US2488997A

US2488997A - Method and apparatus for cooling

Info

Publication number: US2488997A
Application number: US584447A
Authority: US
Inventors: Harold A Thornburg
Original assignee: United States Rubber Co
Current assignee: Uniroyal Inc
Priority date: 1945-03-23
Filing date: 1945-03-23
Publication date: 1949-11-22
Anticipated expiration: 1966-11-22

Description

.2 Sheets-Sheet 1 H. A. THORNBURG METHOD AND APPARATUS FOR COOLING Nov. 22, 1949 Filed March 23, 1945 2 Sheets-Sheet 2 INVEN TOR. #48010 ,4. WWW/ M6 BY 2 I 2 ATTORNE? H. A. THQRNBURG METHOD AND APPARATUS FOR COOLING 0 o o o & o o o o o Nov. 2 2, 1949 Filed March 25, 1945 Patented Nov. 22, 1949 METHOD AND APPARATUS FOR COOLING Harold A. Thornburg, Brooklyn, N. Y., assignor to United States Rubber Company, New York, N. Y., a corporation of New Jersey Application March 23, 1945, Serial N0. 584,447

9 Claims. (Cl. 117-103) This invention relates to an improved method and apparatus for cooling materials by successively evaporating liquid films in intimate contact with the surface of said materials, and thereby utilize the latent heat of evaporation of the films of liquid as a means of absorbing at least 25% of the heat from the surface of the materials to be cooled and reducing the temperature of such materials so treated.

In the practice of the invention, an evaporative liquid is applied in a thin film to the surface of the material and it is quickly evaporated and carried off by the surrounding atmosphere. These operations are successively repeated until the material is reduced to the required temperature in a novel apparatus to be hereinafter described.

This invention is particularly applicable to cooling from above '70" F. water absorptive plastic sheet materials where the absorption of the water in a cooling water bath may be disadvantageous because of its injurious effect on the materials, or because of prolonged drying operations that may be required to eliminate the moisture. Heretofore, such materials have been cooled by circulating air over them. The transfer of heat from such materials to air is relatively slow as compared to the heat transfer from such materials to an evaporating film in direct contact with the materials. The thin films of liquid deposited on the surface of the materials in accordance with my invention do not penetrate into the body of the materials, because they are quickly evaporated by the effect of the heat within the materials and the non-saturated surrounding atmosphere. Also the heat transfer under such conditions is more rapid and emcient than in the case where the heat is transferred directly into the surrounding atmosphere. Therefore, in accordance with my invention the absorption of water into the materials by the immersion of the materials into the water is eliminated, and a more rapid cooling of the material can be obtained with the use of an atmosphere having a lesser temperature differential between it and the materials to be cooled.

The objects and advantages of this invention will be more clearly understood by referring to the following description and the accompanying drawings, in which:

Fig. 1 is a cross-sectional view of an apparatus embodying this invention and adapted to carry out'the method;

Fig. 2 is a cross-sectional view of the apparatus, taken on line 2--2 in Fig. 1;

Fig. 3 is a cross-sectional View of the material to be cooled illustrating the liquid film thereon;

Fig. 4 is a cross-sectional view of another form of an apparatus embodying this invention; and

Fig. 5 is a cross-sectional view of the apparatus shown in Fig. 4 and taken on line 5-5 of that figure.

As illustrated herein the material to be cooled is in the form of a continuous plastic rubber slab as it comes from a mill or extruder. The material is at an elevated temperature, and for example it may be at a temperature of 250 F. Referring to Fig. 1, the sheet material IE] to be cooled is led into the apparatus II over a roller I2 and is supported by a series of wire mesh conveyor belts I3, I4, I5, I6, and H or of any other type adapted to permit the free passage of air and water. The conveyor belts are supported at each end of their runs by means of rollers It, which may be driven from drives located within or without the enclosure for the apparatus. The sheet material It is first deposited upon and passes along the top reach I9 of the belt I3 and then passes successively to the top reaches -20, 2|, 22, and 23 of the belts I4 to Il, inclusive, and after having been reduced in temperature it passes out of the apparatus through an opening 24. In its travel, the material It passes successively through film applying stations 25 and 26 and film evaporating stations 2? and 2B, which latter are arranged in a series with or interposed between the stations 25 and 26.

