-80C Walk-in Cold Room

[quark]

We are in the process of setting up a -80⁰C cold room for product storage. The product (95% water) is stored in 20 liter plastic bags. Bag durability is under test now. The product can't tolerate exposure to -20⁰C for longer periods. The product is to be cooled from +4 to -40⁰C in not more than 4 hours time. We also have plans to have a blast freezer for this reason.

The incremental load is 100 kgs per day and the total load for which cold room is designed is 9000 kgs. The room size is 8.5mx5mx2.7m ht or it will be split into two. I have been using CalcRite and Dossat for cold room design so far, but there is nothing about -80⁰C in either of the references. This is first time for me to work on this cold room. I appreciate if I can get any inputs, suggestions and leads.

Thanks,

 

[IRstuff]

Well, don't you need a cooling fluid whose boiling point is below -80°C? I'd be looking at liquid nitrogen.

TTFN

FAQ731-376

 

[quark]

Standard liquid nitrogen storage system (with storage in vapor phase) is one option. However, investment is too high. I have seen some LN2 flash cooling systems (instantaneous cooling and not storage) in tight chambers but the operating costs are very high.

We are planning for a cascade system with R23 in second stage. The boiling point is -84⁰C at atmospheric pressure, so evaporating pressure is slighty negative.

 

[IRstuff]

Is the Wikipedia article in error, then? They list R-23 as having a -82.1 boiling point:

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

and so does Liquid Air:

http://encyclopedia.airliquide.com/Encyclopedia.asp?GasID=66

That would seem a bit tight to have only a couple of degrees margin. You may need to use extremely good insulation, or at least, run the R-23 at a pretty high volume through the system.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[marcoh]

Can a person walk into -80oC with rapid frost damage?

 

[IRstuff]

That'll depend on how long you're exposed, how much wind chill, how well protected you are, etc.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[marcoh]

I was really thinking about breathing -80oC air into your lungs with no protection. Just curious.

 

[IRstuff]

You have to consider what the thermal mass of a breath of air is.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[ChrisConley]

My uncle moved to Canada from Italy many years ago. He didn't believe that the temperature could get down to -40 because he believed that lungs would freeze at that temp.

Everything else freezes, lungs remain OK at -50C (that's as cold as I've experienced personally).

 

[IRstuff]

Let's reiterate that your lungs aren't even at -50°C, or, at least, not for very long. The tidal volume is typically about 0.5 liters, out of a total capacity of around 5 liters. Moreover, if in a cold clime, you would drop your tidal volume down, and/or alter how air even gets to your mouth. Assuming 0.25-liter tidal volume at -80°C, and assuming perfect mixing, the air in your lungs would drop from 37°C to 31.2°C. Even that's a bit extreme, since the air is warmed up on its way down to your lungs. If you're wearing any sort of face mask, the intake temperature would be appreciably warmer.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[RossABQ]

"Standard liquid nitrogen storage system (with storage in vapor phase) is one option. However, investment is too high. I have seen some LN2 flash cooling systems (instantaneous cooling and not storage) in tight chambers but the operating costs are very high. "

Don't kid yourself that there is going to be a cheap and energy-efficient way to accomplish this kind of cooling.

 

[quark]

Don't kid yourself that there is going to be a cheap and energy-efficient way to accomplish this kind of cooling.

No, I don't. This requirement is part of a bigger scheme, which requires another complicated process and its validation, if I have to go with LN2 system.

I did work out on revenue expenditure with -80C cold room with efficiencies running at single digit. Nevertheless, this seems to be the option. Anyhow, thanks for the warning.

To all,

Thanks for the inputs. I came to know about couple of installations of this kind in US (for which I am going to get help from one of my counterparts) and also ready made containers from MAERSK on lease basis (this seems to be a part of side business for them). Will update once the things are finalised.