[P-man]

Hey I've been working on this system and I need feedback to make it better. I've basically thought of using the heat that the fuel cell in a car generates to boil water and use the steam to run a turbine. Then I could either use the electricity form the turbine to make more hydrogen or help run the motor. I dunno if this would be practical, but it sounded like a good idea, so I started working on it.

[constant thinker]

Good idea but lookup gas turbine engines in cars. They were great concepts. Worked wonderfully at higher RPMS. They had one flaw though. Coming from idle there was a lot of lag. I have a good feeling the same thing would happen with your turbine idea also. The only way to avoid this problem that I can think of is keep the "engine" at high RPMs. This idea may proove to be bulky also. I like your thinking though P-man.

Thinking about it though. If you had a significant amount of steam, really light fan blades, and a small steam turbine this actually could provide a lot of energy without the lag. I actually think this may be worth looking into though. You'll have the energy coming from the fuel cell also. Costs might hold this back too. Also are you sure your/a fuel cell that would be put in a car can produce enough heat to boil enough water.

[buckminsterfullerene]

i like the way you are thinking, about having a use for previously thermal waste energy, but yeah will it really get that hot, it does release heat, but the fuel cells that i have tried, which have the containers right next to the fuel cell, the water never does boil, in any of them.  though your idea made me think of the way that the thermal energy is used in a car, they put it next to the fan, so that if you want warm air on winter, well you really are only using a fan blowing on the hot engine and giving you the hot air that is produced by the combustion of gasoline by the car.  

but i am very curious as to how you will complete this?  are you making a large car with a fuel cell stack, or a very small one with one fuel cell?

[Borek]

P-man - you started working on the idea, so perhaps you will be able to answer simple question:

assuming your fuel cell has 100 deg C (enough for boiling) and the air surrounding your vehicle has 20 deg C, what is maximum theoretical percentage of the heat that can be converted into work?

[buckminsterfullerene]

a PEM fuel cell (which i assume from the previous posts that i have read from you is the fuel cell that you are working on) generally is considered a fuel cell that works at low temperature, generating heat as high as 200^oF (79.1^oC).  

here is a list of fuel cells available in the market:

-phosphoric acid fuel cells, these cells are generally used in nursing homes, hospitals, hotels, office buildings, utility power plants, etc., etc. and operate at about 190.2^oC, they have a 40% efficiency margin, the reason i bring this one up is because the heat that is produced is also used, it uses 85% of the thermal energy it gives up to steam water and be used in cogeneration, though i would also assume this system to be very expensive, bulky, and heavy.

-Molten carbonate fuel cells: they use molten carbonate at about 634.6^oC, however, the fuel cells are mostly for stationary applications, and use hydrogen, carbon monoxide, natural gas, propane, landfill gas, diesel, and simulated coal gasification products

-Solid Oxide fuel cells: the efficiency of this system is about 60% and can be used for very large applications, requiring high-power applications, they have hard ceramic materials instead of liquid electrolyte, and operate at 968^oC.

-Alkaline fuel cells: They usually use potassium hydroxide as the electrolyte and are used by NASA on space missions with a 70% efficiency.  (no mention on temperature though)

-Direct methanol fuel cells:  they use a polymer membrane as the electrolyte, from the anode the catalyst draws the hydrogen from the liquid methanol, eliminating the need for a fuel reformer, and operate between 34.6-73.6^o at 40% efficiency.  (now there is something interesting about these fuel cells and that is that they are being taken by the cell phone and laptop industry, they are going to be in the cell phones in the future and will increase the time that you can use your battery for example in a laptop by about 10 hours, they almost paper thin and the methanol is the catalyst)

-Regenerative fuel cell: basically this fuel cell uses a solar panel in a process of eletrolisys, to break water into hydrogen and oxygen, is used by NASA, pratically new technology, it uses if i am not mistaken the PEM fuel cell to generate the electricity and is basically a good method to create hydrogen and store the hydrogen for emergency use of some kind, as it is being implemented into ships

-there is another fuel cell that i can't recall the name, but it uses propane to gasify the water and then split it into Hydrogen and Oxygen using the hydrogen to generate electricity and has an efficiency of about 70%.  it is the primary reason that platinum is used in fuel cells and that is because this process produces CO and CO₂ both of which can cause damage to the fuel cell, the platinum will not let this happen.

