AU629715B2 - Improvements relating to vacuum cooling - Google Patents

Description

0 39170:HKS:HJB COMMONWEALTH OF AUSTRAL 2 9 7 1 Form Patents Act 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int. Class Application No Lodged

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Complete Application No Specification Lodged Published Priority: Related art: TO BE COMPLETED BY APPLICANT

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r t Name of Applicant: Address of Applicant: Actual Inventor: Address for Service: DONALD GEORGE HARDING nI C i%,k Ui 11 .ter r; l" State of South Australia- -Cmmenwealth oe-Austratia- DONALD GEORGE HARDING 2 bora p-oad H u "are of COLLISON CO., 117 King William Street, Adelaide, South Australia, 5000 Complete Specification for the invention entitled: IMPROVEMENTS RELATING TO VACUUM COOLING The following statement is a full description of this invention, including the best method of performing it known to me: I' 2 II i li J I- iL This invention relates to vacuum cooling.

It is now well known to provide for cooling of materials by placing them in a chamber in which the atmospheric pressure is significantly reduced and resulting water vapour is condensed by being substantially cooled.

Such apparatus and method are particularly useful for rapidly cooling fresh produce in bulk in that the cooling effect is caused by the boiling off at the very reduced vacuum pressure, water vapour within the produce so that the cooling effect is achieved throughout a bulk package of such foods to the extent to where the vacuum can pull out the water vapour.

One of the problems with present equipment and methods however, is that for reasons that have hitherto not been apparent, the cooling effect has not appeared to be easily achieved in some instances which have hitherto appeared to occur on an almost random basis.

Such inconsistency in being able to effect cooling of large quantities of rmaterial have meant that despite the apparent attractiveness of the concept for cooling and therefore providing such cool products for long storage and keeping, there has been only very limited use of this technique in that if the materials are not effectively cooled, such foods or other produce might have to be wasted.

The problem however, has been to establish just what has been going Si,, wrong and how the present process and the appropriate apparatus can be changed to in fact, provide for reliable and efficient and effective 30 cooling using this technique.

S 30 After very long and extensive investigations, I have discovered aspects relating to the process which would appear to have established what the diffict!ty has been and I have found both means to reduce this difficulty and provide a significantly more reliable method for cooling and rC 35 proposed apparatus for use with such a method.

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3 My discovery has been that the major difficulty with being able to effect and maintain a significant vacuum within the chamber depends upon the ability to be able to condense and maintain condensed, the water vapour that is being drawn from the produce.

Conventionally, such water vapour is condensed by being significantly cooled on evaporator coils within the chamber.

The water that is thus condensed is thereafter let to go to waste but of course, it is contained within the pressure chamber until the eventual opening of the chamber.

My discovery is that hitherto the water that is condensed is left to run on the floor of the container and insofar as the container has a floor and outside walls which are at temperatures above the cooling evapcrative coils, means that the water that is considered as waste water, regains heat from such contact and therefore re-contributes water vapour, that is re-vaporises, into the atmosphere of the chamber.

Unless indicated otherwise, the term "fresh produce" herein is used to refer to fresh fruit, vegetable and other foodstuffs, and also any other fresh produce which can be stored by refrigeration.

Herein the term from re-vaporising" is used to refer to the practical prevention of re-vaporisation leading to substantially no re-vaporisation of water from condensed water, though it is appreciated that at least some minor re-vaporisation will occur from any quantity of water at most pressures and temperatures used in cooling and storing of fresh produce.

According to one form of this invention there is provided a method for effecting vacuum cooling including the steps of placing material, containing moisture or having moisture upon its surface, within a chamber; 35 causing a reduction in pressure within said chamber; and condensing vapour extracted from said material by said reduction in pressure characterised in that condensate resulting from condensed t ^L _1 L- li 4 vapour is held so as to be kept from at least substantially re-vaporising whilst vacuum cooling is being effected within the chamber.

In preference, the method is further characterised by holding condensed condensate separately from contact with a source of heat, In preference, the method is further characterised by the chamber being re-pressurised to atmospheric pressure after some or all of the vapour extracted from the said material is condensed.

In preference, the method is further characterised by the held condensate being removed from the chamber after the material is cooled.

In preference, the method is further characterised by the step of cooling the chamber is effected by a cooling means, wherein the cooling is conducted without the condensate freezing upon the cooling means.

Alternatively, according to another form of this invention there is provided a vacuum cooling apparatus including: means to lower the pressure within a chamber; evaporator coils within the chamber adapted to condense vapour within the chamber; an, means to collect and substantially retain condensate condensed upon the evaporator coils.

,n preference, the means to collect condensate includes insulating means preventing such condensate from being in substantial thermal 3 contact with a heat source.

