h a l f b a k e r yOutside the bag the box came in.
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
browse anonymously,
or get an account
and write.
register,
|
|
|
Please log in.
Before you can vote, you need to register.
Please log in or create an account.
|
| |
The problem is that this will only benefit the driver
behind you, leading to potential lack-of-motivation
effects. |
|
| |
Till the melting is compltetly done, it will give a perfect frictionless surface. You will see lot of cars flying off the bridges. |
|
| |
The Specific Heat Capacity of ice is 2.11 kJ/(kg·K),
the Latent Heat of Fusion of ice is 334 kJ/kg, and
the
density of ice is 0.9167 g/ cm³. So every 10 metre
by 2 metre area of road with a 1cm thick layer of
ice on it contains 1000x200x0.9167 = 183kg of ice.
If this is at -5C it will take
(183x5x2.11)+(183x334)=63MJ to melt it.
Let's assume
that you want this
1cm thick layer of ice completely melted after 100
cars have
gone over it, then each car has to put out 630kJ
every 10 metres of travel. If the cars are travelling
at 23 mph, or 10 metres per second, this implies
they are each putting out 630kJ/s or a steady
power output of 630kW. Luckily the calorific
content of petrol is high - about 48kJ/g - so
assuming your flamethrower is 50% efficient, you'll
have to burn about 26g of petrol a second to do
this. A litre of petrol is about 800g so you'll use
about 2 litres of petrol a minute, which will cost
about £2.80 in the UK, a steady expenditure of
£168/hr. |
|
| |
I'm just talking about directing the existing car exhaust at the road, not adding a flamethrower. It might be effective against frosty roads but not 1cm thick ice of course. |
|
| |
As far as the melted water being more slippery than the ice and causing cars to fly off the bridge, ice is much more slippery than water so you're better off melting it if you can. |
|
| |
And as far as people not caring about what happens behind them, I think people understand group efforts towards the common good. I'd be more than happy to flip down my road defroster tailpipe for the folks behind me. |
|
| |
Well OK, if it's 1mm of ice, then you're spending
£16.80 an hour on petrol which is being used for
nothing else but melting road ice. |
|
| |
[bigsleep] No it doesn't. Some of the energy
content of the fuel gets converted into kinetic
energy to move your car forward, a small amount
is converted into sound energy, some is converted
into heat energy in the engine and lost to the
atmosphere either through radiated heat or by
being carried away by the car's cooling system and
then lost to the atmosphere from the radiator,
and *some* is left as hot exhaust gases. What I'm
saying is that the energy content of 2 litres of fuel
a minute per car is needed is needed if you want
100 cars passing over a given point to melt 1cm of
ice (or 200ml of fuel for 1mm of ice). If, say 10% of
the calorific value of the fuel is converted into
exhaust gas heat (a generous estimate) and you
can transfer half of that heat to the road surface
(again, generous) then you can easily see that
using hot exhaust gases is going to be a less
efficient and even more costly way of melting ice. |
|
| |
Scraper mounted on front of car scrapes ice off road, passes it as fine powder through radiator where it melts. Hot ex-ice dumped back on road via exhaust gadget described above. |
|
| |
Even if it didn't eliminate ice completely, it might reduce the number of icy days. |
|
| |
The cost-benefit ratio might be more favourable if the end of the exhaust pipe were simply angled downwards more than usual. Cars sold in freezing-climate areas could have the modification, on the assumption that cars are mostly driven fairly close to where they are bought. There would be no need to make a seasonal switch, as it wouldn't significantly affect performance. |
|
| |
I think [VJW] is saying that wet, melting ice is far more slippery than ice that is well below freezing. Which is true. |
|
| |
A + for "You will see lot of cars flying off the bridges" |
|
| |
I suggest changing the focus of the idea so this is its main aim. |
|
| |
Take it from those who live in places where icy roads are
not a possibility but a foregone conclusion: ice with a thin
layer of water atop it is far, far more slippery than
completely frozen ice. In some respects, it's more slippery
than oil. |
|
| |
I'd think all ice with cars driving on it has a thin layer of water on top just from the friction. Wouldn't it be better to try to melt it? |
|
| |
What about just having the exhaust pipes hitting behind the wheels to concentrate on creating two de-iced channels? Think I'll change the design. |
|
| |
