Heat Dissipation with a Belly Pan
 

I'd read a belly pan can cause heat retention in the differential, exhaust, etc.

Granted, turbulent airflow is a good means of convection- but I doubt this is what the engineers at Ford had in mind for my F-150 (I would expect to see "fins" of some sort attached to vital structures to increase surface area).

Conduction of heat to attached structures would lower the overall temperature and increase surface area. This would help warm fluids and bring parts up to their operating temperatures, but after that is the increased surface area adequate to dissipate the heat OFF of the vehicle should the temperature go too high? Maybe- I don't know?

What if the main mechanism of heat dissipation is radiation? In that case acrylic, coroplast, the pink stuff (board) would all be bad ideas (though clear polyethylene probably would be ok).

How about this:
1. Fashion the under tray from aluminum.
2. Spray the top of the Al belly pan (the side exposed to the vehicle) with Krylon Flat Black 1602 (high absorptivity of long wave), and the bottom (exposed to the road) with Krylon Flat White 1502 (highest emissivity and reflectance). Before painting black, bolt or TIG some Al u-channel along the length to increase the surface area.
3. Drive your car/truck to normal temperatures. Stop, crawl underneath and map out the hot spots with your IR thermometer.
4. Clean and prep the hot spots and paint the bottom exposed surfaces of the hotspots (those facing the road) with the Flat White 1502.
5. Install the belly pan.

Testing may be a bit tough once the belly pan is on. I don't know what a string of thermocouples would cost. An option may be a string (along say 25-30' of a single Cat6 ethernet cable) of "one-wire" temp sensors ($3-4 per in packs of 10) that could just be super-glued to the hotspots. The ethernet cable could be run into the cab and DAQ done on a laptop.

Thoughts?

temps
 

I went online and looked around.
One site mentioned that mineral oils were okay to 250-300-degrees F,while synthetics could see 450-700 degrees F without catastrophe.
Some members are wrapping their exhaust to limit exposure along with heat-shields.
Up to the limits,the hotter the lubes the better for economy.Furnace Creek,Death Valley,California temps would be okay for all oils on a daily basis unless under extreme service.
Low drag achieved through streamlining would lower the road load of the vehicle,and with it,the friction-heating effects of power transmission viscous shearing.So extra heat would actually be welcome.
You might fully warm the vehicle and do a temp survey with I.R. pyrometer,then cobble a low-cost pan together and compare the effects.
In a worst-case scenario,just compromise the pan a bit to allow some strategic airflow,or do some dedicated NACA submerged inlets with ducting to critical areas with outlets, as done in some high end supercars and racing vehicles.

Drove my infiniti Q45 100k+ miles with Belly pans. see link in sig. never had an issue w/ 'heat'.

you make a interesting discussion. And one we all should remember.
But it's hard to remember we drained the swamp when we are up to our asses in alligators!!!!

unintended consequences........

I was kind of thinking of this fellow here: "ecomodder.com thread belly-pan-danger-belly-pan-owners-must-read-26401" (won't let me post the URL)

I want thinking so much about oil and gears as much as heat build up in places not intended, i.e.- gas tank, the pickup bed, trunk, the cabin, and the dangers this may present.

If heat is lost mainly by convection, a well sealed belly pan although desirable Eco wise- is unsafe.

But could the correct selection of materials (if heat dissipation is mainly radiant) allow a tight seal AND be safe?

Either an air dam/skirts or belly pan was to be my next project. So I'm just thinking it through. Currently I'm just trying to finish my "Burning Man hexayurt" inspired removable camper top.

BTW- love the gator analogy. It's the story of my life.

pan/heat/matls
 

Here is an image of the pan on my truck.It's fiberglass and aluminum.
I've taken no care to accomplish any special shielding or insulating and at around 7-years now,have had no issues with lubes or fuel.
I have leakage at the front suspension.The coooling air can escape to the front wheel wells,and also,there is a full-span gap at the rear axle ahead of the diffuser.
So far,deep water is the only thing which has impacted the truck.I drove slowly through a flooded alleyway and the force of the water was enough to rip the diffuser off because of it's sealed rear bulkhead.
http://www.evworld.com/images/pknox_bellypan.jpg

aerohead-

Yeah dude- verrry cool. I've followed links all over the internet about your work and your truck.

My dilemma- great with science; bad with tools and fabrication.Worse, I suffer w/ OCD. Lots of stuff I can't compete due to lack of skill and frustration.

On retrospect, I'm considering a belly pan may actually HELP moderate vehicle temps, especially an aluminum one. I figure up to about 75ºC convection would be the main for of heat loss. Past that I'm thinking radiation would dominate. A large Al belly pan would disperse the concentrated heat energy over a larger potentially improving convection. Additionally, the emissivity of weathered Al approaches 0.95, so I doubt you could expect a worse case of even a 5% temp increase.

