US2634591A - Vacuum cooling system employing chamber surface condensation - Google Patents

Description

w. BEARDSLEY 2,634,591

VACUUM CSOOLING SYSTEM EMPLOYING CHAMBER SURFACE CONDENSATION Filed Sept. 15, 1950 April 14, 1953 INVENTOR. MELl/ILLE MBEWOASLEY Patented Apr. 14, 1953 OFFICE if VACUUM COOLING SYSTEM EIHPLOYING CHAMBER SURFACE CONDENSATION Melville W. Beardsley, Venice, Calif.

Application September 15, 1950, Serial No. 184,915

18 Claims. (Cl. 62-168) My invention relates generally to the cooling H and refrigeration of produce and more particularly to the precooling of such material as let tuce and sweet corn. prior to its shipment. A method and apparatus for this general purpose I disclosed in my copending application, Serial No. 146,784, filed February 28, 1950, and entitled Method and Means for Cooling Produce by the Use of Reduced Pressure. This is a continuation-in-part of said copending application, Serial No. 146,784..

A customary practice in cooling produce such as lettuce, prior to and during the shipment thereof is to interlayer the produce with crushed icewhile it is being packed into shipping crates,

.ther, the operation of packing the crushed ice into crates or other containers with the produce is a costly and time-consuming phase of the shipping procedure.

The above-identified copending application discloses a method and apparatus for precooling produce' by meansof a vacuum causing the evaporation of the surface moisture from the produce. This process is classed generally as vacuum cooling. The present invention concerns further improvements in the method and apparatus for vacuum cooling.

In connection with the present invention it should be noted that the use of vacuum cooling does not entirely dispense with the necessity of ice refrigeration and that ice is still used in the bunkersof refrigtrator cars to maintain the lowered temperature of the produce in spite of the fact that it may have been precooled by the vacuum cooling method. Thus, it is necessary to have iceavailable at or near the shipping point of produce of the class above-described, even though it may be precooled by the vacuum coollng process.

Vacuum cooling i currently practiced by employing 's team-jet pumps to remove the air and water vapor from a closed'chamber containing ,4 the produce. While steam-jet pumps have proven to be the most practical design for pumping-a large volume flow of vapor from the vacuum cooling chamber, the overall system with it's steam generating boiler and associated equipment is very heavy, bulky and relatively expensive. For .these reasons the vacuum cooling plant incorporating steam-jet pumping equipment must necessarily be a large and permanent type installation.

Permanent installations are not, however,' fa complete answer to'th'e problem of 'cooling'produce' prior to shipment. In many instarlc'esjit is desirable for precooling equipment to beef a portable nature so that it can be moved from one growing area to another to correspond 'with the harvest season. As an example, lettuce'is harvested in the Salinas, California, area in the summertime, and in the Imperial Va1ley,- California, in the winter. Equipment which can be moved from one of these areas to the other-is highly desirable. In this manner, the equipment can be in use throughout the entire year rather than idle for several months during which no produce is harvested in the area wheretlie plant is permanently located. Vacuum precooling equipment Which is sufficiently light and portable may be moved out to the field where the crop is actually beingharvested. If precooling is performed in the field, considerable handling and intermediate trucking can be eliminated, so that the overallcosts of packing and shipping are greatly reduced. Additionally, field precooling makes it possible "for long distance transport trucks to beloaded directly at the. field, resulting in a minimumjof delay and expense and providing fresher vegetables at the destination. l Q; In the process described in my above-identified copending application, a certain weight of ice is placed inside a treatment chamber with the produce. The weight of ice is determined by the weight and temperature of the material being cooled, but to assure complete precooling a somewhat larger quantity of ice usually is placed in the chamber to efiect rapid completion of the cooling cycle. Because of this a small amount of ice is always left over after the-process has been completed. Being of odd shape and uhknown weight, the residual ice is usually discarded and a new measured quantity is" employed with the next batch of material to be precooled.

This situation is of course undesirable, Furthermore, the weighing and loading of ice has also been found tobe a time-consuming operation. The present invention concerns improvements by which this undesirable waste of ice is eliminated, the overall process is facilitated, and the equipment made portable.

