Heat exchanger with dry ice

[Eren Kruger]

I want to cool Natural gas from 293 Kelvin to 200 Kelvin in a heat exchanger by using dry ice as the collant. I have to determine the lenght of the heat exchanger but i dont know what the thermal conductivity value of the dry ice is and cant find it anywhere. I would be very glad if someone can help me..

I also have one more question. If i use instead of solid dry ice, an dry ice-glycol solution, would the heat transfer from the pipe to the solution by free convection or would it be conduction?

 

[drawoh]

Eren Kruger,

Does its conductivity matter? Your heat will convert it to carbon dioxide gas, and completely mess up the thermal contact with your heat exchanger. I should think that a cold liquid is a way better coolant.

What will keep your coolant cold, besides another heat exchanger?

--
JHG

 

[btrueblood]

Hard to get good conductivity numbers for dry ice, as it is for snow, the numbers depend on how densely packed the stuff is. Yes, you will get better conductivity with a glycol similar anti-freeze solution.

The big "but" - the dry ice sublimation point at 1 atm is just barely below 200K, and the freezing point of glycol mixtures is similarly just barely below 200K at a 60% by weight mix of ethylene glycol with water. I.e. it's gonna be tough to get to 200K in a heat exchange process with flowing gas, unless the gas flow line is very long. You will probably want something like a large insulated tank filled with dry ice/glycol mixture, with a coil (or a nested trio of coils) of gas flow tubing suspended in it.