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Old 06-10-2008, 13:14   #31
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And you'll also find that Hydrogen has a 2.7 times higher energy density per unit mass, than does gasoline - which makes it great for rockets.
Gasoline 14 KWH of energy per Kg of weight
Hydrogen 38 KHW / kg
Gordon,
Compressed hydrogen has much less energy per amount of volume than Diesel. Have a look at the chart.

http://en.wikipedia.org/wiki/Energy_density

By volume, hydrogen has 10.1 Mega-Joules per liter

By volume, diesel has 34.2 Mega-Joules per liter.

My point was, it will take a much larger tank to store the equivalent amount in heat energy of hydrogen as diesel...by a 34.2/10.1 = 337% factor by volume
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Old 06-10-2008, 13:20   #32
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Gordon,
Compressed hydrogen has much less energy per amount of volume than Diesel. Have a look at the chart.

Image:Energy Density.PNG - Wikipedia, the free encyclopedia
Yep - less energy per unit volume, and more energy per unit mass.
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Old 06-10-2008, 13:36   #33
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Someone has slipped two incorrect facts past you. First, in a modern car, the alternator is idled when it is not needed. You should not be producing any significant amount of power at any time from it. When the regulator senses a charged battery, it cuts back the field voltage and the alternator stops producing excess power--and stops dragging on the engine. Anything that takes more power (your radio, turn signals, or hydrogen machine) will cause the alternator to shift to higher output, and put more drag on the engine.

Second thing, as others have noted, is that it takes more power to SPLIT a water rmolecule, than you can get by recombining the H+O molecules from it. That doesn't mean hydrolysis is always a waste. Sometimes it is a good way to TRANSFER power, despite the cost. For instance, cheap hydroelectric power (6c/kwh) can be used to split water molecules, then the hydrogen can be shipped elsewhere and burned as a fuel--either cleaner, or cheaper, than other local fuels. I doubt that will happen in your car, though.
There is also work being done to lower the amount of power consumed in hydrolysis, recently an MIT lab made the news for using a new catalyst that radically lowers the amount of energy needed. But again--you won't have one of those in your car.

Free hydrogen and free oxygen can also be dangerous things. The hydrogen seeps through conventional materials--even stainless steel--and embrittles them, causing premature failures. Not to mention, the h+o gasses can be explosive around sparks--like the ones produced by a conventional alternator.

The best way to improve your gas mileage? Get the extra weight out of your car! Get rid of the spare tire, the junk in the trunk, the extra materials like soundproofing and carpeting in the trunk. Then drive as if there was an eggshell on your gas pedal, use the cruise control on the highway, and avoid that left pedal. Play the road like a video game, where your goal is to steer around things without ever moving a pedal. Amazing what that can do for gas mileage. (As can a proper tuneup, there are gizmos like oxygen sensors in modern cars that simply wear out, quietly, and steal your mpg as they wear.)

On a boat? Pretty much the same. Throttle back, keep the hull clean, and throw the junk overboard!

Miracle boxes? Inevitably don't work once they are put into a lab. Funny thing about that.
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Old 06-10-2008, 14:40   #34
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Actually, in chemistry you learn the same amount of energy is taken as is returned when an atom is separated and then recombined

What causes an effective difference is that no engine is 100% efficient. Therefore you will never get back as much as what you put into it because of this inefficiency.
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Old 07-10-2008, 12:45   #35
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So where did the heat and radiation come from?
If you were able to contain the heat and radiation, like Gamma and even right down to Photons, and then squeeze it all back down into the atom again, then yes you return the energy, but it's like the magic smoke from electronic components. Once it comes out, you can't get it back in. So the result is that the Atom becomes something else. You split an Atom to become something less and release the energy, or fuse an Atom to become the next heavier element, but still releasing energy.
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Old 07-10-2008, 13:25   #36
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Alan,
I was referring to chemistry and not sub-atomic physics. I don't know of any pleasure boats that have nuclear reactors onboard.
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Old 07-10-2008, 14:01   #37
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Alan,
I was referring to chemistry and not sub-atomic physics. I don't know of any pleasure boats that have nuclear reactors onboard.
I think he was referring to the fact that electrolysis releases heat energy, not to quantum physics.