Bearing in mind the general purpose of vacuum cooling, the fact that ice is usually available in any major produce growing area, and the fact that a vacuum cooling plant employing steam-jet pumping equipment is large, heavy and permanent, it is a major object of the present invention to provide precooling apparatus employing ice as a heat absorbing medium in order that vacuum precooling of comestibles may be accomplished with a portable apparatus.

Another object of the invention is tore'cluce the cost and power requirement of the plant used in vacuum precooling.

Yet another object of the invention is -to increase the speed and facility with which comestibles may be precooled by the vacuum method.

A further object of the invention is to make use :of ice in the .process of vacuum cooling, without placing such ice .in contactwith the produce .being cooled.

.An additional object .is to provide apparatus -for:materiallyincreasing the efllciency of ice refrigeration from the standpoint of theoretical heat absorbing capacity of ice.

.A .still further object is-to provide .precooling apparatus especially adapted to handle crated produce.

Yet another object is toprovidesuflicient means "for removing water from an ice refrigeration eration equipment to be used in connection with vacuum precooling equipment.

The foregoing and additional objects and .advantages will be apparent from a consideration of the following detailed description thereof, such consideration being given likewise to the attached drawings, in which:

Figure 1 is .a perspective view of a light pre- .cooling plant embodying the present invention;

Figure 2 is an enlarged elevational section taken on the line '22 in Figure .1; and

Figure 3 is an enlarged portion of Figure 2 illustrating an automatic condensate tank drain valve mechanism.

For purposes of simplicity, .in the drawings, the apparatus shown in Figure i has been shown "for resting on the ground, although it will be realized that it could be permanently attached to the body of a vehicle such as a truck trailer.

Before proceeding with a detailed description of the apparatus embodying the present invention, the principles of operation will be described briefly as follows. The first principle made use of in the present invention is that evaporating moisture absorbs heat (heat of evaporation) from the surrounding media. Thus, if the surface moisture on, let us say, a head of lettuce is caused to evaporate by reducing the surrounding vapor pressure, the heat of evaporation necessary to "cause such evaporation will be absorbed from the 1 lettuce itself, thus cooling the same.

This principle is also employed in the apparatus described in the above-identified copending application.

The second principle employed in the present invention is that vapor brought into contact with the surface colder than the dew point of such vapor at its then pressure will cause the vapor from the solid body.

4 to condense with the result that a corresponding amount of heat is released by the vapor and absorbed by the cold surface. This condensation, also, of course, results in a reduction of the pressure if it is accomplished in a closed chamber.

The two principles just set forth are employed in the present apparatus by placing the material to be cooled in a hermetically sealed enclosure having a portion of its wall surface refrigerated, and by then removing 'su-bstantiallyall of the air from the enclosure. It will be seen that, as the air is removed and the pressure reduced within the enclosure, apoint will be reached at which the surface moisture present in the comestible being cooled will evaporate, thus absorbing heat The vapor thus formed, which comesin contact with the refrigerated por tion of the inner wall surface will condense thereon, releasing its latent heat of vaporization to this cooler wall surface. The released heat is then conducted through the chamber wall to ice or other refrigerating material outside the chamber which is used to refrigerate the aforesaid fill the same with vapor at the time the pumping of air is stopped, otherwise the aforesaid heat transfer operation will terminate short of the desired reduced temperature of the producedue to the partial vapor pressure of the water'vapo'r, plus that of the remaining air in the chamber being such as to prevent further condensation of moisture on the refrigerated wall surface.

If air is present in the chamber, it soon collects in a blanket over the refrigerated wall surface and prevents or greatly inhibits further condensation thereof. The formation of such. a blanket is due to the fact that condensation on the refrigerated wall surface removes the water vapor from the air-vapor mixture, leaving relatively pure air in a layer adjacent the surface. Thus, Ihave found it advantageous inmost cases to continue the evacuation pumping during the entire cooling cycle in orderjto remove the abovementioned blanket of air as it forms and to-draw the water vapor into intimate heat transfer contact with the refrigerated wall surface.

In the simple form of'the' device'illus'trated "in Figures 1 and 2, a single chamber H is charged with crated produce l2, or other material to'be processed, and ice I? is applied to the exterior of the chamber wall. The chamber l l is then sealed and substantially evacuated of air, and the heat transfer process is allowed to continue until the desired precooling temperature of the produce is reached.