The film applying stations 25 and 26 are substantially alike, and only one of them will need to be described. The station 25 comprises a compartment 29 enclosed in walls 30 through which the material It on the conveyor belts I3, I4, and I5 is adapted to pass. The evaporative cooling liquid is applied in a thin film to the material It by fog sprays 3| which are directed to the upper and lower surfaces of the material from nozzles 32. As the material passes out of the compartment, any excess liquid is wiped off by rubber squeegees 33, which make contact with the upper surface of the sheet material Ill, or the lower surface of the upper run of the belts.

As the material is passed into the evaporating station 21, a drying atmosphere, such as unsaturated air, is circulated about the material. The air is supplied from nozzles 34 and is caused'to circulate about the material as shown by the arrows 35 in Fig. 2. The air may be discharged from the apparatus through any suitable openings, such as at the entry and exit of the material I0, or special openings provided therefor in the 3 enclosure. The unsaturated air quickly or almost instantly evaporates the film and carries it off in the form of vapor.

This quick or so-called flash evaporation of the liquid in contact with the surface of the material, utilizes the latent heat of evaporation of the film for extracting the heat from the material.

The sheet material it next passes by the squeegees 33 into the film applying station 26 Where it is treated in the same manner as described in reference to station 25. The material then passes by the next advanced squeegees 33 into the next evaporating station 2-8, where the film is dried in the same manner as described in reference to the evaporating station 2?. The material ill successively passes through the stations and its temperature is progressively reduced as each film is evaporated from the material Ill. The thickness of the film i8 is relatively thin as shown in Fig. 3. Its thickness is preferably no greater than a film retained by the surface tension of the cooling liquid. Where the term thin film occurs, it means a film no greater in thickness or depth than that retained as a result of the surface tension oi? the liquid on a rough or smooth surface, whether in a horizontal or vertical position, and whether the film is applied in the form of a spray, or by dipping and draining the material. In the final drying operation, a strong drying current of air may be directed upon the top and bottom surfaces of the material by the nozzles 31 to insure complete dryness.

The modified form of the apparatus disclosed in Figs. 4 and 5 is adapted to cool the material 38 as it moves continuously through the apparatus, or to cool the material in a step by step movement therethrough. The apparatus will first be described in reference to the continuous movement. The warm sheet material 33 to be cooled is led into the apparatus through an opening 39 over a roller 30 and onto the top reach ii of a conveyor belt 42. Then it is led successively to the top reaches ll of the belts 33, M, 45 and 46. The material 38 passes from the belt 46 out of the apparatus through an opening 4? at a reduced temperature. Transversely extending rows of fog spray nozzles 28 are arranged above and below the sheet material 38 and are spaced along its path of travel for the purpose of depositing thin films of liquid on the top and bottom surfaces of the material. Additional spray nozzles 48' are incorporated in the apparatus for a purpose to be hereinafter described. After each film of the desired thickness is deposited upon the surface it is evaporated by the effect of the heat imparted thereto by the material 38 and a non-saturated atmosphere circulated in contact therewith, before the next film is applied. Ordinarily the thickness of the films is controlled by the sprays 48, but if desired squeegees or pressure rollers may be used for that purpose.

