Blast Tunnel

[gwapa]

I am working in a Blast Tunnel to freeze shrimps.
The Shrimps are received at +5ºC and should frozen and cold down to -12ºC
The total capacity will be 40 metric tons which correspond to 50 pallets of product
The tunnel will operate 16 h per day .The rest of the time will be used to load it cleaning and unload.
The evaporation will be at -35ºC and the Tunnel temperature will be at -27ºC (ammonia)
Questions:
What should be the fins separation in the evaporator in order to have just one defrost?
There will be 8 hour after the freezing period, How could be the defrost design? Only air, Electrical or hot gas .Could it be manual or automatic?
How many pallets should be located in series to guarantee good air circulation and cooling?
What will be the air velocity around the pallets?
What should be the separation between pallets and pallets with walls
I appreciate your tips
GWAPA

[Oregon Jim]

I have operated freeze tunnels for a long time to freeze farm produce like peas, beans, corn, broccoli, and such, and in all of this we have used belt conveyors to move product, rather than freezing pallets, so my usefulness here may be small.

In our systems warm water is used to defrost our coils, but we deal with the problem of food chips and pieces that fall through our belts and into our freeze coils. Water helps to wash product from our coils.

Water is quick and efficient, but you must purchase water and pay for its disposal, so it is not always the best option. If all you are fighting is snow and frost on your coils, hot gas may be more practical.

I can say for certain that air flow through and around your product is vital to your freezing efficiency. As your air flow decreases your ability to freeze quickly flies out the window.

Someone with knowledge of your particular system should guide you. There is no one best choice for everyone.

[gwapa]

Thanks Oregon Jim for your help

[Peter_1]

I should go for a fin spacing of 8 to 10 mm or more.

8 hours freezing and the defrosting? Seems long for a fresh product covered with water.
You can't calculate the time between defrost, only a practical test will learn you more. Defrosting time and intervals is to dependent on different parameters.

Hotgas defrost while another evaporator is cooling is the most economical way and it goes really fast.
You have to close teh defrosting one with some sort of baffle.

If your freeze pallets, then all the shrimps will freeze to one solid block. Moreover, freezing just to the core will be difficult. It depends on pallet construction, gaps between the pallets, ...
I should go for an IQF belt freezer so that every shrimp will freeze separately..

Circulation 100 times the volume of the freezer per hour.

Separation between pallets? As less as possible or you will have problems.

Try to condense as low as possible. Do you need also preheated water in the production?

Be warned, a freezer to freeze fast products is a hard to design product.

[J.F.C.]

If you want fast defrosting go for a aluminium evaporator and hot gas