US2506578A

US2506578A - Automatic space drier

Info

Publication number: US2506578A
Application number: US772830A
Authority: US
Inventors: James W Case
Original assignee: Individual
Current assignee: Individual
Priority date: 1947-09-08
Filing date: 1947-09-08
Publication date: 1950-05-09
Anticipated expiration: 1967-05-09

Description

May 9, 1950 J. w. CASE AUTOMATIC SPACE DRIER Filed Sept. 8, 1947 FIG. 2

TO H5 V. UNE

JH/UCHYOL JAN/E5 14 C455 FIG.

6 Roan :41

l atented May 9 1956 UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 9 Claims.

My invention relates to improvements in dehumidifiers and more particularly relates an automatic space dryer for automatically controlling the degree of moisture in a cabinet below a safe maximum level.

The purpose of the invention is to provide an inexpensive and compact dehumidifier unit which is self-reactivating and particularly suitable for the protection of delicate instruments and machinery against corrosion and general damage due to moisture.

It has been well recognized that the main source of deterioration and maintenance troubles in many types of ordnance gear, particularly those which are composed of intricate electrical, mechanical or optical components in sealed or unsealed housings, is moisture. The presence of moisture in such units, either as absorbed moisture in metallic and nonmetallic surfaces, condensed moisture on such surfaces, or in the atmosphere surrounding the components, may lead to metallic corrosion, loss of electrical resistance, fogging of optical objectives, or mold growth on insulation, thus making the equipment unusable in service or reducing it to the last stages of deterioration during shipment, storage or periods of disuse.

As a result of research undertaken by the Armed Forces during the past few years in developing means for preservation of ordnance equipment on a long term basis, it has been generally found that dehumidification of the atmosphere in which equipment is stored is by far the most practicable means of protecting large amounts of material, particularly that which must be preserved in a fully assembled condition, due to military readiness requirements. It has been proven by comparative tests that a controlled relative humidity of 30% or below will effectively prevent corrosion and mold growth on all components of ship machinery and ordnance equipment which are susceptible to them. It has also been found that a relative humidity of 50% or below will measurably extend the life of equipment and is recommended if 30% cannot be economically obtained; further, that materials such as silk and other fabrics require storage within a definite humidity range to insure maximum strength of their fibers.

The moisture hazard to ordnance equipment would be entirely eliminated if operating units were thoroughly dried out during initial assembly and enclosed in durable hermetically sealed, moistureproof cabinets. While this has been partially accomplished in the design of optical equipment,

it these units must be dried out with special dry ing equipment or re-gassed with nitrogen or helium at intervals because they are susceptible to leakage through stuiiing glands and objective mountings. The majority of all other types of fire control units are enclosed in so-called watertight housings. While these housings, or more broadly cabinets, are usually made of cast aluminum, bronze, sheet steel, etc., the multiplicity of drive shafting, control shafting, electrical conduit connections and access door gaskets which they incorporate, makes them susceptible to breathing and internal moisture condensation, due to temperature changes which are caused by atmospheric fluctuations or variations in dissipated heat from the units.

My present invention contemplates automati cally maintaining the interiors of such cabinets at a safe maximum value of relative humidity by use of a self-reactivating desiccant to adsorb all moisture which gains ingress due to breathing or diliusion through housing walls or sealed joints. Previous systems for accomplishing this result have been cumbrous, bulky and insusceptible of precise and delicate adjustment without servicing over long periods of time. Therefore, due to the extremely limited applications of such systems, no general use has been made of dehumidifying apparatus for instrument housings or equivalent cabinets.

The primary object of my invention, therefore, is to provide dehumidifying apparatus for cabie nets, including moisture adsorbing means, which is automatically reactivated during operation of the apparatus.

Another object of the invention is to provide dehumidifying apparatus including automatic reactivating means, wherein the reactivation is controlled by the weight of the moisture adsorbing means itself.

Still another object of the invention is to provide dehumidifying apparatus including automatic reactivating means, wherein the combined dehumidification and reactivation cycle maintains the atmosphere below a pre-set maximum value of relative humidity.

Still a further object of my invention is the provision of a compact, portable and inexpensive automatic dehumidification unit.

