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I drive an air-cooled Volkswagon Beetle (73) In this case, air-cooled is really a misnomer. Bug engines use their oil to remove heat and blow cool air past an oil cooler, which functions as a radiator does in a water cooled engine. It should then be possible, with a small about of effort, to create
a peltier cooled oil sump plate with a small set of fins. It would work, in effect, exactly as peltier coolers work for computer cpus. It could cool the oil several degrees, adds no moving parts, and the coolers are already designed to run on 12V, which the bug is (after certain years). Every degree of cooling for the oil helps on those blistering summer days here in Southern California.
Engineering Ratholes
http://www.tinaja.com/glib/ratholes.pdf
[Fussass, Oct 04 2004]
[link]
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I don't know if this idea would work or not... |
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I just wanted to agree that the bug was a marvel of engineering and economy... is there any modern vehicle that is comparable? |
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You would need a second alternator or they would drain the bats really fast. I'm not sure there is a place on the bug for a second one, it's been a while since I have been inside one. |
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A Peltier cooler is a heat pump, i.e. it moves heat from one place to another. As the cool end gets cool, the hot end will get hotter; so you'll need to take care with your heatsinking and / or airflow. |
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I think that the materials involved in a peltier cooler the size of an oil pan would be quite expensive (bismuth, etc.). I think you could get a better and more economical effect by adding an auxiliary oil cooler and using synthetic oil of a low viscosity. |
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Fluted oil pans are availible for VW, and lots of other cars, they disipate heat and control the position of the oil which more effectively "soaks" the bearings and the like... |
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[+] for any idea that keeps the flat four "air" cooled engine design alive. How many miles could a Peltier last under normal dirving conditions? For mechanics to buy in, I would imagine it would have to outlast the spark plugs (~12,000 miles). |
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I don't see the point. A Peltier cooler is usefull for cooling something BELOW ambient temperature. You certainly don't want to cool your oil to anywhere near ambient (even ambient in Southern California). Nature wants to even out the hot and cold - you don't need to add in a 12V heat pump to help her along. |
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If you're having cooling problems, why not just get a larger oil cooler? There's tons of aftermarket parts available for the bug. |
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You could still use all the other methods mentioned, but when the going got tough, you could flip a switch and watch the oil temp fall a few degrees. The idea would be to replace the standard "oil sump plate," also sometimes known as a billet with a peltier version, or maybe even just the oil plate plug. So, we're talking a 5 inch disk or a one inch plug, not that expensive at all. A good heat sink with fins would pull enough heat away (see some of the fanless cpu heat sinks) especially when the car is moving. There is very little chance you could cool the oil enough that it would be considered too cold and not flow. It just wouldn't happen. And the motor is generating more than enough volts when it's running that there would be no worries about draining the battery. |
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I understand what you're talking about, but I don't think you understand the physics. |
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First of all, Peltier coolers are about 50% efficient. That means that half of your electrical energy input is being converted into more heat that you need to get rid of. |
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Secondly, I think you are severly underestimating the energy draw (watts, not volts) needed by the Peltier device to make a significant difference . Dealing with the heat generated by a CPU is pretty trivial compared to a four cylinder engine. I very much doubt that the stock alternator is capable of delivering that energy. |
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Finally, cooling is basically a factor of air flow over the cooling surface, and the temperature differencial between the cooling surface and the ambient air. As it is, you already have a sizeable temerature differential between the oil cooler and the ambient air. A small hit in air resistance by going to a larger oil cooler will deliver much better cooling than a similar energy draw used to increase the temperature differential between the oil pan and the ambient air. |
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Hey! I too had a VW bug in SoCal... (Im originally from Orange County) |
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I can relate that any effort to help with cooling is better than nothing... So I will give it my approval. |
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However, does the cooling benefit outweigh the heat created by generating the electricy? |
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try nikasyl cylinders; you'll be surprised. |
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Bad: As a rough rule, to move a given amount of heat with a Peltier device requires about twice the amount of electrical input. The actual amount of heat that would be needed is unknown, but take it as 1000 Watts and scale from there. 2000 Watts of power would be needed, at 12 Volts that is 166 Amps. Two extra large alternators will be needed and they will extract 3 or 4 horsepower from the engine. |
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Worse: The original 1000 Watts plus the new 2000 Watts now makes 3000 Watts that must be dissipated from whatever heat sink or radiator is attached to the hot side of the Peltier device. |
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Still worse: To get any life from the devices the hot side temperature must be kept down below 100C or so. That is cooler than the original oil pan temperature. To accomplish that on a day when ambient temperature is near there would need a huge heatsink with forced air-cooling or a liquid radiator system. All above assumptions are optimistic. |
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There is mention of this kind of engineering in the LINK, along with several other hopeless ideas that come up every so often. |
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Not good. A heat pump requires a very large power input, similar to the amount of heat you are trying to remove. As a car engine is only about 30% efficient, the engine produces twice as much heat as power. Hence only a small amount of cooling assistance could be provided by a Peltier setup. |
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I'm not a big beetle guy, I must confess, but in stock form I believe they make about 40hp (approx 35kW)? Correct me if I'm wrong... at 30% efficiency that means about 60-70 kW of heat is wasted. To improve the cooling by 10%, you'd need to be pumping 6kW of heat. That's more like 500A and an enormous peltier. |
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The real problem is that a heat pump doesn't dissipate heat, it only pumps it from one place to another. In a PC the peltier has to be connected to a big heatsink to prevent the peltier melting. The same situation applies... you'd need a really big cooler to cope with the heat. Given that you'd need a big radiator, why not scrap the peltier and all the extra heat it produces, and just use a bigger oil cooler instead? |
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