Since the development of freezing techniques and systems, improvements have
continued to increase the end users profits.
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:
- 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.
- 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.
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.
- Double Wall
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.
- Kvaerner Drilled
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.
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
- 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:
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.
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.