GB2171191A - Evaporator mechanical defrost system - Google Patents

Abstract

The present invention relates to a method of and apparatus for defrosting a freezing or cooling apparatus. The invention is embodied in the concept of brushing with a brush 5 the finned evaporator tubes periodically to remove accumulated snow and frost from the surface of the tubes and fins 2. This is especially effective when an airflow through the evaporator is utilized concurrently with the brushing operation. The brush 5 is driven by acme screw shafts 6. <IMAGE>

Description

SPECIFICATION Evaporator mechanical defrost system The present invention relates to a freezing or cooling apparatus, and more particularly to such an apparatus for freezing a product such as a foodstuff.

It is known to freeze foodstuffs by passing them along a conveyor belt while directing a flow of cold air either through them or over them. Certain products, such as meat, chicken, fish fillets, pizzas, fast-food menus in aluminium trays, pastry or ice cream require a medium to long retention time in the freezing apparatus. For industrial use, it is desirable that the foodstuffs are conveyed along such a convoluted path that the total volume of the freezing apparatus is as small as possible consistent with the need for it to contain an economic quantity of the foodstuff to be cooled or frozen. It is known to provide a conveying belt which can be so deformed that itwilltravel along a helical path to emerge art a point either above or below the starting point.Thus the area occupied by the apparatus is the area of a circle defined by the outer edge of the conveyor belt with allowance for the ancillary apparatus such as air cooling apparatus and belt washing apparatus.

The conveying belts used in conventional industrial freezing apparatus are generally mesh, spaced rods or some otherforaminous surface which allows the cool air access to both sides of the product to be frozen. Preferably, the belts are made of stainless steel or some hygienic material. It is known to pass the cool air through the belt, ie, from one side, either top of bottom, to the other. Since the belt is generally disposed substantially horizontally to support the foodstuff being frozen, this direction of airflow may be referred to as substantially vertical. In essence it passes through product and is most effective in cooling it. Such a substantially vertical air flow gives a quick freezing time and may, if it is directly upwardly, by used to fluidise the product to be frozen.

The air flow may also flow from one side of the conveyor to the other passing over the top of and beneath the product on the conveyor. Such air flow may be referred to as substantially horizontal. It is often less effective in freezing the product but may be used with advantage in cooling the product.

UK Patent No. 1 425 076 (Hardy) describes and illustrates an IQF freezing apparatus of this general kind.

In large scale freezing apparatus of the kind under discussion, it is of course necessary periodically to defrost the evaporators. In such apparatus is may typically be necessary to defrost every four hours when the apparatus is operating under normal conditions to freeze initially wet vegetables or similar products into an IQF state (individually quick frozen).

The present invention makes it possible to extend the time between defrosts substantially, and is embodied in the concept of brushing the finned evaporator tubes periodically to remove accumulated snow and frost from the surface of the tubes and fins. This is often especially effective when an airflow through the evaporator is utilized concurrently.

When modified in this manner, a conventional evaporator, previously requiring a full defrost every four hours, say, can go sixteen hours between defrosts if the finned evaporator tubes are brushed every hour or every half-an-hour.

The brushing means may be built into the apparatus and may advantageously be power-operated.

Preferably the brush is a flat brush which travels across the succession of evaporator tubes in line with the fins which conventionally span and link together successive tubes.

For example, the brush could be made to travel along a rotating screw extending across the evapor atortubesand running parallel with the fins of the evaporator. A reciculatory ball system could provide such movement. Preferably the brush travels along an acme screw shaft.

The brush, whether flat or circular, can be rotary driven as it travels across the evaporator.

Preferably the or each brush built into the apparatus is so sized, and so positioned during its travel across the evaporator, that it brushes regions of successive evaporator tubes which lie between one fin and the next fin on each tube.

In large-scale apparatus, the evaporator tubes might be copper of diameter say 22mm and tube wall thickness 1 .5mm with aluminium fins each 0.5mm thick and spaced variously 20mm, 12mm and 8mm apart along each tube.

In such a case, a suitable brush could have bristles made of polypropylene each 1 00mm in length and 1.5mm diameter.

Advantageously the or each brush, when built into the apparatus travels in a double path, i.e. travels once across the evaporator and then returns to its starting point, on each occasion the brush is operated.

It is especially advantageous for the region to be brushed by the brushing means to be defined as being the array of the evaporator which is presented to the incoming air.

