US2871678A - Heat exchanger - Google Patents

Description

. Feb. 3, 1959 R. D. SMITH ETAL ,87 7

- HEAT EXCHANGER 7 Filed Aug. 1955 2 Sheets-Sheet 1 Kc d d. 404/; Ku E Fin/2g 12 GQMEMM HEAT EXCHANGER 2 Sheets-Sheet 2 Filed Aug. 1, 1955 0 0 0 0 0 0 0 9 0 0 1 6 a2 a7 M a a z w m M 1 1 a M 1 1 HEAT EXCHANGER Ralph D. Smith, epulveda, and Kaye B. Swim and Keith 15. Finlay, Los Angeles, Calif, assignors, by mesne assignmeuts, to Northrop Aircraft, Inc., Hawthorne, Calif a corporation of California Application August 1, 1955, Serial No. 525,666

1 Claim. (Cl. 62-440) This invention has to do with heat exchanging devices, and more particularly with an evaporative cooler for equipment which may be electronic, mechanical, or chemical in nature, for example.

It is desirable for certain equipment that a critical operating temperature not be exceeded in order to obtain optimum operation. The ability to obtain and maintain certain types of the aforementioned equipment within the optimum operating range is very often complicated by imposed rigid restrictions. Such restrictions are very often dimensional, i. e. dimensional with regard to weight, and space occupied. As a result of the imposed restrictions, limitations are also established against any medium that may be used to cool and maintain the equipment below the critical operating temperature. Therefore, in order for the equipment to be satisfactorily maintained at a suitable operating temperature, a cooling medium must be resorted to that conforms to the restrictions and defined dimensions.

The principal object of this invention is to provide an evaporative cooler that may be combined with electrical, mechanical, or chemical equipment and the like to provide a single unit, which utilizes the heat discharged from the equipment per se to cool the same.

Another object of this invention is to provide an evaporative cooler for a container of electrical, mechanical, or chemical equipment and the like, for example which uses a liquid absorbing chemical compound that has an unlimited life expectancy, i. e. it may be saturated with liquid and regenerated to dryness an unlimited number of times.

A yet further object of this invention is to provide an evaporative cooler for a container of electrical, mechanical, or chemical equipment, which uses. a liquid absorbing chemical compound, and which has a storage supply of liquid for replenishing the compound when the liquid contained therein is evaporated.

Another object of this invention is to provide an evaporative cooler for a container of electrical, mechanical, or chemical equipment which is efficient in operation, yet simple in construction and is readily fabricated and maintained.

A further object of this invention is to provide a simple, removable cooling device for a container.

Broadly, the invention involves a container having a heat source in the container and a top forming a heat sink. Located in heat exchange relationship to the top is a chemical containing absorbed water such as a silica gel, for example. The heat emanating from the source causes the temperature of the top to rise which in turn causes the water in the chemical to evaporate. The evaporation of the water cools the top and ultimately the contents of the container. A Water supply source can be made available, if desirable, to replenish the water evaporated from the chemical.

Figure 1 is a fragmentary, perspective view illustrating and having embodied therein the present invention.

Figure 2 is an enlarged, perspective view, parts being broken away for purposes of obtaining clarity and illustrating essential structure and material for cooling electrical, mechanical, or chemical equipment.

Figure 3 is a fragmentary, cross-sectional View illustrating a container for a chemical compound and partially showing the method through which the liquid in the compound is replenished.

Figure 4 is a graphic illustration of the efiects the evaporative cooler of this convention has upon the temperature of equipment associated therewith.

Referring to the drawings for a more detailed description of the present invention, 10 designates a container having a top 12. Located within the container 10 is electronic, mechanical, or chemical equipment 13, for example, which when operating, gives off heat. The container 10 preferably contains some gas, to enable heat released in the container to rise to top 12. Top 12 thus forms a heat sink for the equipment 13.

Overlyin'g and on the top 12 of container 16 is a cage 14 having U-shaped channel members 16 that constitute a defining frame for the aforementioned cage. Secured to one leg 18 of members 16 is a screen 20 and secured to leg 22 is another screen 24. Attached to the bight 25 of members 16' adjacent the corners are guide brackets 26, only one of which is shown, for guiding cage 14 onto container 10.

Mounted on the container 10 and cage 14 for the purpose of ready locking and removal of the latter to the former is a quick acting or snap latch 28.

Deposited on screen 20 is a layer of silica gel 29 preferably saturated with water which when cage 14 is in position on container 10 is in heat conducting relation to top 12. This gel layer may be of any thickness, but for purposes of illustration and not for purposes of limitation the graph of- Figure 4 shows the effects of a onequarter and one-eighth inch layer. It may be determined by referring to the aforementioned graph and figure that a one-eighth layer of silica gel saturated with water will maintain the temperature of equipment 13 at a lower level than Will a one-quarter inch layer, providing the granular size of the two layers is the same.

This is due to the fact that the temperature drop through the material is proportional to the thickness of the silica gel layer. Also, as a result tests have shown, that are corroborated by the graph, that the thermal capacitance of the saturated silica gel is in direct proportion to the thickness.

The graph of Figure 4 also shows the results with the same equipment used in container 10 when no silica gel is used and an energy of 3.0 watts per square inch is being dissipated through top 12, the curve rises abruptly from zero toward maximum.

