Method and apparatus for accelerated freeze drying

• US 3,883,958 A
• Filed: 01/14/1974
• Issued: 05/20/1975
• Est. Priority Date: 03/10/1973
• Status: Expired due to Term

• Current Assignee: Antonio Domingos Filipe
• Original Assignee: Antonio Domingos Filipe
• Inventors: Filipe, Antonio Domingos
• Primary Examiner(s): Camby, John J.
• Application Number:
  US05/433,282
• Time in Patent Office: 491 Days
• Field of Search: 34/5,92 426/234
• US Class Current: 34/289
• CPC Class Codes: F26B 3/34 by using electrical effects
• CPC Class Codes: F26B 5/06 the process involving freezing

Abstract

A method and apparatus for freeze drying food products in an accelerated manner. The food product is situated in a frozen condition in an evacuated chamber where the food product is initially exposed to heat resulting from infrared radiation. As soon as a given temperature differential exists between the exterior surface of the food product and the interior of the food product, which contains the water to be driven out of the food product, additional heating is applied to the food product, while maintaining the infrared heating. This additional heating is provided by situating the food product between capacitor elements with the food product itself acting as a dielectric so that the energy of a radio frequency field applied between the capacitor elements is converted into heat by dielectric losses with the food product itself serving as the dielectric material, to achieve in this way an accelerated freeze drying resulting from the simultaneous application of heat by way of dielectric losses occurring in the material to be freeze dried and the infrared radiation. The controls are such that the temperature at the interior of the food product is maintained equal to the temperature at the exterior thereof.

Claims

1. In a process for freeze drying a food product, the steps of situating the food product while it is in a frozen condition in an evacuated chamber between a pair of capacitor electrodes for utilizing the food product as a dielectric between said electrodes, initially exposing the latter food product, while it is situated between said capacitor electrodes, to the heat of infrared rays for extracting water from the food product by sublimation and evaporation, and after initially exposing the food product to the heat of the infrared rays for a given length of time and while continuing the exposure of the food product to the infrared rays, electrically energizing said electrodes in a manner producing between the electrodes the energy of a radio frequency field which is transformed into thermal energy by dielectric losses which occur in the interior of the food product for heating the food product simultaneously with infrared radiation and with said thermal energy resulting from dielectric losses, only after initial heating with the infrared rays for said given length of time.

2. In a method as recited in claim 1 and wherein the simultaneous exposure of the food product to infrared rays and the radio frequency field is carried out while maintaining the temperature at the surface of the food product and at the interior thereof equal at all times.

3. In a methOd as recited in claim 1 and generating the radio frequency field from sources such as electronic valve generators, magnetron generators, Klystron generators, or amplitron generators, with a plurality of the generators which are of relatively small power being joined together in order to achieve more power as required, the evacuated freeze drying chamber including plates which form said capacitor electrodes, and including the step of electrically connecting a group of the plates to each generator.

4. In a method according to claim 1 and selecting the degree of evacuation of the freeze drying chamber in accordance with the material which is freeze dried, in accordance with the organoleptic properties which it is desired to maintain in the material as well as in accordance with the frequency and intensity of the radio frequency field, while maintaining the value of the vacuum in the evacuated chamber between 10 and 1,000 Mu of mercury.

5. In a method according to claim 1 and wherein in order to bring about ionization and polarization of the molecules of free water of the material, to orient the movement and increase the speed of the molecules with respect to a condensing surface and the quantity of water extracted, use is made, for fixing the extracted ionized water, of at least one condenser constituted by a pair of tubular sections while directing a refrigerating fluid through one of the sections toward the other in a tubular section which is electrically and thermally insulated and superficially heating the tubular section by an electrical resistance element.

6. In a method as recited in claim 5 and including the step of establishing an electrostatic field around the condenser by connecting the tubular sections thereof to the poles of a direct current generator such as a direct current generator which is used for driving a high-frequency oscillator.

7. In a method as recited in claim 5 and including the step of utilizing two condensers alternately while making use of heat of the condensers to bring about rapid unfreezing by induction and utilizing as a source of energy that source which is utilized to heat the food product by dielectric losses.

8. In a method as recited in claim 1 and operating a cybernetic feedback system according to variations in the dielectric constant of the food product while responding to variations in temperature and approaching the point of fusion of the food product, while the quantity of water in the food product diminishes for controlling the heating of the food product.

9. In a method according to claim 1 and interrupting the heating of the food product by dielectric losses above and below predetermined values of the dielectric constant, while also interrupting at more elevated values the heating by infrared rays.

10. In a freeze drying apparatus, infrared means for heating a material which is to be freeze dried with infrared radiation, and capacitor means having a pair of capacitor elements for accommodating the material which is to be freeze dried between said capacitor elements, said capacitor elements having with respect to said infrared means a location which will expose the material between said capacitor elements to the infrared radiation, so that heating of the material to be freeze dried is carried out by dielectric losses in the material to be freeze dried as well as by heat resulting from infrared radiation.

11. The combination of claim 10 and wherein a generator means is operatively connected with said capacitor means for generating a radio frequency field between said capacitor elements to achieve the dielectric heating of the material to be freeze dried, said capacitor means including at least a pair of plates to which said generator means is electrically connected.