An important feature of the present process is the fact that if pure water ice is used as the Wall refrigerant, the produce will 'not be cooled to a point less than the freezing point of Water, i. e., the temperature of the ice applied to the portions of the chamber wall, and consequently there is no danger of damaging the produce by freezing the same or portions thereof. I 'have'found by experience, however, that in order to accelerate the cooling especially toward the end'oi the cycle,

it is sometimes advantageous to introduce some solute such as salt to the juncture of the ice and the chamber wall in order to reduce the temperature of the melted ice at that point. I have also found that an accelerating effect can be achieved by adding to the condensate within the chamber, some similar compound which reduces its vapor pressure.

In the form of apparatus shown and described herein, means are provided for continuously removing the water produced by condensation within the chamber. I have found it desirable to remove such water continuously during the cooling cycle so that it is not necessary to cool said condensate to the final desired temperature. In this connection, it will be realized that the condensate produced during the early stages of the cooling cycle will have a temperature considerably greater than the final desired precooling temperature.

Referring now to the drawings for a more detailed description of the simple form of apparatus embodying my invention, it will be seen that the chamber I I is of a generally cylindrical shape disposed with its axis horizontal, and is provided with a pair of hinge mounted hermetically sealed ,doors I0, one being mounted at each end of the chamber I I (one not shown). Within the chamber I I are installed two parallel rows of conveyor rollers I3 adapted to support and allow longitudinal movement of pallets 2i upon which is loaded the crated produce I2. Cakes of ice I! are supported on an ice rack or bunker 22 secured to one side of the chamber II. The ice bunker 22 has its bottom surface sloping toward the chamber I I so that the ice slides inwardly against the chamber wall to effect an intimate heat transfer contact between the wall and the ice.

After the ice I? has been loaded on the bunker 22 and the produce I2 has been placed in the chamber !I, the doors to are shut so that the chamber is made airtight. Air is then pumped out of the chamber II by means of a pump I5 mounted on the top of the chamber, the pump being connected to the interior of the chamber through a suitable conduit I6.

The inner end of the conduit 56 is connected to a longitudinally disposed manifold 23 having a series of induction openings spaced therealong, and so arranged that air is inducted substantially equally along the length of the chamber II. It will be observed that all gas being inducted into the vacuum pump inlet manifold 23 is constrained to a flow path in close contact with the refrigerated portion of the Wall, such constraint means being an inner-lining baffle l4. Accordingly, the water 'vapor constituent of the air-vapor mixture is largely removed by condensation on the refrigerated wall surface, thus making it necessary for the vacuum pump I5 to remove only substantially pure air. This arrangement makes possible the use of a pump of relatively small volume flow capacity as compared with the vacuum cooling systems which pump out all of the gases including the evaporated water vapor.

When the pressure within the chamber is reduced to a point where it is substantially equal to the vapor pressure of water at the thentemperature of the produce I2, pumping may, in some cases, be stopped and the exhaust conduit I6 closed by means of a valve 24 therein. Thereafter, the heat transfer operation will be automatic and continuous, the moisture evaporating from the produce I2 and condensing on the refrigerated surface of the chamber wall. As long as the temperature of the produce I2 is substantially greater than that of the refrigerated surface, the process will continue at a relatively rapid rate, slowing gradually, however, as the temperatures of the produce I2 and the wall approach each other. More rapid cooling can be accomplished by continuing to operate pump l5, thus drawing off any air or other non-condensable gas that may be present tending to form an insulating blanket over the refrigerated wall surface.

As the water vapor from the produce I2 condenses on the inner surface of the refrigerated chamber wall, it releases its latent heat of vaporization to the wall. This heat is conducted through the wall to the ice I I at its surface of contact with the outer surface of the chamber, and some of the ice is melted. The rate at which the ice is melted is proportional to the rate of cooling of the produce and the consequent rate of evaporation and condensation. The water formed by the melting of the ice drains downwardly and is constrained by an exterior shroud l8 to flow in intimate heat transfer contact with the exterior surface of the chamber until its point of discharge at a lower lip 25 of the shroud I8.-

In the drawings, the space between the chamber wall and the shroud l8 has been exaggerated for purposes of clarity. By this arrangement a larger refrigerated surface is available for condensation and the water from the melted ice absorbs part of the heat from the condensing vapor so that a minimum weight of ice is required.