In other words, while the chemical bonds may be the same strength, you still lost some of the energy that you put into the water to split those bonds in the first place due to heat losses that have nothing to do with the bonds themselves. So the net is an energy loss for the whole circuit from H20 to O2 and H2 then back to H20.

Entropy will always win out in the end.
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Old 07-10-2008, 14:40   #38
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I understand that. I was speaking from chemistry theory and not how atoms are separated in reality, which of course always means that some heat will be lost.
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Old 08-10-2008, 03:16   #39
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... Entropy will always win out in the end.
The laws of thermodynamics according to C.P. Snow:

1. You can't win. (You can't create or destroy energy in a closed system. That is, you cannot get something for nothing, because matter and energy are conserved)

2. You can't break even. (You can't convert one form of energy to another with 100% efficiency. That is you, cannot return to the same energy state, because there is always an increase in disorder; entropy always increases)

3. You can't get out of the game. (You can only achieve 100% efficiency at absolute zero, but it's impossible to cool anything down to absolute zero.)

BTW: I can travel through time, and I do ...
at the rate of one second per second.
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Old 08-10-2008, 08:05   #40
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Alan,
I was referring to chemistry and not sub-atomic physics. I don't know of any pleasure boats that have nuclear reactors onboard.
Ah, but David, while true, there were actually a few nuclear powered merchant vessels built (the NS Savannah being the first) back in the late 50's/early 60's. While commercial, at least they weren't warships. And the Savannah actually did look a lot like a large power yacht rather than a cargo ship!

Them's "atoms for peace" for ya! Apologies to the late Pres. Dwight D. Eisenhower...
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Old 08-10-2008, 08:10   #41
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Entropy will always win out in the end.
Heh! Bob Rose, Professor Emeritus of Materials Science at MIT in Cambridge, Massachusetts, owns an Island Packet named Entropy. Known for a keen sense of humor, he'd probably argue that fiberglass is the universe's only known material which can win out over entropy, but still lose against a large rock!
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Old 08-10-2008, 23:30   #42
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Yes. It is a simple law of physics. Simply put, you can not make something from nothing.
thats not what the ad men tell us here in new zealand-
"Efficiency: heat pumps in NZ are an efficient heating option for your home (the most efficient when using electricity). As a general rule, every $1 of electricity used will produce $3 worth of heat."!!!
New Zealand Heat Pumps : Pump, Heating, Cost, Installation, Installers, Electric, Air Conditioning
its convenient to forget to tell you what its being compared against!

3 for 1...i ask you!
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Old 09-10-2008, 04:29   #43
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As a general rule, every $1 of electricity used will produce $3 worth of heat."!!!
How much heat is $3? 1$ of electricity is something that while not static can be measured. I would say if the electricity to run the heat pump is 1$ the heat from the heat pump costs 1$. I guess it depends on the relativity. I assume your source is related to the heat pump salesperson.

We use a heat pump with propane backup at the house. heat pumps are cost effective but when the temperature drops they lose some of the efficiency to the point where the propane is cheaper. With the changes in energy prices you can reset the cross over point. Our reverse cycle AC unit on the boat heats quite well so long as the water temperature is above 50 degrees F. The unit at the house does much better down to some place near 10 degrees F.
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Old 09-10-2008, 04:48   #44
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... "Efficiency: heat pumps in NZ are an efficient heating option for your home (the most efficient when using electricity). As a general rule, every $1 of electricity used will produce $3 worth of heat." ...
A heat pump is subject to the same limitations from the second law of thermodynamics as any other heat engine.

The efficiency of a heat pump is the ratio of heat energy provided, versus the electrical energy consumed to obtain that heat, called its Coefficient Of Performance (COP).

With a COP of 3.0, the cost of heating would be one-third (ie. two-thirds less) of the cost to operate an electric resistance heating system, such as baseboards or electric furnace.

The heat pump is not 3 times more "efficient" - it's 3 times as "cost-effective" to operate (as electric resistance heating).
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Old 09-10-2008, 07:50   #45
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The heat pump is not 3 times more "efficient" - it's 3 times as "cost-effective" to operate (as electric resistance heating).
Even that is not always true. It depends on the temperature difference between how cold it is and how much heat is gained. At low temperatures a heat pump fails to deliver affordable heat. That being the case it would beteer to say that a heat pump can be 3 times more cost effctive under perfect circumstances.
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