US 3564727 A
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Description (OCR text may contain errors)
Feb. 23, 1971 I s, FRASER v 3,564,727
FREEZE DRYER USING AN EXPENDABLE REFRIGERANT Filed March 5, 1969 Fl c 3 INVENTOR DOUGLAS 5. FRASER Q if ZV ZTT'X United States Patent 3,564,727 FREEZE DRYER USING AN EXPENDABLE REFRIGERANT Douglas S. Fraser, New Paltz, N.Y., assignor to The Virtis Company, Inc., Gardiner, N.Y., a corporation of New York Filed Mar. 3, 1969, Ser. No. 803,760 Int. Cl. F26b 13/30 US. C]. 3492 4 Claims ABSTRACT OF THE DISCLOSURE A freeze drying arrangement having means to permit the use of an expendable refrigerant. A transparent door is also disclosed having a metallic layer thereon to permit viewing therethrough while reflecting radiant energy which could affect the temperature level in the chamber.
This invention relates to improvements in freeze drying chambers and, more specifically, to a new and improved refrigeration system adapted for use with an expendable refrigerant and a novel reflective door for said drying chambers.
In the practice of freeze drying, the material is first frozen and then subjected to a high vacuum and controlled heat input. Under these conditions, the frozen water content of the material is removed through sublimation which, by definition, consists of ice going to vapor, bypassing the intermediary liquid phase. In the accomplishment of freeze drying, vacuum chambers have been utilized which are cylindrical or tubular in shape. They are fabricated with a transparent or clear access door which is properly sealed to be vacuum tight. Within the vacuum chamber is provided a product shelf having means to permit it to be heated under controlled circumstances. Ideally, refrigeration should be provided to permit the prefreezing of the materials to be dried and thus eliminating the need for a separate freezing chamber. Even if freezing is done elsewhere, refrigeration should be provided to form a condensing surface to collect the water vapor and prevent it from gaining access to the vacuum pump which continuously evacuates the vacuum chamber during the freeze drying process.
In the past, chambers of this general type have been used with a mechanically operated refrigeration system. Because of the size of the refrigeration system required, the complete freeze drying unit, of necessity, was fairly sizable. Oftentimes, the space required and the cost of such a unit was beyond the space available and the budget of smaller laboratories having only an occasional need for a freeze dryer.
The present invention relates to a freeze dryer of the chamber type which may also be included with connections for manifold-type drying as well as chamber drying. The present design includes a novel refrigeration system which utilizes an expendable refrigerant located outside the freezing chamber. A novel exchange system of closed circuit design is used to transfer the heat from the expendable refrigerant to the interoir of the vacuum chamber. This system may be also utilized to maintain the products in a frozen state or freeze dry products while positioned on the shelf. The exchange system also acts as a condensing surface to collect the water vapor during freeze drying. As an additional feature, the present invention contemplates the use of a novel door which reflects heat energy while permitting viewing of the specimens in the chamber.
The present system provides a refrigeration unit of good efficiency which is considerably less expensive than the mechanical refrigeration units heretofore known. It
3,564,727 Patented Feb. 23, 1971 does not have the drawbacks of previously used techniques of positioning chunks of Dry Ice in receptacles adjacent the vacuum chamber.
The refrigeration unit also serves multiple functions, freezing and condensing out the water vapors. All of the advantages of more expensive systems are gained without a significant sacrifice in refrigeration efiiciency. Other advantages will be seen upon description of a preferred form of the invention.
It is an object of this invention to provide a new and improved freeze drying chamber having a novel door permitting viewing of the contents while reflecting any heat energy which ordinarily would pass through said door.
It is a further object of this invention to provide a new and improved freeze drying arrangement having a novel refrigeration system which will be relatively inexpensive to manufacture and assemble, thereby placing it within the reach of users having only occasional need for freeze drying equipment.
It is a further object of this invention to provide a new and improved freeze drying arrangement having a novel refrigeration system which utilizes an expendable refrigerant.
It is a still further object of this invention to provide a new and improved refrigeration system for use with freeze drying equipment which may be readily manufactured and assembled.
Objects other than those specifically set forth will become apparent to the person skilled in the art upon reference to the accompanying drawings and following description.
In the drawings:
FIG. 1 is a front elevational view of the freeze drying apparatus of the present invention;
FIG. 2 is an enlarged cross-sectional view of the upper portion of the freeze drying chamber shown fragmentarily and the refrigeration system shown in cross section; and
FIG. 3 is a further enlarged cross-sectional view taken generally along the line 33 of FIG 2.
Referring now to FIG. 1, a freeze drying arrangement of the present invention is indicated generally by reference character 10. The freeze drying arrangement includes a vacuum chamber 11 and refrigeration system 1 2 which is disposed on top of the vacuum chamber '11.
The vacuum chamber 11 consists of a cylindrical drum 13 supported on a housing 14. The housing 14 may include suitable controls such as a temperature control 15, stoppering control 16 and shelf heat switch 17, all of which function in a known manner.-
The chamber 11 includes a bottom shelf 18 on which is positioned a tray 20 having bottles 21 of material to be freeze dried. A stoppering plate 22 is located above the bottles 21 and is provided on the underside with an elastomeric diaphragm 23 which, through the use of the stoppering control, expands downwardly to seat stoppers 24 in the mouth of the bottles or containers 21 after freeze drying is completed. This is a conventional or known type of stoppering which is known to the art.
