|MadSci Network: Engineering|
At its atmospheric boiling point, the specific (constant-pressure) heat capacity of liquid hydrogen is about 10 J/(g K). I got this from the database described at: http://www.nist.gov/srd/nist12.ht m You should recognize that this property plays only a small role in how fast something will evaporate (unless the fluid starts much colder than its boiling point). More important will be the heat of vaporization (around 440 J/g) and how fast heat can be transferred to the fluid (which will depend on many environmental factors). For example, if you have a puddle of water, the rate of evaporation will be different if there is a strong wind blowing over it, and a wide shallow puddle will evaporate faster than a narrow deep one. Since the normal boiling point of hydrogen is so far below normal temperatures, I'd expect the vaporization to be very fast under most circumstances. I've seen liquid nitrogen poured on a lab floor (don't try this at home!) and it's gone in a second or so. Hydrogen, being more volatile, would probably vaporize even faster. Allan Harvey, firstname.lastname@example.org "Don't blame the government for what I say, or vice-versa."
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