12. The combination of claim 11 and wherein a plurality of said generator means are connected in a shunt connection and also are capable of being connected in a tank circuit with the frequency controlled by means of a crystal.

13. The combination of claim 10 and wherein an enclosure means encloses the infrared heating means and the capacitor means for situating the latter together with the material which is to be freeze dried in an evacuated atmosphere which has a pressure between 0.004 and 0.0004 inches of mercury.

14. The combination of claim 10 and wherein an evacuated enclosure means houses the infrared heating means and the capacitor means as well as the material to be freeze dried, condenser means communicating with the interior of said enclosure means for condensing water extracted from the material to be freeze dried, and means cooperating with said condenser means for situating the latter in an electrostatic field for achieving an ionization and polarization of the water molecules which travel toward the surface of said condenser means.

15. The combination of claim 14 and wherein said condenser means includes two independent tubular sections and electrically and thermally insulated connecting means interconnecting said sections, a source of direct current being electrically connected with each of said tubular sections, and electrical resistance means situated at the surface of the insulated means which interconnects the tubular sections for heating the insulated means.

16. The combination of claim 14 and wherein a pair of said condenser means communicate with the interior of said enclosure means with said pair of condenser means alternately operating for condensing and unfreezing.

17. The combination of claim 16 and wherein an induction means is electrically connected with each condenser means to achieve the unfreezing operation thereof, each tubular condenser section being in the form of a coil and the insulated means being in the form of a cable situated in the interior of and surrounded by said coil, with the source of energy used for achieving the radio frequency field to provide the dielectric loss at the material to be freeze dried being also electrically connected as a source of energy for the induction means, said insulated means being electrically connected with an insulated terminal of a radio-frequency generator which is connected in shunt.

18. The combination of claim 10 and wherein an enclosure means hermetically encloses the infrared heating means and the capacitor means, said enclosure means being of a cylindrical configuration and having a horizontal axis and carrying in its interior a plurality of plates having a size and shape corresponding to the interior of the enclosure means and situated in horizontal planes in spaced relationship with the distance between successive plates being between 3 and 10 centimeters, each of said plates being hollow and being formed with an internal network of tubes through which a heating fluid is circulated, and a conduit means communicating with the interiors of said tubes for circulating a heating fluid therethrough.

19. The combination of claim 10 and wherein an enclosure means of cylindrical configuration having a horizontal axis encloses said infrared heating means and said capacitor means as well as the material to be freeze dried, and a plurality of electrical resistance plates situated in said enclosure means respectively in horizontal planes and spaced from each other by a distance of between 3 and 10 centimeters.

20. The combination of claim 10 and wherein an enclosure means of generally cylindrical configuration having a horizontal axis encloses said infrared heating means and said capacitor means and carries in its interior a plurality of plates between which the material to be freeze dried is situated, each of the plates except the lower one of the series of plates carrying at its lower surface a material insulated against high frequency current and carrying an electrically conductive network while all except the upper one of the series of plates carry at their upper surfaces also an electrically conductive network which supports the material to be freeze drIed, and high-frequency generator means electrically connected with the networks which support the material to be freeze dried, so that the supports for the material to be freeze dried form the capacitor elements to heat the material to be freeze dried by the dielectric losses therein.

21. The combination of claim 10 and wherein an enclosure means of generally cylindrical configuration having a horizontal axis encloses the infrared heating means and the capacitor means, the latter including heating plates which serve as the capacitor elements and a high-frequency generator means electrically connected with said heating plates to create a radio-frequency field in which the material to be freeze dried is located to provide heating of the latter by way of the dielectric losses.

22. The combination of claim 10 and wherein an enclosure means encloses the infrared heating means and the capacitor means and a condenser means communicating with the interior of said enclosure means and including a pair of separate tubular coils and relatively short insulated tubes connecting said coils with a source of refrigerating fluid, said short insulated tubes carrying at their outer surfaces relatively small electrical resistances forming a heating means for maintaining the exterior surface of said insulated tubes at approximately 40* F, a high voltage source of direct current having positive and negative poles respectively connected with opposite ends of each tubular coil.

23. The combination of claim 22 and wherein a tank means houses said condenser means, and said tank means carrying a plurality of connecting means for respectively connecting the interior thereof to the interior of said enclosure means, to a source of vacuum, and to the outer atmosphere, with a plurality of valve means being respectively situated at said plurality of connecting means for controlling the opening and closing of the connecting means to provide a connection of the interior of the tank means with the interior of said enclosure means and with the source of vacuum while closing the communication with the outer atmosphere and for then opening the connection with the outer atmosphere while closing the connection of the interior of the tank means with the interior of said enclosure means and with the source of vacuum.

24. In a method as recited in claim 1, generating infrared radiation, to provide said infrared rays, in the interior of said evacuated chamber.

25. In a method as recited in claim 1, situating said capacitor electrodes in the interior of said evacuated chamber so that the entire radio frequency field is in the interior of said chamber.

26. In a method as recited in claim 25 and including the step of generating infrared radiation, for providing said infrared rays, in the interior of the evacuated chamber.