In preference, there are means to detect the effective temperature of the evaporator coils and effect a control of such temperature to the extent that vapour condensing upon the evaporator coils is substantially prevented from freezing thereon.

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In preference, the chamber has walls, a floor and a ceiling, and the means to collect condensate comprises at least one tray which is kept tt Ar a ~iiY substantially separate from heat conductive contact with either of the walls, ceiling or floor of the containing chamber.

In preference, the chamber has at least orne door adapted to form a substantially sealed chamber.

In preference, the means to collect condensate includes at least one holding container adapted to hold the condensate and be insulated from a heat source.

In preference, at least one of the holding container is constructed to restrict the re-vaporisation of the condensate.

In preference, there is at least one pipe arrangement communicating between the holding container and outside of the chamber, the pipe arrangement being adapted to drain the holding container and includes at least one valve to control the draining of the holding container, and the valve being adapted when in a shut off state to substantially provide a vacuum seal.

In preference, the chamber is of box like shape having a floor, a ceiling, walls and a door, the chamber being adapted for the space within the chamber to be evacuated, the space within the chamber being such as to accommodate at least one pallet of fresh produce therein, attached to an inside surface of the chamber are the plurality of evaporator coils through which coolant is flowed, the means to collect condensate is a condensate collecting tray adapted to collect the condensate condensed upon the cooling coils, the tray being substantially insulated from thermal contact with the walls and floor of the chamber, and a means to S.

30 drain the tray of collected condensate.

In preference, the means to lower the pressure is adapted to reduce the pressure from atmospheric pressure to less than 25 millibars.

S 35 In preference, the means for collecting condensate is prevented from o having substantial thermal conducting communication with parts of the chamber that will potentially will be at temperatures substantially above the evaporative condensing coils.

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L i a 6 In preference, there are means to direct condensate condensing upon the evaporative cooling coils to the means to collect the condensate.

For a better understanding of this invention it will now be described with reference to a further embodiment being emphasized that the specific description is not intended in any way to limit the broader conceptual basis on which the invention is based.

However, it is also to be clear that particular aspects of the particular description described can of themselves be the invention or aspects of the invention.

Referring now to the preferred embodiment this will be described with the assistance of a drawing in which: FIGURE 1 is a schematic cross-sectional view of a chamber constructed according to this invention, FIGURE 2 is a sketch of the vacuum cooling chamber of this embodiment with a part cut away showing the cooling coils, FIGURE 3 is a schematic drawing of the cooling coils and the tray, and FIGURE 4 is a sketch of the tray, in perspective, side and end views illustrating the shape of the tray adapted to promote draining of the 444141 tray.

4, 30 Referring in detail to the embodiment, there is shown a chamber 1, which is of substantially rectangular shape with side walls, roof and floor, and which is of elongate proportions with an openable door at one or both ends.

I I 1, ,tie 35 The wall shown typically at the floor at 2 is comprised of sheet steel and is uninsulated although it includes outwardly extending strengthening fins shown at 3.

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7 The interior shape of the chamber 1 is such that it will hold one or more palet loads of packaged produce shown in dotted outline at 4 which can be typically supported on a pallet There are appropriate means such as shown at 6 to provide connection into the chamber for extraction of air within the chamber and also of course to some extent water vapour. While this is shown in the side opposite to the cooling coils, it is preferred that this be positioned on a side wall immediately above the cooling coils.

The major part of the water vapour however, is removed by condensation, and this is achieved by having an appropriate refrigeration unit connected to both inlet and outlet pipes 7 and 8 servicing an evaporator coil 9.

All that has been described thus far however, is a relatively traditional system for effecting cooling by use of high vacuum vapour extraction of fresh produce.

According to this embodiment however, and to incorporate the invention, the purpose is to ensure that water which is condensed by use of the evaporative cooling coils, is collected and held separate from access to the warmer external walls of the chamber.

Further, it is considered very useful not to have the water freeze and to this end it is desirable to collect the water from each of the evaporative coils at each height and have this water collectively gathered and held in a common container which can be subsequently removed but which is also held within the chamber in such a way that it will not gain access i 30 to external heating.

This is achieved by providing that there are a plurality of plastic plates shown typically at 10 interleaved between respective layers of tevaporative tubes, each of the plates 10 being inclined so that water that will drip on to theso will run to a left hand side of these and will be collected by a stainless steel mesh 11 which extends fully behind the coils and terminates at a lower end 12 by being located within a tray 13.

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"1 -r -I 8 The tray 13 has an open top and is defined by sides and a floor shown at 14, the floor 14 being supported above substantial thermal communication of the floor of the chamber 2 by insulating block The insulating block 15 is thermally insulating and can be typically a block of polyurethane foam. In an alternate form the tray can be suspended above the floor so that it does not draw heat therefrom.