Other objects and advantages will become apparent from the following description of a preferred embodiment of the invention which has been described in detail in connection with the accompanying drawing in which:

, Figure 1 is a side elevational view, partially in section, showing the dehumidification apparatus incorporating the present invention.

Figure 2 is a schematic view of the electrical circuit control means for the automatic space It may, in fact, be incorporated as a component 11 of the complete instrument. Inlet port I2, -intake conduit I4 and port I permit intake'of'reactivating air from outside the cabinet -I into the casing 3 of the space dryer unit. A conventional blower 8 operated by motor 9' causes reactivating air to be drawn through casing 3 and exhausted to the outer atmosphere through a conduit and outlet port (not shown) whichfare duplicates of I4 and I5 respectively. Thehousing 5, preferably of perforated sheet metal, contains the moisture adsorbent material 4, such as silica gel, attracts particles of moisture vapor "from'the free space enclosed by the cabinet I, 'in-to'the interior of the casing 3 and thence to the moisture adsorbent material 4 through a plurality of moisture porous membranes 2 lodged Within the casing 3. In a specific embodiment of my invention, these moisture porous membranes consist of four equally spaced windows of glass cloth or unbleached muslin. Other materials andarrangements thereof may be utilized to obtain the maximum possible area for economical moisture diffusion rate. A spring 6 adjustable icy nut I6 acts as a bias against the weight of the moisture adsorbent material .4. The switch actuator bar I'I, held'within limit stops I8 and I8 operates a low weight differential switch 1, of any well-known design, by depressing pin I9.

Referring to Figure-2, it will be seen that closing of the contacts I I of the switoh 'l placesthe motor 9 and 'heatingelement Illacross the electrical power line.

Referring again to Figure '1, it will besee'n thatin the static condition, the moisture of the air within the chamberI to be dehumidified-permeates'through the moisture-porous windows 2 lodged within the casing 3 of the space dryer unit; The purpose of these moisture-porous membranes is to permit the air contained in'the instrument housing I which is to be dehum'idifiedpto enter the space dryer unit during the static condition of operation, while acting during ther'eactivation cycle, as a baffie against the purging of reactivating air which may be as high as 100% relative humidity and inhibiting itfrom enteringthe free air space" of the casing I.

In the static condition, the weight of the moisture adsorbent material 4, contained within the perforated housing 5, is very delicately-balanced against the bias of spring 6, adjustable by-nut I6,'and'is insuificient toactuate the switch I. When, however, the dehumidifying unit is ready for reactivatiomi. e., when the moisture adsorbent-material has taken up suflicient water to overcome the bias of the spring 6, the weight of the moisture adsorbent material 4 causes the switch actuator or bar I! to operate the switch 1 by depressing pin I9. This initiates the reactivation cycle.

As seen in Figure '2, the'contacts II of the switch 1 when closed, make the electrical circuit to the motor- 9 and heating elements It). As seen Figure 1, heating elements I0, embedded within the moisture adsorbent material 4,serv'e to evaporate moisture from the "moisture adsorbent material during the reactivation process. Blower 8, when operated by motor 9, causes purging air to be drawn into the unit through inlet port I2, conduit I4, and port I5 which communicates with the dehumidifier unit. The immediate efiect of the flow of air is a pressure drop in'the port-"15 and in the interior of the casing '3. The purging'air circulates through the casing 3 taking up moisture vapor which is lbeing liberated from the porous housing 5 and is then drawn through the blower 8 and is forced from the blower outlet into a conduit (similar to conduit 14) which leads to the reactivation air outlet (not shown) to exhaust into the outer atmosphere, leaving the moisture adsorbent material I purged of moisture and then ready for another cycle of static drying operation. The reason whythe purging'air and its moisture content do not migrate reversely through the membranes 2 is that the slight pressure drop inside of the casing 3 prevents it. The-pressure in the-cabinet-would be substantially that of the external atmosphere so that-ifany migration takes place during purging it would -be I from the cabinet I, through the membranes 2 into the easing-'3. It WiHIlOW beolearthat the nextcycle is-initiated by the openingof the-contacts II of switch 1, since the weight of the reactivated moistureadsorbent material is now insufficient to overcome-the bias of the'sprin'g Ii. The operation of the motor 9 for the blower 8 and -the heating of element lfl'is now stopped andthe dehumidifier unit is ready for "another stage of dehumidification.

