Abstract:
Humidity within the workspace of a cryogenic aerosol spray cleaning system is controlled by circulating the workspace atmosphere through a dehumidifier. Advantageously, the need for purging of the workspace atmosphere prior to each cleaning cycle is eliminated. A system and method are thereby provided for cleaning of large workspaces. The system amd method of the invention are especially well-suited, economical, and practical for cleaning operations in which a dry air or inert gas purge of a large volume cleaning chamber would be impractical.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a division of U.S. patent application Ser. No. 09/150,441, filed on Sep. 9, 1998, and now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to cryogenic cleaning systems, and more particularly, to a system and method for controlling the humidity within the workspace of a cryogenic aerosol spray cleaning system by circulating the workspace atmosphere through a dehumidifier to eliminate the need to purge the workspace prior to each cleaning cycle. 
     2. Description of the Prior Art 
     Precision cleaning using solid, liquid, or gaseous carbon dioxide, or other cryogenic based cleaning materials and methods, including mixed carbon dioxide 20 phases, solid or liquid argon sprays, liquid nitrogen sprays, and even ice (H 2 O), or combinations of these materials and methods, has been disclosed by patents and prior art publications. The cryogenic spray cleaning technologies disclosed by the prior art have evolved in response to many commercial, industrial, and practical concerns, including environmental concerns, and the need for better and more effective cleaning methods for both particle and organic-based contamination. 
     Carbon dioxide snow cleaning was first disclosed by S. A. Hoenig around 1985. The process typically involves cleaning, using a source of fluid (i.e., liquid or gaseous) carbon dioxide provided at a certain enthalpy condition (i.e., temperature and pressure). Such liquid carbon dioxide (or gaseous carbon dioxide if proper adiabatic conditions are met by the nozzle design) is passed at high velocity through an orifice of a spray nozzle. Upon exiting the orifice, a stream of dry ice particles having varying sizes and densities and traveling at varying velocities is directed at a workpiece for removal of contaminates deposited on a surface thereof. The stream of dry ice particles may be combined with CO 2  gas, nitrogen or other dry gases to boost 10 the dry ice velocity. 
     Another form of cryogenic cleaning uses macroscopic CO 2  pellets and was first described by Rice et al. in U.S. Pat. No. 3,676,963, and by Fong in U.S. Pat. No. 4,038,786. This snow cleaning method feeds dry ice pellets into a dry carrier gas stream such as nitrogen or dry compressed air, at a pressure typically in the range of between 40 and 300 psi and possibly greater. The dry ice pellets are accelerated toward the surface of a workpiece at such high velocity that even thick coatings such as paint can be removed. 
     One limitation in cryogenic spray cleaning methods is the fact that extremely cold streams (e. g., typically −60° C. for carbon dioxide snow cleaning) of cleaning medium are applied to the surface of the workpiece being cleaned. Consequently, when the cleaning processes are conducted at room temperature, or in any unsealed and uncontrolled environment, condensation can form on the workpiece surface being cleaned, or on the spray nozzle. The moisture condensation, present as water, frost, or ice, interferes with and impedes the cleaning process. Prior art attempts to eliminate moisture include direct heating, heating with blanketing gases or heating only specific portions of the surface of the workpiece, insulating the cleaning chamber, cleaning in vacuum environments, purging with nitrogen, air or other dry inert gases, purging using specially constructed chambers, and other methods utilized to produce dry environments. 
     Patents directed to clean and dry chambers for cryogenic spray cleaning systems and methods typically include vacuum chambers and/or require purging a clean dry box with a dry inert gas. For example, U.S. Pat. No. 4,631,250 to Hayashi was the first to mention indirectly the need for a sealed chamber for a cleaning system that had mixed CO2 and nitrogen for cleaning a wafer surface. The sealed chamber included a vacuum exhaust line for removal of contaminants. Of course, a vacuum environment also assists in moisture reduction. 