Removal of the water from the tray can be effected from time to time after evacuation by having a valve 17 connected to a conduit 16.

The location of the valve 17 shall be such as not to diminish the need for preserving the temperature status of condensed water within the tray 13 and likewise the location of the conduit 16 and the material from which the conduit 16 is chosen should also be such that it can firstly withstand the high degree of vacuum that will be effected in a system of this type and also will not prejudice the heat loss position.

The conduit 16 and the valve 17 are formed from low thermal conductivity material such as PVC and the conduit 16 is kept as short as possible.

The chamber 1, in this embodiment, is closed by a steel door 18 which can be moved on rollers 19 and 20 in cooperation with a rails 21 and 22 from a closed to an open position and vice versa. The door 18 is adapted to form a seal with the walls of the chamber 1 so as to allow for the reduction of air pressure within the chamber 1.

A control box 23 is mounted to the side of the chamber 1 to allow the control of the cooling system and the vacuum system.

The tray 13 is made such that with the plastic drip directors 10 the water condensed upon the cooling coils 9 is collected into the tray 13. In this preferred embodiment the tray is made a little longer than the horizontal length of the cooling coil 9 and also wider than the cooling coil 9 so as to catch any drips.

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9 The tray 13 as illustrated in Figure 4 is shaped so that there is one corner to which any water therein will drain. At this corner there is a drain hole 24 which in cooperation with the conduit 16 and valve 17 allows the tray to be drained of water. Figures 4 and show a side and end view of the tray 13 respectively illustrating the shape of the tray 13 which allows the water within the tray 13 to drain therefrom.

In use, the equipment as shown is used by firstly in storing the produce within the chamber.

The doors are closed and evacuation commences from atmospheric pressure, typically 1013 millibar, and after approximately two minutes of evacuation, the refrigeration equipment is commenced so that the evaporator coils can provide substantial cooling effect.

As the evacuation continues, a flash point is reached at about 25 millibar after approximately four to six minutes and at this stage the extracted water vapour is being condensed by the cooling of the evaporator coils.

In a typical instance then, the evacuation is continued until it is down to approximately 6.4 millibars at which stage it will also be expected that all of the water vpnour will have been condensed that has been extracted, and of course according to this invention, is being held separate -,'om any heating source above the temperature of the evaporator coils.

S In operating the cooling coils, the temperature of these is chosen so that there is a maximum condensation effect while at the same time not so fit cold as to cause freezing of the condensate on the coils themselves.

If the condensate does freeze around the coils, this reduces the efficiency of heat transfer of the coils significantly so the temperature is ti, held quite tightly at a temperature just at or above freezing point but such that by reason of time and by reason of overall temperature balance, the water will drip off the coils and be collected in the manner previously described.

iDependent upon the total liquid load within the fresh produce, the process continues until sufficient vacuum has been drawn as described 'f Rr4 at which stage, a repressurization is effected, the chamber opened, the water tray emptied of water by opening valve 17 and the now very much cooled fresh produce removed and of course further loading can occur with more material.

An overall cyclic time for a substantial body of material has been found to be effective on a thirty minute period.

This has been found to be able to be provided reliably for a substantial load and provides very significant increases over previously erratic cooling rates that were perceived to be achievable with previous equipment.

While reference has been made to a tray being kept from thermal communication with walls of the chamber, it is to be clear that the purpose of the device is to ensure that the condensate does not provide a further source of water vapour into the chamber so simply recirculating and ensuring that a full vacuum is very unlikely to be pulled.

We have described one way which is very simple of providing a collection tray kept out of thermal contact with the external walls which can be expected normally to be at a temperature above the evaporative coils.

S 25 There are however, other ways that such water can be kept from providing a further source of water vapour and fairly obviously, if the l water itself is caused to be frozen or kept very cold by any cooling t ,,,means to such a low temperature, it may not then matter that the water itself is in contact with the chamber walls insofar that the water or cooling means will of themselves cooled the walls.

The matter is a question of providing a temperature containment and the C ,invention resides around the discovery that it is this previously carelessly discarded water that has shown to be the problem.

Whilst the above problem is illustrated with reference to fresh produce it will be understood that the invention is not limited to the cooling of fresh produce but is applicable to the cooling of other materials and R AZ~ -7 ;VI64- 11 condensing other condensates other than water. For example, the curing of transformer windings potted in a potting compound may be done over a longer time than without use of the invention, this providing the advantage of a greater length of time for voids between windings to be filled with the compound. Another example, the drying or partly drying of materials can be accomplished using this invention without having to apply heat and so drive off the water. In short, this invention can find application any where that a condensate is desired to be extracted from a quantity of goods or articles.