Preferably a screen of mesh material is employed in the airflow path after the brushes to collect the snow and frost and particles of bristles or product debris loosened by the brushing.

This may take the form of a stainless steel mesh with 25 holes per square centimeter. This is preferably attached to the air outlet of the evaporator array.

In a further embodiment the mesh may be in the form of an endless loop of mesh held apart by end shafts which, when rotated, move the contaminated section of the mesh out of the airflow stream for cleaning. Alternatively, a conveyor belt within the freezing apparatus could be adapted to perform this function.

An example of a method and apparatus in accordance with the invention will now be described with reference to the accompanying drawing which is a schematic perspective view of the apparatus The Figure shows an evaporator 1 having a finned surface 2. Refrigerant is passed into and out of the evaporator 1 via inlet and outlet 3 and 4.

Conventionally, such an evaporatorwould have to be defrosted very frequently, for example once every four hours. Clearly this is inefficient.

In order to keep the defrosting frequency down to a minimum an elongate flat brush 5 is mounted along the edge ofthe evaporator 1 perpendicular to the fins 2 of the evaporator and arranged to move in a direction parallel to the fins 2.

The flat brush 5 is mounted at each fin end 2 with an acme screw shaft 6. The direction of rotation of the acme screw shaft 6 is shown in the diagram and the drive to the shaft 6 is provided by a drive shaft 7.

Micro switches 8 are positioned to define the limit positions of the brush 5. When the brush 5 reaches a micro switch 8 the drive to the acme screw shafts 6 is interrupted.

Whilst brushing takes place, air flows through the evaporator in the direction of arrow 9 which blows away the debris and snow and frost loosened by the brush 5.

The brush 5 is operated to move up and down the acme screw shafts 6 once every half-hour. This reduces the frequency of defrosting required considerably, ie for up to twelve hours.

Claims (18)

1. A method of defrosting freezing apparatus comprising brushing the finned evaporator tubes periodically to remove accumulated snow and frost from the surface of the tubes and fins.

2. A method according to claim 1, in which air is passed through the evaporator at the same time as the brushing takes place.

3. A method according to claim 1 or 2, in which the brushing takes place at intervals of between 30 and 60 minutes.

4. Freezing apparatus including brushing means for brushing the finned evaporator tubes.

5. Apparatus according to claim 4, also including means to pass air through the evaporator during the brushing operation.

6. Apparatus according to claim 4 or 5, in which said brushing means are power operated.

7. Apparatus according to claim 4,5 or 6 in which the brush is a flat brush which travels across the succession of evaporatortubes in line with the fins which conventionally span and link together succes- sive tubes.

8. Apparatus according to claim 7, in which the brush travels along a rotating acme screw shaft extending across the evaporator tubes and running parallel with the fins of the evaporator.

9. Apparatus according to any one of claims 4 to 8 in which the brush is rotary driven.

10. Apparatus according to any of claims 4 to 9 in which the or each brush built into the apparatus is so sized, and so positioned during its travel across the evaporator, that it brushes regions of successive evaporator tubes which lie between one fin and the next fin on each tube.

11. Apparatus according to claim 4, in which the brushing means comprises a brush having bristles made of polypropylene each 100mm in length and 1.5mm diameter.

12. Apparatus according to any one of claims 4 to 11, in which the or each brush, when built into the apparatus, travels in a double path, ie travels once across the evaporator and then returns to its starting point, on each occasion the brush is operated.

13. Apparatus according to any one of claims 4to 12, in which the area to be brushed comprises the array of the evaporator which is presented to incoming air.

14. Apparatus according to claim 5, or any one of claims 6 to 12 when dependent upon claim 5, also including a screen of mesh material positioned within the airflow path downstream of the brushing means to coilect snow, frost and debris loosened by the brushing.

15. Apparatus according to claim 14, in which the mesh comprises a stainless steel mesh with 25 holes per square centimeter.

16. Apparatus according to claim 14 or 15, in which the mesh is in the form of an endless loop wound around two spaced apart shafts which can be rotated to move the air path to leave an area of clean mesh in the air path.

17. A method of defrosting of freezing apparatus substantially as described herein, with reference to and as illustrated in the accompanying drawing.

18. Freezing apparatus arranged substantially as herein described with reference to and as illustrated in the accompanying drawing.