|SITE ASSEMBLED IQF SPIRAL FREEZER|
The main carrying belt that is used on a spiral, can be metal, plastic or a combination. This is the belt which comes into direct contact with the product in the spiral.
Typically made in a plastic material, these sprockets directly engage the belt and are located near the take up drive.
Elongation of the belt due to physical wearing, not to be confused with thermal elongation.
The force that can be measured on the outer edge of the belt, which is a function of the overdrive on the cage. When this tension gets to high, the outer edge of the belt wants to lift upward, causing potential problems.
The central part of the spiral which is used to supply the force that drives the belt, sometimes referred to as the drum or center cage.
A varying factor applied to the belts being used in a spiral. This collapse factor affects belt lengths in a system, as well as being affected by varying cage diameters.
The point where the belt enters the cage and changes state from straight to radius.
The rod which connects the belts together. Typically in metal or plastic materials.
Sometimes known as tiers, this is the belt surface area where the product rides. Can also be referred to as a surrounding platform which is used for sanitation or air flow purposes.
The point where the product leaves the spiral.
A spiral where the product is fed at the top and exits at the bottom.
Includes the drive motor, reducer, chain and drive sprockets which are usually found either under, on top of, or outside the central cage.
Drive Chain Oiler:
Brush assembly which is used to manually or automatically lubricate the main drive chain.
Belt length increase / decrease due to temperature differences, not to be confused with belt stretch.
The point where the belt changes state from a radius to a straight.
Usually associated with metal belt performance or structural damage due to vibrations, it is a failure of varying consequences.
Located on the edges of the belt and having one side raised, these pulleys help keep the belt guided and assist in tracking.
Metal belting with specific characteristics of strength, weight and application.
Typically referred to the belting either lifting on the outer edges, or the need to turn over the belt in the system in order to evenly wear on each side on a usage basis.
The structural frame work which everything else in the spiral is attached to.
Metal belting with specific characteristic of strength, weight and application performance.
The point where the product enters the spiral
Required for drive assembly, selected drive chains, and selected track or belt in given applications that use metal belts.
The central moving force which turns the cage, also called the cage drive, or drum drive.
Main Drive Chain:
The chain that is used to turn and drive the central cage or drum.
Maximum Product Height:
Dimensional number that should not be exceeded for proper clearances.
Term applied to a method of continuous turning the belt over as it travels through the spiral system. Usually associated with equalizing wear on both edges of the belt.
Term applied to the cage speed differential as compared to the belt speed, as measured on the inside edge of the belt. In all cases the cage must travel faster than the belt.
When there is to much take up drive force being applied, a belt over tension occurs, decreasing belt life and possibly causing belts to flip upward on the outer edges.
Any point of contact area where proper clearance is not met.
Modular plastic belting with various types and styles having specific application performance.
The maximum distance between the top surface of the belt and the closest support structure on the next deck or tier.
Various precautions used throughout spiral systems which include sensors and switches to assist in plant safety.
Any point of contact area which can cause product shearing.
Pulleys or strips, usually made from plastic, which help guide the belt near the infeed and discharge pulleys.
Attached to the main drive motor, this unit allows for selected belt speeds to be had.
Used throughout spirals for reverse bends of the belt, or to help guide the belt in selected areas.
Take Up Assembly:
The area where excess belt is gathered and controlled automatically.
Take Up Drive:
A secondary drive to the main cage drive, this drive acts in conjunction with the main drive to govern the tension on the belt.
A force which is measurable either on the outer edges of the spiral belt, or on the main drive chain.
The distance from one belt level to the next, also know as tier spacing.
A device which is typically used on the take up drive to act as a safety slip in case of jam's in the system.
Horizontal carrying supports where the belt rides on.
Track Wear Strips:
Usually plastic materials placed on top of the track, for decreased friction on the sytem.
A state where there is too little drive force being applied to the cage/belt interface causing uneven belt surging.
A spiral where the product is fed at the bottom and exits at the top
Vertical Cage Bars:
Structural supports which run vertically near the inside edge of the belt (the outside diameter of the cage), normally a material which has enough effective force to drive the edge of the belt properly.
Vertical Wear Strips:
Typically plastic wear strips which are attached to the vertical supports to interface with the inside belt edges.
Common Terms Used in Food Freezing Industry
BTUs: (British Thermal Units)
A standardized energy (heat) measurement. A BTU is defined as the amount of energy required to heat one pound of water 1 degree Fahrenheit.
Example: Assume you want to chill a pound of product from 90°F down to 35°F. Your change in temperature is 55°F, but in order to effect that temperature change, you need to remove 45 BTUs of heat from the product.
When we refrigerate an object we are removing heat from it. Heat transfers from the warmer object (the food product) to the colder object (the cryogen or mechanically chilled air) until both objects reach the same temperature.
