Electric resistance heating devices – Heating devices – Fluid-in-circuit type heater
Reexamination Certificate
2000-09-12
2001-10-16
Walberg, Teresa (Department: 3742)
Electric resistance heating devices
Heating devices
Fluid-in-circuit type heater
C392S338000, C099S358000
Reexamination Certificate
active
06304718
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to generally to methods and apparatus for electroheating of foodstuffs and particularly to electroheating
BACKGROUND OF THE INVENTION
Electroheating is a method of rapidly heating substances, such as solid or liquid foodstuffs, by passing a current through the material, wherein the material acts as a resistive heater. Such rapid heating methods are disclosed in applicant/assignee's U.S. Pat. Nos. 4,739,140; 5,583,960; 5,636,317 and 5,863,580, the disclosures of which are incorporated herein by reference.
The fluid to be electroheated must be in contact with a large area of the electrode in order to prevent a high current density on the electrode that might lead to arcing. U.S. Pat. Nos. 5,583,960; 5,636,317 and 5,863,580 describe apparatus for increasing the electrode contacting area and thereby reducing the current density. The apparatus includes a narrow tube which terminates at both ends thereof in funnel-like cones. The electrode is the size of the large base of each cone.
A problem exists when attempting to electroheat semi-solid materials, such as coagulated proteins or dough. It is difficult to form good electrical contact between a flat electrode and the semi-solid material. The narrow tube apparatus of the abovementioned patents solves this problem by providing good contact area and low current density at the cone ends. However, although this arrangement provides low current density, it increases the dwell time in the electroheater, since the volume of the cones is much larger than that of the narrow tube. The increased dwell time presents another problem by making it difficult if not impossible to pass the semi-solid material through the electrode, since the semi-solid material tends to thicken and harden during the dwell time.
Another problem associated with electroheating of a biological fluid, is that the fluid contacts the electrode. The electrodes are usually made of graphite, which is preferable to metal because metal ions can dissolve in the contacting fluid, whereas graphite does not. Nevertheless, even with graphite electrodes, there is an electrolytic reaction with the fluid, and the fluid becomes reduced. Although in some cases this can be beneficial, such as in recovery of oxidized vitamin C in electroheated orange juice, nevertheless in some cases this may not be desirable.
Applicant/assignee's U.S. Pat. No. 6,088,509, the disclosure of which is incorporated herein by reference, describes an electrolytic bridge that solves the abovementioned problems. The electrode of the electrolytic bridge does not come into direct contact with the flowable material which is to be heated. The electrode is generally conical in shape and defines a chamber which is also conical. The chamber is filled with an electrolytic solution which wets a porous, electrically non-conductive conduit through which the flowable material is passed. Electrical current passes from the electrode through the electrolytic solution to the conduit and into the flowable material, thereby electroheating the material.
Due to the conical shape of the electrode and chamber, the current is not concentrated at the upstream base of the chamber, but rather is distributed along the length of the conduit and the electrode, thereby ensuring a relatively low current density. Most preferably, the electrolytic solution is chosen to have an electrical conductivity such that, taking into consideration the electrical conductivity of the flowable material, there is generally an equal distribution of current through the flowable material along the entire length of the conduit. There is a short dwell time because the flowable material flows through a cylindrical conduit rather than through a cone.
However, even with the electrolytic bridge of U.S. Pat. No. 6,088,509, certain coagulation problems can still occur. Coagulation of proteins occurs when a particle is caught and is delayed in the electroheater. The high electrical current heats the snagged particle up to ignition temperatures. Once the particle burns, it forms an obstacle to the flow and more proteinaceous matter coagulates and burns. This can also lead to arcing, since the carbon is more conductive than the flowable material, meaning that the current prefers to flow through the carbon. When using plastic tubes, the hot carbon burns the plastic.
In order to prevent the risk of arcing, the material should flow very fast without any obstacles. Even a change in diameter of the tube through which the material flows can lead to deposition of conductive proteins that eventually tend to burn. Although the porous tube and electrolytic bridge of U.S. Pat. No. 6,088,509 enable a straight line flow with no appreciable change in diameter, nevertheless the porous tube must still be connected to a non-conductive tube, and some flowable material can get caught at the connection between the two tubes. After processing a large amount of material, there can be an accumulation of caught material which then burns.
SUMMARY OF THE INVENTION
The present invention seeks to provide improved methods and apparatus for electroheating flowable materials, which solve the abovementioned problem of the prior art. The electroheater includes a straight, porous (preferably ceramic) conduit with electrodes that are preferably constructed as described in U.S. Pat. No. 6,088,509. In contrast to U.S. Pat. No. 6,088,509, the portion of the porous conduit which must be non-conductive is surrounded by a cylinder that is filled with an electrically non-conductive fluid, e.g., water, air or oil, under the same pressure as that of the flowing product or higher. Both the electrolyte and the non-conductive fluid are supplied under pressure by pumps. Since the pressure of the electrolyte and the non-conductive fluid is greater than or equal to that of the flowing product, the product does not tend to enter the pores of the porous conduit. In this manner, the product does not enter or accumulate in the pores of the conduit, and no particles are caught and delayed in the electroheater. Thus the present invention solves the problem of burning, coagulated particles, and prevents fouling of the electroheating apparatus.
There is thus provided in accordance with a preferred embodiment of the present invention electroheating apparatus including a conduit adapted for flow therethrough of a flowable product having a pressure, an electrode circumferentially surrounding the conduit, the electrode defining a first annulus between an inner wall of the electrode and an outer wall of the conduit, an electrolytic solution disposed in the first annulus which contacts the outer wall of the conduit, an electrical power source connected to the electrode for passing an electrical current through the electrolytic solution, a Generally electrically non-conductive sleeve circumferentially surrounding the conduit axially adjacent the electrode, the non-conductive sleeve defining a second annulus between the inner wall of the sleeve and the outer wall of the conduit, and a generally electrically non-conductive fluid disposed in the second annulus which contacts the outer wall of the conduit.
In accordance with a preferred embodiment of the present invention the conduit is constructed of a porous, electrically non-conductive material, and wherein the electrolytic solution and the non-conductive fluid are at a pressure not less than the pressure of the flowable product, such that the product does not tend to enter pores of the conduit.
Further in accordance with a preferred embodiment of the present invention a flowable product flows through the conduit, wherein electrical current passes from the electrode through the electrolytic solution to the conduit to the flowable product, thereby electroheating, the flowable product. Preferably the electrolytic solution is chosen to have an electrical conductivity
30
such that there is Generally an equal distribution of electrical current through the flowable product along a length of the conduit opposite the electrode.
Still
Campbell Thor
Darby & Darby
Walberg Teresa
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