BUT-- I would also stand to reason that you would get to operating temps much quicker in the above case. IOW, I wouldn't be freezing for the first 10 miles, only 5.

Then the 2 questions that tempt me are:
1.) after the belly pan, did you notice any change in how fast your truck warmed up, and
2.) if you ever consider bolting or TIG'ing some Al U-channel lengthwise along the bottom (not that you would or need)- I'd love to know if there were any changes.

Me? I'm thinking of one of the aftermarket steel pans just so I don't knock my underside off. Pretty sure anything I try to fabricate would be tore to shreds. I was looking at some 1/8th X 8" rubber for the dam and skirts, but I'd need a way to unbolt them easily where the highway ends, cause I still got that 60 mile each way highway to deal with.

And thanks for the input. Like your rig a lot and appreciate y'alls work in the area of saving me money (also the Aerocap guy, and the guy with the little chevy truck that did the spoiler, chin, and dam). And almost forgot the red F-350 getting 27mpg!

warmup/additional heat sink
 

I was never able to instrument the truck properly and document a database of large enough volume so as to scientifically assess thermal dynamics.
My time working around HVAC equipment did suggest that without the airstream licking the oilpan,transmission housing,differential/axle,that warmup would come sooner and also heat retention after parking.
The dead air space would act as a partial insulation.
-------------------------------------------------------------------------
Ford Motor Company incorporated an insulated exhaust pipe,along with coolant tubes within an extruded aluminum channel which was integrated into their 1984 Probe-IV concepts belly pan.The insulation mitigated heat transfer to the coolant lines,and the additional heat sink area provided by the cooling fins of the extrusion helped reject a little heat flux between the engine and rear-located radiator and back.
-------------------------------------------------------------------------
Your selective surface coatings for the radiant loads is a good idea.Air-cooled motorcycles used this strategy with cylinders and heads,and racers used the white coatings on the underside of intake manifolds to help shield radiation from the heads and rocker valley.

Yea, heat, the car get hot inside in the summer with a full belly pan. Put some vents around the gas tank to help keep it cool, or the gas might boil and build up pressure. I wrapped the exhaust pipe and muffler with fiberglass cloth and foil. Also, need to add vents to let the radiator air flow out underneath the car (truck). i run thinner synthetic oil, 5w less than oem spec.

some basic simplified heat transfer equations

highest heat transfer is conduction = Area x thermal conductivity x delta T

convection is next = A x convection coefficient x deltaT
forced convection is ~ 10 times as effective as natural convection

radiation is least effective unless its really hot as it varies by temperature to the 4th power. = emissivity x A x (deltaT)^4, so I would assume it to be negligible at the temperatures we're dealing with.

ya you can feel heat radiating if you put your hand near a radiator, but you would feel it a lot more if the fan was blowing hot air, or I dumped hot coolant on your arm, if you get what I mean.

@arcosine- and hence the problem with being a fat dude in texas during the summer

@Thenorm- so as airflow/convective loss decreases, radiant loss will become the dominant mechanism. My thoughts then would be to either avoid interfering with airflow, or maximize radiation.

I'm saying that radiation is not an effective mechanism at our temperatures. Convection (forced air) is really the only real way to shed heat in vehicles.

Hi
with a full or nearly full belly pan could you fit nasa? Style ducts to help air flow without drag penalty. as fitted to bonnets on nasa cars. this is just a random thought but could work.

Nasa
 

I found a forward bellypan section of some kind of Audi laying in an intersection and brought it home to look at.
It has 3-NASA submerged inlets leading upwards towards some under-engine components,so they were thinking exactly as you are.:thumbup:

I am the one with the failed belly pan in question in the first post. My gas tank overheated with a partial aluminum belly pan, complete 4’ wide down the middle but with the sides fully open. The air from the engine bay was free to enter and flow through the pan and out the back. The sides were open by several inches as it wasn’t yet completed, yet it still didn’t allow the heat to dissipate. It melted plastic parts up under my car. It heated the bolts holding my seat down up so much you couldn’t hold your finger on them for more than a second or two. And it boiled over a gallon of gas out of my tank. I went back and cut holes in the pan under the exhaust to let more heat escape, but things kept heating up and I ended up removing the back portion of the pan halfway home.

I thought the exact same thing about heat dissipation with my belly pan, painting the top and bottom, cutting holes, insulating the exhaust pipe, etcetera. I have some even crazier/better ideas than those for dealing with the issue. Note the pan overheated while driving down the interstate and highway, 65-75 MPH the entire time. I don’t want to think about what would have happened if I had suddenly been stuck in stop and go traffic for an hour.