     Another attempt to control the humidity in the cleaning chamber of a cryogenic cleaning system is disclosed in U.S. Pat. No. 5,316,560 to Krone-Schmidt et al. This patent discloses purging an enclosed space (i.e., a cleaning chamber) with dry nitrogen gas to control the humidity within the chamber. Essential to this system is the chamber within a chamber design having a purged airlock between the enclosed interior cleaning chamber and the exterior of the system. The system disclosed by this reference requires lengthy purge times to dry out the cleaning chamber before initiation of a cleaning cycle, and may therefore not be practical for cleaning a large workpiece in a large volume cleaning chamber. 
     In U.S. Pat. No. 5,315,793 to Peterson et al., an apparatus for precision cleaning using CO 2  snow or other cryogenic sprays is disclosed. The apparatus disclosed is intended only as a final cleaning station and has some design features in common with U.S. Pat. No. 5,316,560. The dryness of the sealed chamber is maintained by vacuum or by an external inert gas purge. The preferred method for maintaining a dry environment involves pumping out and then back-filling the chamber with a dry gas after each cleaning cycle, i.e., to purge the cleaning chamber. 
     Cryogenic argon spray cleaning developed as an alternative to CO 2  snow cleaning. Cryogenic argon spray cleaning, and, in parallel, cryogenic nitrogen spray cleaning, were first mentioned in U.S. Pat. No. 5,062,898, and later in U.S. Pat. No. 5,294,261, and still further developed in U.S. Pat. No. 5,209,028, all to McDermott et al. These patents disclose the nozzles and cleaning stations for cryogenic argon spray cleaning, and methods and procedures for ensuring a dry cleaning station based upon a flush gas for removal of contaminants. 
     Further developments in cryogenic argon spray cleaning are disclosed in U.S. Pat. No. 5,486,132 to Cavalier et al. and in U.S. Pat. No. 5,366,156 to Bauer et al., wherein argon spray cleaning methods and apparatus are extended to include cryogenic nitrogen or mixed argon and nitrogen. These patents also clearly discuss means to reduce and prevent moisture condensation from forming on the apparatus, nozzles, argon or nitrogen lines, and on the workpiece surface to be cleaned. 
     Moisture elimination methods discussed and claimed included purge means, such as dry gas purge methods with purge ports and purge gas sources, providing a vacuum about the cryogenic argon lines and nozzle, providing thermal insulation and barriers and positive pressure within the enclosures, and other suggestions unrelated to the present invention. 
     A means for eliminating moisture in a CO? dry ice pellet system cleaning apparatus is disclosed in U.S. Pat. No. 5,651,723 to Bjornard et al. The apparatus disclosed therein includes separate load locks for loading and unloading a workpiece, a cleaning chamber between the two load locks, and the necessary equipment to provide airflow through the cleaning chamber and apparatus and to purge the cleaning chamber. Dry compressed air is required for accelerating the dry ice pellets only. A dry environment was ensured in the load locks by purge methods and all chambers were kept at positive pressures to keep moisture out. 
     Systems and apparatus for maintaining a dry and clean manufacturing environment abound within the electronic, chemical and pharmaceutical industries. However, none of the known systems, apparatus, methods, processes, etc. use a dehumidifier in conjunction with a cryogenic spray cleaning process to control the humidity within a cleaning chamber, thereby obviating the need for time-consuming and expensive purging of the cleaning chamber. For large cleaning chambers, purging as a means for controlling humidity within a cleaning chamber becomes cost-prohibitive, and therefore, commercially impractical. 
     The present invention overcomes the shortcomings of the prior art by providing a system and method for controlling the humidity within the workspace of a cryogenic aerosol spray cleaning system by circulating the workspace atmosphere through a dehumidifier placed in the airflow path of the cleaning system. The present invention obviates the need to purge the workspace atmosphere at any time during a cleaning cycle and further eliminates the need to provide a sealed cleaning chamber. The present invention provides for rapid moisture removal from the workspace atmosphere and for dehumidifying the entire atmosphere in a relatively short period, typically approximately two minutes. This, in turn, leads to increased productivity for the cryogenic cleaning system. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system and method for controlling the humidity within the workspace of a cryogenic aerosol spray cleaning system by circulating the workspace atmosphere through a dehumidifier to eliminate the need to purge the workspace prior to each cleaning cycle. The system and method of the present invention are especially well-suited, economical, and a practical necessity for cleaning of large workpieces, where a dry air or inert gas purge of a large volume cleaning chamber, as required by prior art methods and apparatus, would be impractical. 
