PLATE EVAPORATORS FOR FREEZING
Plate evaporators are formed by cladding a tubular coil with sheet metal, welding together two embossed plates, or from aluminium extrusions.
The extended flat face may be used for air cooling, for liquid cooling if immersed in a tank, or as a Baudelot cooler, but the major use for flat plate evaporators is to cool a solid product by conduction, the product being formed in rectangular packages and held close between a pair of adjacent plates.
In the horizontal plate freezer (Figure 7.14(a)), the plates are arranged in a stack on slides, so that the intermediate spaces can be opened and closed. Trays, boxes or cartons of the product are loaded between the plates and the stack is closed to give good contact on both sides. When the necessary cooling is complete, the plates are opened and the product removed.
The vertical plate freezer (Figure 7.14(b)) is used to form solid blocks of a wet product, typically fish. When frozen solid, the surfaces are thawed and the blocks pushed up and out of the bank.
Figure 7.14 Plate freezers. (a) Horizontal. (b) Vertical (Jackstone)
To ensure good heat transfer on the inner surface of the plates and achieve a high rate of usage, liquid refrigerant is circulated by a pump at a rate 5-12 times the rate of evaporation.
Posted in Refrigeration and Air Conditioning