My high school chemistry teacher did that, with a coffee can. I gather that when he's done it in the past, the lid did not smash through a fluorescent light fixture like it did for us...
-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
Hydrogen vs. Battery
- Thread starter siry
- Start date
My high school chemistry teacher did that, with a coffee can. I gather that when he's done it in the past, the lid did not smash through a fluorescent light fixture like it did for us...
But you’re wrong. Inside LEL and UEL the gas/liquid is flammable, outside it is not. I know what it stands for and it has the word explosion in it, but this isn’t what it is referred to in the industry, manufacturers always refer to LEL and UEL, LFL and UFL is not used. You can not determine how something can explode out from LEL and UEL, because that varies a lot on volume, mixture and enclosure. Explosion is basically just a quick fire.
Inside the can the hydrogen is above UEL and won't combust, since small amounts of hydrogen leaks out the top it enters below UEL making it burn. But as hydrogen exits the can, oxygen is drawn in from the hole he used to fill it with on the bottom of the can. And when there’s enough oxygen inside to bring the hydrogen inside the can below UEL it will ignite from the flame, releasing lots of energy in an enclosed area making the can propell.
Just read the pdf you attached, Hydrogen has a LEL of 4% and UEL of 75%, and it simply wont burn outside that range. And there’s tons of information about gas characteristics and explosions online.
nicely explained, and I absolutely agree that there is a lot of variation based upon volume, mixture and enclosure
but i would describe a chemical reaction propagating via shock wave as different to just a quick fire. even if energy/chemistry is the same.
Will a hydrogen fire proceed to detonation? I don't know, that very dependent upon particulars of the situation. But once it is expected to enter the LEL/UEL range, personnel need to be evacuated just in case.
JRP3
Hyperactive Member
I saw this on the news here, very sad. Haven’t worked or have that much experience with pure oxygen. But I know pure oxygen basically accelerates the flames if there’s already fuel and fire since its an oxidizer. But for that large of a boat theres a large dieseltank as well, and if its old and not well maintained I guess that could be a factor.
Yes, it's all dependent upon particulars of the situations. Theres a whole process and C&E of whats happening when one or multiple detectors detect gas, PSD/ESD, evacuate etc..[/QUOTE]
Curious George
Member
Exactly! There is danger in lot of things around us. Can you name the most common causes of house fires in USA?
Here they are from nfpa: Top fire causes
51,000 fires out of 352,000 fires are electrical, with 500 deaths every year.
What are the most common causes of house fires?
Yet we have gas and electric connection in every home. People take their chances and try to be safe.
Here is a little demo of Toyota's tank safety.
I just googled if Tesla has a similar demo. There was a case for spontaneous fire. Tesla struck a deal with the owner to avoid negative press. Later, Tesla denied him the new car, saying there was a bullet hole in the pack. Then settled with the owner again. The entire story sounds really strange, if true. And yeah, there was NO ALERT here either. He just figured it out from the smoke and flames coming out of the rear seat.
Tesla says someone fired a bullet into battery pack of a Model S that caught on fire - Electrek
Tesla driver who settled when his car caught fire forgot to mention someone shot the battery with a gun
I think it's quite likely that pack had a manufacturing defect and came with that hole.
Last edited:
(.....but we've spend many billions on this and don't want to lose face..... ?)
Same as Dieselgate.
[/QUOTE]
That's the main problem.
There are several things that can go wrong with Hydrogen.
If one detector, or a pipe, or connection fails.
If one "non- professional" connects something incorrectly, it can become a bad situation very quickly.
Best to not start too many rumors...I don't think divers use pure oxygen...but just compressed air which is ~21% oxygen.
Yes, if it was pure oxygen it would be a fire that can't be put out even by submerging.
Can be either. Your average scuba diver is using standard compressed air that's got the same chemical mixture as the atmosphere.
Serious technical divers that are pushing the extreme boundaries for depth do use pure oxygen, mixed with helium if I remember right.
I don't think there are very many people in the world that actually do that - the costs and risks tend to make it a realm for professionals or more often for (would be) record setters.
Sorry for the late response. This is interesting, because everything I see about FCEVs looks to put their onboard H2 efficiency at 40-60%, and EV efficiency is generally quoted as being 80-90%. So we're taking the power plant efficiency (~60%) and the vehicle efficiency (~85%) plus grid losses (~5%), and comparing those against the steam reformation efficiency (which I cannot source anywhere near 95% -- I see it quoted frequently at 65-75%) minus distribution compression, onboard compression and transportation, etc.
But as you conclude, efficiency isn't as important a measure when renewable choices are being used, and even in that case, directly charging the vehicle is going to always be more efficient than performing electrolysis/compression/etc.
I was working from a 50-60% CCGT efficiency and a 60-70% fuel cell efficiency that I'd read in the past to have the numbers more or less work out.
And I'm still not recommending it as a solution, just pointing out where the math is somewhat close.
Curious George
Member
The wikipedia page on fuel cells is quite informative and has enough details on effiiency. On the page, search for "efficiency" and check section 3 on that topic.