The length of'the conduit "I4, and its equal (not' shown) "at the blower exhaust "should "be very largein'relation to their internal diameter. Aratio of 'length 'todiameter of-40 m1 is preferable,"inorder thatmoisture vapor is inhibited from entering'the space of the cabinet I, 'from the outer atmosphere-during the static drying phase and that, during-the reactivation phase, free'entry andpassageotpurging air through the "space dryer'unit may 'be' permitted.

An "added and -useful purpose is provided by thec'onduit I4and itsequal at the blower exhaust, wherein they permit free breathing of the cabinet, "during "diurnal temperature change, thereby "permittinggreat simplification in the design "of *such "cabinet, packing,- access door sealsfetc. 'In addition, such breathing action forcesthe exchanged air to pass-either through or adjacent to the body "of "moisture "adsorbent material' lfwhich thereby takes upexcess moisture from ":the air 'entering "the "cabinet I "and later "discharges it by the reactivation process previously described.

i In contemplationof the "use of "this invention for thoseapplications requiring control of-the relative humidity within "a specified range, a spring adjustment I6 "shown on the control switch "I in'Figure 1 "may be utilized-to set in a'dvance'the'desired humidity level. This featureis based nponthekriotvn characteristic of silica gel to adsorb'amamount'of moisture dependent upon "the relative humidity of "the air surrounding it. For example, suppose that the adjusting nut' ispresent'to close the switch contacts at 5.2 pounds total" weightjor 4poundsdry weight plus 'lizpo'unds of moisture. The latter corresponds to the saturation value or an equilibrium conditiondfsilica-gel' at 50%RH. Now suppose that dehumidification of the space in the cabinet starts "with the RH level at 70 When moisture adsorption by the desiccant reaches 1.2 pounds, reactivation will automatically take place and reduce the adsorbed weight 02. (the switch operating difierential) thereby permitting the desiccant to take up more moisture and further reduce the RH of the space. It may take one or more steps of operation for the unit to bring the RH of the space down to 50% and when this is reached the unit will continue to operate the desiccant at saturation corresponding to 50% RH with occasional reactivations, depending upon the rate of ingress of moisture to the housing. Other levels of relative humidity may be obtained by presetting the pointer 20, to a desired value shown on the graduated scale 2|.

It is clear that various modifications in construction and arrangement of parts may be made without departure from the spirit and scope of the present invention and the invention is not therefore limited by the illustration of the specific preferred example or otherwise than by the appended set of claims.

The invention herein described may be manu factured and used by or for the Government of the United states of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. A dehumidifying apparatus comprising in combination, an outer casing having a plurality of moisture-pervious membranes, an inner perforated housing, means movably supporting said housing, a body of moisture adsorbent material contained within said inner perforated housing, a blower having associated air conduits communicating with said outer casing for passing a stream of air between said casing and housing for purging said moisture adsorbent material, heating elements associated with said body for drying said body, and an adjustable automatic electric control mechanism, substantially instantaneous in operation, said mechaanisin being operable by said supporting means when moved in response to variations in the weight of the moisture content of the adsorbent material at various relative humidities for controlling the operation of said blower and heating elements.

2. The combination defined in claim 1 above wherein said conduits are characterized further,

in that their length is at least forty diameters, whereby to inhibit moisture intrusion into said casing.

3. Dehumidifying apparatus comprising a unit installable in a substantially closed cabinet, a desiccant for abstracting the moisture from the air in the cabinet, means for periodically flooding the desiccant in a purging air current from a source external to the cabinet and at a pressure lower than that of the cabinet, and an enclosure for the desiccant located in the cabinet, partly guiding the air current and having at least one membrane allowing slow migration of moisture in one direction to the desiccant at cabinet air pressure but acting as a barrier to reverse migration from the desiccant enclosure to the cabinet.

