Electric resistance heating devices – Heating devices – Fluid-in-circuit type heater
Patent
1991-11-18
1993-07-06
Bartis, Anthony
Electric resistance heating devices
Heating devices
Fluid-in-circuit type heater
99451, 204294, 392320, 392338, H05B 360, H05B 303, A23L 3005, C25B 1112
Patent
active
052261069
DESCRIPTION:
BRIEF SUMMARY
This invention relates to surface fouling resistant materials, and in particular to such materials for use as structures which have to contact flowable media which deposit surface fouling deposits.
Ohmic heating is a well known technique for heating flowable media and is well established in the food processing industry where it meets the need to cook or sterilise foodstuffs. The basic principle is to arrange for an electric current to flow directly in the medium between a pair of electrodes. Such direct ohmic heating cf the medium can permit high rates of heat input to the medium thus enabling rapid heating. Proposals for ohmically heating liquids, specifically pasteurising milk, are described in the article "Pasteurisation of Milk by Electricity" by McDowall, pp 275-291 The New Zealand Journal of Science and Technology, February 1929. In the "Electro-Pasteur" described in this article, electric current flows between electrodes spaced at intervals along a pipe through which milk is flowing. The current flow is therefore essentially parallel to the flow of milk. Reference may also be made to GB-B-2067390 which describes a particularly advantageous form of electrode for use in ohmic heating apparatus. Platinum or platinum coated electrodes are commonly used to provide corrosion resistance in such devices
In addition to heating foodstuffs, there is also a requirement to heat flowable media such as corrosive chemical reagents up to a required reaction temperature. Hitherto, attempts to apply the technique of ohmically heating such reagents have met with difficulties associated with surface fouling of the electrodes, in particular the deposition of crystals from the reagants. With many reagants the crystal growth is itself electrically insulating so that continued deposition results in a non-functional electrode. Often the deposition process is sufficiently rapid to render ohmic heating unworkable due to the frequency of having to clean or replace the fouled electrodes.
In accordance with the present invention, surface fouling resistant means arranged to contact flowable media comprises material of closed microporosity.
It has been found experimentally that such materials are unexpectedly resistant to surface crystal growth. Whilst the reason why materials of closed microporosity should exhibit this property is not fully understood, it is presently believed that some other sorts of material surfaces are vulnerable to fouling because they allow for trapping of pockets of reagants in the open structures or pores cf the material surface. Such pockets may be the site for nucleation and crystal growth No such trapping of pockets of reagants may occur with materials of closed microporosity, thus rendering such materials resistant to surface fouling.
Conveniently, ohmic heating apparatus may comprise electrodes made of such closed microporosity material, as may other components in such apparatus where fouling by crystal deposition is detrimental. Preferably, the closed microporosity material is vitreous or glassy carbon. Conducting ceramics may also be suitable. It may be appreciated that although such materials are particularly suitable for structures which have to contact flowable media which rapidly deposit surface fouling crystals on other sorts of electrodes, their applicability is in fact to any sorts of flowable media where surface fouling might be a problem It may also be appreciated that the material may also have to be electrically conducting and chemically inert.
Another aspect of the invention is the use of closed microporosity materials for surface fouling resistant means arranged to contact flowable media.
An example of the invention will now be described with reference to the accompany drawing, the sale view of which illustrates an ohmic heating apparatus embodying the present invention.
In this figure, there is indicated generally at 20 a pipe for the flowable medium which is to be heated. The medium is typically corrosive chemical reagants which have to be heated to attain a desired reaction temperatu
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patent: 4220846 (1980-09-01), Rice et al.
patent: 4417132 (1983-11-01), Simpson
patent: 4434357 (1984-02-01), Simpson et al.
patent: 4461347 (1984-07-01), Layton et al.
patent: 4959525 (1990-09-01), Stirling
Bartis Anthony
Electricity Association Technology Limited
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