I see this happening anyway with cars driving on icy roads to some extent. I think this would just assist the process and add friction to the wheel/pavement contact point. (See link) |
|
| |
// I'd think all ice with cars driving on it has a thin layer of
water on top just from the friction. Wouldn't it be better
to try to melt it? // |
|
| |
Yes, it does, and yes, it would be, which is why our plow
trucks spread rock salt or brine, which melts the ice fairly
quickly, as well as sand for traction. |
|
| |
Doing a little research on the temperature of car exhaust, it looks like it's a bit more than a very hot hand held hair dryer by the time it reaches the exhaust pipe outlet. |
|
| |
I'm thinking if you have the right kind of tip, you could "deposit" that hot gas in a vortex close to the ground so it stays in place for the most part until the next car drives through it. This opposed to just blowing apart and being disbursed. The vortex disbursal would give the gas some "stability" to stand up to the ambient air gusts blowing around due to the car's disrupting air and moving it around. This would effectively create a hot zone in those tire channels as long as you've got heavy traffic flow. |
|
| |
Vortexes can be very sturdy and large ones, such as those generated from an airliner's wingtip can disrupt a plane flying through it many seconds after the first plane has generated it. |
|
| |
What [Alterother] said, both times. |
|
| |
If you duct heat from the radiator and mix it with the exhaust, you'll have rather more hot air; but even then, if the air is cold enough, you might just melt a thin surface layer which rapidly refreezes as a glassy smooth surface. |
|
| |
// ice is much more slippery than water // |
|
| |
Dry ice (water ice, not solid co2) is not particulalry slippy; wet ice is - very much so. "Ice on Ice" with a layer of water in between has a near-zero frictional coefficient, close to that of MagLev and Air bearings. |
|
| |
// I think people understand group efforts towards the common good. // |
|
| |
And how long exactly have you been suffering these troubling delusions ? |
|
| |
This is pretty much a recipe for a highly inefficient
Zamboni. |
|
| |
// recipe for a highly inefficient Zamboni. // |
|
| |
Thats .... the one with egg, and marsala ? The sort of creamy one ? |
|
| |
Or do you mean a Zabaglioni, the machine for preparing ice rinks ? |
|
| |
Seems like an inefficient Zamboni is better than no Zamboni. |
|
| |
I don't think this ice is dry anyway due to the friction of the wheels rolling across it. I think you're going to have a little boundry layer of water in any but the coldest conditions. |
|
| |
Remember, I'm talking about a highway here with a car a second blasting over the ice at 50 miles per hour. That's a lot of friction. |
|
| |
// I think people understand group efforts towards the common good. // |
|
| |
//And how long exactly have you been suffering these troubling delusions ?// |
|
| |
Ever since that Coke commercial from the 70s where all the hippies are standing on a hill singing about world peace and caffinated sugar water. Changed my life man. (link) |
|
| |
// Remember, I'm talking about a highway here with a car
a second blasting over the ice at 50 miles per hour. That's
a lot of friction. // |
|
| |
Oh, I'm not arguing that the passage of cars doesn't melt
the ice; it does. I was simply pointing out that we have
much better methods already in use. One went past my
driveway as I was typing this. |
|
| |
// due to the friction of the wheels rolling across it // |
|
| |
The presence of friction between the wheel and the surface does not mean the transfer of energy. |
|
| |
The point of contact of the wheel with the surface is in fact stationary, and exerts pressure; only if there is slip will energy be transferred. That's why wheels are such an efficient way of moving objects. |
|
| |
// you're going to have a little boundry layer of water in any but the coldest conditions. // |
|
| |
Assume an ambient temperature of -10C and a layer of frost on the road. A motor vehicle tyre at 0C, applying a force of 2.5kN normal to the surface and with a contact area of .003 m2 passes over the surface at a lateral velocity of 20m/s, giving a contact time of 1 mS. |
|
| |
Work out the change in temperature of the ice. Go on, we dare you. |
|
| |
// One went past my driveway as I was typing this. // |
|
| |
What, another white-tailed deer ... ? |
|
| |
There's not just the friction that we're talking about, it's what happens to that patch of ice during that millisecond of having a quarter ton of car land on top of it. There's the erosive process of being pummeled by car after car. On the other side of that ice there's a hard rough survace. This ice needs to stand up to the hammer of the car tire on one side and the anvil of the road on the other. Add a little heat to the equation and and badda-big, badda-boom. No more ice. Or less anyway. |
