X-Message-Number: 5708 Date: Mon, 5 Feb 1996 22:35:48 -0500 From: (Ralph Dratman) Subject: Re: CryoNet #5701 - #5706 >a) Microwave freezers seem to violate the 2nd law, I'm told. :-( Do you have a reference on that topic? I've been wondering about it for years. >Problem: Is it possible to make a micro-dewar? Even in theory? The ratio of volume to surface area for a 2-micron dewar would be a million times smaller than the ratio for a 2-meter dewar. Since thermal leakage is proportional to the surface area, while thermal reservoir is proportional to the volume, I believe that a tiny dewar could not work. This might sound absurd, but would it be possible to force liquid nitrogen directly through the circulatory system? Okay, okay, I can just *assume* that this idea won't work, but maybe someone could take a moment to tell me *why* it won't. Of course, there would be the gas phase to remove, that is one problem, and the gas pressure could do a lot of damage, and I suppose the arteries might tend to freeze in a closed position, so that liquid flow would be blocked. >My previous message about quick freezing contains an important technical error. >I gave the heat-of-fusion for water (the amount of heat removed to freeze >a certain amount of water) as 540 calories/gram. The correct figure is only >80 calories/gram, which makes some of my wild ideas slightly less impossible. >(540 c/g is the heat to vaporize water at 100C.) Okay, it's 80 cal/g; what's the practical meaning of that? Let's put it another way: What mass of LN2 must be vaporized to freeze a gram of water? And how much gas is evolved? We need the heat of vaporization of LN2. Oh, I have that: 5.77 kJ/mole = 1.37 kcal/mole = 1.37 kcal/28 g = .049 kcal/g = 49 cal/g. Someone correct me. That means it takes the vaporiztion of about 80/49 = 1.6 g of LN2 to freeze 1 g of water, if all of the above is error-free, hah. And the LN2 gas volume from freezing that 1 g of water would be very roughly 22.4 * (1.6/28) = 1.28 liter, a *very* substantial amount of gas evolved to freeze one lousy gram of water. Tell me where I made my mistakes. Also, how about Freon? This is brainstorming, so I'm allowed to bring up totally outlandish, even stupid ideas without being ridiculed, right? How about hyperbaric ideal gases, such as liquid neon? Of course, all this is predicated on the idea that quick freezing is the way to go. Comments on that idea, please? Would quick freezing cause additional damage from cracking and related effects of thermal stress? I find it counter-intuitive to imagine that quick freezing is what you want, but I'm also almost certain that my intuition is worthless in this situation. Certainly it must be true that embryos and sperms freeze very quickly... Ralph Dratman Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=5708