Previously, the freezing of food products was almost exclusively done by air blast systems, due to the ease and convenience of using off the shelf blower coil evaporators that made simple powerful freezing systems. However, associated with the ease and convenience, users have found that there are considerable hidden costs. The most important being product deterioration and dehydration. Users have realized a weight loss of 5% and over, depending on a wide variety of conditions such as TD through the coil, the air velocity, the surface and nature of the product. In many cases neither the potential degradation nor the value of the product lost through dehydration have warranted the use of anything but a straightforward blast freezing system, but there are many processors of delicate and high value food items who should seriously measure and consider the hidden costs and penalties.

It is the purpose of this article to introduce the reader to the whole family of direct contact plate freezers in general and to a powerful new version in particular.

There are essentially four different types of plate evaporators:

1. Serpentine Plate
   
   
   
   The moulded SERPENTINE PLATE evaporator uses two sheets of metal moulded and bonded together to allow the refrigerant to flow in a serpentine path between them. This is the traditional standard for domestic refrigerator freezer compartments. Highly efficient and inexpensive. Since mass-produced, it is more or less ruled out for smaller runs and custom installations, though it has been used, in certain standard sizes, as a freezer plate. One recent version of this plate was developed for use as a liquid chiller and is now in use in marine refrigeration.
   
   
2. Dole Plate
   
   
   
   The DOLE PLATE is another traditional plate evaporator. It consists of an envelope of two steel sheets bonded and sealed all around the edges and kept clamped to the serpentine steel coil by means of a vacuum. Sometimes, instead of being evacuated, these plates are filled with a eutectic salt solution, which, as it melts at some selected temperature below 32° F, provides a kind of reserve refrigeration, which will maintain temperatures for some time after the refrigeration has been shut down. Refrigeration connections to the plates are made with copper stubs brazed to the steel tubes after they exit from the envelope.
   The advantages of the dole plate are low cost and availability in those plates filled with eutectic solution.
   The disadvantages are in their poor conductivity between the smooth steel tubes and the outer surfaces, the common loss of vacuum with age and the roughness of the spray-galvanized surfaces.
   Nearly extinct in many areas, these plates have survived and are still in use in the marine and fishing industry. Their crude simplicity has mostly been a virtue there. A variety of "homemade" versions of this plate are also in use.
   
   
3. Double Wall Extruded Plate
   
   
   
   The DOUBLE WALL EXTRUDED PLATE is made from an aluminum extrusion with a cross-section in the shape of a ladder. The resulting hollows are manifolded together at the ends in a variety of ways and usually flooded with refrigerant by some overfeed or recirculating method.
   These plates are following the early times use of Dole Plates now a must for any double contact freezing system where the plates move up and down to contact or even compress the top surface of the product. They are the ultimate in power and speed of freezing, but they do have a number of drawbacks in many situations:
   • They have large hollows, which require large quantities of refrigerant to fill and a method of maintaining velocity in that hollow.
   • They are available in limited, predetermined sizes and configurations.
   • They are the most expensive of all the plates, both to buy and to use.
     
     
4. Kvaerner Drilled Plate
   
   
   
   The KVAERNER DRILLED PLATE, manufacture in Denmark, Kvaerner Kulde, makes and incorporates into their equipment, a plate made by drilling holes lengthwise through a solid slab of aluminum This alleviates the first of the problems above, but exacerbates the rest. They do have a loyal following in Europe due to their extreme durability and rigidity.

Single Contact Freezer Plates

Many of the disadvantages mentioned have been addressed in a new and improved evaporator plate that has proven itself many times over in the North American market. This is the FAREXCEL PLATE, which received its ultimate test for 15 years in the harsh environment of the fishing industry, is now distributed through Gunthela Enterprise of Sechelt, B.C. It is also made from an aluminum extrusion, but in this case incorporates all the features of an ideal single contact freezer plate:

• A flat surface on top of a heavy aluminum bed for maximum conductivity and heat transfer out of the product placed on it.
• A heavily finned bottom surface for maximum heat exchange with the air over the product.
• A sturdy, augmented (internally finned) refrigerant passage every four inches, keeps the amount of refrigerant required to a minimum, while providing a maximum of heat exchange surface with that refrigerant.

These plates are being manufactured in widths that can be any multiple of 8 inches (20 cm) wide and any length from less than 4 feet (1.2 meters) to 20 feet (6.0 meters) long. Longer plates are generally more economical, since much of the cost of manufacturing them is in the end weldments, which remain the same.

Besides their use in product freezing, they are also ideal as ceiling plates in low temperature storage areas where their particular advantages are required:

• Low product dehydration
• Constant uniform temperature
• Minimum space requirement (compared to blower unit air circulation)
• Availability in wide range of shapes and sizes to suit any space
• Low cost especially in longer length

The construction of these plates is very strong, with all piping for instance equivalent to schedule 40. This makes them highly resistant to damage and abuse as well as to corrosion. Their aluminum construction makes them suitable for use with any refrigerant currently in service including ammonia and also makes them ideal for ultra low temperature applications.

Individual and custom plates are supplied with simple inlet and outlet flanges. Assemblies of plates into complete freezer racks with a wide variety of sizes and configurations are also available. Some of these use an innovative branch circuiting for maximum efficiency and simple installation.

The freezer plates, assembled into a rack are built into a compact, self-contained, cabinet freezer capable of freezing 2,000 to 4,000 pounds of product a day. This unit is complete with all refrigeration and controls and is ready for connection to power and water supplies. The freezer plates are also fabricated into a standard production line freezer/storage chest, designated for use on smaller fishing vessels and sport camps.

Large plate racks are also available in fully flooded versions.

As you will notice this freezer plate has many advantages over the commonly known Dole plates:

• Its heat exchange capacity is at least 50% higher.
• Multiples of 8 inches in width and length of up to 20 feet in small increments give almost unlimited possibilities for freezer rack sizing and ceiling coverage in fish holds and plants.
• Fastening to ceiling or walls is simplified in comparison, since it can be bolted anywhere through the plates into available hard points.
• Outstanding durability; there are installations on fishing vessels and fish plants which have served for more than 10 years.

We work closely together with refrigeration contractors. If you have a refrigeration contractor with whom you are comfortable and acquainted, please let us know and we will make sure that he receives all the necessary information to familiarize him with our product.

There are a few interesting facts we should mention:

• Outstanding Warrantee: Our plates are of the highest quality in material and workmanship. We believe so strongly in our product, that we will unconditionally guarantee the plates for a period of ten (10) years, as long as they are protected from electrolytic corrosion by avoiding contact of the aluminum with dissimilar metals.
• Continuing Development: We always working to further improve our product, i.e. we have enlarged the surface area of the refrigerant passages, which has enhanced the heat exchange characteristics and increased the freezing capacity by at least 20%.
• Flexible in Application: Cabinet freezers and freezer/storage chests are now available in unlimited sizes to fit the, often limited, space on fishing vessels. As a matter of fact, we have produced units as small as 3 feet by 4 feet as well as large freezer enclosures for in between deck installation of 4 feet by 16 feet by 9 feet high. We also have exported a fair number of fully self-contained freezers, built into multiple compartments of standard shipping containers.
• Low Cost: One of the great advantages of single contact plate freezers compared to double contact freezers is their low cost. Really, a double contact is only necessary where a standard, solid fish meat block is to be frozen. As a matter of fact, in many instances one would rather prefer not compacting the top surface of a product, giving it a better appearance.
• Competitive Edge: Our plates in combination with low temperature condensing systems have enabled tuna fishermen to successfully pursue the very demanding Japanese market. The same applies to a large number of prawn and shrimp processors.