The curves of the one-eighth inch and one-quarter inch layer of silica gel are typical of those curves when saturated silica gel is activated or regenerated.

The cage 14, as illustrated, is divided by partition,

bafiles 30 into compartments 32. This procedure may or may not be followed in actual practice. In some instances it may be convenient to compartment the cage 14; in other instances it may be inconvenient.

Associated with container 10 and cage 14 is a compartmented water filled reservoir tank 34 that may be adjacent to or remotely located with respect to the containers. Extending from each compartment of the tank is a water feeder tube 36 having a valve 38 therein that may be adjusted to supply a predetermined amount of water. Further, each tube 36 extends into a compare ment 32 of cage 14, and is held in place overlying the silica gel by mounting brackets 39.

The silica gel 29 is an amorphous, extremely porous form of silica and is an inert clear material that is commercially available in many mesh sizes. Regardless of the mesh size it will function to store water. It is slightly softer than window glass having a hanrdness of 5 in Mohs Mineralogical Scale. Therefore, it will not erode or dust in service or while being cycled. By virtue of this fact it may be deposited on a screen 20, havign openings smaller than the particle size, without danger of it passing through.

The water absorption properties of silica gel are purely physical, and there is no change in size or shape of the particles as they become saturated. No injurious or corrosive compounds are given ofi as may be the case when chemical absorption takes place. Even when saturated, the particles of silica gel feel and appear perfectly dry. The porous structure of silica gel gives the material its power to absorb or drink in liquids and condensable vapors.

Silica gel containing water may be regenerated by subjecting it to an elevated temperature, which operation is known as activation or regeneration. During water evaporation cooling takes place. It is possible to cycle silica gel for an unlimited number of times without loss in efliciency or capacity.

The operation of the invention is as follows: A layer of silica gel preferably pre-saturated with water is deposited on screen 20 and the cage 14 is locked by latch 28 to container 10. The tubes 36 from the reservoir tank 34 are positioned in compartments 32 of cage 14 and secured in place.

As the equipment 13 in container is energized heat is emitted therefrom and heats top 12 of container 10. The silica gel layer being in heat conducting relation to top 12 is raised in temperature. When the temperature exceeds a particular level the water of the sicila gel evaporates, cooling the surrounding area and top 12. The water evaporated from the layer of silica gel 29 is replenished by the water in tubes 36 and tank 34. As a result a continuous process of evaporation and replenishmg of the water in the silica gel is initiated. In other words the silica gel absorbs water and the heat from equipment 13 tends to regenerate it. Knowing the amount of heat to be removed from top 12, the rate of water replenishment can readily be adjusted to maintain the water content near but not over the gel saturation point. Under these conditions and assuming substantially constant heat emission of equipment 13 the temperature thereof can be well regulated over substantial time periods. By virtue of the operation and characteristics of the invention it may be seen that the heat of evaporation for the water in the silica gel is obtained from the equipment 13, and removed from the container.

However, it is to be understood that the equipment used as an example is not to be considered a limitation. For instance, the electrical, mechanical or chemical equipment can have substituted therefor other materials and structures including a human being. Further, the heat of evaporation does not haveto originate from that which is in container 10, but can originate from a source outside of both containers, such as, for example, the surrounding atmosphere. 2

In order to reduce, if not prevent, the surging or slopping of water in cage 14, the amount of water carried in tank 34 may be calculated to correspond to the water evaporated and the heat generated, to cause evaporation. For instance, the operating time of the equipment, for a given set of circumstances, may be determined. The operating temperature of the equipment 13 in the absence of a cooling medium is known. As a result it can be determined from the aforementioned temperature the amount of water that will be evaporated from the silica gel 29. Knowing the amount of water that will be evaporated from the silica gel in a given length of time will be tantamount to knowing how much water to carry in the tank 34. As a result only that amount of water necessary to replenish the water in the silica gel 29 need be carried. Therefore, the amount of water needed to cool the equipment 13 for a predetermined length of time is reduced to a minimum. As a result the silica gel layer 29 is not supersaturated with Water and surging or slopping in cage 14 is reduced or does not occur.

While in order to comply with the statute, the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise a preferred form of putting the invention into efiect, and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claim.

What is claimed is: p

A heat exchanger comprising a container having a top thereon; a cage on the top of said container comprising U-shaped perimeter defining structure; a screen attached to each leg of said structure; at least one partition between said screens to divide said cage into compartments; a silica gel containing a liquid to be evaporated locatedin said compartments; a liquid supply means for said silica gel to replenish the liquid evaporated therefrom comprising a compartmented tank each compartment of which has a liquid therein; a liquid feeder tube in communication with each compartment of said tank and cage; brackets on one of said screens and attached to said feeder tubes for retaining said feeder tubes in a communicating relationship with the compartments of said cage; a valve in each feeder tube for opening and closing the feeder tube and making accessible and inaccessible the contents of said tank to said silica gel; and quick acting latch structure on said container and cage for readily attaching and detaching said container and cage.

References Cited in the file of this patent UNITED STATES PATENTS 1,231,088 Stafford June 26, 1917 1,268,053 Poetschke May 28, 1918 1,409,364 Dobbs Mar. 14, 1922 2,241,843 Buddrus May 13, 1941 2,303,332 Dauphinee Dec. 1, 1942 2,420,358 Culligan May 13,1947 2,604,311 Summerhill July 23, 1952

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