It will be realized that in place of the ice rack 22 and the ice I! therein, conventional cooling coils as are commonly used in mechanical refrigerators, can be secured in close heat transfer relation to a wall of the chamber II whereby to cool a portion thereof. In such modification, the temperature of the portion of the wall which is refrigerated can be maintained at a substantially constant value by conventional thermostatic controls employed in connection with mechanical refrigerators of known design.

The condensate forming on the interior refrigerated surface flows by gravity to the bottom of the chamber II and thence drains through a drain pipe I9 into a collecting tank 20. The height of the drain pipe I9 must be sufficiently great to establish a head of water which is greater than any probable difference in pressure between the main chamber II and the tank 20. Such difference might be due, for example, to a difierence in temperature between the chamber I I and the tank 20. The tank 20 has a sufiicient capacity to collect all of the condensate which would be formed by cooling the maximum probable load of material tobe cooled.

The tank 28 is formed with a sump 26 into which the drain pipe I9 extends and in the bottom of which is located a drain valve 21. The drain valve 21 is preferably of an automatic type such as that illustrated in Figure 2. In a particular form illustrated, a conical drain valve 21 is seated in a complementary seat 28 and supported on one end of a balance beam 3| on the other end of which is a counterweight 32. Secured to the upper part of the valve plug 21 is a tubular 'm-ember 29 open at the upper end and pierced by small peripheral holes near the base. The weight and balance of the elements connected to the beam 3| are such that when the pressure in the tank 253 is equal to atmospheric and the .upper .tubular portion 29 .of the valve port 21 is filled with water, the sum of the moments about; the

collected condensate. of the valve always places the tank in readiness :for the next cooling cycle.

fulcrum 3 3 is such that the plug 2'! drops and the sate from the tank 20.

After the condensate is drained from the tank 20 and also from the tubular member 29 (through .-supplied with a freezing-point-lowering solution -(e. g., brine) from a solution hopper 35 under the control of a valve 36,

is mounted longitudinally above the ice if and is pierced along its length with uniformly spaced ports. Thus, chemical solution may be fed into the juncture of the ice and the chamber surface with a resultant lowering-of the melting temperature of the ice.

As an additional or alternative means for accelerating the cooling cycle, a similar distribution pipe 3? fitted with spaced spray nozzles 38 is located inside, the chamber H and so positioned that the nozzles 33 may spray a vapor pressure reducing solution against the inner refrigerated surface of the chamber. As this chemical solution mixes with the condensate on the refrigerated surface, the vapor pressure of the mixture :is reduced. This reduction in vapor pressure increases the pressure differential between the main part of the chamber (containing the produce l2) and the condensing zone adjacent the refrigerated surface; thus the rate of the vapor flow from the main part of the chamber is increased with a consequent increase in the rate of cooling.

When the produce l2 has been cooled to the desired temperature, air is admitted to the chamber I! through an inlet valve 39 in the vacuum pump conduit it. As soon as the pressure inside the chamber H has reached atmospheric, the access doors H; at the end of the chamber l I are opened and the cooled produce [2 is removed from one end following which (or concurrently therewith) additional produce to be cooled is loaded into the chamber through the other door. After this produce is loaded into the chamber, the doors are closed and sealed, and the cooling process is-repeated.

The tank 20 assumes atmospheric pressure siof the interconnecting drain pipe it. As previc'usly explained in the description of the tank drain valve, when the condensate tank pressure is atmospheric, the valve operates to drain the The automatic operation While the method and apparatus shown herein are fully capable of achieving the objects and providing the advantages hereinbefore stated, it

will be realized that they are capable of some modification without departure from the spirit of the invention. For this reason, I do not mean to be limited to the forms shown and described, but rather to the scope of the appended claims.

