VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics


Go Back   VAF Forums > Main > RV General Discussion/News
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #21  
Old 06-30-2017, 08:24 AM
rv7boy's Avatar
rv7boy rv7boy is offline
Forum Peruser
 
Join Date: Jan 2005
Location: Austinville, Alabama
Posts: 2,458
Default

Brad's (ChiefPilot) idea is similar to one I've thought of before. Think of the diffusers as fins, as those on our cylinder heads. First you need a good contact area for each piece of SS to contact the pipe for good conduction heat transfer. Then you need enough fin area for good convection heat transfer into the air stream.

There are equations from too far back in my education to calculate the optimum size of the fins. Also, I'm not sure SS offers the best Thermal Conductivity compared with other alloys like Aluminum or copper. But if Brad says it works, then I believe him. (P.S. The Thermal Conductivities of Aluminum and Copper are about 5X and 8X, respectively, that of Stainless Steel, per The Engineer's Toolbox.)

Fin design is a science, although there is room for empirical development. The thickness of the fin is as important as the height and length of the fin.

The problem I see with the steel wool and coiled safety wire is inadequate contact area (square inches) with the pipe to assure good conduction heat transfer from the pipe.

Back to the original topic regarding welded studs. IMO, the studs won't have enough surface area for good convection heat transfer into the air stream unless you use a fan to increase air velocity. And the fan would draw more electrical load. And the hose clamp idea offers less chance of damaging the exhaust pipe than welding. You don't want any cracking of the exhaust pipe especially in this area. (Engine exhaust to the cockpit.)

Disclaimer: Comments appearing here are the opinions of the author. Any use of these comments for commercial or private endeavors are done at the risk of the reader and the author will not be held responsible for any resulting losses or harm.
__________________
Don Hull
RV-7 Wings
KDCU Pryor Field
Pilots'n Paws Pilot
N79599/ADS-B In and Out...and I like it!

?Certainly, travel is more than the seeing of sights;
it is a change that goes on, deep and permanent, in the ideas of living." Miriam Beard

Last edited by rv7boy : 06-30-2017 at 09:15 AM.
Reply With Quote
  #22  
Old 06-30-2017, 09:36 AM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 5,516
Default

This thread is deja vu all over again.

__________________
Bill

RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
Reply With Quote
  #23  
Old 06-30-2017, 09:38 AM
PerfTech's Avatar
PerfTech PerfTech is offline
 
Join Date: Sep 2010
Location: Redlands, Ca.
Posts: 1,458
Default

Quote:
Originally Posted by Carl Froehlich View Post
Put Stainless Steel pot scrubber pads inside the heatmuff. Huge increase in heat output.

Don't pack it in too tight.

Carl
...Actually the best for this is the copper ones (Chore Boys). You still will be lacking when the throttle is retarded. Another option that works well is a 12 volt car heaters of the 300 watt variety. Many available on E-Bay under $20. I have also used 12 volt electric hair dryers for heating, and they lend themselves well to attaching a scat tube for heat placement. Cheap, portable and easy fix. Thanks, Allan...
__________________
Allan Nimmo
AntiSplatAero.com
Innovative Aircraft Safety
Products, Tools & Services
Info@AntiSplatAero.com
Southern California (KREI)
RV-9A / Edge-540
(909) 824-1020
Reply With Quote
  #24  
Old 06-30-2017, 01:31 PM
rv7boy's Avatar
rv7boy rv7boy is offline
Forum Peruser
 
Join Date: Jan 2005
Location: Austinville, Alabama
Posts: 2,458
Default

Quote:
Originally Posted by BillL View Post
This thread is deja vu all over again.

Obviously my description of fins was not understood. Vetterman indicated the studs don't work.
__________________
Don Hull
RV-7 Wings
KDCU Pryor Field
Pilots'n Paws Pilot
N79599/ADS-B In and Out...and I like it!

?Certainly, travel is more than the seeing of sights;
it is a change that goes on, deep and permanent, in the ideas of living." Miriam Beard
Reply With Quote
  #25  
Old 06-30-2017, 02:05 PM
vetterman vetterman is offline
 