     Prior art systems and methods for controlling the humidity in a cryogenic cleaning system require time-consuming inert gas purges, expensive vacuums or other means, most all in conjunction with load locks. On the other hand, the present invention eliminates the need to purge the cleaning chamber workspace and produces a dry, cleaning environment quickly and economically. The present invention also eliminates the need to provide a sealed cleaning chamber and to provide load locks at the input and output sides of the cleaning chamber; all directed to maintaining a clean and dry environment within the cleaning chamber. The workspace atmosphere is cycled through the dehumidifier many times a minute to insure a fast dry out time. 
     An integral aspect of the humidity control system of the present invention is the handling of the gaseous and particulate constituents, i.e., moisture and particulate matter, present in the atmosphere within the cleaning chamber workspace. More specifically, cryogenic snow cleaning requires a virtually moisture-free and particle-free workspace atmosphere within the cleaning chamber. The present invention satisfies this requirement in a manner not disclosed or suggested by the prior art. 
     The humidity control system of the present invention incorporates a dehumidifier into at an airflow path defined through a cryogenic aerosol spray cleaning system including a cleaning chamber having a workspace defined therein. 
     The workspace atmosphere is continuously or intermittently circulated through the dehumidifier to remove moisture before, during, and/or after a cleaning cycle. An optional HEPA filter may be provided in the airflow path to remove particulate contaminants from the workspace atmosphere. A secondary airflow path may be defined through the cleaning system through which a portion of the workspace atmosphere is continuously or intermittently circulated. The dehumidifier and optional HEPA filter are located in the secondary airflow path to remove moisture and particulate contaminants from the workspace atmosphere. 
     The present invention is directed to a method for controlling the humidity within a cleaning chamber of a cryogenic cleaning system. The cleaning chamber has a workspace defined therein within which a workpiece may be removably placed for cryogenic cleaning during a cleaning cycle. The workspace has a partly gaseous (defined hereinafter) atmosphere therein and the cleaning system has an airflow path defined therethrough. The method of the present invention comprises the step of circulating the workspace atmosphere through a dehumidifier of an air handling system located in the airflow path for removing moisture from the gaseous part of the workspace atmosphere to reduce the humidity in the workspace atmosphere without having to purge the workspace prior to the initiation of a cleaning cycle. 
     The present invention is also directed to a humidity control system for a cleaning chamber of a cryogenic cleaning system. The cleaning chamber has a workspace defined therein within which a workpiece may be removably placed for cleaning during a cryogenic cleaning cycle. The workspace has a partly gaseous atmosphere therein and the cleaning system has an airflow path defined therethrough. 
     The cryogenic cleaning system further includes a spray nozzle located within the cleaning chamber and connected to a cleaning media source for producing a stream of solid or liquid cryogenic spray entrained by a gas phase for cryogenically cleaning the workpiece during a cleaning cycle. The humidity control system comprises a dehumidifier of an air handling system located in the airflow path and through which the workspace atmosphere is circulated for removing moisture from the gaseous part of the workspace atmosphere to reduce the humidity in said workspace without having to purge the cleaning chamber prior to initiation of a cleaning cycle. 