-Now something interesting about PEM fuel cells, according to my teacher they have reached 90% margins, making them probably one of the most efficient energy application in current existence, off curse breaking the water does require energy, and i really do not know if she took that into consideration.

most of the information here was basically sumarized from a packet that my teacher handed out to us.  though some i found from researching for my project also dealing with PEM fuel cells...
hope this helps

[constant thinker]

And to think..

A gasoline engine is what like 10-20% efficient at best. Has tons of moving parts. Every moving part is a likely place for failure.

I'm like the idea of just stopping by the gas station. Filling up your extremely air tight "gas" tank with liquid hydrogen. Then you can (in theory) bypass anything complicated in theory and set up your fuel cell to use elemental Hydrogen and Oxygen. Only problem is the water vapor. People who live in places that regularly see freezing temps (like me) would have a problem with ice build up on the roads in the winter.

On second thought why not just put the refilling station in peoples homes. Sell it with the car. It'll put quite a few people out of work though. I also can't find a digital article about the Hydrogen Car the students at MIT are/have devoloped. I read it in PopSci. Very intresting, smart, futuristic design. I'd buy one.

[buckminsterfullerene]

well you can produce the hydrogen at home to fuel up your car, the problem is getting it compressed into the car, the costs immediately rises easily to hundreds maybe a few thousand dollars to assumre maximum safety.  but you can have hydrogen gas stations to do this.  there is the theory of using metal hydrates.

right now you can see for example the bl-120 which holds about 120 liters of hydrogen and is the size of almost a pen, cost around $1500± .  the primary element in the metal hydrate is palladium, which is expensive, but it has the amazing ability to hold 900 times its volume on hydrogen.  however, there is also research going along graphite, which according to some articles that i read, says it could hold 30 liters of hydrogen per gram of graphite, if this is so, then that would mean that the graphite would be capable of holding dozens of times more hydrogen for the same mass of palladium, and that it would be extremelly cheap, and the possible solution that will start the hydrogen economy, and the production of cars, that will be very safe, there is only one draw back, the temperature that is needed to extract the hydrogen from the graphite is very high, i think it was 327^oC, as for palladium its at about 27-33^oC basically room temperature (in South Florida atleast)  

[P-man]

Well thanks for the feedback, guys.

Borek- I think it would be something like 80%. But in Canada, the air in winter can get to -35.

I was thinking, if we accumulated the heat in a thermal kind of "room", then it wouldn't matter the temperature outside, because the thermal "room" would block out the cold.

I'm not actually building anything yet because it's too expensive, but I'm designing a lot and thinking a lot as well.

[Borek]

Borek- I think it would be something like 80%. But in Canada, the air in winter can get to -35.

Don't guess, it can be easily calculated. And it will be much less.

[P-man]

But what about my thermal "room" idea?

[buckminsterfullerene]

they actually have applied a thermal idea kind of like what you are talking about in thermos.  what they have is an evacuated area between the wall is inside the cup and the outside of the cup, capable of maintaining more heat and having less escape of heat.  

[P-man]

Do you think it would work? How could I trap the heat form the engine?

[constant thinker]

You could incase it in Reinforced Carbon Carbon(RCC).

Just joking. Way to expensive for anything economical.. I forget what the underside of the space shuttle is made out of. I know the nose and leading wing edges are made out of RCC though. I think useing like fiberglass threads (like some types of building insulation) may work somewhat, but probably not that well.

[Donaldson Tan]

3.314's post is very interesting.

Although the fuel cell may beat the combustion engine in terms of efficiency, it does not generate enough horsepower. Can a fuel cell car go accelerate from 0-100km/h in less than 10s?

P-man's suggestion of trapping the waste heat and use it to generate steam remind me of the golden days of the steam engine. haha.. It's a wonderful idea to make use of the heat, but water has such high heat capacity and I don't think the fuel cell would actually generate so much waste heat. Hence, we will end up with a case where there is a negligible steam or stream with negligible kinetic energy to run the turbine. Perhaps we can use another another fluid for this application - carbon dioxide.

Are there other means of converting heat into electricity? After-all, we have a heat source and therefore a temperature gradient which can be used to generate electricity.

[P-man]

After thinking about the different issues of my system, I have thought of using the water vapour that is the exhaust form the fuel cell to run the turbine, then use the heat in a Stirling engine.