Intermediate Temperature Storage

[jordansparks]

Our ITS dewar arrived last month, and we are trying to find time to test the LN2 consumption rate, etc.
http://www.oregoncryo.com/intermediateTempStorage.html
I'm really curious to see what the cost is to keep it running.

I was really excited about it last year. But as I've thought hard about the pros and cons, I've lost some of my enthusiasm. Yes, it might prevent some cracking. But maybe cracking isn't even currently a big problem. We need to do some experiments to answer that question. Maybe it would be cheaper. But it might just as easily be the same or more expensive than standard LN2 storage. So, we'll move forward with it, but I'm pretty ambivalent about it now. We will not be hyping it.

[jordansparks]

It's been cooled down to -135, now. The thermostat is set so that if it warms to -131, it will start a cooling cycle with liquid nitrogen. The cooling cycle is gentler than I thought it would be, and takes well over an hour. Even more surprising to me is that it only has to cycle about once every 15 hours. Preliminary results show that it is using 4 times less liquid nitrogen for the same volume of storage, compared to the liquid dewar. I would have been happy with equal cost, but lower cost is very exciting.

[DetnPx]

Hi Jordan,

Does your new ITS unit maintain a homogenous temperature throughout the vertical space of the dewar, and if so, how does it do this? And what are the critical electronic parts in the ITS that could cause a failure and temperature rise, besides the thermostat?

[jordansparks]

It's a short and fat dewar, unlike many of the tall dewars in use in cryonics, so the stratification is not as significant. The cooling heat exchanger is at the top of the space. The top and bottom of the space do have slightly different temperatures. Might be a 5-6 degree difference? That spread is maintained as it cycles. The temperatures I gave were for the bottom. If the lid is accidentally left open, the spread widens to about 10 degrees and it cycles more. If LN2 supply is lost while the lid is closed, and nobody takes action for some reason, then it warms up by about 10 degrees per day. These numbers assume a full inventory, so we'll probably fill the empty space with ballast. I think if the contents are insulated somehow, they should cycle much less than the space itself. Insulation would also be necessary to protect the contents when the lid is temporarily open. And since there may be a future need to transfer to another dewar, each item should be individually insulated to prevent rapid warming during any transfer. Because there is no liquid, items could be in hermetically sealed containers. Insulation reduces the space available for storage.

[DetnPx]

Interesting. Perhaps a specially (industry)designed vacuum-insulated sealed polymer/fiber container around each specimen? This might provide the most insulation vs. space benefit compared to traditional insulation such as XPS.

Where does the LN2(l) go, is it at the bottom of the actual storage area, or is there space between the bottom/walls where the LN2 runs through?

[jordansparks]

The LN2 slowly hits a heat exchanger at the top of the space. Some gas gets vented out the top of the unit as this happens. If the heat exchanger gets too cold, it will pause for about 10 minutes to prevent liquid from coming out the heat exchanger and to prevent the exhaust gas from being too cold. This is why each cooling cycle takes over an hour, because it keeps stopping the flow of LN2. There is no liquid at the bottom, and there are no tubes in the walls of the dewar.

[jordansparks]

I'll have to make a web page to explain the cost comparisons. It's not lower cost after all. When compared to a CI Cryostat, it uses 3x as much LN2 per volume, and when compared to an Alcor Bigfoot, it uses 2x as much LN2. Those larger dewars are more efficient. But, for its size, it's probably about the same to use ITS versus liquid storage. Oh well.

[lisc]

Thanks for your honesty in the posts. Cryonics will only improve with this type of honesty and transparency. Thank you.