Manifold units in the form of valves 25 may be provided along opposite sides of the vacuum chamber 11. Each valve may be of the type described in co-pending application Ser. No. 650,134, assigned to the assignee of the present invention. The disclosure of that application is incorporated herein by reference. The front of the chamber is closed off by a transparent door 26 of plastic having vacuum metal deposited thereon. This permits the operator to observe the freeze drying process while reflecting heat from outside sources and maintaining the heat level in the chamber fairly constant. External heat is reflected while full viewing of the specimens being dried is available. The total reflectance should be of the order of about 75%. The chamber 11 is provided with suitable connections (not shown) for attachment to a vacuum pump capable of evacuating the interior of the chamber 11. Ideally, the vacuum connection is lo cated where the fiow of vapor will be past the condensing surface in the chamber.
The expendable refrigeration unit 12 is of box-like form and disposed on the top of the vacuum chamber 11. As seen in FIGS. 2 and 3, the refrigeration unit includes a closed tube 30 having heat exchange means 31 located centrally of a receptacle 32 which is located within a housing 33. An insulating foam 34 is formed in the space between the receptacle 32 and the housing 33, both of which may be rectangular as shown or of any other suitable shape. The closed tube 30 extends within the vacuum chamber 12 and communicates with a generally X-shaped condenser having a plurality of condensing fins 35, 36, 37 and 38 at the respective ends. Obviously, the condenser may be of any desired configuration. The heat exchange surfaces 31, 35, 36, 37 and 38 are formed by a plurality of metallic fins which are joined to the closed tube 30 by suitable means such as soldering, welding or the like to provide for optimum heat transfer.
The heat exchange means 31 is surrounded in the Well 32 by an expendable refrigerant 40 which may include Dry Ice chunks 41 immersed in an alcohol or acetone bath 42. Inasmuch as the well 32 is well insulated from the outer housing 33 by a layer of foam several inches thick and covered by a suitable cover 43, the expendable refrigerant will last for approximately 24 hours.
The tube 30 forms a closed refrigeration circuit and is filled with a suitable refrigerant such as Freon 13 which boils at about 115 F. Gases which would serve as a refrigerant in this system are nitrous oxide, refrigerant 503, ethane ethylene and possibly others. The pressure range would vary between about 200 p.s.i. to 700 p.s.i., depending upon the refrigerant.
The refrigeration cycle which occurs is as follows: As the refrigerant is cooled at the upper end of the tube 30 by the expendable refrigerant 40, it goes to a liquid state, draining down to the bottom of the tube and into the condensing area of the heat exchangers 3538. As the heat exchange means in the chamber 12 is warmed through loss of heat during the freeze drying or refrigeration of the material to be freeze dried, the refrigerant is heated to above its boiling point and assumes a gas form, rising in the tube 30 to the area of the heat exchange means 31. There the refrigerant is again cooled and the cycle repeats itself.
It is contemplated that the refrigerant will be maintained in the tube 30 under a pressure. As indicated, this will vary with the type of refrigerant used, however, in the preferred form, when a refrigerant known as Freon 13 is utilized, it is under a pressure of the order of 300 It can be appreciated from consideration of the foregoing embodiment that the freeze drying system of the present invention is complete with the exception of a suitable vacuum source. Because of its simplified construction, it may be produced economically to place it within the economic range of small laboratories. With the refrigeration system shown, it may be used as a freezer to freeze the materials to be dried and thereafter used as a @ondenser u g the freeze drying process. Because of the novel construction of the refrigeration system, it will operate etficiently and utilize a minimum of Dry Ice. Heat is transferred in the present invention by latent heat of liquid used, permitting large amounts of heat to be transferred through a relatively small tube which, in one embodiment, had an outside diameter of five-eighths /8) inch. The location of the condenser permits the temperature to be maintained until the last fragment of Dry Ice has been expended. The reflective door prevents heat loss or gain by radiant heating exterior of the chamber while permitting a full view of the chamber contents during drying.
' Upon a consideration of the foregoing, it will become obvious to those skilled in the art that various modifications may be made without departing from the invention embodied herein. Therefore, only such limitations should be imposed as are indicated by the spirit and scope of the appended claims.
1. A freeze drying unit comprising a closed vacuum chamber adapted to be evacuated, condensing and refrigeration means for cooling said chamber and condensing vapors during freeze drying, said refrigeration and condensing means including a housing for a receptacle, said receptacle being located adjacent said vacuum chamber and adapted to receive an expendable refrigerant, a closed tube forming a refrigeration transfer medium, said closed tube extending from said receptacle into said vacuum chamber, a first heat exchange means formed on said closed tube within said chamber, a second heat exchange means on said tube in said receptacle and adapted for directly contacting said expendable refrigerant and a pressurized gas in said closed tube to maintain said first heat exchange means in said chamber at a temperature below the temperature required to condense the vapor out of the materials being dried.
2. The freeze drying unit of claim 1 wherein said refrigerant in said closed tube is under a pressure in the range from about 200 pounds per square inch to about 700 pounds per square inch.
3. In a chamber-type freeze dryer having a door thereon to gain access to said chamber, while maintaining said chamber vacuum-tight, the improvement comprising said door having a metallic substance thereon to reflect heat energy on both sides thereof while permitting viewing therethrough.
4. The improvement in chamber-type freeze dryers as defined in claim 3 wherein said door is about reflective.
References Cited UNITED STATES PATENTS 1,176,313 3/1916 Pfund 1l733.3 1,975,868 10/1934 Schlumbolun 62-333 2,097,685 11/1937 Botton 62--333 2,437,332 3/1948 Newton 62-332 2,564,708 8/1951 Mochel 11733.3 2,907,117 10/1959 Parkinson 34-92 3,242,575 3/1966 Moudresi 34-92 3,264,747 8/ 1966 Fuentevilla 34-92 WILLIAM J. WYE, Primary 'Examiner US. Cl. X.R, 62-119, 332, 333