Food Freezing Application
The commonly employed processing of canning, thermal processing such as pasteurization and sterilization, dehydration, freezing, etc. has been already well known as the proper food preservation techniques.
Nowadays food freezing has become one of the most important unit operations in food processing and preservation. Almost all food products, raw, partially processed, and prepared foods, can be preserved by freezing. This is mainly visible in the meat, fruit and vegetable sectors.
Due to in converting water into ice, food freezing reduces water activity. Thus, the growth of microorganisms and enzymatic activity are reduced.
At a reasonable cost and good quality product to consumers is the successful key of food freezing process. Short freezing time, energy efficient freezer, automation operation can reduce the processing costs.
Using very low temperature air as cooling medium is one of freezing process. Air blast belt tunnel freezers, fluidized bed freezers, and Spiral quick freezer fall into this category.
Convective heat transfer coefficients and freezing times in air blast freezer
| Freezer | Convective heat transfer coefficients | Freezing time at -18 ℃ | Freezing food |
| Tunnel Belt Freezer (5m/s) | 25-30 W/m2.K | 15-20 min | Unpacked peas |
| Fluidized Bed Freezer | 90-140 W/m2.K | 3-4 min | Unpacked peas |
| Spiral Belt Freezer | 25 W/m2.K | 12-19 min | Unpacked peas |
Using Air As Cooling Medium Air Blast Freezer
Air Blast Tunnel Belt Freezer
An air blast tunnel belt freezer consists of an insulated tunnel in which the cooling air is circulated by fans or blowers, a continuous perforated stainless steel mesh belt which carries the product to be frozen.
Air velocities in the range of 1-6 m/s, which serves a high heat transfer rates, are generally used in this tunnel freezer.
Fluidized Bed Freezer
Cold air at high velocities is forced through the perforated mesh belt gives very high heat transfer coefficients. As the air velocity is increased, incipient fluidization occurs. At this point the particles start vibrating around themselves.
Air used as a cooling medium is generally at a temperature of -40C and velocity of the air depends on the product size, density, and fluidization characteristics.
A fluidized bed freezer works on an individually quick freezing process. The products frozen include diced carrot, peas, corn kernels, small onions, diced food, and vegetables.
Spiral Belt Freezer
In a spiral belt freezer, a continuous conveyor belt moves around a cylindrical drum giving.
Air flow can be upward or downward through the spirals.
This type of arrangement is well suited for products requiring longer freezing times, packaged products, and bigger size products.
More information, pls visit: IQF Freezer