The path of travel of the material 38 in the apparatus is enclosed by walls 49. The air for evaporating the films of liquid is supplied to the enclosure under a suitable pressure through an inlet duct 50. The air is discharged from the duct 50 into the enclosure through an upper set of air circulating nozzles iii, and a lower set of air circulating nozzles 52. As shown in Figure 4, the nozzles 5! and 52 are arranged so that the incoming streams of air flowing therefrom do not fall directly upon the sprays of fog delivered by the fog spray nozzles 48. Therefore the fog will fall or impinge upon the surface of the material 38 and form a film thereon before it is evaporated by the incoming streams of air. In order to increase the capacity of a given quantity of air to conduct heat away from the material 38 and to vaporize the films of liquid or absorb moisture, the incoming air is circulated around the cooler portions of the material 38 first, and then progressively circulated around the warmer portions of the material. This increase in the capacity of the air to absorb heat and moisture results from the air being heated to the highest temperature by the hottest portion of the incoming material 38 and from the air being capable of absorbing more moisture at the increased temperature. With this in view bafiles 53 and 54 are provided to cause the incoming air from the nozzles 5i and 52 to progressively circulate over the films in a direction from the cooler portions of the material 38 towards the warmer portions of such material. The incoming material 38 above the baffle 53 is the hottest, and it is progressively cooled in the compartment between the bafiies 53 and 5t and the compartment below the bafile 54. The battle 53 is positioned above the nozzles 5! and is attached to the wall of the duct 50, and a space or opening 55 is provided between the edge of the baffle 53 and the wall 49 so that the air delivered by the nozzles 5i can pass over the hottest portion of the material 38 after having circulated about the cooler portions on the upper reaches of the belts 53 and #1 3, which are positioned between the baffles 53 and 54. The bafile 54 is placed immediately above the nozzles 52 so as to separate the incoming air of those nozzles from the air delivered by the nozzles 5|, until the air from the nozzles 52 has circulated about the cooler runs of the material 38 on the top reaches 4! of the belts "iii and .6. The bafile 54 is attached to the Wall 59, and a space or opening 5% is provided between the edge of the baiile 54 and the Wall of the duct so as to permit the air from the nozzles 52 to pass by the bafile 54 and mix with the air discharged from the. nozzles 5|, after the air from the nozzles 52 has been first circulated around the cooler portions of material 3-8 carried by the belts 45 and 46. The air from the nozzles 52 commingles with the air from the nozzles 51 in the compartment between the baiiles 53 and 5 and is further heated, thereby increasing its capacity to take up additional moisture. The commingied air passes through the opening 55 around the baiile 53 in the compartment above the latter baiile, where the temperature of the atmosphere is the hottest. Consequently, the air in the compartment above the baiiie 53 will become additionally heated and will be capable of taking up additional moisture and will have a further cooling effect on the first and top run of the material 38, although the film of liquid deposited by the nozzles 48 in that compartment may not be completely evaporated. The moisture laden atmosphere is discharged through the outlet 5?.

In the operation of the method in connection with the continuously moving material 38 through the apparatus disclosed in Figs. 4 and 5, the hot sheet material 38 in the compartment above the bafiie 53 is sprayed by two rows of fog spray nozzles 48 above and below the sheet during the continuous travel of the material. The film cleposited by the first row will immediately flash into vapor, if the temperature of the material is sufiiciently high. As many more additional rows of spray nozzles are provided as may be necessary todeposit filmsthat maybe carriedby the mate-- rial through an opening 58 in the .bafile 53 to the compartment below. Any films carried to that compartment or deposited on the material therein are evaporated in succession by the heat of the material 38 and the air from the nozzles 5| or the air commingled therewith from the nozzles 52. The air is directed over the films as indicated by the arrows in Fig. 5, and each film is substantially evaporated before the next is applied. The sheet material then passes through the opening 59 in the baffle 54 and onto the top reach 4| of the belt 45. Any film remaining thereon is evaporated by air from the first of the air nozzles 52, and thena succeeding film is deposited by the next spray nozzles 48. A series of air nozzles 52 following the last row of spray nozzles 48 is provided in order to insure the complete evaporation of the last film of liquid applied.

The operation of the apparatus shown in Figs. 4 and 5 will now be described for cooling the material in a step by step movement through the apparatus. This method is best suited for cooling material which is intermittently delivered from a mill in batches. Each batch is introduced into the apparatus in a continuous movement and then it remains at rest for a period before the next batch is introduced. This intermittent introduction of the batches one after the other produces a step by step movement of the material through the apparatus in each step of which the batches are moved forward an amount substantially equal to the length of the batch being introduced.

The apparatus shown in Fig. 4 is designed to hold three batches of material when it is fully loaded. When loaded, the last batch in extends from the right end of belt 42 to the point 60 on the belt 43; the next preceding batch extends from the point Bl] to the point 6| on the belt 45; and the next preceding batch extends from the point 5| to the point 62 on the belt 46.

