Please Register or Log in to view the hidden image! Ever notice how a tire is round except for the part that's resting on the ground? That part is flat and flanked by short segments of bulging sidewalls because the tire is being pressed into the pavement by the weight of the vehicle on which it's mounted. As the tire rolls, that flattened section of tire pops back into its natural round shape, and the next section of tire is pressed flat, until the entire tire revolves and every part of it has been flexed flat and back again. This constant flexing creates a tiny amount of heat, which adds up with time. A typical tire revolves roughly 750 times as it travels a mile. At 60 mph, that's 750 revolutions per minute. As the miles roll by, the tire gets hotter, which is why the tire pressure increases by about four pounds per square inch (psi) after a tire has been driven for a while. If a tire's air pressure is too low, it will get even hotter because reduced pressure results in more flexing. Taken to the limit, maximum tire flex occurs when pressure is zero and the tire is flat. Increased load on the tire has the same effect because it causes the tire to flatten more at the contact patch. Higher speed also makes the tire hotter because it flexes more often. Finally, the outdoor temperature matters. Whatever the mix of tire pressure, load, and speed, a tire will get hotter when it's 90 degrees outside than when it's 30 degrees. How hot does the tire get? Typical tires experience a temperature increase of roughly 50 degrees after running on the highway for a half-hour. If it's a 70-degree day, this suggests a tire temperature of about 120 degrees. If it's a hotter day, or you're driving faster, or you're hauling a heavier load, or your tires don't have the proper air pressures, they could get hotter. To limit these temperatures, some automakers recommend increasing tire pressures for heavier loads or sustained high speeds. But if it gets hot enough. # (from google) And if thermoelectric generators(low temperature difference "hot>cold) transform the heat energy of tyres into electric energy like this photo, So what do you think about it ? Thanks.
Well no doubt you could do that, using thermocouples. But, due to the operation of the laws of thermodynamics, any such attempt to extract energy will increase the rolling resistance of the tyre.
Not in that case since the hysteretic waste heat has already been generated and either it's simply lost entirely or a tiny fraction can be thermoelectrically converted to useful electrical power. But for sure so inefficient and costly just not worth considering. Seems the thread title was a typo, but who cares.
I see what you mean, but I was thinking that the temperature increase will increase the tyre pressure, which will limit the flexing and heat generation. If you cool the tyre, the pressure will tend to drop and the flexing will be greater, won't it? But we are arguing about tiny effects it it true.Please Register or Log in to view the hidden image!
Ah right - 2nd or higher order feedback process(s). Well I hadn't thought of that - looks like some lost sleep coming up!Please Register or Log in to view the hidden image!
At this rate we'll go the whole hog and start talking direct conversion via fuel cells. Then again, that ones been looking promising for just too long.
Thanks a lot ! Actually I knew about wasted heat from exhaust and thermos but didn't know about tires(what problem will come when we transform the heat energy of tires into electric energy ?!)
Tyres need heat to opperate at their best so one would need to consider what heat will be available. Perhaps heat from the brakes would be better as their efficiency improves with less heat (or so I believe). Have you a formula which shows how many watts per unit of temp allowing for expected inefficiencies. Even a "ball park" figure would show if the idea is worthwhile. You may find you only get enough electricity to power the radio. Yet if it is an all electric car just powering the radio via tire heat would be helpful. Ever bit helps so work out how many watts may be on offer. Alex
Tyres need heat to opperate at their best. So after gained enough heat, the friction between tyres and road and massive pressure( of truck/car) on rubber of tyres will produce extra heat so thermos could transform the extra heat into electricity. Isn't it ?
