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STAND OUT TECH
STAND OUT TECHNOLOGYNOLOGY

Air Blast Freezer - What’s so Good About It?

A Circulation of Cool Air Inside Freezer

The air circutation in the freezer is very important. If condenser is modeled according to the requirements. If the goods have
properly designed, the goods will have a good quality, been often overloaded, it can damage the compressor. And if goods were
while it can also save time and reduce production cost. loaded less than the design, it would cause an inefficiency of the machine
With good designed freezer, the cool air must pass and not economically worth.
through the goods with the same velocity in all areas. Tray Layout and Placement To place the goods in the tray, put
There should have enough space on ceiling as well as them on the cart before bringing to the freezer, we need to concern on the
between the goods and the cart in order to allow the cool space between each tray to ensure there is enough space to allow cool
air flow through it. air to pass through. Therefore, we should ensure that the height of the tray
must not be higher than the goods because the edge of the tray will shield
the cool air that blows through the goods. The material used to make the
Theoretically, air is the medium for poor heat conduction because the
air has a specific heat capacity which is low, so it is necessary to provide tray is also important, it must be strong, durable and can conduce thermal
effectively to make the goods cooler. The preferred material is aluminum
high air velocity flow to remove the heat from the goods. If we need higher
air velocity, the fan must operate under overload condition or must change (14-16 gauge). The distance between the top and bottom of the trays
for optimal cooling is 2: 3, meaning that if the tray is 3 inches high, the
a bigger size. This will exothermic heat as a burden for the cooling system.
But if we estimated suitable cooling rate, heat that was caused from the distance between the top of the trays and bottom is 2 inches, as shown in
Figure 3.
fan will create no impact. The wind speed that passes through the goods
is approximately 5.08 m/s, as shown in Figures 1 and 2. The tray must be filled up in the cart before entering to the freezer.
There should have no space in the cart as large amount of cool air would
Temperature of Cool Air in the Freezer The temperature of flow through the empty area of the cart, creating a loss and taking longer
cooling air circulated by the fan should be sufficient to allow the goods to period to freeze goods, and finally the quality of the goods would be
freeze quickly. The core temperature of goods must be below -18 °C and decreased while it consumes high energy.
the cool air temperature must be lower than -18 °C. The temperature of Impact from Packaging The packaged products that use air blast
freezing air is usually below -35 °C. To freeze goods with very low
temperature cool air, freezing time will be shortened. However, do not freezer, such as a bag, foil paper, and soaked with saline solution in the
tray cause longer time to freeze and could not know a specific period for
forget to consider on the size and appropriate placing method as it will
affect on the speed and the air circulation flowing through the goods. freezing. It absolutely causes the compressor works harder. Consequence,
before creating an air blast freezer, we need to find out what kind of goods
The lower temperature is used for freezing, the higher cost of production
will be seen. Therefore, the relationship between the air velocity through will be frozen to provide the right information for the designer.
the goods and the air temperature passing through the goods should be Defrost When the air blast freezer is used for a period of time, the ice
considered. The air velocity appropriate with the air blast freezer for both will rise such as on the wall, the ceiling, the floor, the door, or even the
batch freezer and continuous freezer is 1.5-6 m/s, as shown in Table 1, and evaporator itself. Ice must be melted at the appropriate time. If too much
the air temperature flowing through the goods is between -30 to -40 °C. accumulation, it would create problems and harm the system as well as
users. The direct effect on the evaporator is that the heat transfer efficiency
Freezing Time To design the air blast freezer, the quantity of goods
and time will determine the size of the freezer, cold coil, as well as freezing between the air flow and the evaporating temperature will decrease and
will take longer freezing time. Three causes of ice in the freezer are as
rate of the system. To use the air blast freezer, the user must well
understand the freezing time. The factors that affect the change in time follows.
1. The water evaporates from the goods frozen. This is about 1-3
are quantity or volume of goods, goods sorting method, air velocity, and
temperature of goods before freezing, etc. There is no specific formula or percent by weight of the product. (In case of no packaging)
2. The steam causing from the outside air flows into the freezer when
equation to find the right timing. That is because there are variable factors
over time, as shown above. Nevertheless, we can do this by experimenting the door opened, or through the air pressure regulator inside the freezer.
3. The air leaks into the freezer through the wall joints.
at a condition by controlling certain factors such as quantity, and sorting
method, etc., in order to know the time of freezing at one condition. From the above causes, the last two causes could be prevented or
reduced. A room will be built in front of the freezer to adjust the temperature.
Impact on the System When Loading Inappropriate This room will have temperature between 0-5 °C, which is called the Ante
Goods To design the system, we will have the requirements of the goods Room to reduce the temperature and vapor in the air. If we designed to
that will lead to freezing, such as type, weight, temperature of goods before open the door direct to atmospheric temperature between 25-30 °C,
entering to the freezing process. However, when we have actually used accumulated ice would be higher as higher vapor into the freezer as shown
it, the result may not meet the requirements. If goods is over loaded, which in Figure 4
will cause higher temperature on coil and it will take longer freezing time. Many factors and details should be considered before building up the
As a result, the discharge pressure of the compressor is higher. The high- air blast freezer. If we follow all processes, it will help achieve the objectives,
pressure protection system will stop the compressor, so the system will including energy saving and have good quality products for delivering to
stop that may misunderstand that the condenser is too small. In fact, the consumers.
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