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Comment Re:How efficient is hydrogen really? (Score 1) 199

OMG, I made a terrible mistake. That'll teach me to post such things late at night with a low blood sugar...

For the temperature, of course, you need the increase factor, not the difference! So there is T1=20 C=293 K and T2=3200 C=3473 K. So now properly we get T2=3473*T1/293=>T2=12*T1 (approximately).

So there you have it: Factor 12 pressure increase from the temperature and factor 0.67 pressure decrease from the molecule change. The temperature still wins.

Sorry about the confusion.

Comment Re:How efficient is hydrogen really? (Score 1) 199

You need an equation of state. Let's assume that we're dealind with ideal gas mixture so we get: P*V=n*R*T. R is a constant and since you ask about the pressure, I'll assume that you keep the volume constant, so V is also a constant. Now you need to write the equation down for the before/after case, say with subscript 1 for the reactants and with subscript 2 for the products:
P1*V=n1*R*T1 and P2*V=n2*R*T2. Now you divide them, cancel off the constants and you get: P2/P1=n2*T2/(n1*T1). Wikipedia tells me that if I burn hydrogen at the stoichiometric ratio with pure oxygen starting at 20 C and a pressure of P1=1 bar I'll, get a flame at 3200 C (look for adiabatic flame temperature). So this is an increase in temperature by 3180 K. Also, you go from 3 moles down to two so there's: T2=3180*T1 and n2=2*n1/3. BTW, we usually talk about moles, not molecules but they are essentially the same thing since a single mol of a substance contains an amount of molecules equal to the Avogadro number, which is a constant. So now by substitution we have: P2/P1=3180*2/3.

So you see that the rise in temperature incresed the pressure by a factor of 3180 whereas the fewer amoumt of molecules in our theoretical non-expandable perfectly isolated box only led to a pressure drop by a factor of rougly 0.67.

However, at the resulting pressure of about 2120 bar (!) it's not correct to use the ideal gas equation, but you see where this is going. The temperature increase wins by a longshot in this case, and I would expect this to be so for any reasonable fuel combustion.

Comment Wrong metrics (Score 1) 210

Trackers measure parameters like steps and calories and bring them out of context. If you ate 500 kcal worth of chocolate right before the workout, then burning 500 kcal will do little in terms of fat reduction. You don't work out to burn the fat while you exercise, you work out to change your metabolism so that you burn fat while you don't exercise. Trackers won't reward you for doing muscle training (no steps involved!) although building muscle is awesome for losing weight (give your body enough mitochondria and you'll practically lose weight while you sleep!). Trackers are a fun gadget, but of more entertainment value than anything else.

Comment Re:$399 per month (Score 1) 67

In ten years? I've had my Ford for 4 years and I've only opened the hood for adding windshield wiper fluid. The air pressure (and a bunch of other things) is checked at the dealer's where I drive it to get the tyres replaced twice a year (in November they take the summer tyres off, put them in storage and bolt on the winter tyres on, vice versa in May).

Comment Re:Unarmed ships are helpless. (Score 3, Insightful) 104

Get Gatling guns on one ship, the next pirate crew will show up with an RPG. If I was a sailor on one of those ships, there would be no chance in frozen hell I would fire back on a pirate to protect some rich dude's shit on board that's probably insured anyway. You can be as gun-ho about this as you want from your armchair, I'm throwing my hands in the air and letting the pirates go with the cargo.

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