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Old 10-08-2019, 12:15 PM   #41 (permalink)
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No, not necessarily. While modern batteries have poor energy density compared to gasoline, they're still way lighter and more compact than hauling a water heater tank around in your Prius. The other thing to think about is, in a hybrid car, you ALREADY have a storage mechanism - the batteries - built in. All you have to do is build the steam generator and add a heat exchanger to condense the steam back into water.

As for the efficiency of the steam generator, so what if it's not as efficient as a modern steam plant? You're recovering waste heat anyway, so anything you get back is a win. I would think that the reason they don't already have this technology on hybrid cars has more to do with weight, complexity, packaging and safety than thermal efficiency.
Steam engines lost out to ICE because of cost and maintenance issues. Hauling a supplemental, low-efficiency one around would not pay. I'm not talking about hauling a plain water tank, but a phase-change tank.

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Old 10-08-2019, 01:18 PM   #42 (permalink)
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Steam engines lost out to ICE because of cost and maintenance issues. Hauling a supplemental, low-efficiency one around would not pay. I'm not talking about hauling a plain water tank, but a phase-change tank.
OK, I'm not understanding your position, since you're effectively arguing for driving around with a boiler in your car but not doing anything with the steam once you generate it.

Thermal efficiency is not the only consideration in an engineering solution. Regular tank, phase change tank, doesn't matter. The energy density of that solution is way too low to work.

A phase change for water would release about 2,200 joules per liter of liquid water (where are you going to store the steam while you're driving, BTW?). Compare that to the WORST battery in terms of energy density, the lead acid car battery. The lead acid battery has an energy density of about 180,000 joules per liter. In other words, you'd need 80 liters of water to equal 1 liter of battery. From a weight standpoint, it's almost the same - 70 kilograms of water for every 1 kilogram of battery.

You see, even if your solution is more thermally efficient, it's simply not practical. Whereas, adding a "low efficiency" generator will still recover lost energy without turning the car into a rolling tank truck.
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Old 10-08-2019, 02:27 PM   #43 (permalink)
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You see, even if your solution is more thermally efficient, it's simply not practical. Whereas...
So we're 42 posts in. Has anyone looked at Wikipedia?

https://en.wikipedia.org/wiki/Exhaus...ecovery_system
Quote:
This technology can be used either on a hybrid vehicle or a conventional one: it produces either electric energy for batteries or mechanical energy reintroduced on the crankshaft.
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Old 10-08-2019, 02:39 PM   #44 (permalink)
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So we're 42 posts in. Has anyone looked at Wikipedia?

https://en.wikipedia.org/wiki/Exhaus...ecovery_system
Great minds think alike, I guess. \_(ツ)_/
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Old 10-08-2019, 03:18 PM   #45 (permalink)
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OK, I'm not understanding your position, since you're effectively arguing for driving around with a boiler in your car but not doing anything with the steam once you generate it.

Thermal efficiency is not the only consideration in an engineering solution. Regular tank, phase change tank, doesn't matter. The energy density of that solution is way too low to work.

A phase change for water would release about 2,200 joules per liter of liquid water (where are you going to store the steam while you're driving, BTW?). Compare that to the WORST battery in terms of energy density, the lead acid car battery. The lead acid battery has an energy density of about 180,000 joules per liter. In other words, you'd need 80 liters of water to equal 1 liter of battery. From a weight standpoint, it's almost the same - 70 kilograms of water for every 1 kilogram of battery.

You see, even if your solution is more thermally efficient, it's simply not practical. Whereas, adding a "low efficiency" generator will still recover lost energy without turning the car into a rolling tank truck.
OK, I see the disconnect. I'm talking about the phase change from solid to liquid in wax or a similar substance - no steam involved. The last time I ran the numbers on it, a modest weight would handle an average day's waste heat. The system delivers exactly what we buy for houses with low cost hardware.
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Old 10-08-2019, 04:01 PM   #46 (permalink)
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OK, I see the disconnect. I'm talking about the phase change from solid to liquid in wax or a similar substance - no steam involved. The last time I ran the numbers on it, a modest weight would handle an average day's waste heat. The system delivers exactly what we buy for houses with low cost hardware.
It doesn't matter. A simple phase change cannot match the energy density of chemical bonds.
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Old 10-08-2019, 04:45 PM   #47 (permalink)
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If I burn 2 gallon of gas a day and say I capture and store 1/3 of the energy as waste heat that would be about 80,000 btus. (little less the a gallon of propane). Wax latent heat of fusion is 90-95 btu/lb, melts around 130F. Normal heat capacity is 0.6 btu/lbs.

So useful heat for the house starts starts at 70 degrees and heat it to 200, 130 degrees change. 78 btus stored plus the 95 to melt it, 173 btus per lb stored. To store that 80,000 btus of waste heat would take 462 lbs of wax.

Wax weighs 7.75 lbs per gallon, so would need 60 gallons + the tank to hold the coolant to circulate around it.
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Old 10-09-2019, 08:59 AM   #48 (permalink)
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Get an EV and setup a "Totem" system, which uses an ICE to run a generator and catches the waste heat for domestic water heating, that way you can be sure your fuel is being utilized in an efficient manner, you can do this with gas,diesel or natural gas even propane.The advantage, one fuel source, the disadvantage equipment to maintain which if balanced by storage would last a long time.
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Old 10-09-2019, 09:13 AM   #49 (permalink)
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Actually that is a pretty good balance.

While you are away no heat or energy consumption in the house. When you come back, you have heat on and you charge your car.
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Old 10-09-2019, 11:32 AM   #50 (permalink)
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I didn't see anyone mention cooking in this thread... there are a few different ways to plumb a sealed chamber into the exhaust system to capture waste heat for cooking food, heating water, whatever fits in the box. Definitely unconventional and perhaps some people will feel it's risky with the potential toxins, but a quality system should be pretty safe and effective.
My $0.02 for this thread.

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