I claim: 1. A method of cooling material having surface .moisture thereon which includes the steps of:

removing substantially all air from said enclosure to effect rapid evaporation of said surface moisture; introducing a vapor-pressure-reducing material into said chamber adjacent said refrigerated wall to lower the vapor pressure of moisture condensing thereon; and leaving said material in said enclosure until the temperatures of said material and said wall are substantially equal, due to latent heat of evaporation being taken up from said material by said evaporated moisture and given up at said wall by condensation of said moisture thereon.

2. A method of cooling material having surface moisture-thereon which includesthe'steps of placing the material to be cooled in'an airs tight enclosure; placing a body of refrigerant against an exterior portion of the wall of said enclosure to refrigerate said all portion; exhausting said chamber to remove substantially all air therefrom and to effect rapid conversion of said surface moisture into Water vapor; di recting the flow of said air and water vapor from said chamber past the interior surface of said wall portion in heat transfer relation therewith; and leaving said material in said enclosure until the temperature of said material and wall portion are substantially equal due to latent heat of evaporation being taken from said material by said moisture evaporated therefrom and given up at said wall portion by condensation of said moisture thereon.

3. A method of cooling material havin surface moisture thereon which includes the steps of: placing the material to be cooled in an airtight enclosure; placing a body of refrigerant having a temperature of substantially 0 centigrade against an exterior surface of the wall of said enclosure; removing substantially all the air from said enclosure to effect rapid evaporation of said surface moisture and to cause condensation of said evaporated moisture on the interior surface of said wall; continuously draining condensed moisture from said enclosure; and leaving said material in said enclosur until the temperatures of said material and Wall are substantially equal due to latent heat of evaporation bein taken from said material by said evaporation and given up at said wall by condensation of said moisture thereon.

4. A method of cooling material having surface moisture thereon which includes th steps of: placing the material to be cooled in an airtight enclosure having heat conducting Walls;

placing ice against the outer surface of said enclosure; removing substantially all the air from said enclosure to effect rapid evaporation of said surface moisture; and leaving said material in said enclosure until the temperatures of said material and said wall are substantially qual, due to latent heat of evaporation being taken up from said material by said evaporated moisture and given up at said wall by condensation of said moisture on the interior surface thereof.

5. A method of cooling material havin surface moisture thereon Which includes the steps of: placing the material to b cooled in an airtight enclosure having heat conducting walls; placing ice against the outer surface of said enclosure; removing substantially all the air from said enclosure to effect rapid evaporation of said surface moisture; introducing a, freezing-pointlowering solution into the juncture of said 108 9. and enclosure to lower the temperature thereat; and leaving said material in said enclosure until the temperatures of said material and said wall are substantially equal, due to latent heat of evaporation being taken up from said material by's'aid evaporated moisture and given up at said wall by condensation of said moisture thereon.

6. A method of cooling material having surface moisture thereon which includes the steps of: placing the material to be cooled in an airtight enclosure having heat conducting walls; placing ice againsta first portion of the outer surface-.of said enclosure; flowing water produced by melting of said ice past a second portion of said outer surface; removing substantially all the air from said enclosure to effect rapid evaporation of said surface moisture; constraining the flow of air leaving said enclosure to a pa h first past an interior surface portion opposite said second exterior portion and then past an interior surface portion opposite said first exterior portion; and leaving said material in said enclosure until the temperatures of said material and said wall are substantiall equal, due to latent heat of evaporation bein taken up from said material by said evaporated moisture and given up at said wall by condensation of said moisture thereon.

7. In apparatus for vacuum treatment of material having surface moisture thereon: an airtlght chamber having a scalable access door to admit material for treatment in said chamber; means secured in heat transfer contact with a portion of the wall of said chamber to refri erate said wall portion; evacuating mean including a pump connected to said chamber to withdraw fluid therefrom; and baiiie means in said chamber to constrain the flow of fluid therefrom to a path in intimate heat transfer contact with said refrigerated wall portion.

8. In apparatus for vacuum treatment of material having surface moisture thereon; an airtight chamber having a scalable access door to admit material for treatment in said chamber; means secured in heat transfer contact with a portion of the wall of said chamber to refrigerate said wall portion; means including a distribution conduit within said chamber to supply a vapor pressure reducing fluid to said refrigerated wall portion; and evacuating means including a pump connected to said chamber to withdraw fluid therefrom.