     The humidity control system of the present invention may be used in an automated or manual cryogenic cleaning system. For automated systems, motion control equipment may be included in the workspace to manipulate the workpiece (e.g., movement into and out of the workspace and manipulation therein) and cleaning components (e.g., spray nozzles). For manual cleaning systems, a glove port may be provided on a front side of the cleaning chamber through which access to the workpiece and cleaning components is provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be more fully understood and further advantages will become apparent when reference is made to the following detailed description of the preferred embodiments of the invention and the accompanying drawings in which like reference characters denote similar elements throughout the several views and wherein: 
     FIG. 1 is a schematic block diagram of a humidity control system having a dehumidifier connected in series with a primary airflow path and constructed in accordance with the present invention; 
     FIG. 2 is a schematic block diagram of a humidity control system having a dehumidifier connected in series with an secondary airflow path which runs parallel to a primary airflow path and constructed in accordance with the present invention; 
     FIG. 3 is a detailed view of the humidity control system of FIG. 1; 
     FIG. 4 is a detailed view of the humidity control system of FIG. 2; 
     FIG. 5 is a front view of a preferred embodiment of a cryogenic aerosol spray cleaning system having an air handling system including a dehumidifier and constructed in accordance with the present invention; 
     FIG. 6 is a side view taken along the ling A—A of FIG. 5; and 
     FIG. 7 is a side view of a hand-held cryogenic cleaning system having a humidity control system constructed in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides a system and method for controlling the humidity within the workspace of a cryogenic aerosol spray cleaning system. By continuously or intermittently circulating at least a portion of the workspace atmosphere through a dehumidifier, the present invention eliminates the costly and time-consuming practice of purging the workspace before each cleaning cycle to ensure a dry environment within the workspace. Also eliminated by the present invention is the need for load locks at the ingress and egress points of the cleaning chamber and the need to provide an airtight or sealed cleaning chamber. Workpieces of all sizes may now be cleaned virtually without regard for the time-constraints that heretofore have accompanied purging of large volume cleaning chambers. Quite simply, the system and method of the present invention significantly improve the performance, robustness, and operation of cryogenic aerosol spray cleaning systems. 
     Referring to the drawings, in FIGS. 1 and 3 there is shown a first embodiment of a humidity control system  10  for use in a cryogenic aerosol spray cleaning system  100  (see FIG. 6) and constructed in accordance with the present invention. The humidity control system  10  includes a cleaning chamber  20  that defines a workspace within which a workpiece  70  (not shown in FIG. 1) may be cleaned using virtually any precision cleaning process and preferably, a cryogenic aerosol spray cleaning process (i.e., snow cleaning). While carbon dioxide snow is the preferred cleaning medium, argon, nitrogen, dry ice pellets, and combinations thereof may also be used in connection with the present invention. The workpiece  70  is placed into and removed from the cleaning chamber  20  by automatic or manual means, preferably through a chamber door  28 , which may or may not make an airtight seal with the chamber, r front surface  32 . The atmosphere within the workspace  22  comprises air, or some other inert gas or combination of gases and various particulate matter. The atmosphere is continuously or intermittently circulated through the humidity control system  10  (i.e., through the cleaning chamber  20  and through the workspace  22 ) over a primary airflow path  24 . 
     As used herein, the terms “atmosphere” and “partly gaseous atmosphere” refer to the gaseous and particulate contents of the workspace  22 . It will be obvious to persons skilled in the art that the workspace atmosphere may consist of various inert gases, either singularly, or in combination, and that the term “atmosphere” is used for ease of discussion and is in no way a limitation of the present invention. The term “air” is used generally herein to refer to the workspace atmosphere as it travels over the primary and secondary airflow paths  24 ,  26 , as it moves through the air handling system  140 , and as it otherwise travels through the various tubes, pipes, conduits, openings, and other liquid transport means of a humidity control system  10  and of a cryogenic cleaning system  100 . 
     The cleaning chamber  20  includes a particulate filter assembly  40  having a particulate filter  42 , preferably a HEPA filter, and a blower  44  that facilitates circulation of air over the primary airflow path  24  and of the workspace atmosphere within and through the workspace  22 . Ductwork  46  spreads the dry air uniformly as it enters the workspace  22 . The output of the filter assembly  40  is clean, dry, and particle free, providing an ideal atmosphere for cryogenic cleaning. 
     A seal, which may or may not be airtight is created between the door  28  and a front surface  32  of the cleaning chamber  20  by a gasket  34 , O-ring or other generally pliant or sealing material to minimize leakage about the door  28 . The door  28  may include a glove port  36  having two gloves (not shown)that facilitate insulated communication with the workspace  22  and permit manual manipulation of a workpiece  70  or other cleaning equipment located within the workspace  22 . The glove port  36  is typically provided for manually operated cryogenic cleaning systems  100 . When a humidity control system  10  in accordance with the present invention is configured for automatic operation (as described in detail below), a glove port  36  is not provided in the door. 