Fuel cell - Wikipedia
"The energy efficiency of a fuel cell is generally between 40–60%; however, if waste heat is captured in a cogeneration scheme, efficiencies of up to 85% can be obtained"
Also, the waste heat is not always waste. It can keep the occupants warm during cold winters. Also keeps the windshield properly defrosted.
Electric cars pay dearly to produce that heat. Check AAA study of upto 50% range loss. If we compare winter efficiency, FCEV might come out ahead.
Curious George
Member
In the same article. there is speculation about nitrox. Thankfully, most of the crew members are alive and they can tell what happened or what they know.
The key thing is, many of these accidents happen when people let their guard down. If dangerous is dealt with properly and people know about how to detect and deal with them, much of the impact can be mitigated. Like the Norway hydrogen station fire. No one was injured or killed. In these stations, the hydrogen storage tanks are enclosed with well ventilated metal enclosures. Even if the tank bursts, the shrapnel like material will be contained within the enclosure. Precautions like that.
There is also an article that describes how Boeing could never root cause the battery fires or ensure no fire from Lithium batteries on board. So they just enclose them in a fire safe enclosure. These are safe design practices.
Likewise, thermal runaway and short detection methods will be part of safe design practice for battery packs. The Titanium shield was a good thing.
Last edited:
This is just a comedy 
Prefer less efficient vehicle to keep yourself warm.
It's like keeping vacuum cleaner at home switched on during winter month - so you could reduce your gas bill
Range loss has little to do with energy used for heating.
Efficiency has nothing to do with energy per distance travelled. One is a ratio, another is actually a unit.
Everybody should stop for 2 minutes and THINK BEFORE POSTING INCOMPETENT CRAP ONLINE just for the sake of writing something
Prefer less efficient vehicle to keep yourself warm.
It's like keeping vacuum cleaner at home switched on during winter month - so you could reduce your gas bill
Range loss has little to do with energy used for heating.
Efficiency has nothing to do with energy per distance travelled. One is a ratio, another is actually a unit.
Everybody should stop for 2 minutes and THINK BEFORE POSTING INCOMPETENT CRAP ONLINE just for the sake of writing something
Curious George
Member
All that matters at the end is miles traveled with same amount of energy.This is just a comedy
Prefer less efficient vehicle to keep yourself warm.
It's like keeping vacuum cleaner at home switched on during winter month - so you could reduce your gas bill
Range loss has little to do with energy used for heating.
Efficiency has nothing to do with energy per distance travelled. One is a ratio, another is actually a unit.
Everybody should stop for 2 minutes and THINK BEFORE POSTING INCOMPETENT CRAP ONLINE just for the sake of writing something
Just read the Wikipedia link, see how efficiency changes with heat recapture from the FC stack.
THINK BEFORE POINTING FINGERS! THERE I PROVED IT WITH CAPS. <LOL>
And read section 3 most carefully to prove yourself wrong. If the heat is useful, it is part of the efficiency. Here, I put that in bold.
===
Theoretical maximum efficiency
The energy efficiency of a system or device that converts energy is measured by the ratio of the amount of useful energy put out by the system ("output energy") to the total amount of energy that is put in ("input energy") or by useful output energy as a percentage of the total input energy. In the case of fuel cells, useful output energy is measured in electrical energy produced by the system. Input energy is the energy stored in the fuel. According to the U.S. Department of Energy, fuel cells are generally between 40–60% energy efficient.[65] This is higher than some other systems for energy generation. For example, the typical internal combustion engine of a car is about 25% energy efficient.[66] In combined heat and power (CHP) systems, the heat produced by the fuel cell is captured and put to use, increasing the efficiency of the system to up to 85–90%.[46]
The theoretical maximum efficiency of any type of power generation system is never reached in practice, and it does not consider other steps in power generation, such as production, transportation and storage of fuel and conversion of the electricity into mechanical power. However, this calculation allows the comparison of different types of power generation. The maximum theoretical energy efficiency of a fuel cell is 83%, operating at low power density and using pure hydrogen and oxygen as reactants (assuming no heat recapture)[67] According to the World Energy Council, this compares with a maximum theoretical efficiency of 58% for internal combustion engines.[67]
JRP3
Hyperactive Member
Using waste heat for efficiency reminds me of an almost identical argument I once heard for incandescent bulbs over LEDs. "We're heating the house anyway." But of course, that's no argument at all because heating should be done as needed, on demand, and not as a random capture mechanism. Sure, waste heat isn't always wasted. I'll accept that. But even when you're using waste heat to heat an ICE, you're operating at a lower efficiency than you would with an EV and a resistance heater. Watch the plumes of heat escape an ICE on a freezing cold day.
None of this really matters in the end, though, because the goal is a move to renewables. And I think it's quite clear that using solar or wind power to create, compress, and distribute H2 will never be as efficient as charging an EV directly. So H2 will never have the edge on efficiency in the context of sustainable transport, which is the dress that FCEVs are trying to wear to the ball.
Similar threads
