A Thought Experiment - Thermoelectrics and Cars

[WildBoar]

I just had a idea. Wow, that was painful!<p>My dad, and everyone in the small town where I
grew up drove large, full size sedans. This was
during the 60's and 70's. Remember those old
Buick station wagons. They were so long, wide,
and heavy that the shocks could be blown out
and you would hardly notice the difference.
When you lifted the hood there was so much
room around the engine a small child could
climb over the bumper and stand next to the
engine without getting cut or scrapped.<p>There wasn't any accessory you couldn't fit
under the hood. You could hang a second fan
in front of the radiator which effectively created
a push and pull air flow through the radiator.
This helped a lot if you were towing a trailer
or had a wife and six kids. I remember a friend
who's dad gave him the old family sedan as
his first car. He turned it into a hotrod. In
order to cool the thing he added two smaller
fans to supplement the bigger ones that were
bolted to the front and back of the radiator.<p>Starting in the early 90's everything changed.
Engine compartments now look like jigsaw
puzzles, where each piece is separated just
enough so that they don't crush each other!
Mechanics, who would have rather worn
pantyhose and a dress, now wear high tech
cut resistant gloves so they can force their
hands into places were human hands were
never meant to be.<p>Recently, a colleague asked me if I could think
of a way to add some additional cooling power
to his car. We both took a good look above and
below (using ramps) the engine compartment.
Adding an additional fan is out to the question.
There isn't even enough room for an auxiliary
radiator cooler, despite the fact the these
coolers take up very little extra space.<p>I started to think, could the wonderful world of
modern electronics come the rescue?<p>What if you cut the upper and lower radiator
hoses in half. These hoses are very easy to
spot. They are more than twice the diameter
of any of the other hoses that circulate coolant.<p>You purchased or fabricated two copper cubes,
slightly larger than the hoses and soldered a pipe
stub to either end of the cube that would slip
inside the cut ends of radiator hoses. On each
of the remaining four sides of the cube you would
cement a thermoelectric cooler using thermally
conductive adhesive. A thermostat, relay, or
switch (or a combination of all three) would control
power to the cubes.<p>I haven't spent a dime on this idea. It was really
just a thought experiment. The question is would
it have any effect on coolant temperature, or would
the hot coolant pumping through the hoses overwhelm
any cooling effect from these devices?<p>I think I already know the answer. Still, it was such
a fun thing to discuss with my colleague I couldn't
resist posting this query. Oh well, it's sometimes
nice to dream about elegant solutions to difficult
problems.<p>WildBoar<p>[ July 11, 2004: Message edited by: WildBoar ]</p>

[jwax]

Keep on thinking, WildBoar!
Entropy being what it is, the 10, 20, or 50 amps you draw from the alternator to power the Peltiers has to come from somewhere, right? That at a glance would require more engine output, which would create more heat, which would....you see.
If you want to do some more thinking along those lines, imagine this: Peltiers can be electrical power generators by cooling one side and heating the other! Now you get to remove heat, and get "free" electrical current!
(When your royalty checks start rolling in, remember you heard it here first!)
John

[Chris Smith]

Try five million plus amps? <p>75% of all the gas dollars you spend, goes out the tail pipe and radiator.<p> Try cooling that with a Peltier? <p>19,000 BTUs per pound of gas, times amps, minus inefficiency,..times, yeah, im dizzy already!!!

[MicroRem]

Try the same idea only passive... in effect, just replacing the rubber hose with copper would make the hose itself a more efective radiator of heat. Maybe the trick would be to add "fins" to the copper to make it an even better heat sink. <p>Who knows? you still have to get that heat from under the hood, so maybe just the lower hose??<p>good luck
Tom

[toejam]

maybe you could tuck another radiator somewhere under the car with an electric fan and connect it to the cooling system.

[Chris Smith]

Or use a standard over the counter heavy duty radaitor for the job?

[jollyrgr]

YOU CAN'T MAKE THINGS COLDER!!!! YOU CAN ONLY MOVE THE HEAT!!!!<p>Now that I got that out, let me explain. You can generate heat by some means such as chemical reaction (burning gasoline). You cannot create cold!!! All you are going is MOVING heat when you make things colder. It does not matter if it is the radiator of a car; moving heat from inside the engine block with a liquid coolant, or moving heat from inside a house with an air conditioner. The Peltier junctions only MOVE heat from their cold side to the hot side. Thus you move heat from the metal cube to the other side of the Peltier. Most likely this will need a heat sink and fins. What have you achieved? You moved the heat from the coolant to the inside of the engine compartment.<p>And as Jwax points out Peltiers need energy to operate. This translates into a draw on the electrical system; which means the alternator works harder; which means more load on the engine; which means more heat.<p>The fan(s) on the radiator provide more air flow. A better radiator or larger air volume fan would be better solution.<p>Another thing to check is your coolant mixture. You MUST use a good coolant mixture. Coolant should NEVER be all antifreeze. Nor should it be all water. The antifreeze does not have the "heat capacity" (ability to absorb heat energy) to cool an engine. My brother's friend got the bright idea that he would spend the "extra few dollars" and put all antifreeze in his car. He became very surprised when the car would always overheat. The heat capacity of water is 1 BTU/(lb F). The heat capacity of ethylene glycol (antifreeze) is anywhere from half to 70% that amount. Thus using pure antifreeze is a bad idea. Once he got the 50/50 ratio of water to antifreeze (the mixture is coolant) his car stopped overheating. <p>As Chris has suggested, a better radiator would help. I suggest a stronger/more powerful fan. If the fan is mechanical, there are higher flow fans. <p>Other things to check is for a "bubble" in the cooling system. I don't know how many people I've helped with this problem. And even some mechanics don't correct this situation or even understand the problem. When a radiator system has been opened a bubble sometimes forms inside the engine, radiator, or other component in the cooling system. This means that there is a lack of coolant to properly cool the engine. If a radiator is cleaned/removed or if a hose blows out and spills coolant, you can bet there will be a bubble in the system. I replaced a water pump on one of my cars last fall. It took me nearly an hour to just "burp" the system and fill it to capacity. (Imagine a mechanic spending an hour on doing this when replacing a hose.) Once burped I was able to add an additional gallon of coolant to the system. What appeared full really was not. This trick has also helped restore heating to cars in the cold of winter. You need to start with the engine cold. Remove the radiator cap. DO NOT confuse this with the overflow tank! You need to remove the real radiator cap. You MUST do this with the engine cold or you could get boiling coolant spraying everywhere! (ASIDE: Radiator systems are pressurized to raise the boiling point of the liquid. That is why when a hose/radiator bursts a car boils over quickly. The pressure in the system is around 15 PSI above atmospheric pressure. Once the hose bursts the pressure is lost and the boiling point drops below the temperature of the hot liquid. It now boils rapidly.) Start the engine and turn on the heating system to full. (If you have rear heating as in larger SUVs, turn on both front and rear heaters.) As the engine heats you will notice the coolant level start to drop (as the thermosat opens). Keep adding the 50/50 mix of coolant. When you are very full, drive the car a round a bit and make some hard stops to splash the water around inside the engine. If there is a bubble in the system, sooner or later you will note that the coolant level in the radiator has dropped significantly.