4. Dehulmidiiying apparatus comprising a cabinet subject to a humid air content at atmospheric pressure, conduits and means for producing in one of its components a current of external purging atmospheric air at reduced pressure, a desiccant in the cabinet, and means enclosing the desiccant, being in communication with the conduits and having at least one membrane penetrable by the cabinet moisture at its atmospheric pressure but resisting reverse penetration by moisture because of the reduced pressure in said one conduit component during purging.

5. Dehumidifying apparatus comprising a casing adapted to be installed in a cabinet, intake and exhaust conduits communicating with the interior of the casing and leading to remote points of atmospheric air entrance and discharge, the discharge conduit containing a motor-operable blower for inducing a current of atmospheric air through the casing to purge it, at least one moisture-porous membrane constituting rpart of the casing, being penetrable by static water vapor ambient in the cabinet but becoming a barrier to the reverse migration of water vapor during purging, a desiccant in the casing and having an embedded heating coil, said desiccant adsorbing the penetrant water vapor but yielding its excess to the purging current, an anchored spring suspending the desiccant, said spring expanding and contracting with the accretion and loss of water by the desiccant, and an electrical circuit con-. taining the blower motor and the heating coil, and having a switch subject to closing and opening as the spring expands and contracts.

6. Dehumidiiying apparatus comprising inlet and outlet conduits arranged to establish proxi mate and remote ends, said conduits being of a. high iength-to-diameter ratio to inhibit the entry of external atmospheric air at the remote ends during the static condition of the apparatus, a casing with which the proximate ends of the conduits are connected to provide intake and outlet ports, said casing being installable in a cabinet the atmosphere of which is to be controlled as to moisture content, a blower connected to the outlet port and having a motor for driving it to set up a purging lair current and a pressure drop in the ports and casing due to the length of the inlet conduit, a desiccant located in the casing and having an embedded heating coil in electrical connection with the blower motor, suspension means for the desiccant yielding to an increase of desiccant weight upon its accretion of moisture during said static condition and contracting by reduction of said weight upon the loss of moisture by action of said purging air current, switch means set in operation by yielding of said suspension means to activate the motor and heating coil, and at least one membrane set in the casing, yielding to a slow migration of moisture from the cabinet to the desiccant during, pressure equalization in the cabinet and casing when the apparatus is static but becoming a barrier to return migration of moisture during purging because of the pressure differential in the cabinet and easing.

7. Dehumidiiying apparatus comprising the combination of a cabinet the atmosphere of which is adapted to be limited as to moisture content, a desiccant to adsorb moisture from said atmosfphere, said desiccant having a heating coil embedded therein, a casing in which the desiccant is situated, said casing sheathing the desiccant from the cabinet atmosphere excepting for at least one membrane window through which the moisture is permeable toward the desiccant, supporting means by which the desiccant is sustained in the casing, said supporting means including a spring inherently yieldab-le to predeterminedly low gain and loss of moisture by the desiccant, and having means for its adjustment so that the yielding of the spring can be adjusted to any setting in an adopted range of probable moisture gain by the desiccant, intake and exf tecommunicaltingwithzthelinterior bfithenasingeatad: leadingzto: remotezpointxofatmospherimzair-zentrance..:anda.diseharge, aicmotoroperableiblowerzintm exhaust-conduit, and. a.

' switcn embodiediinsaid supporting mea-ns,'.rbeing connectedwith e; source of-aelectricaicnrrent and with Lthe heating n coil :and blower motor, said swlteh being operable-by movement of the desiccant-mpon-xgainor loss of moisture in low.- incrementsl'at any setting-of the spring.

A dehumidifyi-ng apparatus adapted to be contained -'wibh-in-a, cabinet, said apparatus inblu'dmg -an outer casing having a plurality of moisture-pervieus membranes; aperforated hous- 'ing within said'casing, a body of moisture adsorbant mmaterial contained within said1 periomted housing; and conduits connecting with said casinQfor-oirculating atmospheric air through-maid oasingtojpermitbreathingof- [atmospheric airinto and ouvof said cabinet through said; membranes.

9. The combination" defined in e1aim'8;wherein thewonduit openings to. said outer easing-are REEERENG S CITE