Patent Grant
8424317
This invention relates to a thermal insulation technique for ultra low temperature cryogenic processors.
Vacuum insulating panels are used conventionally for thermal insulation. Known vacuum insulating panels consist of a pre-compressed porous filling, a porous pressboard or an open-cell rigid foam as substrate, which is enveloped by a gas-tight film, wherein the film is heat-seated or bonded after the evacuation.
The following, for example, are used as filling materials for vacuum insulating panels: precipitated and dried silicas, silica gels, fly ash, open-cell foams on an organic base such as open-cell rigid polyurethane foams or bonded rigid polyurethane foam paste. Vacuum insulating panels of this type are used in the manufacture of cold rooms, e.g., refrigerators or refrigerated containers, with the latter being inserted between the outer and inner casing and the gap left between the outer and inner casing being filled with foam.
The fitting of the vacuum insulation panels into refrigerator casings nevertheless presents problems. According to the current state of the art, they are bonded onto a plate—for example, a metal cassette—by means of a double-sided adhesive film. This combination plate can then be processed further into a sandwich panel, for example, a refrigerator door, wherein the cavity left is conventionally filled with foam.
As a result, on the one hand, a complicated, multi-step process is required, and on the other hand, the insulation volume is affected by the foam, which is less efficient in insulation terms when compared with a vacuum insulation panel. Arrangements of this type are also, to only a limited extent, without thermal bridges.
U.S. Pat. No. 6,164,030 discloses an apparatus which consists of a rigid plate and a vacuum insulation panel, in which the vacuum insulation panel is fixed to the rigid plate by a polyurethane foam applied as a liquid reaction mixture, wherein the vacuum insulation panel contains open-cell rigid plastics foam and/or open-cell rigid plastics foam recyclate.
In a first aspect, systems and methods are disclosed to provide an ultra low temperature (ULT) cryogenic processor apparatus. The apparatus includes an external housing with flat sides; an inner housing coupled to the external housing to define a vacuum region there between; material disposed in the vacuum region to provide redundant insulation and structural support; and a cryogenic heat exchanger contained in the inner housing.
Implementations of the above aspect may include one or more of the following. The material can be an insulation material with one of: a silica micro balloon, polyisocyanurate. The vacuum region can be processed by removing residual water vapor and other partial pressure of contaminants. The vacuum region is evacuated to a partial pressure of approximately 0.2 milliTorr. The cryogenic heat exchanger can include one or more tubings and may include redundant tubings. The cryogenic heat exchanger can be U-shaped tubings covering at least three walls of the payload bay. The cryogenic heat exchanger can include tubings covering at least four sides of the payload bay. Alternatively, the cryogenic heat exchanger can be one or more coils positioned on the top and/or the bottom of the vessel. A port can connect to the one or more tubings to provide input and output connections thereto. A door can allow access to the payload bay, wherein the door comprises three or more materials having different thermal characteristics.
In another aspect, a method to provide ultra low temperature processing and/or storage includes providing insulation and structural support using a material disposed in a vacuum region between an external housing and an inner housing; and cryogenically processing one or more compartments contained in the payload bay.
Implementations of the above aspect may include one or more of the following. The material can be an insulation material with silica micro balloon technology. The process can remove water vapor, partial pressure contaminates and atmospheric gases from the vacuum region. The process includes evacuating the vacuum region to approximately 0.2 millitorr. The cryogenic heat exchanger can have one or more heat exchange tubings, and can include redundant tubings. The redundant tubings can be a complete set of heat exchange tubings operating in parallel with the primary heat exchange tubings. The redundant tubings can have one or more tubings branched from the primary heat exchange tubings. The cryogenic heat exchanger can also include U-shaped tubings covering at least three walls of the inner housing. The tubings can cover at least four sides of the inner housing. A door can be formed with a plurality of materials each having different thermal characteristics. A changeable rack assembly is supported in the chamber. The system can transmit energy from the payload bay into the heat exchanger through the changeable rack assembly. A negative pressure in the payload bay can be maintained through the use of pneumatic seals on the main door assembly. The cryogenics vacuum pumping via the heat exchanger can provide energy removal from the payload bay and into the heat exchanger. The surfaces of at least one of the external and inner housing can be flat surfaces.
In another aspect, a method to insulate a vessel includes placing a plurality of shells on all sides of the vessel without providing a direct energy pathway from outer walls of the vessel to the inner walls of the vessel; placing the shells under a vacuum; cryogenically cooling the shells to a cryogenic temperature; and while under vacuum, allowing the shell temperature to rise from the cryogenic temperature to ambient temperature.