During the movement of the material 38 in the apparatus, the nozzles 48 opposite the material and shown to be in operation are continued in operation as in the continuous movement of the material through the apparatus, and air is preferably delivered continuously from the nozzles 5| and 52 all of the time the material is inside the apparatus. As the two batches of the material last introduced remain stationary between their steps of movement, substantially their entire top and bottom surfaces are intermittently covered with the thin film of liquid by the combined simultaneous action of the fog spray nozzles 48 and 48 opposite such surfaces. The nozzles are turned on and off in groups adapted to cover the separate batches, and the film deposited by each group is evaporated before the next film is deposited. The application and evaporation of the films are repeated at each step until the temperature of the material 38 has been reduced the desired amount at the particular stage "to cause a progressive reduction in its temperature as it passes through the apparatus and so that the batch of material ready to leave the apparatus may be discharged at the desired low temperature.

The amount of liquid supplied to the material 38 is successively reduced as the temperature of the material falls in the successive stages of cooling. The amount of liquid delivered in 7 these stagesmay be controlledby reducing the flow of the liquid to the sprays, or by changing the length of time the sprays remain turned on. It

is desirable not 'to spray the batchwhich is ready to leave the machine, and it is acted on only bythe unsaturated air in order to insure complete dryness of the material 38 as it passes through the exit 41. y g

This invention is particularly applicable to the cooling of slabs of rubber coming from a mixer in a raw or unvulcanized state and whichis' capable of absorbing moisture. The rubber is tacky in that condition, and in order to reduce its tackiness so that it will not adhere to any surface upon which it is deposited after leaving the apparatus herein described, the surfaces of the rubber slab are coated with an adhesive pre- Venting material as it passesthrough the apparatus. Such material is referred to as a lubricating material, and may consist of ordinary washing soap, or other similarly acting materials used by the rubber industry and which will not readily settle out of the liquid appliedtothe rubber slab. In accordance with my invention, the lubricant may be mixed withthe water used to form the evaporative films on the surface of the rubber, and after the liquid is evaporated, the lubricant remains on the surface of the sheet material. The lubricant may be mixed. in the desired quantity with the water in orderto deposit the desired quantity on the surface of the material. It is preferable, however to increase the concentration of the lubricant and use it only in a limited number of rows of spray nozzles in order to control the deposit of lubricant on the surface of the material.

It has been found that my apparatus and process operates eificiently with water as a film forming agent and with atmospheric airv as a film evaporating or absorbing agent for cooling rubber slabs, and that the average temperatures of the water and the air encountered throughout the United States during all of its seasons can be employed efficiently. As an example in the operation of my apparatus and process, a slab of rubber A. inch thick, 5 feet wide, weighing 400 lbs., and having a specific heat of .5 will be delivered per minute and may be cooled from 250 F. to 110 F. when the distance traveled by the rubber is such that it remains in the apparatus for approximately 3.2 minutes. That requires the removal of 28,000 B. t. u. per minute. Such removal is effected by vaporizing 26 lbs. of Water with 3300 lbs. of air at the average summer temperature of water at 54 F. and at the average summer outdoor atmospheric condi tions of air at F. dry bulb, 75 F. wet bulb, 40% relative humidity, 66.8 F. dew point, and containing 98.5 grains H2O per 1b., a total heat of 37.66 B. t. u. per 1b., and weighing 1 lb. per 14.3 cu. ft. In such example the outlet temperature rose only 1 F. dry bulb and the air had a relative humidity of 59%. In this example approximately 97% of the heat was absorbed by the latent heat of evaporation of the liquid. It will be understood that as the outside air approaches saturation, less fog spray will be required. However, if no fog spray had been used and the air in the above given condition had been relied upon to remove all of the heat from the rubber in the above case, approximately 18,820 lbs. of air would have been required with a rise in temperature of 5 F. dry bulb between the atmospheric air inlet and outlet. The relative humidity at the outlet would have been 34.5%. 'It will thus be seen that a considerable increase in the volume of air circulated is required where air only is employed as a cooling agent, and that due to its lower relative humidity at the outlet the rate of conduction of heat is lower than in the case of the higher outlet humidity produced by the fog spray.

