US2269172A - Apparatus and process for storage of dry ice - Google Patents

Description

Jan. 6, 1942.

W. T. BIRDSALL APPARATUS AND PROCESS FOR STORAGE OF DRY ICE Filed Nov. 4, 1937 2 Sheets-Sheet 2 Patentecl Jan. 6, 1942 APPARATUS AND rnoonss Fon" STORAG e OF DRY ICE Wilired T. Birdsall, deceased, late of Montclair,

N. J., by Alvin C. Birdsall, administrator, Washington, D. C., assignor to Mergenthaler Linotype Company, Brooklyn, N. Y., a corporation of New York Application November i, 1937, Serial No. 17:2,715

` 5 c'aimsl (c. (az-91.5 e l i 4 This invention relates to the preservation of materials which tend to melt, evaporate or sublime, under conditions of ordinary atmospheric pressure and temperature and particularly to the preservation of low temperature refrigerants such as dry ice and liquid air.

to or from the stored material is .reducedor eliminated. a

The desired result is attained bydoing two things; first, by reducing the flow of heat as much as possible, and second, by dive'rting'the remaining heat in a manner to prevent continued change in equilibrium conditions.

The flow of heat to the stored material may be reduced by surrounding the storage space with material of low heat conductivity such as balsa Wood, kapoc fibre, cork board, orother heat insulating materials .such as those described in applicant's co-pending application' Serial No. 172314 filed Nov. 4, 1937, andalso may be reduced by the use of further elementsof design, Construction or material which make such" insulation more efiective for its purpose. e such an element would'be an additional layer. of material of high heat conductivity such, as copper or aluminum disposed upon either or both surfaces of the material of low thermal'conductivity in a manner to prevent localized differences in temperature which might result in the flow of considerable heat through a small area of .the

insulation, or the creation of temperature dif ferences inside the storage space withthe formation of `destructive convection currents around the stored material. A similarly functioning element would be a coil of pipe forming the desired isothermal surface and filled with a mixture of a suitable volatile fluid and its vapor whereby condensation of the vapor in the pipe automatically will heat any portion thereof which becomes too cold, while evaporation of fluid will cool any point which becomes too warm.

In order to 'divert any heat penetratng .the

the invention. v I

the stored material, means are employed; which are hereinafter referred to as a "guafd ring, and which serve to absorb or remove from the interier of the casing such heat as may pe'netrate the insulation. This guard ring insome instances may consist of the outermo st' layers of a charge of the stored material itself but preferably consists of material separated from 'that being stored and interposed between thestored material and insulation;

In most cases the material used in the guard ring is one which absorbs heat by 'a change of state. However, a fluid may be used' which absorbs the undesired heat by a Chemical or physical change other than a change of state. For instance, :benzoL 'certain mineral oil' distillates, and many other materials when passed over the surface of solid dry ice dissolve some of the ice and thereby reduce its surface temperature. The material which produces -this result can be reactivated (with the evolutiofrof 'the dissolved refrigerant in vapor form) by slight warming so that it can be circulated continuously. ObViously othermethods and means for absorbing heat may be used in 'the guard ring of -the present invention.

In order to illustrate the invention more fully, reference is made hereafter to the accompanying figures of the drawings, each of .which is a diagrammatc representation of an alternative form of means adapted for use in the practice of In the drawings: i r

Figures 1 and 2 represent one typical installation for the storageof dry ice;

tFigure 3 represents mechanism particularly designed for the preservationof materials such as liquid air and the like; and

`Figures 4, 5 and 6 illustrate mechanism which is particularly useful in varying the operation of the guard ring.

Inthat form of the invention villustrated in Figure 1 the guard ring embodies a chamber 2 formed of insulating material such as cork board, kapoc, cellular insulation or the like within which islocated a metallic liner 4of copper, aluminum or other material which is a good heat 'conductor. The chamber 2:'is preferably located 'in a depression 6 in the earth 'so that a layer of cold air will accumulate above thesurfa'ce of the chamber so as to shield the upper portion thereof from heat transfer to the stored' material from above.

The material 8 to be stored 'is'represented as insulation and thus further aid in preserving blocks of dry ice or the like immersed in a'highly viscous liquid or any other continuous or substantially continuous medium o serving to prevent or reduce diffusion of vapor from the stored material and further diminish the flow of heat to the material by avoidance of convection currents in the space about the stored material. Since most liquids or substances employed as the medium in contact with the dry ice are very viscous or stiff, such substances are referred to in the claims as a substantially fluid" medium.