This is the number of BTU's of heat a refrigeration source can remove, expressed as BTUs per pound of cryogen. This number can be expressed as a maximum refrigeration value, or as the actual refrigeration value that can be expected in a production environment. Example: One pound of liquid CO2 has a maximum value of 120 BTUs of refrigeration (see Latent Heat of Vaporization from gas properties chart); but we know from practical experience that a CSE designed freezer will deliver about 100 BTUs per pound of liquid CO2. This becomes the basis for calculating your cryogen usage and that portion of your freezing cost. Maximum values are always the same, but actual values vary based on freezer design and freezing process parameters.
The actual refrigeration value of a cryogen as it performs in a specific freezer. Regardless of whether a freezer is mechanical or cryogenic, it will operate at less than 100% heat transfer efficiency (which only occurs in a laboratory setting). This is because there are many variables that impact its performance and "rob" BTUs. These variables include undesirable (but avoidable) elements such as warm air infiltration into the freezer, less than optimum belt loading, and improper operating procedures. They also include unavoidable refrigeration losses due to the steady state losses of keeping the freezer at operating temperature, freezer cool down procedures or less than optimum storage conditions of the cryogenic gases.
HEAT TRANSFER RATE
The speed at which a freezer can remove heat. This information is very specific to both the type of freezer, the cryogen and the food product being processed; it is the basis of calculating what kind and size of freezer is required.
HEAT TRANSFER MODE
Describes how the actual heat transfer occurs. This is a major consideration in freezer design.
There are three modes of heat transfer:
Vapor-to-solid heat transfer - This is cold vapor being passed over a warm solid food product (could be N2, CO2, or mechanical refrigeration). This is sometimes referred to as "vapor-stripping", because BTUs are being "stripped" from the cold vapor.
Solid-to-solid heat transfer - This is solid dry ice particles (CO2 snow) being directed at the food product (CO2 only)
Liquid to solid heat transfer - Liquid nitrogen can be sprayed on the product, or the product can be placed in a liquid nitrogen bath (LN2 only)
To get a sense of the impact of heat transfer rates, envision this:
* Putting your hand in a bucket that contained 40°F air (vapor-to-solid).
* Burying your hand in a bucket that contained 40°F sand (solid-to-solid).
* Plunging your hand into a bucket of 40°F water (liquid-to-solid).
Obviously, 40°F water would be very unpleasant immediately, the sand wouldn't be far behind, and after a couple of minutes, the 40°F air would be equally uncomfortable. All three modes transfer heat out of your hand, and the temperature in the bucket is the same, but the heat is transferred at different rates.
Several important concepts
1. The Freezing Process
Pure water freezes at 0°C. The water in most foods contain dissolved salts and proteins, this causes the freezing point of water to be lowered. The water freezes out as pure ice, thus the concentration increases in the remaining free water-further depressing the freezing point. At about -5°C, one third of the water could still be unfrozen. Even at –30°C, 10% of the water is unfrozen. Thus, some spoilage mechanisms may proceed, but at very much slower rates.
2. Latent Heat-Changing From Water To Ice
Between about 0°C and -5°C, the water is freezing. To change from free water to solid ice, a relatively large amount of energy needs to be removed. This energy is known as the latent heat of freezing. Latent heat is the energy required to cause a change of state, from liquid to solid.
3. Sensible Heat- Changing From Warm Water To Cold Water
Complimentary to latent heat is the concept of sensible heat. Sensible heat is the amount of energy removed to change temperature without a change of state. That is, for example, the amount of heat needed to be removed to lower the temperature of water, but not freeze, sensible heat is removed between 40°C and 0°C.
4. Heat Removal Below Freezing
Below about -5°C, the energy removed is a combination of latent heat and sensible heat. Latent heat is removed to freeze the remaining free water. Sensible heat is removed to lower the temperature of both the free water remaining unfrozen and the ice.
5. Heat Removal At Different Temperatures
When proposing a freezer, a freezer manufacturer should always state the amount of heat, in kJ/kg, the freezer will extract as well as the product outlet temperature and the time taken to reach this temperature. Note that to change temperature from 0°C to -10°C (or tem degrees) requires SEVEN TIMES more heat to be removed than to change from +10°C to 0°C (or ten degrees).
What is Temperature?
Temperature is a convenient method of measuring the amount of heat (or energy). The higher the temperature, the higher the energy content.
Care must be taken when measuring temperature. Use a thin, needle-like probe. Ensure it is inserted into the product.
Measuring the air or water surrounding a sample of food product is not measuring the temperature of the food. Measure more than one sample. Measure each in a few places, for example, just below the surface and in the middle of the thickest part. If the measurements are different, then a different technique, measuring the EQUILIBRATED TEMPERATURE is required.
The equilibrated temperature is measured when all parts of the product sample are at the same temperature. This can be achieved by placing the product sample, for example, a fish fillet, in an insulated container (such as an Esky) for a few minutes. After a few minutes, all parts of the fillet will be the same temperature.
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