Implementations of the above aspect may include one or more of the following. The process can include milling spaced-apart pathways in the shells. Such millings facilitate an evacuation of the trapped spaces of the shells and allowing for a desorbtion of a surface area of the shells. A vacuum pump can maintain a partial pressure of the vacuum in the vessel to below approximately 10 millitorr. The vacuum pump is a non-oil based pump. Initially, the process evacuates the shells to a total pressure of approximately 500 millitorr. The process then cryogenically cools the shells to a temperature of less than approximately −175° C. Next, gettered gases can be removed by a pseudo thermo/kinetic energy transfer during the rise to ambient temperature. The shells can be a foam material. The shell layout prevents heat gain energy from migrating from the outer walls to the inner walls by presenting at least two 90 degree flow pathway changes.
In another aspect, an insulated vessel includes outer walls; inner walls spaced apart from the outer walls to define a vacuumed insulation volume; and a plurality of shells placed in the insulation volume without providing a direct energy pathway from outer walls of the vessel to the inner walls of the vessel, wherein the shells are cryogenically cooled to a cryogenic temperature and while under vacuum, the shell temperature is raised from the cryogenic temperature to ambient temperature.
Implementations of the above aspect may include one or more of the following. Spaced-apart pathways can be milled in the shells. The pathways facilitate an evacuation of the trapped spaces of the shells and allowing for a desorbtion of a surface area of the shells. A vacuum pump can maintain a partial pressure of the vacuum in the insulation volume to below approximately 10 millitorr. The vacuum can be provided using a non-oil based pump. The pump can initially evacuate the insulation volume to a total pressure of approximately 500 millitorr. A cryogenic heat exchanger can cryogenically cool the shells to a temperature below approximately −175° C. Gettered gases can be removed by a pseudo thermo/kinetic energy transfer during the rise to ambient temperature. Each shell can be a foam material. The shells prevent heat gain energy from migrating from the outer walls to the inner walls by presenting at least two 90 degree flow pathway changes.
Advantages of the preferred embodiment may include one or more of the following. The system has a thermal insulation technique that combines a highly non-compressible foam and traditional vacuum processing techniques to produce a novel insulation technique. This technique can be used to reduce the heat gain properties of a low temperature vessels and allow for the manufacture of square, flat walled vacuum chambers that demonstrate no structural deformation or metal fatigue during the evacuation process. The theoretical R-value of this technique is greater then 100 as measured by the International System of Units—RSI.
In one embodiment, each foam piece is four inches thick and is made from a polyisocyanurate material. The vacuum vessel is made of austenitic stainless steel, type 302, 304, 316, 321 or 347. The foam design places foam sections on all sides of a vessel and will be designed so that there are no direct energy pathways from the outer walls to the inner wall. The arrangement challenges any heat gain energy from migrating from the outer wall to the cryogenically tempered inner surface by presenting at least two 90 degree flow pathway changes. All energy migrating from outer to inner is gettered by the kinetic properties of the foam, while in molecular flow regime. All foam sections will have vacuum pathways milled into them which are 0.065″ in cross section, spaced in an arrangement that facilitates the evacuation of the trapped spaces of the foam sections and allowing for the desorption of the surface area of the foam to a minimum of 100 monolayers in one embodiment. After the milling operation, the foam itself has enough surface area and flow obstructions as to prevent serious back flow of contaminates into the vacuum space. Vacuum channels are placed on the foam to allow for two processes to happen. First, the channels facilitate the general evacuation of the chambers and second, the channels facilitate the desorption of water vapor from the foam surface. The vacuum processing reduces the partial pressure of the vacuum vessel to a point lower than 10 millitorr as measured by a thermocouple or similar total pressure gauge. The use of non-oil based vacuum pumps prevents the back streaming of residual water and oil vapor with its contaminating gas load.
In addition to using oil free vacuum pumps, a cold processing technique is applied to the shells. The technique includes of three separate steps.
Firstly, the assembly is evacuated to a total pressure of approximately 500 millitorr. The specific ultimate pressure is not important.
Secondly, the assembly is then cryogenically cooled to a temperature of no more then −175° C. as measured on the inner wall of the vacuum chamber. This getters contaminant gases onto the inner wall of the vacuum chamber via thermodynamic processes, thus conditioning the foam.
Lastly, while the vacuum pump system is connected and applied to the vacuum chamber, the temperature is allowed rise to ambient. The vacuum pump removes all of the gettered gases by way of a pseudo thermo/kinetic energy transfer.
The following examples are intended to explain the invention in greater detail, but without limiting it in its scope. In one exemplary embodiment, the foam is a Polyisocyanurate Insulation that has the following specifications:
The rigidity and high compressive strength of the shell material serve to counteract and minimize inward bending distortion of the two opposed metal sheets due to stress from the internal vacuum and external atmospheric pressure as the shell material provides sufficient compressive strength.
Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.
This application is a continuation of application Ser. No. 11/934,696 filed on Nov. 2, 2007, the content of which is incorporated by reference.
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| Number | Date | Country | |
|---|---|---|---|
| 20120055936 A1 | Mar 2012 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11934696 | Nov 2007 | US |
| Child | 12894206 | US |
