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  #1  
Old 01-18-2022, 04:42 PM
rmarshall234 rmarshall234 is offline
 
Join Date: Jun 2008
Location: San Diego, CA
Posts: 346
Default Bronze Wool for heat muff

Has anyone tried using this instead of SS Wool for their heat muff? Anybody care to comment on bronze as a substitute for SS in this application?
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  #2  
Old 01-18-2022, 04:46 PM
gasman gasman is online now
 
Join Date: Mar 2007
Location: Sonoma County
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Want more heat?..... Reduce the inlet size to reduce the speed of the air passing through the muff.
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  #3  
Old 01-18-2022, 05:27 PM
Freemasm Freemasm is offline
 
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Location: Orlando
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Quote:
Originally Posted by gasman View Post
Want more heat?..... Reduce the inlet size to reduce the speed of the air passing through the muff.
Yes/no. Itís not quite so straight forward. Yes, reducing the mass flow will raise the HEx air outlet temp; however , the overall heat transfer goes down. Most of the related parameters are fixed. The primary heat transfer influence is the mean temperature difference (MTD); Heat exchanger temp to air temp.

Increasing surface area of the heat exchanger relevant surface area (A) can increase heat transfer though it would have to have physical contact with the hot surface or it could act like a sink.

Q=U*A*MTD. U being a function of film coefficients and fluid specific heats for those who suffered through Heat Transfer in college.

Itís a balance.
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  #4  
Old 01-18-2022, 05:33 PM
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Vlad Vlad is offline
 
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Quote:
Originally Posted by gasman View Post
Want more heat?..... Reduce the inlet size to reduce the speed of the air passing through the muff.
Or add a second muff in sequence.
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  #5  
Old 01-18-2022, 06:24 PM
gasman gasman is online now
 
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Quote:
Originally Posted by Freemasm View Post
Yes/no. Itís not quite so straight forward. Yes, reducing the mass flow will raise the HEx air outlet temp; however , the overall heat transfer goes down. Most of the related parameters are fixed. The primary heat transfer influence is the mean temperature difference (MTD); Heat exchanger temp to air temp.

Increasing surface area of the heat exchanger relevant surface area (A) can increase heat transfer though it would have to have physical contact with the hot surface or it could act like a sink.

Q=U*A*MTD. U being a function of film coefficients and fluid specific heats for those who suffered through Heat Transfer in college.

Itís a balance.
Well, It's a good thing that I didn't read this fifteen years ago.

I installed a 1.5 inch scat to the inlet of my heat muff with no noticeable change to outlet temps or comfort in the cabin. What I do notice is way more service room to the back of the motor. I do live in mild climate.

I sure can't argue with the educated. Please disregard my response to the OP.
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  #6  
Old 01-18-2022, 07:45 PM
Freemasm Freemasm is offline
 
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Quote:
Originally Posted by gasman View Post
Well, It's a good thing that I didn't read this fifteen years ago.

I installed a 1.5 inch scat to the inlet of my heat muff with no noticeable change to outlet temps or comfort in the cabin. What I do notice is way more service room to the back of the motor. I do live in mild climate.

I sure can't argue with the educated. Please disregard my response to the OP.
Wasn't supposed to come off that way but it's my superpower and I had a few minutes before a meeting to get my geek on.

Think about the iterations/improvements of GA heat muffs over time. Smooth surfaces gave way to corrugated-ish ones to increase area and turbulation (air mixing.) Air is a poor heat conductor, an insulator actually so it's important to have a good bit of turbulence/recirculation/etc. to bring as much of the quickly passing air into contact with the hot surface. Studs were added to increase both of the aforementioned; A and a component of U in the equation.

Putting steel wool into the heat muff could help; the steel that has contact with the hot surface specifically. The heated steel wool would increase the hot surface area plus the extra turbulation would bring more of the air into contact with the hot surface. Too much would probably be detrimental relative to the optimal amount. Bronze would probably be great; at first. It's a better conductor but once the surface started to oxidize, that would quickly diminish.

A decent design shouldn't need it. As Vlad mentioned, another HEx in series will help but it is diminished returns because of the MTD in the second muff.

As mentioned, the overall Heat transfer is more important than the outlet temp alone. The air passes into a cabin that is basically a big heat sink.
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  #7  
Old 01-18-2022, 08:06 PM
rmarshall234 rmarshall234 is offline
 
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Location: San Diego, CA
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Quote:
Originally Posted by Freemasm View Post
Bronze would probably be great; at first. It's a better conductor but once the surface started to oxidize, that would quickly diminish.
Thank you.

So maybe it becomes a consumable and I replace it each year at annual. At $10 / year that sounds like a good investment to me. Except for the servicing issue, I'd pay that much _per flight_ to stay warm.
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  #8  
Old 01-18-2022, 08:39 PM
rockwoodrv9 rockwoodrv9 is offline
 
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Location: Meridian ID, Aspen CO, Okemos MI
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Quote:
Originally Posted by rmarshall234 View Post
Thank you.

Except for the servicing issue, I'd pay that much _per flight_ to stay warm.
Boy you got that right. Ive been freezing on m flights! I am changing oil this week and looking to see if there is space for a second heat muff!!
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  #9  
Old 01-18-2022, 09:00 PM
Freemasm Freemasm is offline
 
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Location: Orlando
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If it oxidizes, it eventually comes apart. The pieces have to go somewhere.

I havenít tested such nor have any directly related experience. I have no idea how long it would be OK but I would be concerned.

Second or larger heat muff?

And/or heated seats?

Stay safe.
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  #10  
Old 01-18-2022, 10:43 PM
Darin Watson Darin Watson is offline
 
Join Date: May 2011
Location: Calgary, AB
Posts: 205
Default Have a look here

Posted this earlierÖ works great!

https://vansairforce.net/community/s...67&postcount=6
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