Desiging a small forced air cooling system 2

[daviddor]

Hii everyone
So i want to test my cooling system using it as a forced air cooling , but i am not sure if its possible.

The system consists of a vessel that mixes co2 with air and discharge it with minimum temperature of -20c at a max flow of 300[liter/min].

Now i want to put few boxes of fruits on each other, inside a small tank , putting a fan on the other side and create a force cooling. something like this:

my question is how to determine the fan size and power ,and if its possible at all to suck air from one side and not inlet much in .

thank you very much

 

[FMJalink]

Hi daviddor,

The sketch above gives the impression that a once through cooling containment is envisaged. In the other posting you showed a recycle of the air inside the fruit containment to the carbon dioxide mixing vessel. That recycling of the air is much more economical, as cooling is quite expensive.

I think the following publication from the Wageningen University & Research gives you more information, than I can put here in the posting: Link

That article is on maintaining carbon dioxide level in the a cooled reefer container. The container's own cooling is set to 0 °C. You can see the solution for ventilation quite well. Only a small quantity of fresh air is entered, as you will have to cool that air and you do not need fresh air for the stored fruits.

You can put the dry ice box in a separate containment next to the chilled fruit containment or in a separate closed compartment made inside the containment. That would allow putting new dry ice there from the outside without having to go into the fruits containment.

Unless you have access to large quantities of dry ice or problems with electric power supply, I doubt whether the use of dry ice to cool is an interesting option.
Most solutions you can find on the internet are with airco split unit type refrigeration or cooling units driven by means or electric power, which could be supplied by solar or wind power installations.

Some points of attention with dry ice cooling:
[ul]
[li]Lowest temperature allowed for the fruit type.[/li]
[li]Maintaining the pre-set temperature in the fruit containment.[/li]
[li]Ventilation of fruit containment before fruits are entered or removed from the fruit containment.[/li]
[/ul]

 

[LittleInch]

The min temp of the cooling air I think needs to be above 0C otherwise you will freeze the fruits closest to the air entry, or at least a few of them.

Fan size will need to be equal to the flow entering as in steady state the two must balance. A fan system as you propose would most likely result int he chamber being slightly below atmospheric pressure, but this for most fans is measured in low numbers of inches of water column. Once this is reached the fan won't continue to evacuate any more air volume than what is being allowed into the chamber.

As FMJ states, this seems like a very wasteful system and maybe what you need is in fact a recirculation fan inside the enclosure to blow the cool air around at a higher rate than the cool air entering and the warmer air leaving.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Compositepro]

I once used dry ice to cool a watermelon in an ice chest. After several hours of cooling you could taste the carbonation in the fruit.

 

[daviddor]

Thank you very much guys, yeah as i suspected its not really possible to create a velocity inside the tank of 1[m/s] and above with this kind of air flow. I guess air circulation back to the vessel would be the best.

Previously i calculated that if we put the fruits in an atmosphere of 10c for 2 hours the fruits will change from a temperature of 30c to 10c as well . we gonna make experiments with the system, but roughly , any one has an idea how to calculate how much flow do i need from my system to keep this air at 10c [All the data about the fruits/container exists].

 

[chicopee]

And allow enough air space between the packages of fruits so that the fruits are cooled as evenly as possible. Another word don't stack the packages into a solid pile.