In this Construction heat which tends to flow toward the material from external sources through the walls of the chamber 2 or otherwise is distributed about the material due to the heat conducting liner 4 so that but very little heat flows inwardly through ea'ch separate unit of surface of the liner. The blocks of stored material l I, which are located adjacent the walls of the chamber, receive any heat which penetrates the liner and which is transmitted thereto through the medium ID surrounding the stored material.

Due to the presence of the medium ID in and about the stored material, heat can be transferred to the stored material only by conduction, since convection and radiation are substantially eliminated. For this reason heat flowing inwardly toward the stored material reaches only those blocks 'of material H which are closest to the liner 4, whereupon it is absorbed as latent heat of vaporization at the surface of the outer blocks within the chamber. Heat does not penetrate to the inner blocks or even beyond the outer surface of the outer blocks within the chamber so that destruction of the stored material and disturbance of equilibrium conditions within the main body of stored material is reduced to a minimum. Thus the outer surface of the blocks H of the stored-material constitutes the guard ring protecting the inner stored material.

If broken or scrap dry ice is located about the blocks 8 heat penetrating the insulated walls of the chamber does not destroy the blocks or disturb the condition of thermodynamic equilibrium between the solid and vapor of the material in storage and only the scrap material is destroyed. As illustrated in Figure 2, the stored material 8 is located within an inner casing l2 and is immersed in a highly viscous liquid or other medium O serving to prevent the creation of convection currents about the stored material; The broken dry ice l4 or other means employed for preventing or compensating for heat transfer to the stored material f or convenience is located between the casing l2 and the chamber 2 so as to be separated from the stored material. Means such as the coil IS 'containing a Volatile refrigerant may be used as an iso-thermal device to prevent localized heat transfer to the stored material. The coil may also serve to aid in absorbing heat flowing inwardly through the Chamber 2 and may be used either by itself or in c onjunction with the broken dry ice l4 to absorb heat flowing into or out of the stored material. A suitable cover such as the dry ice containing receptacles !8 may 'be located on the top of the casing !2 to further protect the stored material from the influence of external heat and a substantially non-fluid medium 2!! such as a highly viscous liquid or comninuted or fibrous material serving to prevent the creation of convection currents may surround the broken dry ice.

By constructing the inner casing |2 of heat insulating material or applying heat insulation to the casing, it is possible further to guard the stored material from the influence of external heat since that heat penetrating the outer chamber 2 is taken up by the broken dry ice or other heat absorbing means between the chamber and the casing !2. Furthermore, a temperature differential is preserved between the heat absorbing means and the stored dry ice due to the insulating character of the casing [2. In this Way equilibrium is maintained and the material preserved without material loss or evaporation thereof, and the rate of evaporation of the broken dry ice is limited to that necessary to protect the stored material from external influences.

In those cases wherein the material being stored is in theform of blocks stacked in tiers and surrounded by a liquid or plastic substanca, those blocks in the lower tiers are subjected to greater hydrostatic pressure than those blocks in the upper tiers. Those blocks in the upper tiers therefore tend to sublime or evaporate more rapidly and at lower temperatures than those in the lower tiers so that it may be desirable or necessary to provide more effective heat absorbing means about the upper portion of the storage casing than about the lower portion thereof. In some instances, the guard ring may in fact. be located about only the upper portion of the casing, particularly when the material 20 surrounding the broken dry ice is relatively fluid and serves to flow downwardly about the exterior of the casing.

As illustrated in Figure 3 of the drawings, the material to be stored, which may be liquid air, is of a homogeneous character' and is located within a receptacle 22 spaced from an outer chamber 24 surrounded by insulation material 26. Additional liquid air or other heat absorbing means 28 is located between the receptacle 22 and chamber 24 to absorb heat passing inwardly toward the stored materiaL The function and operation of this form of device is substantially the same as that of Figures 1 and 2 and is especially applicable for the storage of liquid refrigerants. Evaporation of the liquid air or heat absorbing means* in the space between receptacle 22 and chamber 24 prevents the transfer of heat to the stored material while the temperature of theliquid air itself remains` the same and is sufiiciently low to preserve that within the receptacle. A

In the Construction of Figura, 4.. the g-uard ring is provided with broken dry ice 30 or other material having a high latent heat of vaporization and a solvent 32 for the vapor of the dry ice or other means for removing said vapor. is placed in contact or communication therewith; Circulation of the solvent in contact with. the dry ice causes the latter to evaporate at a rate which may be controlled at will by the introduction of fresh solvent to vary the amount of heat taken up by the guard ring. Recirculation of the solvent may be effected by drawing off the same after it has become partially or completely saturated so as to permit evaporation of the dissolved vapor, and return thereof to the system in a regenerated state. As shown, an outlet pipe 34 is provided for conducting saturated solvent to an evaporator 36' from which' it is returned as desired through a pipe 38.

