Heat transfer rate of dry ice with a mass flow rate of air across it

[nprince5]

I am trying to calculate the amount of dry ice needed to cool a room down to a certain temperature. To find this amount of dry ice needed I am trying to calculate the heat transfer rate per unit mass of dry ice with a given mass flow rate of air across it. I have not been able to find much so far, any input is helpful, thanks!

Nick

 

[IRstuff]

Is this for school? Student posting is not allowed.

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[nprince5]

No this is not for school. I am trying to build a heat pump demonstration unit and I am planning to cool the area enclosed around the evaporator side of the heat pump with dry ice and a fan control system.

 

[IRstuff]

Well, it's forced convection, and there are lots of resources and calculators on the web for that sort of thing.

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[chicopee]

This subject not totally related to your situation has been discussed I believe in this thread. Just do a search using some key words.

 

[dvd]

Off the top of my head, the heat transfer rate is not going to be very constant. If the air blowing over the dry ice were completely dry, then the dry ice would sublimate and lose surface area, thus decreasing heat transfer rate. If the air is not dry, then the moisture in the air will condense and freeze on the surface of the dry ice thus insulating it and slowing the heat transfer rate. With that said one could place dry ice on an insulated platen on a digital scale and get a real time readout of the mass loss. The heat transfer rate could be correlated to the mass loss. Depending on the amount of CO2 in the air, the properties of the air may change and you would not get the same results as if the experiment were conducted with actual cold air.

 

[chicopee]

dvd, I agree with you,however there is one more consideration that we should be aware and that is even if the air temperature reaches the dry ice temperature there will still be a loss of dry ice under isothermal condition until there is no more diffusitivity of dry ice molecules.