9. In apparatus for vacuum treatment of material having surface moisture thereon: an irtight chamber having a heat conducting wall and a scalable access door to admit material for treatment in said chamber; means to support a quantity of ice outside of said chamber and against the exterior surface of a portion of said wall; and evacuating means including a pump connected to said chamber to withdraw fluid therefrom.

10. In apparatus for vacuum treatment of material having surface moisture thereon: an airtight chamber having a scalable access door to admit material for treatment in said chamber; means to support a quantity of ice against a first portion of the wall of said chamber; means adjacent said ice supporting means to direct the flow of melted ice in a path in heat transfer relation with a second portion of said wall; and evacuating means including a pump connected to said chamber to withdraw fluid therefrom.

11. In apparatus for vacuum treatment of material having surface moisture thereon: an airtight chamber having a scalable access door 'to admit material for treatment in saidchamber; means to support a quantity of ice against a portion of the wall of said chamber; means adjacent said ice supporting means to supply melting point reducing fluid to the juncture of said ice and chamber; and evacuating means including a pump connected to said chamber to withdraw fluid therefrom.

12. In apparatus for vacuum treatment of material having surface moisture thereon: an'airtight chamber having; a sealable access door to admit material for treatment in said, chamber; means to support a quantity of ice against the exterior of a first portion of the wall of said chamber; means adjacent said ice supporting means to direct the flow of melted ice in a path in heat transfer relation with the exterior of a second portion of said wall; evacuating means including a pump connected to said chamber to withdraw fluid therefrom; and bafiie means in said chamher to constrain gas leaving the same to a path past the interior surface of first said second wall portion and then said first wall portion.

13. In apparatus for precooling produce having surface moisture thereon: a cylindrical airtight chamber having heat conducting walls and disposed with its axis horizontal, said chamber having scalable access doors in the end walls thereof to admit material for cooling therein and internal conveyor means to support said material for axial movement through said chamber; an ice bunker secured to a side of said chamber and adapted to support a quantity of ice in heat transfer contact with a portion of said chamber wall; and a gas pump connected to said chamber to withdraw air and/ or vapor therefrom.

14. The construction of claim 13 further characterized by having a shroud member surrounding a portion of said chamber wall under said bunker, and slightly spaced from said chamber, the space between said chamber and shroud being communicated with said bunker whereby to pass water produced by melting of ice in said bunker in heat transfer contact with said chamber wall.

15. The construction of claim 13 further characterized by having an internal baffle in said chamber supported in closely spaced relation with said chamber wall and extending over an interior surface opposite said bunker, the space between said wall and baffle being open at one edge to the interior of said chamber and closed at the opposite edge, and communicated adjacent said closed edge with said pump, whereby gas withdrawn from said chamber by said pump passes through said space and in heat transfer contact with a portion of said wall refrigerated by ice in said bunker.

16. The construction of claim 13 further characterized by having a container and distribution conduit mounted above said bunker positioned and adapted to deliver a melting-point-reducing solution to the juncture point of said chamber wall and ice in said bunker.

1'7. The construction of claim 13 further characterized by having a distribution conduit inside said chamber positioned and adapted to deliver a vapor-pressure-reducing solution into said baflle space, whereby to mix said solution with moisture condensed on said chamber wall and lower the vapor pressure of the resultant mixture.

18. In apparatus for vacuum treatment of materials having surface moisture thereon: an airtight chamber having a scalable access door to 1 I admit material for treatment in said chamber; refrigerant flow-directing means secured in heat transfer contact with a portion of the wall of said chamber to refrigerate said portion, said flowdirecting means being arranged to direct refrigerant in a predetermined path across said portion whereby to produce a decreasing temperature gradient thereacross; evacuating means including a pump connected to said chamber adjacent the coldest point in said wall portion to withdraw fluid from said chamber; and bafile means in said chamber to constrain the flow of fluid therefrom to a path in the direction of said decreasing temperature gradient and in intimate heat transfer contact with said refrigerated. wall portion.

MELVILLE W. BEARDSLEY.

References Cited in the file of this patent;

UNITED STATES PATENTS.

Fischer Aug. 14, I951.-

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