With this Construction the material evaporated in the guard ring may have a higher or lower vapor pressure than the material to be preserved and the temperature of the guard ring may be reduced below that of the stored material. Very effective protection of the material from the infiuence of external heat is thus provided and any heatproduced by condensation of vapor of the stored material due to an increase in atmospheric pressure or other changing conditions is readily absorbed.

In a similar manner evaporation of the material in th guard ring to absorb heat tending to flow into or out of the stored material may be efiected by the construction illustrated in Figure wherein the guard ring isclosed at the top and a pump 40 is provided to draw off vapors of the material 42 therein. Pressures below or above that of the atmosphere can be applied to the material in the guard ring so that the rate of evaporation and amount of heat absorbed by the material in the guard ring may be carefully and Conveniently controlled to insure storage of material in chamber 44 without transfer of heat thereto from externalsources. The same means can be employed to compensate for other forms of energy transfer to the stored material, such as changes in atmospheric pressure, which tend to disturb equilibrum conditions in the storage material.

In the Construction of Figure 6 the rate of evaporation of material in the guard ring is controlled by varying the hydrostatic pressure to which the evaporating material is subjected. For this purpose the chamber 48 in which material 50 is stored is provided With heat insulating means 52 spaced therefrom to provide a guard ring within which broken dry ice 54 or other material to be evaporated is located. A medium 56, such as a 1iquid,-surrounds the broken dry ice and extends to a level which may be considerably above the broken dry ice. Change in level of the liquid is eflected by supplying additional liquid to the space about the chamber or withdrawing liquid therefrom through -the pipe 58 connected to a liquid reservoir 60. The reservoir is closed at the top and provided with a two-way valve 62 for supplying compressed air to the reservoir to force liquid therefrom to raise the level of liquid above the broken dry ice so as to increase the hydrostatic pressure and reduce evaporation thereof when the amount of heat flowng inwardly through the heat insulating means is low. Upon increase in the heat so transmitted, or other energy change giving rise to heat within the storage chamber, the valve 62 is operated to release the pressure on the liquid in the reservoir and allow the liquid in the guard ring to be lowered by drainage through pipe'58 to the reservoir 60. The hydrostatic pressure is thus reduced, permitting more rapid evaporation of th broken dry ice so that a prevent or compensate for transfer of energy to i or from the stored material. However, it should b'e understood that the constructions shown and described are intended to be illustrative of the invention rather than to limit the scope thereof.

What is claimed is:

1. A method for the preservation of low temperature refrig erants such as dry ice, liquid air and the like, which comprises the steps'of enclosing the refrigerant in an insulated chamber, surrounding the chamber with a barrier of dry ice immersed in a liquid and insulating said dry ice from its surroundings.

2. A method for the preservation of low temperature refrigerants such as dry ice, liquid air and the like, which comprises the steps of surrounding the material to be preserved with a similar low temperature refrigerant immersed in a liquid and controlling the rate at which the surrounding low temperature refrigerant evaporates by varying the level of said liquid.

3. A structure for use in the storage of low temperature refrigerants comprising an insulated chamber for receiving material to be stored, heat insulating means spaced from the walls of said chamber, and a heat absorbing barrier comprising dry' ice immersed in a liquid located in the space betwen said chamber and said heat insulating means' 4. Apparatus for storing dry ice comprising a storage chamber enclosing the dry ice to be stored, a heat insulating casing surrounding and spaced from said storage chamber, additional dry ice in the space between said heat insulating casing and said storage chamber and means movable into and out of contact with said additional dry ice to vary the rate at which heat is absorbed thereby.

5. Apparatus for storing dry ice comprising a storage chamber formed of insulating material, a casing formed of insulating material spaced from said storage chamber and surrounding the same, dry ice 'located in the space between said storage chamber and casing, removable cover members for the storage chamber each containing additional dry ice and substantially fluid media surrounding the dry ice in said storage chamber and the dry ice in said cover members and in the space between said casing and storage chamber. i

- ALVIN C. BIRDSALL, Administrator of the Estate of W'lffed T. Birdsall, Deceased.

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