     The bottom  54  of the cleaning chamber  20  includes at least one chamber output port  50  through which the workspace atmosphere exits the cleaning chamber  20 . An optional prefilter  58  may be provided at the output port  50  for removing particulate matter from the workspace atmosphere before it enters the air handling system  140 . Of course, more than one output port  50  may be provided, with prefilters  58  as required. 
     The air handling system  140  comprises a section of the primary airflow path  24  and includes a blower  144  or other gas moving device, a particulate filter  142 , preferably a HEPA filter, and a dehumidifier  150 . In FIGS. 1 and 3, the blower  144  is located at the air handling system input  146 , the HEPA filter is located at the air handling system output  148 , with the dehumidifier  150  fluidly connected therebetween. It will be obvious to persons skilled in the art that the components of the air handling system  140  may be arranged and connected in a variety of ways, in accordance with the scope and spirit of the present invention; as long as at least a portion of the workspace atmosphere is directed through the dehumidifier  150 . When connected as shown in FIGS. 1 and 3, moist air exits the cleaning chamber  20  and enters the air handling system  140  via an input port  146 . The blower  144  facilitates continuous movement of the air through the air handling system  140  and directs the moist air to the dehumidifier input port  152 . Moisture is removed from the air and ported out of the humidity control system  10  via a dehumidifier exhaust port  156 . Dry air exits the dehumidifier via a dry air output port  154  and is directed into the HEPA filter  142 , where particulate matter is trapped and removed from the dry air. Clean dry air is now returned to the cleaning chamber  20  (i.e., to the workspace  22 ) via an air handling system output port  148 . In FIG. 1, a primary airflow path  24  is defined through the humidity control system  10  which flows, in its entirety, through the air handling system  140  and dehumidifier  150 . Thus, the dehumidifier  150  is placed in series with the primary airflow path  24  of the humidity control system  10 . 
     The dehumidifier  150  may be either a membrane or desiccant type, such as the Cargocaire model “HC-150” manufactured by Munters, the specification of which is incorporated herein by reference. As used herein, the term “dehumidifier” refers to any device, component, system, etc., that receives a moisture carrying or a moisture laden gas, removes moisture from the gas, exhausts the removed moisture, and outputs a dry gas. The preferred dehumidifier  150  should be powerful enough to recirculate the workspace atmosphere between approximately two and four times per minute. However, the capacity of the dehumidifier  150  depends in part on the volume of the workspace  22  and the present invention is not limited or otherwise defined by the capacity of the dehumidifier  150 . 
     There are two outputs from the dehumidifier  150 : an exhaust port  156  and a dry air output port  154 . The exhaust port  156  provides the path through which moisture enriched air or gases from the workspace  22  are channeled out of the humidity control system  10  and preferably out of the cryogenic cleaning system  100 . The exhaust port  156  also serves as an exhaust line for any over-pressurization that exists within the cleaning chamber  20 . A filter (not shown) may be provided at the exhaust port  156  and located within the cleaning chamber  20 . Anywhere along this exhaust and vent route defined by the exhaust port  156 , filters, scrubbers, or any other necessary environmental units can be installed. 
     In a second embodiment of the present invention shown in FIGS. 2 and 4, primary and secondary airflow paths  24 ,  26  are defined within the humidity control system  10 . The primary airflow path  24  flows through the workspace  22  and also through a conduit or channel  30  defined adjacent thereto. Preferably, less than 100% of the workspace atmosphere (i.e., the volume of air in the workspace  22 ) flows through the conduit  30 , with the remaining atmosphere flowing through the air handling system  140  over the secondary airflow path  26 . Preferably, a minimum 10%, and more preferably 20%, of the volume of workspace atmosphere flows over the secondary airflow path  26 , although this amount may vary. The blower  44  of the particulate filter assembly  40  primarily facilitates the movement of the workspace atmosphere over the primary airflow path  24 , while the blower  144  of the air handling system  140  facilitates the movement of air over the secondary airflow path  26 . Air exits the workspace  22  and enters an uptake region  60  defined therebelow. From the uptake region  60 , the airflow through the cleaning chamber  20  is divided between the primary airflow path  24  and the secondary airflow path  26 . The air flowing over the primary airflow path  24  flows through the conduit  30  and is drawn into the workspace  22  by the blower  44  of the filter assembly  40 . The air flowing over the secondary airflow path  26  is drawn through the dehumidifier  150  (i.e., through the air handling system  140 ). Air Bowing over the secondary airflow path  26  re-enters the cleaning chamber  20  and the workspace  22  through the chamber input port  52  and is directed through the workspace  22  by the blower  44 . 