What I ended up deciding for myself is that a 90% belly pan is good enough for me. As I rebuild by belly pan V2 I am going to leave the 10% or so of the exhaust exposed. I am going to radius the edges of the pan as I near the exhaust to limit the aerodynamic consequences of having a small section of the pan missing. If you look at other “full” pans, many of them have screen wire under where the exhaust is, so basically the exhaust is kind of “exposed” on those pans anyway.

Just conceptually, my vehicle is less than ideal in a number of areas. There are still a lot of aerodynamic areas for improvement with my car. It isn’t impossible to reduce the heat transfer from the exhaust to the car as it travels from the engine bay out the back. Honestly it isn’t rocket science or really that hard. All it takes is thinking, time, money, and effort. But since my car isn’t perfect in so many other areas, I decided that I will start with my 90% pan, and then focus on fixing all the other areas on my car that need work. As it sits now, I don’t even know if you would be able to measure the difference in effectiveness between a 90% and 100% pan. Maybe if I get all the other areas taken care of I will revisit the 10% of the pan under the exhaust.

I tell you nothing makes you want to stop eco-modding more than spraying a boiling gas tank with a garden hose or trying to take a belly pan off a low car on the side of the road with no lift. Frankly it is very discouraging. I would try to stick to the easier no risk almost guaranteed reward projects first.

Maybe your vehicle will work with a 100% full pan with no special work around the exhaust. Several people on here state it will work fine. Why do you think I tried it in the first place? All I know is mine won’t.

mine won't
 

aardvarcus,that's a lot of work to go through to end up 'punished' after your good deed.
Thanks for attempting it and sharing all the warts and moles of the project.Countless individuals will no doubt benefit from the info.
If we all lived closer we could laugh,scream,cuss,kick,and throw things together.
Collective brainstorming would be easier too.Tool and materials sharing also.
Your project is still a success as we've access to invaluable information thanks to your contribution.Thanks again.:thumbup:

Audi NACA submerged ducts
 

Here is a link to illustrate how Audi is harvesting air under their belly pans
Sorry,tools don't show above.
The image is at :GOOGLE IMAGES @ Audi smooth belly pans

aardvarcus,

Firstly, please understand my mentioning your experience was academic and not for fun.

I value what the folks here can teach me, but in general we seldom mention our failures- and these are priceless. Personally, when I find someone with the humility and honesty to willing write up an (again, please forgive) "Epic Fail", I am forced to acknowledge they are probably a better person than I.

I tip my hat to you sir.

That said, I assume the gas tank doesn't warm itself and most tanks are not attached to parts that generate large amounts of heat. And you mention yours was only partially covered. We can infer (since you didn't mention it) that there was no "forced convection" to cool the tank.

From this I would suggest the mechanism of heat transfer to your tank was via radiation, and that this radiation would have normally been transferred to another site (by conduction) where convective loss could occur, or (with respects to Thenorm) the primary mechanism of heat loss from the heat producing agent is via radiation.

I also have noticed some modders using screen coverings, I'm assuming steel or Aluminum. As I write this I'm looking at a 12'X12" Al screen with 1/8" holes and can easily imagine it absorbing radiant energy from a 1,000º catalytic converter or a 700º muffler. This screen would begin radiating the same energy downhill. First to a cool vehicle itself (that warms up quickly because it dissipates heat poorly), and then into the planet itself- which wouldn't even notice it.

As my screen is mostly just "holes", there is nothing there to prevent radiation going into the ground to start with. But I also imagine there IS enough there to promote laminar flow of air over it as well as significant pressure drops though it.

In other words, again with respects to Thenorm, I'm not buying that radiation is "not effective" and that "Convection (forced air) is really the only real way to shed heat in vehicles.". Indeed, it seems the opposite may be true.

Convection IS important, but it is also linear and I do not see how it can account for even half of the heat flux, especially (as Thenorm mentioned) radiant loss increases to the 4th power of the dT.

I may be wrong though, and will continue reading on this.

Once more, my respects to you and your work. Thank You.

drrbc

audi

http://i678.photobucket.com/albums/v...underbelly.jpg

mine:
http://i678.photobucket.com/albums/v.../mpgq45115.jpg

Thanks for the kind words, I mainly posted my story for fear of others safety.

I agree that most of the problem was radiant heat transfer, aggravated by the reflective aluminum panel right under the exhaust reflecting the additional rays back up. Without the belly pan though, the convective heat transfer of the cool air blowing up under the car would have removed all that built up heat. With the belly pan though there was only a limited amount of air that could not remove the heat. Hence problem.

