Advise on do-it-yourself blast breezer building project

One of the missing pieces of information is the leaving air temperature off of the evaporator. The LAT is largely determined by how long it takes for the center of your product to be cooled. For instance, if you find that with a -20 LAT it takes over an hour for the product to reach -16, then you need to drop the LAT or increase airflow over the product. Once you pick the LAT and know the total evaporator load based on product load and system losses, the equipment manufacturers will be able to recommend the proper refrigerant and components using their own software.

Another question is the configuration of the final product? A single sphere or cube will take longer to freeze than 1500 thin molds of product. Air cirulation between multiple molds will accelerate the freezing process.

The LAT is largely determined by how long it takes for the center of your product to be cooled.

The product in question has a round cross-section, 22 mm diameter. Supplier carries evaporators of all sizes with airflows of up to 7 m3/sec. The blast freezer dimesions is 2 m x 3 m x 3 m high. The question is how to pick the LAT. Maybe I´m asking to much as far as free advise goes. Thanks for your input Ginserbacher.

Even if you did pay me, I would have a hard time to calculate the required LAT. There are a lot of variables and some of the coefficients needed for the equations are probably unknown. It might be easier to toss a couple of these things in the freezer with a fan blowing on the product and see how long it takes for it to cool down. Then reduce the temperature on the freezer and repeat the experiment. Those two points will give you a rough idea of where you need to be. Keep in mind that the closer you run the experiment to actual conditions, the better.

Like Ried was saying, a lot will depend on the product configuation. You will want to maximize the air velocity on the surface of the product to minimize freeze time. It also may be important to have even velocities on the surfaces otherwise one side of the product will freeze before the other.

Have fun!

Thanks Ginsenbacher and Ried for your insights.

For what is worth the product will be placed on trays, a stack of trays will go on a trolley with head space between trays for air circulation.

I just recalled a friend of mine would construct crude bomb calorimeters for sizing food freezers.

http://en.wikipedia.org/wiki/Calorimeter (and no, this is not a terrorist device!)

He would take frozen product samples and measure heat gain from frozen state (usually 0 or -10F) to room temperature. He would then use that heat load and upscale to the desired production rate.