It is to be understood that the cooler the temperature of the air directed upon the material, the less liquid film will be required to remove a given quantity of heat from the material in a given time in the operation of this process. When the point is reached where less than 25% of the heat transferred from the body to be cooled is absorbed by the latent heat of evaporation of the film, it is more economical to dispense with the application of the film and use air only for cooling because the volume of air required at the lower temperatures is relatively small. The following is an example of an air condition where it is desirable to dispense with the application of the liquid film to the rubber slab above: 60 F. dry bulb, 56 F. wet bulb, 80% relative humidity, 538 F. dew point, and containing 61.5 grains of H per 1b., a total heat of 23.7 B. t. u. per 1b., and weighing 1 lb. per 13.25 cu. it

While I have shown the preferred forms of my invention herein, it will be understood that changes in details may be made without departing from the spirit of the invention and the scope of the appended claims.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. The method of transferring heat from a body of tacky plastic heated material comprising the steps of repeatedly and intermittently spraying a thin film of liquid containing a lubricating agent to the surface of the body and at a, lower temperature than said body, quickly evaporating the liquid in intimate contact with said surface between the applications of said films, whereby at least of the heat transferred from said body goes into supplying the latent heat of evaporation of the liquid and the lubricant contained therein is deposited upon said surface.

2. The method of reducing the temperature of successive batches of plastic sheets comprising successively passing the batches in series through cooling zones in a step by step movement, contin uously applying thin films of liquid to said sheets at spaced stations in the first of said zones and evaporating said films between said stations during the movement of said batches, intermittently applying thin films of liquid to said sheets in other of said zones and evaporating each film before the next film is applied while said batches remain stationary in said zones.

3. An apparatus for cooling sheet material comprising fog sprays arranged in groups, said groups being arranged in series and adapted to deposit individual films of liquid on to the surface of the sheet material, means for circulating a gaseous atmosphere over said films between each group of said fog sprays to evaporate each film before the next one may be applied, means for directing said gaseous medium progressively from the coolest portions of said sheet material towards the hottest portions of said sheet material, and means for conveying said material in position to be operated upon by said spray and circulating atmosphere.

4. The method of transferring heat from a flat sheet-like body comprising the steps of repeatedly and intermittently spraying a thin film of liquid onto the surfaces of said body on each side thereof and at a temperature lower than said body, quickly evaporating the films in intimate contact with said surfaces by the heat of said body and in the presence of an atmosphere capable of absorbing the vapors of said liquid, and controlling the intermittent application of the films to permit the film deposited on a'surface to be substantially evaporated before the next film is applied to the same surface.

5. An apparatus for cooling sheet material comprising an open mesh support for said material, means for applying successive thin films of liquid to a surface area on each side of said material on said support, and means for quickly evaporating the film on said surface area before another is applied to that area.

6. An apparatus for cooling sheet material comprising an open mesh support for said material, means positioned on opposite sides of said support for spraying successive thin films of liquid on a surface area on each side of said material on said support, and means for quickly evaporating the film on said surface area before another is sprayed on that surface.

7. An apparatus for cooling sheet material comprising an open mesh movable support for said material, film applying units arranged in series along the path of said support on each side thereof, film drying units alternating with said film applying units for quickly drying the films deposited by said film applying units before another film is applied to same surface area, and means for moving said support past said film applying and drying units.

8. An apparatus for cooling sheet material comprising alternately arranged spraying and drying compartments, means for conveying the sheet material in succession through said compartments, means in said spraying compartment for spraying liquid upon the surfaces of the sheet material therein, means for passing currents of air over the sheet material in said drying compartments to evaporate the liquid sprayed on the sheet before it is carried into the succeeding spraying compartment.

9. An apparatus for cooling sheet material comprising alternately arranged spraying and drying compartments, means for conveying the sheet material in succession through said compartments, means in said spraying compartment for spraying liquid upon the surfaces of the sheet material therein, means for wiping excess liquid from the surface of said material as it leaves the spraying compartments, means for passing currents of air over the sheet material in said drying compartments to evaporate the liquid sprayed on the sheet before it is carried into the succeeding spraying compartment.

HAROLD A. THORNBURG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Moifit Dec. 19, 1944