Join Date: Oct 2006
Location: TX
Posts: 53
Default Heat transfer in muffs

Fins as Don calls them do work. They not only provide more surface area for heat transfer but they redirect or in some cases restrict the airflow. We know that heat muffs with the inlet and outlet in line simply allows the air to flow directly from one to the other and the air is not in the muff long enough to heat up. I placed partial heat muff end plates close to the inlet and exit by riveting them to the heat muff and using a radiator clamp right above them to draw them down tightly on the exhaust pipe. The temperature of the air increased more than other things I tried.
Then mufflers came along. I use that term loosely as most units with a flame tube or flame cone started out as spark arrestors. Then one day they were called mufflers. When we first tested mufflers we were surprised that there was no power loss, it did quiet the exhaust by a few decibels and the cabin heat was greatly improved. It took quite awhile for mufflers to be accepted but when the RV-9 came out, a lot of builders decided to get them. Also most builders in Canada wanted them to be able to fly in really cold weather. So why do they put out so much more heat? Mufflers use a 3 inch piece of tubing vs 1 3/4 inch common on most systems. The heat transfer area is simply much larger. Hope this explanation helps a little
Reply With Quote
  #26  
Old 06-30-2017, 02:09 PM
civengpe civengpe is offline
 
Join Date: Nov 2010
Location: Houston, Texas
Posts: 212
Default

On a similar note...

I forgot to cut holes in my carpeting for the heater discharge ports in my -10. I only noticed it When I opened the heater valve for the first time. I had warm air rising all around me instead of just on my right calf. The warm air is flowing under the carpet and escaping around the edges into the cockpit. It's like a radiant heat floor! The mistake has turned into a really nice feature!
__________________
Shannon
RV-10
Flying September 2015
Reply With Quote
  #27  
Old 06-30-2017, 04:02 PM
tim2542 tim2542 is offline
 
Join Date: Aug 2009
Location: Redding,Ca
Posts: 633
Default

FWIW custom aircraft parts in El Cajon, Ca will install the studs if someone wants them.
No endorsement but I did ask them once if they could instal lthem.
Tim Andres
Reply With Quote
  #28  
Old 06-30-2017, 04:16 PM
krhea krhea is offline
 
Join Date: Nov 2011
Location: Peck, Kansas
Posts: 137
Default Increase Heat Transfer in Heat Muff

Actually I think that using a Nichrome heating element wire is the best(cheapest) heat transfer method because the wire in a normal application could be somewhat "red hot" in normal usage. This type of "heat element restring kit" can be purchased at wholesale heating and air-conditioning distributors or appliance distributors( clothes dryer element restring kit) pretty reasonable (<$20.00) voltage and wattage doesn't matter in this case, but may be available in 3/8,7/8 or other diameters. You just need to pin each end down and put as much as you can inside your heat muff. The contact area of the nichrome wire with the exhaust is what will get the heat in to the air. I have tried a few other methods since if been in HVACR all my life and this is the least amount of work, cost for what you get.


Keith Rhea
RV7
Reply With Quote
  #29  
Old 06-30-2017, 05:18 PM
vetterman vetterman is offline
 
Join Date: Oct 2006
Location: TX
Posts: 53
Default Heat transfer

Tim 2542. You are talking about Clinton at custom aircraft, he's been a friend for many years and does excellent work.
Reply With Quote
  #30  
Old 06-30-2017, 06:10 PM
rzbill's Avatar
rzbill rzbill is offline
 
Join Date: Nov 2005
Location: Asheville, NC
Posts: 2,692
Default

Quote:
Originally Posted by rv7boy View Post
There are equations from too far back in my education to calculate the optimum size of the fins. snip

Fin design is a science, although there is room for empirical development. The thickness of the fin is as important as the height and length of the fin.
Don,
I was in school about the time Mandelbrots stuff was coming out but fractals were not recognized as being as applicable to the physical world as they are today.

I remember a presentation on cooling fins that discussed the math to optimize heat rejection. The resulting fins had exponentially curved walls (wide base and pointy tip) instead of the parallel ones we have on our motors. The funny bit is that they recognized data that did not fit the exponential curves. When the calcs were run at a finer sample rate, the fins had what looked like a sinusoid overlaid on the exponential sidewall. They looked like christmas trees. So... there were still some points that did not fit and the engineers were still scratching heads. Unfortunately, that was the end of it and my career has not included fin design. I strongly suspect (but have no proof at hand) that fins are a fractal.


Somebody talked about using oil cooler air. Here is a link to the first page of my oil cooler and double heat muff revision.
Heat revision
__________________
Bill Pendergrass
ME/AE '82
RV-7A: Flying since April 15, 2012. 850 hrs
YIO-360-M1B, mags, CS, GRT EX and WS H1s & A/P, Navworx
Unpainted, polished....kinda'... Eyeballin' vinyl really hard.
Yeah. The boss got a Silhouette Cameo 4 Xmas 2019.

Last edited by rzbill : 06-30-2017 at 06:20 PM.
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 02:26 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.