modification. For those who have done this I would like to know the pros and cons of muffs in series vs parallel; and of course learn from your experience.
I think I have a solution, however. MOVE TO ARIZONA!
. . . . . Someone suggested filling the muff with aluminum "wool". Any PIREPS on that?
Jon, that's good info about two muffs in series not increasing heat appreciably -- but disheartening, because I've been meaning to do just that for the last few years. When it gets below about 25 degrees up there, my single heat muff and even electrically-heated seats just don't work that well. I end up feeling like I'm sitting in a refrigerator!
I think I have a solution, however. MOVE TO ARIZONA!
Besides, with the number of friends with -8s who have suffered from cracked canopies from the cold, I avoid it like the plague.
Well, my experience has been a little different. EVERY TIME I add a second heat muff in series I get MORE HEAT.......period . No exceptions.
...or Florida!
Dang it, just received a second muff ($130) from Spruce and $30 worth of Scat. Looks like I'll still be freezing my buns off! FYI, the last several seasons I had Vetterman mufflers installed. The heat was MUCH better than with a single stock muff.
Someone suggested filling the muff with aluminum "wool". Any PIREPS on that?
Yes, they have, but what ever is in there needs to be able to handle EGTemps and aluminum does not sound good for that. Others have used stainless scrubbers but most reports (in my memory) did not report it as a solution.
To Alex's point, counterflow is theoretically more efficient. However, in this application, it is insignificant, methinks. The velocity of the primary fluid is very high, the amount of heat being transferred is a small percentace, and the exit delta Ts are still huge. SCAT is a draggy conduit, minimizing its length will increase flow on the secondary side and may deliver more heat to the cockpit.
I put some guesses together. A good cockpit heater might produce as much heat as a big hair dryer. Call that 1500 watts or 1.5 kW. A 200 hp Lycoming produces 50 hp per cylinder. Internal combustion is very inefficient from a thermal perspective, so let's say twice as much heat goes out the stack as is converted to useful shaft power. 100 hp is about 75 kW. So it looks like 3 % of the heat in an exhaust pipe is recovered by the muff. FWIW.
Reducing cockpit draftiness made a huge difference.
Stay warm!
Roger
Bill, is 25 cfm a known value? That would require 19 ft per sec airflow through a 2 inch scat, which sounds a bit high to me. Years ago I melted my crew id tags by leaving them too close to the heat inlet in a 172...
Roger