Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
2003-04-24
2004-08-31
Van, Quang T. (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
C219S505000, C219S771000
Reexamination Certificate
active
06784405
ABSTRACT:
BACKGROUND AND SUMMARY
This invention pertains to methods and apparatuses for the capacitive radio frequency (RF) dielectric heating of food and biological products.
A variety of different methods are available for the thermal processing of various materials. Heat is supplied by hot water, steam, resistive heating elements, burners, torches, ovens, electrical conduction (ohmic heating), induction heating (magnetic), capacitive heating (dielectric), and electromagnetic radiative heating (resonant ovens, cavities or chambers) and many other heating methods. Applications include sterilization, pasteurization, thawing, melting, curing, drying, bonding (e.g., laminates), welding, brazing, heating for chemical reactions, and many others. Heated materials include ceramics, rubber, plastics (and other polymers), composites, metals, soils, wood and many types of biological materials including food.
An important application of heating technologies is in the area of the pasteurization and sterilization of foods, particularly foods in large-dimensioned packages. Food safety and quality is becoming an increasingly important topic with the many incidents where people have become sick or died due to unkilled microbial populations in food. For example, alfalfa and radish seeds are raw agricultural commodities that can become contaminated with organic material that harbor pathogens such as Salmonella or
E. coli
O157:H7 during growing and harvest. Seed processing and storage procedures are aimed at reducing varietal contamination of seeds through the elimination of weed seeds and foreign matter. Such seed cleaning and certification programs insure varietal purity, but provide no means of food safety intervention for seeds destined for sprouting and consumption as food. As a result, there are increasing reports of microbial outbreaks in sprouted seed products such as radish and alfalfa sprouts. Human salmonellosis (due to Salmonella bacteria) and outbreaks of
E. coli
O157:H7 have been associated with the consumption of alfalfa and radish sprouts in several countries. Alfalfa and radish sprouts, a definitive highly nutritious and perceived healthy food, have been implicated in multi-site outbreaks of food-borne illnesses. Seeds were linked to about 150 confirmed cases of salmonellosis in Oregon and British Columbia in 1996. Also in 1996, radish sprouts were associated with Japan's largest recorded outbreak of
E. coli
O157:H7 infection with an estimated 11,000 cases that led to eleven deaths. In June and July 1997, simultaneous outbreaks of
E. coli
O157:H7 infections in Michigan and Virginia were independently associated with eating alfalfa sprouts grown from the same seed lot. A total of 60 people with
E. coli
O157:H7 infection were reported to the Michigan Department of Community Health and 48 cases reported to the Virginia Department of Health. Recently, the California Department of Health Services identified six cases of
E. coli
O157:NM with illness onsets from June 16 through Jun. 27, 1998, caused by eating an alfalfa-clover sprout mixture.
The lack of standardization in some heating time/temperature relationships that are required to ensure food product safety is also attracting more focus. In addition, food quality or taste/texture issues are important in our selective consumer oriented society. Therefore there is a need for a heating technology that will achieve the desired microbial kill rates uniformly over that whole food product in a reasonable amount of time with a minimum altering of the overall quality of the food.
In the seafood industry, for example, existing heating technologies for the pasteurization of seafoods employ either hot water or steam. These technologies have several limitations including reliance on thermal conduction from the product surface (resulting in non-uniform heating), slow heating rates (especially in the product center), large floor space requirements, poor overall energy efficiency, generation of large amounts of waste water and limitations on the product geometry (i.e., need to be thin or flat).
Capacitive radio frequency (RF) dielectric heating is used in several industries. They include the drying of various wood and sawdust products in the timber industry, preheating and final drying of paper, drying of textiles, drying of glass fibers and spools, drying water-based glues in the paper-cardboard industry, drying pharmaceutical products, welding plastics, sealing, preheating plastics prior to forming, firing foundry cores in casting, polymerization of fiber panels, gluing of woods such as laminated plywood, printing and marking in the textile, leatherware and shoe industries, melting honey, heating rubber prior to vulcanization, welding glass formed sections, bonding multi-layer glass products, drying of powders, drying leathers and hides, curing of epoxy, curing of plastisol, curing of brake linings, impregnating resins, thermosetting adhesives, curing hardboard and particle board, and many other applications.
The use of capacitive (RF) dielectric heating methods for the pasteurization and sterilization of foods offer several advantages over non-electromagnetic heating methods. These include rapid heating, near independence of the thermal conductivity of the medium (i.e., heat internal portions of medium directly), high energy efficiency, good heating even in the absence of DC electrical conductivity, high energy densities, reduced production floor space, and easy adaptation to automated production batch and/or continuous flow processing. Because capacitive (RF) dielectric heating is rapid, the food product being heated loses less moisture than in conventional heating processes, which is advantageous.
Another application of this technology is in the thawing of frozen foods. Common thawing applications again rely on the thermal conduction of heat from the surface to the interior to provide thawing. Due to freshness and product quality constraints thawing often is done by immersion in water baths that are only slightly above freezing themselves or in refrigerators set to slightly above freezing (e.g., 35-40° F.). Thawing times are often very long. With capacitive heating technologies that heat over the entire volume uniformly, thawing can be performed much more rapidly.
Capacitive (RF) dielectric heating differs from higher frequency electromagnetic radiative dielectric heating (e.g., microwave ovens) in that with capacitive heating the wavelength of the chosen frequency is large compared to the dimensions of the sample being heated whereas with electromagnetic radiative heating the wavelength is comparable or even small compared to the dimensions of the sample being heated. An example of capacitive heating is two large parallel electrodes placed on opposite sides of a wood sample with an AC displacement current flowing through it to heat and dry the wood. An example of electromagnetic radiative heating is a metal chamber with resonant electromagnetic standing wave modes such as a microwave oven. Capacitive heating also differs from lower frequency ohmic heating in that capacitive heating depends on dielectric losses and ohmic heating relies on direct ohmic conduction losses in a medium and requires the electrodes to contact the medium directly (i.e., cannot penetrate a plastic package or air gap). (In some applications, capacitive and ohmic heating are used together.)
Capacitive (RF) dielectric heating methods offer advantages over other electromagnetic heating methods. For example, capacitive (RF) dielectric heating methods offer more uniform heating over the sample geometry than higher frequency radiative dielectric heating methods (e.g., microwave ovens) due to superior or deeper wave penetration into the sample as well as simple uniform field patterns (as opposed to the complex non-uniform standing wave patterns in a microwave oven). In addition capacitive (RF) dielectric heating methods operate at frequencies low enough to use standard power grid tubes that are both lower cost (for a given power level) as well as allow for generall
Flugstad Benjamin A.
Kolbe Edward R.
Ling Qingyue
Park Jae W.
Wells John Henry
Klarquist & Sparkman, LLP
The State of Oregon, acting by and through the State Board of Hi
Van Quang T.
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