Scale-inhibiting heating element and method of making same

Details Scale-inhibiting heating element and method of making same Scale-inhibiting heating element and method of making same

1999-08-25

2001-03-20

Walberg, Teresa (Department: 3742)

Electric resistance heating devices

Heating devices

Tank or container type liquid heater

C392S489000, C392S503000

Reexamination Certificate

active

06205291

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to heating elements, and in particular to heating elements utilized within water heaters.
BACKGROUND OF THE INVENTION
Conventional electric water heaters have elongated heating elements comprising an outer tubular sheath enclosing an inner electrical resistance wire. In a typical element, the internal metallic resistance wire is surrounded by a material such as magnesium oxide which is an electrical insulator but is capable of a reasonably high heat transfer rate. The outer sheath may be formed of a metal such as copper or an INCOLOY material. Thermal energy passes from the hot resistance wire through the insulating material and sheath wall to the sheath surface, thereby heating the water.
Over time electric water heater elements tend to develop scale or calcium carbonate, which is a poor heat conductor. The heating element has a high heat flux so the poor thermal conductivity of the scale film tends to cause the heating element to overheat, which can lead to failure of the heating element. Also, the growth of scale on the element may physically deform the element and cause failure. Finally, as scale grows thick it tends to flake off from the element and into the heated water.
Various solutions have been proposed to alleviate the problems created by scaling of heating elements. For example, U.S. Pat. No. 5,586,214 to Eckman shows a water heater heating element which is alleged to minimize lime depositing. The Eckman heating element replaces the customary metallic sheath of the heating element with a plastic sheath. Attempts to coat heating elements with unconventional materials are usually unsuccessful due to adhesion problems or overheating.
In another proposed solution, the watt density is reduced so that scale will form at a lower rate, thus extending the element life. This may be accomplished by using a resistance wire of lower wattage rating, or increasing the sheath diameter and/or length. The disadvantages of this method are that an element of greater surface area is required, causing difficulties and fitting the element into smaller heater tanks, or increasing the cost through enlarged element size and enlarged port and mount size.
A scale-inhibiting water heater element suitable for use in conventional water heaters would be desirable.
SUMMARY OF THE INVENTION
The present invention provides a scale-inhibiting heating element and a method of making the same. The heating element is coated with a diamond-like coating which has a low surface tension and prevents scale from forming on the heating element. The diamond-like coating is also thermally conductive; in other words, the coating permits heat to flow out away from the heating element and into the water. In addition to inhibiting scale formation, the coating has also been found to be electrically resistive which is desirable because it decreases the drain on the anode caused by the presence of a metal heating element in contact with the water.
Although diamond-like coatings (DLCs) are known, these coatings are typically used for corrosion resistance to protect the substrate to which they are applied (see, for example, U.S. Pat. No. 5,728,465 to Dorfman, and U.S. Pat. No. 5,529,815 to Lemelson), or for wear resistance (see, for example, U.S. Pat. No. 5,458,927 to Malaczynski). Heating elements, for example, in water heaters, are not subject to wear during use, and are not typically subject to corrosion because customary heating element materials are corrosion resistant metals such as an INCOLOY or copper material. Therefore, the use of diamond-like coatings on heating elements to inhibit scale formation is unique. Diamond-like coatings have been found to provide low surface tension and thermal conductivity sufficient to provide suitable scale-inhibiting properties to heating elements without over-heating the element.
To inhibit scale formation, a diamond-like coating may be applied to other surfaces in contact with unpurified, heated water, such as heat exchangers, bottoms heads and flues of gas water heaters and internal sides of water heaters. Other proposed applications include heating elements for coffee pots and tea kettles, valve assemblies and hot water fixtures.
One embodiment of the present invention is a scale-inhibiting heating element comprising a heating element, and a diamond-like coating at least partially coating the surface of the heating element. The invention also provides a water heater comprising a tank for containing water and a heating element as described above.
Another aspect of the invention is a method of manufacturing the scale-inhibiting heating element. The method involves applying a diamond-like coating to the surface of the heating element.
Yet another aspect of the invention is a method of inhibiting scale formation on the surface of a heating element by applying a diamond-like coating to the surface of the heating element. Preferably, an interfacial layer or an adhesion layer is applied prior to applying the diamond-like coating.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description in claims.
Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction, or to the steps or acts set forth in the following description. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In a preferred embodiment, the present invention is a scale-inhibiting water heater element which comprises a conventional water heater element, and interfacial layer disposed on the surface of the water heater element, and a diamond-like coating disposed on the interfacial layer. Preferably, the interfacial layer comprises an amorphous silicon. The resulting heating element may be placed in a water heater. A typical water heater has a tank for containing water, and a heating element within the tank. In normal operation, the scale-inhibiting heating element will be immersed in a fluid medium such that the fluid medium comes in direct contact with the diamond-like coating. The fluid medium is typically water that contains impurities.
In a highly preferred embodiment, the present invention provides a method of inhibiting scale formation on a surface of a water heater heating element by applying a diamond-like coating to the surface of the heating element. More specifically, a water heater element is provided which comprises an electrical wire, an electrically insulating layer surrounding the electrical wire, and a corrosion-resistant metal sheath surrounding the electrically insulating layer. An amorphous silicon interfacial layer is disposed on the surface of the heating element. Then, the diamond-like coating is applied.
Another aspect of the invention is a method of minimizing galvanic corrosion of a metal in contact with water which contains an electric heating element immersed therein. When the two dissimilar metals are in contact with water, galvanic current flow between the metals tends to cause galvanic corrosion of at least one of the metal surfaces. For example, when a metal water heater element is immersed in a metal water heater tank, galvanic current tends to corrode the less corrosion resistant metal. If a sacrificial anode is placed in the tank, the anode corrodes. For further discussion of galvanic corrosion and electrical heating elements, see U.S. Pat. No. 4,848,616 which is herein fully incorporated by reference. The method of the invention comprises applying a diamond-like coating to the surface of the heating element. Employing a DLC-coated heating element provides a method of minimizing galvanic corrosion. The DLC is electrically resistive (or electrically insulating) and insulates the heating element fro

Affiliated with

Also associated with

Rating

Scale-inhibiting heating element and method of making same does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Scale-inhibiting heating element and method of making same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Scale-inhibiting heating element and method of making same will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2543570