     Referring to FIGS. 5 and 6, there is shown a preferred embodiment of the invention. The cryogenic cleaning system  100  of this embodiment is constructed for automated cleaning and generally includes a controller section  80  and a cleaning section  90  comprising a humidity control system  10  including a cleaning chamber  20  and an air handling system  140 . The controller section  80  houses the electrical, mechanical, and electro-mechanical components for the cryogenic cleaning system  100 . In this embodiment, the controller  80  includes a plurality of cabinets which house control circuitry, robotics, cleaning medium sources and spray devices, etc. 
     The cleaning chamber  20  is generally a rectangular cube that is sized and shaped to accommodate large workpieces  70  such as, for example, long glass tubes. The cleaning chamber  20  may include components for automatic loading and unloading of the workpiece  70 , components  92  for automatically moving the workpiece  70  within the workspace  22 , components  94  for automatically cleaning the workpiece  70  using a cryogenic aerosol spray cleaning process including a spray nozzle connected to a cleaning media source  98  (e.g., carbon dioxide), and any other components necessary for performing any other functions or operations related to the cryogenic cleaning process. 
     At least one chamber output port  50  is provided in the chamber bottom  54  to permit the workspace atmosphere to pass out of the cleaning chamber  20  and through to the air handling system  140 . The output port  50  may be equipped with a prefilter  58  to remove contaminants from the workspace atmosphere as it exits the cleaning chamber  20  and enters the air handling system input port  146 . The moisture- and particle-laden air is drawn through the air handling system  140 , at least in part, by the blower  144 . The air enters the air handling system  140  through air handling system input port  146  and passes directly into the dehumidifier  150  via the dehumidifier input port  152 . 
     There are two outputs from the dehumidifier  150 : an exhaust port  156  and a dry air output port  154 . The exhaust port  156  provides the path through which moisture enriched air or gases from the workspace  22  are channeled out of the humidity control system  10  and preferably out of the cryogenic cleaning system  100 . The exhaust port  156  also serves as an exhaust line for any over-pressurization that exists within the cleaning chamber  20 . A filter (not shown) may be provided at the exhaust port  156  and located within the cleaning chamber  20 . Anywhere along this exhaust and vent route defined by the exhaust port  156 , filters, scrubbers, or any other necessary environmental units can be installed. 
     Dry air exits the dehumidifier  150  via the dry air output port  154 , and is drawn through the blower  144 , and into the HEPA filter  142 . Clean dry air is output from the air handling system  140  via the air handling system output port  148  and is returned to the cleaning chamber  20  via cleaning chamber input port  52  to provide a clean, dry workspace atmosphere. The blower  144  also boosts the velocity of the return airflow into the cleaning chamber  20 . The blower  144  is preferably a high capacity air movement device designed to create a certain flow rate of clean dry air into the cleaning chamber  20 . The HEPA filter  142  is optional, but recommended for most cleaning operations. 
     The bottom  54  of the cleaning chamber  20  may be perforated and configured to support the components  92  for automatically moving the workpiece  70 . The cleaning chamber back wall  62  extends down to the bottom  54  of the cleaning chamber  20 , as shown in FIG.  6 . Located beneath the chamber bottom  54  is the uptake region  60  which is fluidly connected to the conduit  30  and which together define a portion of the primary airflow path  24 . It can be seen in FIG. 6 that the conduit  30  is adjacent to and extends generally vertically behind the workspace  22 . The workspace atmosphere is drawn through the conduit  30  and up behind the cleaning chamber  20  by the blower  44  of the filter assembly  40 . This recirculated air passes through the HEPA filter  42 , into the ductwork  46 , and back into the workspace  22  where it blends with the clean dry air from the secondary airflow path  26 . 