The more I think about the issue with the exhaust heating, the solution I like is instead of trying to only deal with the heat after it has left the exhaust, but first to significantly reduce the heat transfer out of the exhaust pipes. Several ways would be ceramic coating the exhaust system, using exhaust wraps, putting the exhaust pipe within another pipe, putting reflective barriers or other insulation above the exhaust pipe. Additionally, going a step further in complexity the exhaust or exhaust cover could be made with a flat bottom where the bottom of the exhaust was actually part of the belly pan, but allowing direct conductive cooling of the exhaust or outer exhaust cover.

As I said before, it is just thinking, time, money, and effort.

My thoughts as well, and I imagine that may be the future. On the down side, no matter who does this would make serviceability of the system a nightmare. In the mean time however I think my wife may have a nice aluminum cookie sheet that I could small scale.

mcrews,

From the top photo only- it appears the exhaust system is recessed and unlikely to receive airflow from directly underneath. In the front there appear to be vanes which seem to be directing airflow toward the center- but also away from the wheel wells. Also, is there ducting (?) in the front wells (inside, behind the axles) into the exhaust system channel?

The question is "is the channel simply a radiant barrier, does the ducted air to cool the car above the channel, or is it ducted air meant to cool the system".

Since I don't see any "fins" to increase surface area of either the channel or the cat/muffler, I'd say the Audi engineers weren't betting on big chances of conductive losses. Also, and article I just read doesn't suggest any great temperature differences whether at idle or at speed for the warmed up auto. Since conductive losses would improve with the mass of the air that came in contact- I would assume conductive losses to be considered negligible by engineers.

So once again I'm just guessing but I'll throw out some numbers now and make my bet: Mechanism for temps <300ºC = convection
Mechanism for temp >300ºC = radiation

i tip my hat to you, u absorb the subject matter well. My all encompassing statement about convection was mostly for the engine bay and the cooling system which are around 100°C. when you get upto 1000°C at a cat converter, radiation will play an effect. I guess that's why they put heat shields on it.

Maybe that can be our rule of thumb. If there is a heat shield on an item (like muffler and cat), then you need to manage its radiant heat

Camaro belly
 

Here's a contemporary Camaro:
https://www.google.com/search?q=Ferr...0%3B1024%3B681
Here's a Ferrari pan:
http://www.tamiya.com/english/produc...enzo/enzo6.jpg
Here's a fella's scale model pan:
http://acmenovelties.net/scale_model..._undertray.jpg

Thenorm,

Thank you for the kind compliment.

You have brought up another excellent point- did aardvarcus' misadventure give us more than one "learning opportunity"?

I'm very happy he was kind enough to share his experience, and doubly happy he didn't blow himself up. But what makes me most happy is that it didn't happen to me.

Would it be safe to say 50% or more of the "ecomodding" inspired MPG gains are a result of "adjusting the nut behind the wheel"?

Would it be just as safe to say 40% or more of the "ecomodding" inspired MPG gains are a result of aerodynamic mods? And that the remaining 5-10% are mechanical?

I don't use all of the hyper-miler tricks (not sure all are safe, practical or prudent), but I use enough to return me almost 3 mpg more than I was getting in my monster flying brick supercrew. The CAI/exhaust, and tonneau have given me another 2, maybe 2.5 mpg.

And now I'm considering aeromods devoid of any professional automotive safety engineer input that I will personally and incompetently install myself. Fortunately, I feel it's fairly obvious that things like bondo's Aerocap, and garden edging air dam are pretty safe (unless my home made one flies off at highway speed), at least for me.

How many times have brakes or steering failed in an engine off coast? Have their been any unusual fires or system failures that put life or property at risk related to modding. I know I can save a bit more mpg if I remove all of the weight of the airbags and restraints, but should I?

As I said, I don't find all of the hyper-miler tricks to be that wise (for safety issues). Nor do I necessarily find all of the aero and mechanical mods wise for the same reasons.

With more negative feedback we may find a lot of RoT's waiting to be discovered.

I plan on being more active in this forum in my quest for my personal grail- 25mpg, and I promise I will try to bear in mind always your suggestion "maybe we need a rule of thumb" for the safe promotion of ecomodding, since I suspect there is a whole lot more than a single rule that is needed. We should encourage people to publish more of our failures- especially when "learning opportunities" are present (I personally learn more from the failures anyway).

How about even a "Rule of Thumb's" sticky? Putting our bad outcomes in one place would provide an excellent knowledge base.

I'll even suggest Rule #1:

1. Thenorm/aardvarcus Rule (aka the "Make Sure it Can Cool Off" Rule)- All mods should consider the potential to create conditions where unanticipated heat energy may build up, as well as the potential to impair the convective and radiative dissipation mechanisms engineered in the stock, which may result in catastrophic failure.

What do ya think?