Sublimation process of dry ice in a closed space
Sublimation process of dry ice in a closed space
(OP)
Hello everybody,
I would like to understand a bit better the sublimation process for the purpose of my study.
I then have a dry ice block (m = 3kg, Vice = 2.10^-3 m3) in a closed space (Vtot = 4.10^-3 m3), in an ambient temperature. The temperature of the inside of the box (the closed space) is at Ti = -80°C and at Pi = 1 atm.
This dry ice block will thus sublimate due to the heat coming from the outside, and after 15 hours all the dry ice is sublimated and the Pressure P is thus Pf = 87.4 atm (I calculated by myself so it may be wrong).
With the help of www.thermofluids.net/ I found the enthalpy of formation at the first state is h1 = -95.2 kJ/kg and at the end h2 = -298.6 kJ/kg. The value given by wikipedia for the sublimation of the dry ice is 574 kJ/kg. I would like to know how to interpret the increase of pressure on the energy absorb by the dry ice. How do I have to link the h1, h2 and the value given by wikipedia?
Thank you very much.
I would like to understand a bit better the sublimation process for the purpose of my study.
I then have a dry ice block (m = 3kg, Vice = 2.10^-3 m3) in a closed space (Vtot = 4.10^-3 m3), in an ambient temperature. The temperature of the inside of the box (the closed space) is at Ti = -80°C and at Pi = 1 atm.
This dry ice block will thus sublimate due to the heat coming from the outside, and after 15 hours all the dry ice is sublimated and the Pressure P is thus Pf = 87.4 atm (I calculated by myself so it may be wrong).
With the help of www.thermofluids.net/ I found the enthalpy of formation at the first state is h1 = -95.2 kJ/kg and at the end h2 = -298.6 kJ/kg. The value given by wikipedia for the sublimation of the dry ice is 574 kJ/kg. I would like to know how to interpret the increase of pressure on the energy absorb by the dry ice. How do I have to link the h1, h2 and the value given by wikipedia?
Thank you very much.





RE: Sublimation process of dry ice in a closed space
RE: Sublimation process of dry ice in a closed space
You want to check my linkedin profile?
RE: Sublimation process of dry ice in a closed space
RE: Sublimation process of dry ice in a closed space
I already did quite a lot of experiments that proves that there is almost no dry ice left after 15 hours in our condition (T = 22°C and P = 1 atm), but with a NOT airtight box.
We now would like to learn if it is interesting (and how much it is) to build an airtight box around the dry ice to increase the cold capacity of the dry ice. I would like not to add to many parameters at the same time to understand it properly. So lets forget the heat transfer through the tank for now, assuming that by changing the material of the tank we can make sure that the sublimation is total at the end of the 15 hours.
RE: Sublimation process of dry ice in a closed space
It could be you've already talked to them; I don't know. You haven't shared that information.
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RE: Sublimation process of dry ice in a closed space
RE: Sublimation process of dry ice in a closed space
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RE: Sublimation process of dry ice in a closed space
I will take a look at the equation.
The box around the dry ice is very small because it is only here to store the dry ice. So, let say 2 times the volume of dry ice.
The box is not specifically insulated and heat comes from the environment around the box.
RE: Sublimation process of dry ice in a closed space
RE: Sublimation process of dry ice in a closed space
(Does that theoretical box touch the ground (If so, what kind of ground/pavement/plate/wood/table/plastic is conducting heat upwards into the lower floor of the box?) , or is it in mid-air?
Heat from the outside (air or combination of air and support plate) heats the floor and walls of the small box, then that heat heats up the very cold CO2 bolck AND begins to sublimate the CO2.
You have both latent heat gain and sensible heat gain to think about inside the box.
RE: Sublimation process of dry ice in a closed space
Your final answer should be consistent with the phase diagram
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RE: Sublimation process of dry ice in a closed space
RE: Sublimation process of dry ice in a closed space
RE: Sublimation process of dry ice in a closed space
The dry ice is used as a buffer to suck hot from the environment.
RE: Sublimation process of dry ice in a closed space
That is why I am investigating, maybe too much, where the company never investigate before.
RE: Sublimation process of dry ice in a closed space
http://www.union.dk/media/CO2-GB.pdf
From this you can see that at 20ºC your dry ice will increase the pressure to around 70 barg
Best regards,
Morten
RE: Sublimation process of dry ice in a closed space
RE: Sublimation process of dry ice in a closed space
RE: Sublimation process of dry ice in a closed space
Some threads that may be of interest:
thread71-231218: (ask) Dry Ice for cooling air intake temperature
thread135-76882: transportation of dry ice on aircraft
thread391-193500: Keeping the ice chest cold