     A second airflow path  26  is provide in parallel with the primary airflow path  24 . The air handling system  140  is provided in the second airflow path  26  and at least a portion of the workspace atmosphere is either continuously or intermittently directed along the second airflow path  26 . In this way, moisture and particulate matter are removed from the workspace atmosphere. 
     Another feature of the humidity control system  10  of this embodiment is the door  28 . Since the embodiment shown in FIGS. 5 and 6 is constructed for automated cryogenic cleaning of a large, long workpiece  70 , the door  28  must permit for the entry and exit of such a large workpiece  70 . As such, there are rails (not shown along which the door  28  may be guided generally in an up and down direction. The rails are designed such that when the door reaches a closing height, it is automatically forced toward the cleaning chamber front surface  32 , and sealed thereto by the gasket  34 . The large size of the door  28  prevents the formation of an airtight seal between the door  28  and front surface  32  of the cleaning chamber  20 . However, this will not affect the performance or operation of the humidity control system  10  of the present invention because the dehumidifier  150  will remove any moisture entering the cleaning chamber  20  through the door  28 . 
     In operation, the humidity control system  10  of the present invention circulates the entire workspace atmosphere between two and four times per minute. This may be continuous or intermittent, as a matter of design choice. For continuous circulation, the workspace atmosphere is quickly dehumidified when a new workpiece is placed in the cleaning chamber  20  for cleaning. In situations where the cleaning chamber  20  is not sealed against an outside environment, the humidity control system  10  of the present invention removes any moisture in the workspace atmosphere introduced from the outside environment. 
     The present invention may also be applied to portable cryogenic cleaning systems, such as depicted in FIG. 7, where a hand-held cleaning chamber  20  connects to a humidity control system  10  for controlling the moisture content in the atmosphere within the workspace  22 . One side of the cleaning chamber  20  is substantially open and may be placed over a workpiece  70 . Cryogenic cleaning of the workpiece  70  is effected using a spray cleaning nozzle  96  connected to a cleaning media source  98  (not shown in this figure). The humidity control system  10  draws the workspace atmosphere out of the workspace  22  through a chamber output port  50 . The humidity control system  10  includes a dehumidifier  150  through which the workspace atmosphere flows and which removes moisture from the workspace atmosphere. A HEPA filter  142  may be included in the humidity control system  10  for removing particulate matter from the workspace atmosphere. A blower  144  is provided in the humidity control system  10  to drawn the moisture- and particle-laden workspace atmosphere out of the cleaning chamber through output port  50 . The blower  144  also directs clean, dry air back into the workspace through chamber input port  52 . 
     While the various cleaning chamber  20  embodiments shown in the figures and discussed herein were either generally rectangular cubes, enclosed on all sides, or generally rectangular cubes having an open side, it will be obvious to persons skilled in the art that these are not limitations of the present invention but rather, merely illustrative examples of preferred embodiments of the present invention. The humidity control system  10  of the present invention is not restricted to such cleaning chamber  20  geometries. Therefore, cleaning chambers  20  having various other geometries and having openings, doors, loadlocks, etc., are also contemplated by the present invention. 
     The present invention provides a humidity control system  10  for cryogenic aerosol spray cleaning systems that continuously or intermittently circulates the workspace atmosphere through a dehumidifier, and then through an optional HEPA filter, to provide the clean and dry environment necessary for precision cleaning, in general, and specifically for cryogenic cleaning. Purging with dry gases or inert gases is no longer necessary. Load locks located at the ingress and egress locations of the cleaning chamber are also eliminated by the present invention. Furthermore, long dry out times for cryogenic cleaning chambers are no longer necessary with the humidity control system  10  of the present invention. The advantage of a dehumidifier also allows for simpler chamber design in that critical drying out of the cleaning chamber is not necessary—the dehumidifier performs the function of drying the chamber quickly. The actual drying out time is determined by the chamber volume, the extent on which the chamber is sealed, and the flow rates of the dehumidifier. 
     Having thus described the invention in rather fall detail, it will be recognized that such detail need not be strictly adhered to but that various changes and modifications may suggest themselves to one skilled in the art, all falling within the scope of the invention, as defined by the subjoined claims.