Cold store construction

The purpose of a cold store is to provide an insulated and refrigerated enclosure suitable for the handling and storage of perishable goods, at some predetermined temperature. 

The shape and size of the cold store will depend on  

Since the handling methods require power-driven fork-lift trucks, nearly all cold stores are now erected as single-storey buildings with the insulation in the form of factory-made panels. The main loading bay will probably be at tailboard height, so that products can be taken directly in and out of insulated vehicles. 

Example 15.1 What will be the internal dimensions of a cold room to store 900 t of boxed frozen meat if the box size is 700 X 450 X 150 mm and the net weight 30 kg  

These can be stacked on pallets 1200 X 1000 mm, the height per pallet being 1400 mm, say a box height of 1250 mm, allowing for the base of the pallet. Boxes would be loaded flat, three per layer and eight layers high, making 24 boxes per pallet  

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Traditional cold store construction was to build an insulated lining within a masonry shell. The outer skin would be erected in brick and concrete, and rendered as smooth as possible inside with cement plaster, to take the insulation. When the surface was dry, it would have several coats of bitumen applied as a vapour barrier and slabs of insulation material stuck to this with hot bitumen. This was normally carried out in two or more layers so that joints did not pass right through the insulant, but were staggered. The inner skin would be finished with cement plaster, reinforced with wire mesh. The usual insulant was slab cork. 

Care must be taken regarding the method of supporting ceiling panels. Large portal framed steel holdings may provide a cheap outer shell but do have a considerable amount of roof movement. Panels hung from this type of structure can be subjected to movement which cannot be tolerated in cold store construction. A tied portal, however, can be acceptable [38]. The outer shell may also be required to bear the weight of the evaporators and, in the case of stores for carcase meats, the rails and the product itself. 

In most cases, the insulation will be the greatest resistance to heat flow and other materials in the construction and surface resistances are ignored in estimating heat gains through cold store walls, ceilings and floors. 

Conducted heat is that going in through cold store surfaces, tank sides, pipe insulation, etc. It is normally assumed to be constant and the outside temperature an average summer temperature, probably 25-2/°C for the UK, unless some other figure is known. Coldroom surfaces are measured on the outside dimensions and it is usual to calculate on the heat flow through the insulation only, ignoring other construction materials, since their thermal resistance is small. 

Institute of Refrigeration, Code of Practice for the Design and Construction of Cold Store Envelopes Incorporating Prefabricated Insulating Panels, IR,... 

The total quantity of heat evolved by a calcium aluminate cement on hydration is typically 325-400 kJ kg , which is somewhat less than that for a typical Portland cement, but due to the speed of the reaction, nearly all of it is produced during the first day. Calcium aluminate cements arc therefore suitable for use at low temperatures (down to —IOC), e.g. for winter construction in cold climates or repairs in cold stores. 

Cryogenic liquids are gases that have been transformed by refrigeration into extremely cold liquids, which are stored at temperatures below -130°F (-90°C). They are stored at low pressures in specially constructed, multiwalled, vacuum-insulated containers. 

Both mechanical and hydraulic presses can be used to forge, stamp, and compression-mold glass-reinforced sheets. However, to successfully stamp composites between cold, matched metal dies the presses must have a pneumatically or hydraulically operated clutch and brake, tie-rod construction if over 60 tons, and must run between 6 and 30 strokes per minute (spm). Hydraulically operated presses must have an adjustable stored energy system to form at a prescribed force level . 

Fig. 3.13. Construction details of the combination of a temperature variable 22-pole ion trap and a pulsed supersonic beam. Primary ions are produced in a storage ion source and mass selected in a quadrupole mass filter (from the bottom, not shown). After deflection in an electrostatic quadrupole bender the ions are injected into the trap (see Fig. 3.12). There the ions are confined in radial direction by the rf field and in axial direction with dc voltages applied to the entrance and exit electrodes (less than 100 mV). Buffer gas is used, usually He, for thermalizing the ions. From the left a skimmed molecular beam traverses the trap without colliding with the cold surfaces. For detection, the stored ions are extracted to the right, mass selected and counted via a Daly detector. A laser beam can be injected via the detector tract for state selective excitation of the trapped ions.

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