|
| |
// hippies are standing on a hill singing about world peace and caffinated sugar water. Changed my life man. // |
|
| |
"Little boxes on the hillside, Little boxes made of ticky tacky, Little boxes on the hillside, Little boxes all the same ...." |
|
| |
No, you collective smart-ass, a spreader, although I think
that one was just carrying sand. The deer don't come
around until 9 o'clock or so, which is nice because it gives
the dogs something (else) to bark at. If you're referring to
_teleporting_ deer, on the other hand, I haven't seen many
of those around lately. |
|
| |
A 1000 kg car, with a rolling CD of 0.01, travelling at 20 m/s, generates about 2,000 W of heat in the tyres. I would guess that less that half of that would be transferred to the road, though. |
|
| |
One way of looking at this would be to ask "How much nett power (as heat) will a road at slightly more than 0ºC transfer to the environment, under a given set of conditions?", because that is the minimum power that the vehicles will need to transfer to the road to keep it ice free. That would vary a lot, but might typically be in the hundreds of watts per square metre. Work out road surface per car; that would also vary widely, but could be as low as 20 m² in very heavy (but still freely flowing and safely spaced) traffic, allowing only a Œ m strip for each tyre track. |
|
| |
So at best, each car might only need to transfer a few kilowatts to the road surface. Within a couple of orders of magnitude. |
|
| |
As for the comparison with salting, although it's efficient (because everything stays near ambient temperature, so you don't have to keep pumping energy in), surely the cumulative rust damage alone means you have a lot of resources to spare on an alternative while remaining in the black. |
|
| |
My guess is that current cars mainly heat the road by radiation from the hot engine and exhaust system. This is based on the observation that roads dry out first in the middle of the lane, where most of that hot stuff is, rather than to the sides, where the wheels and exhaust outlets mostly are. |
|
| |
So my recipe would be to route the exhaust pipe(s) underneath the side(s) of the vehicle (in line with the wheels), make it do a dog leg around the rear wheel*, then angle the last bit down by pi/4 or so, and fit it with a very gentle nozzle (like a hair dryer). The straight run could be somewhat flattened dorso-ventrally to increase the area available for radiation. Any catalytic converter should especially be in line with the wheels. |
|
| |
* Or even terminate it just in front of the rear wheel, now that exhaust is sometimes not quite as disgusting as it used to be. |
|
| |
So we're really talking about a little transient micro-climate here. One that might be optimised to reduce ice conditions utilizing all that waste heat a car is throwing out if you just stick it down there where it can do some good. So ok, don't use it when you're driving over a frozen lake but in most ice conditions I think the heat coupled with the erosion/impact from the wheels could really reduce the ice you're dealing with. |
|
| |
Rust damage from salt is only a big issue if you park your
car in a heated garage, where the accumulated salty-ice
build-up melts and oxidizes the metal as it drips off. If you
park outside and visit the car wash once a month or so, the
problem is significantly diminished. |
|
| |
I think I have the solution. Hydrophobic road surfaces. |
|
| |
Good idea. Now work out how to make them provide
decent traction, withstand extreme weather conditions,
and cost less to install and maintain than asphalt. |
|
| |
Never mind that -- how are you going to infect
pavement with a neurotropic virus? |
|
| |
Easy; I plan to use 120mm Tranquilizer Mortars. I have a
few left over from my blink-deer live-capture program. |
|
| |
//Hydrophobic road surfaces// This is something I'm already playing with. I have superhydrophic polymers I can spray onto existing ashphalt but they wear away with traffic. It might not matter if it wears off the convex surfaces of the stones as the water goes to the concave/low point surfaces. We will see how it goes but it would have to be a maintenance product rather than a construction product. |
|
| |
Salt doesn't work by melting the ice per se. It migrates through the snow and ice to form a brine on the road surface which breaks the bond between the bitumen and the snow/ice making it easier to plow away. Obviously if there is just a thin glaze of black ice then lowering the freezing point is all that is required. |
|
| |
As cars get more efficient, this get more pointless.