The inventive concept can, accordingly, reside in either the method by which the condensate during the evaporation step is kept in such a state either by being encosed or other wise being kept at a temperature or kept isolated from a temperature source such that it will not substantially 1 5 re-evaporate and re-circulate within the chamber.

The apparatus of course, is apparatus which is intended to achieve this function. This can be achieved by a tray thermaiiy insulated but it can be by a separate contained vessel having mechanical means by which any vapour pressure is constrained.

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Claims (19)

1. A method for effecting vacuum cooling including the steps of placing material, containing moisture or having moisture upon its surface, within a chamber; causing a reduction in pressure within said chamber; and condensing vapour extracted from said material by said reduction in pressure characterised in that condensate resulting from condensed vapour is held so as to be kept from at least substantially re-vaporising whilst vacuum cooling is being effected within the chamber.

2. A method for effecting vacuum cooling in a chamber as in claim 1 including the step of holding condensed condensate separately from contact with a source of heat.

3. A method for cffecting vacuum cooling in a chamber as in claim 2 in which the chamber is re-pressurised to atmospheric pressure after some or all of the vapour extracted from the said material is condensed.

4. A method for effecting vacuum cooling in a chamber as in claim 3 in which the held condensate is removed from the chamber after the material is cooled.

A method for effecting vacuum cooling in a chamber as in any S 25 previous claim in which the step of cooling the chamber is effected by a caouSng means, wherein the cooling is conducted without the condansate freezing upon the cooling means. tI

6. A vacuum cooling apparatus including: means to lower the pressure within a chamber; evaporator coils within the chamber adapted to condense vapour within the chamber; ,it and means to collect and substantially retain condensate condensed upon the evaporator coils.

7. A vacuum cooling apparatus as inr claim 6 in which the means to collect condensate includes insulating means preventing such condensate from being in substantial thermal contact with a heat source. L 1 i i LF I LL III~ 13

8. A vacuum cooling apparatus as in claim 7 in which there are means to detect the effective temperature of the evaporator coils and effect a control of such temperature to the extent that vapour condensing upon the evaporator coils is substantially prevented from freezing thereon.

9. A vacuum cooling apparatus as in claims 7 or 8 in which the chamber has walls, a floor and a ceiling, and the means to collect condensate comprises at least one tray which is kept substantially separate from heat conductive contact with either of the walls, ceiling or floor of the containing chamber.

A vacuum cooling apparatus as in claims 6 or 7 in which the chamber has at least one door adapted to form a substantially sealed chamber.

11. A vacuum cooling apparatus as in claims 6, 7, 8, 9, or 10 in which the means to collect condensate includes at least one holding container adapted to hold the condensate and be insulated from a heat source.

12. A vacuum cooling apparatus as in claim 11 in which at least one of the holding container is constructed to restrict the re-vaporisation of the condensate.

13. A vacuum cooling apparatus as in claims 11 or 12 in which there is at least one pipe arrangement communicating between the holding container and outside of the chamber, the pipe arrangement being adapted to drain the holding container and includes at least one valve to control the draining of the holding container, and the valve being adapted when in a shut off state to substantially provide a vacuum seal. 1

14. A vacuum cooling apparatus as in claim 7 in which the chamber .is of box like shape having a floor, a ceiling, walls and a door, the chamber being adapted for the space within the chamber to be CCevacuated, the space within the chamber being such as to t a aaccommodate at least one pallet of fresh prcduce therein, attached to an inside surface of the chamber are the plurality of evaporator coils LT a 1 fti (4";2 me oest menod of performing it known to me: 14 through which coolant is flowed, the means to collect condensate is a condensate collecting tray adapted to collect the condensate condensed upon the cooling coils, the tray being substantially insulated from thermal contact with the walls and floor of the chamber, and a means to drain the tray of collected condensate.

A vacuum cooling apparatus as in claims 8, 9, 10 or 14 in which the means to lower the pressure is adapted to reduce the pressure from atmospheric pressure to less than 25 millibars.

16. A vacuum cooling apparatus as in claim 6 with the means for collectirj condensate being prevented from having substantial thermal conducting communication with parts of the chamber that will potentially will be at temperatures substantially above the evaporative condensing coils.

17. A vacuum cooling apparatus as in any of the preceding apparatus claims in which there are means to direct condensate condensing upon the evaporative cooling coils to the means to collect the condensate.

18. A method for effecting vacuum cooling in a chamber substantially as described in the specification with reference to and as illustrated by the accompanying drawings.

19. A vacuum cooling apparatus substantially as described in the i *specification with reference to and as illustrated by the accompanying "drawings. Dated this i4th day of August 1992. L t t t t DONALD GEORGE HARDING By his Patent Attorneys, COLLISON CO. it t i N 1 1 ff-^