Electric resistance heating devices – Heating devices – Tank or container type liquid heater
Reexamination Certificate
1996-05-17
2001-09-25
Lu, Jiping (Department: 3749)
Electric resistance heating devices
Heating devices
Tank or container type liquid heater
C122S00400R
Reexamination Certificate
active
06295411
ABSTRACT:
FIELD OF THE INVENTION
This invention is an improvement for heaters or boilers using electric heating elements that are submerged in an aqueous fluid being heated, such as water or a chemical process stream. It provides means for minimizing the formation of scale on the surface of such heating elements. It is particularly applicable to electric hot water heaters, but may be used for industrial fluid heaters using electric heating elements as well.
BRIEF DESCRIPTION OF THE PRIOR ART
Fluid heaters are generally known in residential and industrial use. In water heaters, a tank is generally provided, having an inlet for cold water and an outlet for heated water. In gas- or oil-fired heaters, the bottom of the tank is heated by combustion. In electric heaters, one or more heating elements is mounted within a tank. Such heating elements are intermittently energized by electric current controlled by a thermostat to maintain the fluid at a designated temperature.
The problem of scale buildup in heating tanks is ages old. In combustion heaters, scale tends to form as a sludge at the bottom, where the fire supplies the heat. Current expedients to control the buildup of such deposits include efforts to keep water in the tank agitated, sometimes described as a “hydroswirl” feature. For example, U.S. Pat. No. 4,838,211 shows a vertical circular water heater with gas heat applied from the bottom of the tank. Within the tank near the bottom is a circular pipe ring; the ring carries pumped water in a closed loop coming from the top of the boiler. The water in turn exits the pipe ring through a series of holes facing upward and inward so as to produce a swirling action in the entrained water. The pump is driven from an external source and is switched on when heated water is extracted for use. Water movement within the boiler is said to prevent accumulation of scale and other solid particles in the bottom portion of the water heater.
Similarly U.S. Pat. No. 4,790,289 discloses a pump and circulating pipe external to a water heater. The pump moves water from the top of cylindrical heater to the lower portion. The moving water is said to keep sediment or lime from building up on the bottom head of the tank and to prevent temperature stratification in the vertical tank.
U.S. Pat. No. 4,898,124 shows a circular plastic tube provided with perforations around the inner surface of the periphery. The circular tube is attached horizontally to the side wall of a water heater near the bottom of the tank. By ejecting water at an accelerated velocity through the perforations, scale from the bottom of the tank is said to be brought into suspension and carried out with the flowing water.
The prior art teachings address the problem of deposits forming at the bottom of heater tanks, but fail to deal with the buildup of scale on electric heating elements having an elongated rod-like shape within the tank. When a tank with the conventional “hydroswirl” feature contains an electric heating element, scale builds up on the heating element nevertheless.
SUMMARY OF THE INVENTION
The present invention provides an improved heater for fluids, comprising a tank having an inlet pipe for unheated fluid and an outlet pipe for heated fluid and an elongated electric heating element within the tank, wherein the improvement comprises means for directing a jet of fluid from the inlet pipe onto substantially the entire length of the electric heating element, thereby minimizing the buildup of scale on the heating element before it hardens thereon. The means for directing a jet of fluid desirably comprises a portion of the inlet pipe disposed parallel to the heating element and having an opening for fluid therein which is directed towards the electric heating element. In preferred embodiments, the opening comprises a multiplicity of perforations, the perforations being adapted to direct jets of fluid towards the vicinity of the electric heating element. The present invention applies to heaters and boilers for water and industrial aqueous fluids such as chemical process streams.
In some embodiments, a deflector is disposed opposite the electric heating element from the aforesaid portion of the inlet pipe, the deflector being adapted to redirect the jet of fluid toward the heating element and thereby improve the turbulent scrubbing action at the heating element.
In some embodiments, an induction coil or a permanent magnet is provided on the inlet pipe. When a coil is used, it desirably carries an electrical waveform supplied by an electronic descaling unit as described in pending U.S. patent application Ser. Nos. 08/544,156 and 08/601,553, the disclosures of which are incorporated herein by reference.
The present invention also provides a method for minimizing buildup of scale on an electric heating element in a hot water tank, comprising the step of directing a jet of water onto the heating element when water is added to the tank, while the building-up scale is still soft. Optionally, this is preceded by the step of pretreating water being added to the tank by subjecting the water to electronic descaling as it passes through an inlet pipe, such that the scale forming on the heating element becomes even softer than it would be in the absence of such treatment and thus easy to be removed.
Furthermore, the present invention provides a method of retrofitting a fluid heater to minimize scale buildup on an electric heating element therein. Such a heater comprises a tank having an inlet pipe for unheated fluid and an outlet pipe for heated fluid, plus an electric heating element within the tank. The retrofitting would comprise the step of:
A. Providing an extension of the inlet pipe that is parallel to the electric heating element and terminates in the vicinity of the heating element and that has an opening adapted to direct the unheated fluid towards the heating element.
Optionally the retrofit may also include a step of providing a deflector on the side opposite the heating element from the inlet extension pipe, containing the aforementioned perforations. Moreover, the retrofit would desirably include the step of using an induction coil or permanent magnet on the inlet pipe, to produce soft scale for easy removal from the surface of the heating element. Such an induction coil would be adapted to deliver to the fluid in the pipe solenoid-induced molecular agitation generated by an electronic descaling unit.
Scale Formation in Hot Water Heaters
Conventional electric hot water heaters generally employ an elongated electrical heating element of the type commonly known as “calrod.” Such elements generally contain a resistance wire that is encapsulated within a metallic rod-shaped sheath of approximately ¼ inch diameter. For convenience in supplying electric power to both ends of the element, the the rods are generally bent so that the ends are adjacent. Commonly they are U-shaped; alternatively some such elements have an additional bend so that four substantially parallel arms are adjacent each other, which may be described as “W-shaped.” Another alternative would be the configuration that is common in dishwashers, wherein the elongated element is bent to form the major portion of a circle, essentially “Omega-shaped.”
The usual electrical heating element transfers heat energy at the density of 300 watts per square inch (compared to heating plates at the base of a usual gas-fired water heater, which transfer heat at about 30 to 50 watts per square inch). When the heating element of an electric water heater is energized, the temperature at its surface rises, for example to 200° F. As a result of the temperature rise, mineral ions in the vicinity of the element, such as calcium and magnesium, come out of solution in response to the altered equilibrium conditions, in the form of calcium and magnesium salts. These mineral salts tend to deposit on the surface of the heating element. This deposit is referred to as scale.
Initially the scale builds up as a soft deposit, but within a short period the scale stabilizes and hardens. This layer of
Electronic De-Scaling 2000, Inc.
Lipton, Esq. Robert S.
Lipton, Weinberger & Husick
Lu Jiping
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