And electric cars?? I have a solution for you: |
|
| |
SNOW TIRES. Yes, they make that much of a
difference, this exhaust meltier thought would not
have made it into your brain. |
|
| |
So everybody just buys snow tires for year round
use. Wow, great idea. I wonder why that thought
never made it into anybody's brain before. |
|
| |
"I don't know what happened. I bought these great new snow tires and now have all kinds of traction, but for some reason my fuel economy is terrible..." |
|
| |
Wouldn't snow tyres just melt if you used them when it was above freezing? |
|
| |
A truck with two hoppers: one is a cold weather plant bacteria; the other finely ground garbage for the bacteria to eat. |
|
| |
// I have superhydrophic polymers I can spray onto
existing ashphalt but they wear away with traffic. // |
|
| |
If they wear away with normal traffic, the snowplows will
scrape them up before the first storm is over. Around here,
they have to re-paint the lines every spring. |
|
| |
// It might not matter if it wears off the convex surfaces
of the stones as the water goes to the concave/low point
surfaces. // |
|
| |
Water does, but ice doesn't. Ice goes up, down, sideways,
and everywhere else you don't want it to. To make things
even more interesting, there are times in the late winter
when not even the plows are touching the asphalt--all
those melted and re-frozen layers of ice, impregnated
with countless applications of sand, form a Pikrete-like
substance locally known as 'rock ice'. Come the beginning
of March, we're driving on an inch or so of the stuff.
Fortunately, it's very gritty... |
|
| |
As an ex-Canuck who had something to do with supplying salt on roads etc., I am familar with 'rock ice'. If you look closely at a road surface, a surprisingly small portion of the road (only the convex surfaces) comes in contact with tires or snowplow blades. The coarser the aggregate and less rich the bitumen content the more this holds true. |
|
| |
If I can keep the water, hence the ice, from fully adhering to 60% of the road's surface then I will reduce the effort required to remove the snow and ice from the road - even 'rock ice'. Polymers and even bitumen, which is a soft substance in its own right, will quickly wear off the top contact points but this holds true for ice too. The layer of polymer will only be molecularly thin. |
|
| |
I'm sorry, I forgot you were Canadish. I know, it's in your
username. I sit in box and feel the shame. |
|
| |
I wish you luck with these experiments; anything that
makes life easier makes life easier. I hope you'll understand
and forgive my ingrained northerner's skepticism. |
|
| |
If the ambient air temperature is still below zero, then won't the constant thawing and refreezing of the ice speed up the degradation of the road surface?
Aside: 8th's nod to 'Little Boxes' is quite amusing really. For most of us it's seen as a protest song, for the Borg it's more of a mission statement. |
|
| |
Hah, someone spotted the twist ... we did wonder if anyone would. |
|
| |
// won't the constant thawing and refreezing of the ice
speed up the degradation of the road surface? // |
|
| |
Yep, it does. Roads (or major sections of them) are
repaved on an average of every 5-6 years up here, and
that's just from seasonal damage, barring washouts,
undermining, and all forms of rhinoceros-related damage.
Some major routes are repaved every 2-3 years, especially
those that see particularly heavy rhinoceros activity. |
|
| |