Original Concept[ edit ] The operational principles incorporated in the XM25 were first recommended by a government contractor who attended a summer study on Urban Combat in
Every 1 h 1 In both examples in Table 5, the freezer is correctly loaded since the product load matches the plant capacity in the weight of fish that can be frozen in 1 h. The above freezer would therefore be designed to hold 2 t of product A and when product B is frozen, only 1 t will be loaded and the product distributed to give uniform air flow.
If however, 2 t of product B are loaded into the freezer at one time, the refrigeration plant will be overloaded. This is probably one of the most difficult aspects of freezer operation to explain clearly but in simple terms it means no matter how spacious your freezer and how much product can be loaded, you cannot freeze more fish than the refrigeration plant will allow.
Good performance in batch air blast freezers is obtained by freezing the product in open trays without wrapping.
Trays used in air blast freezers should transfer heat readily, be easily emptied and also be robust. Normally they are required to produce a pack that is of regular shape but when the product M2 justify design their use, trays with a taper on the sides of about one in eight can be emptied by applying a cold water spray on the underside for a few seconds and then giving a gentle tap on the edge.
Trays used in this manner should never be filled above the tray edge or the product will be damaged during release. Cleaning and drying of trays before re-use is necessary to maintain a high standard of hygiene. Where the rate of production justifies the cost, an automatic tray washer may be installed.
The reader will no doubt find other types of freezer available on the market which have not been mentioned. The design of many of M2 justify design is based on combinations of two or more of the basic methods described.
For instance, a variety of freezers make use of both contact and air blast freezing techniques. Other freezers may be identical in every respect with one of the methods described, but may use some other liquid, gas or contact method for heat transfer.
These freezers will be seen to be similar to one of the types described and will therefore have the same advantages and disadvantages. Plate freezers do not have the versatility of air blast freezers and can only be used to freeze regularly shaped blocks and packages.
Plate freezers can be arranged with the plates horizontal to form a series of shelves and, as the arrangement suggests, they are called horizontal plate freezers HPF Figure 2 1.
When the plates are arranged in a vertical plane they form a series of bins and in this form they are called vertical plate freezers VPF Figure Modern plate freezers have their plates constructed from extruded sections of aluminium alloy arranged in such a manner as to allow the refrigerant to flow through the plate and thus provide heat transfer surfaces on both sides Figure Plate freezers are fitted with hydraulic systems which move the plates together and apart.
The two main uses for this type of freezer are the freezing of prepacked cartons of fish and fish products for retail sale and the formation of homogeneous rectangular blocks of fish fillets, called laminated blocks, for the preparation of fish portions. The thickness of package or block frozen is 32 to mm and the freezer can readily adapt from the thicker to the thinner package provided the range required is made known to the supplier at the time of purchase.
There is no direct contact between the fish and the freezer plates when freezing by this method since the fish is always packaged before freezing. If the operator is also careful not to spill water on the plates during loading and unloading, the freezer may be operated with only a light brush between each freeze to remove surface frost.
The door may be left open overnight to allow the plates to defrost fully after being hosed down with warm water. A hot gas defrost arrangement is the quickest method to defrost an HPF, but even with this method, it may take 30 min or more. The defrosted plates must be completely free from frost or ice and dried before the freezer is used again.
Horizontal plate freezers intended to be operated with a hot gas defrost are fitted with additional pipework which allow the cold refrigerant to be discharged from the bottom of the freezer as the defrost proceeds.
Without this special pipework and operating valves, a hot defrost would clear the top plates only and leave the cold refrigerant in the plates at the lower levels. As in all hot gas defrost systems, the refrigeration system must have an adequate load to provide sufficient hot gas for an effective defrost.
This system would therefore be better applied when there are two or more freezers operated from a common refrigeration system and each freezer will then be defrosted in turn while the others are in operation.
An HPF will only operate correctly if good contact is made on both the top and bottom surfaces of the pack or tray to be frozen. The faults shown in Figure 24 are some of those which make freezing times longer than necessary. If the product is frozen from one side only due to poor contact on the upper surface, the freezing time could be three or four times as long as the time achieved with good contact on upper and lower surfaces.
The plates of the HFP are closed by means of a hydraulically operated piston to make contact with the upper surface of the product.
The plate pressure applied to the product can easily be varied between 70 x mbar to suit the product and is increased by a factor of two as the fish expands during freezing.The XM25 Counter Defilade Target Engagement (CDTE) System, also known as the Punisher and Individual Semiautomatic Air Burst System was an airburst grenade launcher derived from the XM29 tranceformingnlp.com was fielded to soldiers serving in the War in Afghanistan in , after which malfunctions and program budget cuts delayed official entry into service, planned for early Professional monitors always come at a premium price.
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